Recent Progress in Mesostructured Materials, Volume 165: Proceedings of the 5th International Mesostructured Materials Symposium (IMMS 2006) Shanghai, ... (Studies in Surface Science and Catalysis)

Studies in Surface Science and Catalysis 165 RECENT PROGRESS IN MESOSTRUCTURED MATERIALS This page intentionally left...

Author: Dongyuan Zhao | Shilun Qiu | Yi Tang | Chengzhong Yu

31 downloads 2161 Views 109MB Size Report

This content was uploaded by our users and we assume good faith they have the permission to share this book. If you own the copyright to this book and it is wrongfully on our website, we offer a simple DMCA procedure to remove your content from our site. Start by pressing the button below!
Report copyright / DMCA form

DOWNLOAD PDF

Studies in Surface Science and Catalysis 165 RECENT PROGRESS IN MESOSTRUCTURED MATERIALS

This page intentionally left blank

Studies in Surface Science and Catalysis Advisory Editors: B. Delmon and J.T. Yates Series Editor: G. Centi Vol. 165

RECENT PROGRESS IN MESOSTRUCTURED MATERIALS Proceedings of the 5th International Mesostructured Materials Symposium (IMMS2006), Shanghai, P.R. China, August 5-7, 2006

Edited by Dongyuan Zhao Fudan University, Department of Chemistry, Shanghai 200433, P.R. China Shilun Qiu Jilin University, Department of Chemistry, Changchun, Jilin 130023, P.R. China Yi Tang Fudan University, Department of Chemistry, Shanghai 200433, P.R. China Chengzhong Yu Fudan University, Department of Chemistry, Shanghai 200433, P.R. China

Amsterdam – Boston – Heidelberg – London – New York – Oxford – Paris San Diego – San Francisco – Singapore – Sydney – Tokyo

Elsevier Radarweg 29, PO Box 211, 1000 AE Amsterdam, The Netherlands The Boulevard, Langford Lane, Kidlington, Oxford OX5 1GB, UK First edition 2007 Copyright © 2007 Elsevier B.V. All rights reserved No part of this publication may be reproduced, stored in a retrieval system or transmitted in any form or by any means electronic, mechanical, photocopying, recording or otherwise without the prior written permission of the publisher Permissions may be sought directly from Elsevier’s Science & Technology Rights Department in Oxford, UK: phone (+44) (0) 1865 843830; fax (+44) (0) 1865 853333; email: [email protected]. Alternatively you can submit your request online by visiting the Elsevier web site at http://elsevier.com/locate/permissions, and selecting Obtaining permission to use Elsevier material Notice No responsibility is assumed by the publisher for any injury and/or damage to persons or property as a matter of products liability, negligence or otherwise, or from any use or operation of any methods, products, instructions or ideas contained in the material herein. Because of rapid advances in the medical sciences, in particular, independent verification of diagnoses and drug dosages should be made Library of Congress Cataloging-in-Publication Data A catalog record for this book is available from the Library of Congress British Library Cataloguing in Publication Data A catalogue record for this book is available from the British Library ISBN-13: 978-0-444-52178-1 ISBN-10: 0-444-52178-X ISSN: 0167-2991

For information on all Elsevier publications visit our website at books.elsevier.com

Printed and bound in The Netherlands 07 08 09 10 11

10 9 8 7 6 5 4 3 2 1

v

PREFACE

Since the first discovery in the early of 1990's, the research of mesostructured materials is continuously growing in a fast speed and has attracted more and more scientists from area to area. More than 10,000 research papers and patents have been reported, related to the fabrication of mesostructured materials. The recent progresses include extending the mesostructures ranging from hexagonal to cubic structures, accessible pore sizes, compositions for example silicates, metal oxides, carbon and polymers, surface functionalities, as well as morphologies such as powders, films and monoliths. The efforts to the applications of mesostructured materials have achieved great outcomes and breakthroughs in many fields, such as catalysis, adsorption, separation, optical and electrical devices, biological systems and so on. Many outstanding results have already exhibited the great potential of mesostructured materials to be utilized in our modern society. The International Mesostructured Materials Symposium (IMMS) organized by the International Mesostructured Materials Association (IMMA) has become a routine and fruitful meeting for scientists working on all aspects in mesostructured materials all over the world since it was firstly held in Baltimore, USA, in 1998. During all the symposiums held so far, the communications among scientists and students have connected all the researchers together and inspired them with great views and new ideas. This eventually accelerates the development of mesostructured materials community. During August 4th - 7th, 2006, the 5th International Mesostructured Materials Symposium was successfully held in Shanghai, China. Over 50 oral presentations were delivered and 400 posters were exhibited on 5 sessions as following: i) application of mesoporous materials and their devices; ii) non-siliceous mesoporous materials; iii) functional mesoporous materials and mesoporous zeolites; iv) mesoporous films and functional mesoporous materials; and v) synthesis and structural characterization of mesoporous materials. The contents of the current volume present a selection of more than 200 oral and poster papers from all submitted (more than 500 papers), which covers most of the research aspects of mesostructured materials and reflects the research level and developing trends in this area. This book is believed to be contributing to the progresses of mesostructured materials and will attract the attention of scientists from broad realms.

Dongyuan Zhao Shilun Qiu Yi Tang Chengzhong Yu December 1, 2006


vii Vll

ORGANIZATION COMMITTEE Honorary Chairman Dongsheng Yan Shanghai Inst. Ceram, Shanghai, China Ruren Xu Jilin University, Changchun, China Mingyuan He Bejing Petroleum Science Inst., Beijing, China Chairman Dongyuan Zhao

Fudan University, Shanghai, China

Co-Chairman Shilun Qiu

Jilin University, Changchun, China

Secretary Yi Tang

Fudan University, Shanghai, China

INTERNATIONAL ADVISORY BOARD Michael W. Anderson George S. Attard Laurent Bonneviot JeffBrinker Avelino Corma Francois Fajula Daniella Goldfarb Shinji Inagaki Mietek Jaroniec Serge Kaliaguine Kazuyuki Kuroda G. Q. Max Lu Alexander V. Neimark Joel Patarin Thomas J. Pinnavaia Ryong Ryoo Clement Sanchez Ferdi Schtlth Galen D. Stucky Baolian Su Takashi Tatsumi Osamu Terasaki James C. Vartuli Jackie Y. Ying Wuzong Zhou

UMIST, UK Univ. Southampton, UK Laval Univ., Canada Sandia National Lab,USA Univ. Politecnica de Valencia, Spain ENSCM, France Weizmann Inst., Israel Toyota Central R&D Labs., Japan Kent State Univ., USA Laval Univ., Canada Waseda Univ., Japan Univ. Queensland, Australia TRI Princeton Univ. Haute Alsace, France Michigan State Univ., USA KAISY, Korea Univ. Pierre, France Max-Planck-Institute, Germany UC Santa Barbara, USA Univ. Namur, Belgium Yokohama Univ. Japan Stockholm Univ. Swenden Mobil, USA MIT, USA Univ. St Andrews, UK


ix

Contents Preface

v

Organizing Committee

vii

International Advisory Committee

vii

I. Synthesis and structure of mesoporous materials 1.

2.

3.

4.

5.

6.

7.

Synthesis of thick-walled SBA-15 in PEO27-PPO61-PEO27 template under relative low temperature and acidity Hailan Liu, Xiuguo Cui, Sik-Won Moon and Wang-Cheol Zin

1

Synthesis of tetrakaidecahedronal SBA-16 by acidity adjusting Xiuguo Cui, Sik-Won Moon and Wang-Cheol Zin

5

In-situ x-ray diffraction study on the formation of a periodic mesoporous organosilica material Michael Tiemann, Cilâine V. Teixeira, Maximilian Cornelius, Jürgen Morell, Heinz Amenitsch, Mika Lindén and Michael Fröba

9

Is constant mean curvature a valid description for mesoporous materials? Michael W. Anderson, Philip J. Hughes, Osamu Terasaki, Yasuhiro Sakamoto and Ken Brakke

13

Salt effect in the synthesis of highly ordered, extremely hydrothermal stable SBA-15 Changlin Li, Yanqin Wang, Yanglong Guo, Xiaohui Liu, Yun Guo and Guanzhong Lu

17

Hydrocarbon templated sol-gel Synthesis and characterizations of mesoporous silica xerogel Halina Misran, Mohd Ambar Yarmo and Ramesh Singh

21

Microwave Synthesis of SBA-15 mesoporous silica material for beneficial effect on the hydrothermal stability Sang-Cheol Han, Nanzhe Jiang, Sujandi, David Raju Burri, Kwang-Min Choi, Seung-Cheol Lee and Sang-Eon Park

25

x

8.

9.

10.

11.

12.

13.

14.

15.

16.

Control of pore size of mesoporous silica utilizing noncovalent supermicelles Zhurui Shen, Yuping Liu, Pingchuan Sun, Zhongyong Yuan and Tiehong Chen

29

Synthesis of supermicro-macroporous silica with polypeptide-based triblock copolymer Yuping Liu, Liying Li, Zhurui Shen, Pingchuan Sun, Zhongyong Yuan and Tiehong Chen

33

Synthesis of silica nanostructures using synthetic block copolypeptide Yuping Liu, Liying Li, Huijing Zhou, Zhurui Shen, Pingchuan Sun, Zhongyong Yuan and Tiehong Chen

37

Synthesis of mesoporous silica materials from kenyaite Ziyu Liu, Yingxu Wei, Yue Qi, Shiyun Sang and Zhongmin Liu

41

Fluorinated surfactant with short carbon chain templating macropores in hierarchically mesoporous/macroporous silica Xiangju Meng and Takashi Tatsumi

45

Synthesis of mesostructured silica with strongly hydrophilic surfactant templates Weibin Fan, Xiangju Meng, Toshiyuki Yokoi, Yoshihiro Kubota and Takashi Tatsumi

49

Synthesis of stable colloidal suspensions of ordered mesostructured silica from sodium metasilicate using pluronic P123 and mildly acidic conditions Andreas Berggren, Krister Holmberg and Anders E.C. Palmqvist

53

Three-dimensional large pore cubic silica mesophases with tailored pore topology: developments and characterization Freddy Kleitz and Tae-Wan Kim

57

A novel method of mesostructured material architecture using DBD plasma on illite with non-expandibility Myung Hun Kim, Il Mo Kang, Kiwoong Sung, Bui Hoang Bac, Jeong Hun Kim, Yungoo Song, Hi-Soo Moon and Su Dok Yi

61

xi

17.

18.

19.

20.

21.

22.

23.

24.

25.

26.

Production of highly mesostructured SBA-15 silicas at pH around the PZC Alexandra Chaumonnot and Emmanuelle Trela

65

Three-dimensional large pore cubic niobosilicates: direct synthesis and characterization Izabela Nowak and Mietek Jaroniec

69

Synthesis under different conditions of NbMCM-48 with an epoxidation activity Izabela Nowak and Maria Ziolek

73

Composite hydroxyapatite -Na/MCM-41 for the fluoride retention in contaminated water Oscar A. Anunziata, Andrea R. Beltramone and Jorgelina Cussa

77

Direct synthesis of cerium-incorporated SBA-15 mesoporous molecular sieves Qiguang Dai, Guoping Chen, Xingyi Wang and Guanzhong Lu

81

Direct synthesis of MgO modified HMS solid basic materials Zheng Ying Wu, Xin Dong and Jian Hua Zhu

85

Nitrided BaO-MCM-41 as a new mesoporous basic material Shaoliang Jiang, Fuxiang Zhang, Qingfeng Li and Naijia Guan

91

Synthesis and characterization of SBA-15 type mesoporous silicate containing niobium and tin Izabela Nowak, Iveta Nekoksová and Jirí Cejka

95

Effect of concentration of nitric acid on transition of mesoporous silica structure Shuhua Han, Wanguo Hou, Xirong Huang, Liqiang Zheng and Youshao Wang

101

Structure characterization of mesostructured silica nanowires formed in porous alumina membranes Baodian Ya and Ning Wang

105

xii

27.

28.

29.

30.

31.

32.

33.

34.

35.

36.

CRISP and eMap: software for determining 3D pore structures of ordered mesoporous materials by electron crystallography Hong Zhang, Ting Yu, P. Oleynikov, Dongyuan Zhao, S. Hovmöller and Xiaodong Zou

109

A mechanistic study on the degradation of highly ordered, non-ionic surfactant templated aluminosilicate mesoporous materials Al-CMI-1 in boiling water Alexandre Léonard and Baolian Su

113

Tailoring the phase and texture of mesoporous silica by using tetraethylenepentamine and ethanol Ming Bo Yue, Xin Dong and Jian Hua Zhu

117

Synthesis of mesoporous aluminosilicates via recrystallisation of pure silica MCM-41: a stepwise post-synthesis alumination route Robert Mokaya

123

One-pot Synthesis of ionic liquid functionalized SBA-15 mesoporous silicas Yong Liu, Jiajian Peng, Shangru Zhai, Ningya Yu, Meijiang Li, Jianjiang Mao, Huayu Qiu, Jianxiong Jiang and Guoqiao Lai

127

Preparation of novel mesostructured titanium-pillared hydrotalcite Myung Hun Kim, Seok-Heung Jang, Youngho Lee, Il Mo Kang, Yungoo Song, Myongsoo Lee, Jin-Won Park and William Jones

131

Synthesis, characterization and catalytic activity of titania and vanadium grafted and substituted on mesoporous silicas T. Williams, J. N. Beltramini and G. Q. Lu

135

Synthesis and characterization of B- and Ti-MCM-36 Se-Young Kim, Gon Seo and Wha-Seung Ahn

139

Delamination and intercalation of layered aluminophosphate with [Al2P3O12]3- stoichiometry by a controlled two-step method Chen Wang, Ying Li, Weiming Hua, Yinghong Yue and Zi Gao

143

Novel Synthesis method of mesoporous MoSiOx Yanying Zheng, Tao Dou, Aijun Duan, Zhen Zhao and Shanjiao Kang

147

xiii

37.

38.

39.

40.

41.

42.

43.

Birch templated Synthesis of macro-mesoporous silica material for sustained drug delivery Huiming Lin, Fengyu Qu, Shiying Huang, Guangshan Zhu and Shilun Qiu

151

Synthesis of metal-doped mesoporous silica by spray drying and their adsorption properties of water vapor Akira Endo, Yuki Inagi, Satoko Fujisaki, Takuji Yamamoto, Takao Ohmori and Masaru Nakaiwa

157

Structural characterization and systematic gas adsorption studies on a series of novel ordered mesoporous silica materials with 3D cubic Ia-3d structure (KIT-6) Freddy Kleitz, Chia-Min Yang and Matthias Thommes

161

Synthesis and characterization of mesoporous MCM-41 silica with thick wall and high hydrothermal stability under mild base solution Chi-Feng Cheng, Po-Wen Cheng, Shu-Hsien Chou, Hsu-Hsuan Cheng and Hwa Kwang Yak

165

A facile Synthesis of MCM-41 by ultrasound irradiation Alina-Mihaela Hanu, Eveline Popovici, Pegie Cool and Etienne F. Vansant

169

Crystalline micro- and meso-porous materials from inorganic molecular clusters Xiaodong Zou, Tony Conradsson, Kirsten E. Christensen, Tiezhen Ren and Michael O’Keeffe

173

Aluminum incorporation into plate-like ordered mesoporous materials obtained from layered zeolite precursors Raquel García, Isabel Díaz, Carlos Márquez-Álvarez and Joaquín Pérez-Pariente

177

II. Characterization of mesoporous materials 44.

Shaping of mesoporous molecular sieves Martin Hartmann, Sebastian Kunz, G. Chandrasekar and V. Murugesan

181

xiv

45.

46.

47.

48.

49.

50.

51.

52.

53.

A new temperature-programmed calcination route to remove the organic templates from mesoporous aluminophosphate materials Jing Yu, Juan Tan, An J. Wang, Xiang Li and Yong K. Hu

185

Calcination mechanism of block-copolymer template in SBA-15 materials François Bérubé and Serge Kaliaguine

189

Evolution of mesoporosity and microporosity of SBA-15 during a treatment with sulfuric acid Anja Rumplecker, Bodo Zibrowius, Wolfgang Schmidt, Chia-Min Yang and Ferdi Schüth

195

Framework modification and acidity enhancement of zirconium-containing mesoporous materials Lifang Chen, Xiaolong Zhou, Luis E. Noreña, Guoxian Yu, Chenglie Li and Jin-An Wang

199

Pulsed field gradient NMR studies of n-hexane diffusion in MCM-41 materials Ziad Adem, Flavien Guenneau, Marie-Anne Springuel-Huet, Juliette Blanchard and Antoine Gédéon

203

TEM studies of bicontinuous cubic mesoporous crystals Yasuhiro Sakamoto, Chuanbo Gao, Shunai Che and Osamu Terasaki

207

Characterization of vesicular mesostructured silica synthesized under alkaline conditions Cheng Chi, Bo Wang, Wei Shan, Yahong Zhang and Yi Tang

211

Zirconium species created within the mesopores of MCM-41 and NbMCM-41 Joanna Goscianska and Maria Ziolek

215

Synthesis and characterization of tetrahedral aluminumspecies-containing SBA-15 and its application for selective t-butylation of naphthalene M. Selvaraj and S. Kawi

219

xv

54.

55.

Adsorption–desorption characteristics of volatile organic compounds over various zeolites and their regeneration by microwave irradiation K.-J. Kim, Y.-H. Kim, W.-J. Jeong, N.-C. Park, S.-W. Jeong and H.-G. Ahn

223

Reversible and irreversible adsorption of dye on mesoporous materials in aqueous solution Shaobin Wang and Lili Tian

227

III. Non-siliceous mesoporous materials 56.

57.

58.

59.

60.

61.

Thermal stability of mesotructured aluminas obtained from different procedures Sébastien Royer, Charles Leroux, Alexandra Chaumonnot, Renaud Revel, Stéphane Morin and Loïc Rouleau

231

Self-formation phenomenon of hierarchically meso- (micro-) macroporous zirconium oxide Aurélien Vantomme and Bao-Lian Su

235

Synthesis and characteristics of hierarchically porous zirconia-based composite oxides Hangrong Chen, Jianlin Shi and Dongsheng Yan

239

Synthesis of ordered mesoporous zinc oxide obtained by dry gel nanocasting from the mesoporous carbon CMK-3 Helwig H. Thiel, Pablo Cascales de Paza, Martin Hartmann and Stefan Ernst

243

Synthesis of mesostructured TiO2 through self-assembly of nanocrystals of rutile Wenfu Yan, Zuojiang Li and Sheng Dai

247

Synthesis of a lamellar mesostructured calcium phosphate using hexadecylamine as a structure-directing agent in the ethanol/water solvent system Nobuaki Ikawa, Yasunori Oumi, Tatsuo Kimura, Takuji Ikeda and Tsuneji Sano

253

xvi

62.

63.

64.

65.

66.

67.

68.

69.

70.

71.

Formation of pt nanowires in mesoporous materials and SiO2 nanotubes Inga Bannat and Michael Wark

257

Synthesis of Pd nanoparticles in la-doped mesoporous titania with polycrystalline framework Shuai Yuan, Qiao R. Sheng, Jin L. Zhang, Feng Chen, Masakazu Anpo and Wei L. Dai

261

Fabrication of metal oxide nanowires templated by SBA-15 with adsorption-precipitation method Renlie Bao, Kun Jiao, Heyong He, Jihua Zhuang and Bin Yue

267

Facile Synthesis of hierarchically structured titanium phosphate with bimodal wormhole-like mesopores and macropores Hailong Fei, Xiaoquan Zhou, Pingchuan Sun, Zhongyong Yuan and Tiehong Chen

271

Synthesis of mesoporous alumina using anionic, nonionic and cationic surfactants Jagadish C. Ray, Kwang-Seok You, Ji-Whan Ahn and Wha-Seung Ahn

275

Synthesis of b-SiC nanofiber using PMOs as a single precursor Jeong-Rae Ko, Ju-Won Min, Byung-Don You and Wha-Seung Ahn

279

Synthesis of porous TiO2 monolith by organic membrane template Jianxi Yao and Dan Wang

283

Template-free synthesis of hierarchical mesoporous alumina-based materials with uniform channel-like macrostructures Tiezhen Ren, Zhongyong Yuan and Baolian Su

287

Mesostructured powder of tungsten oxide-surfactant compound: influence of calcination on the material’s structure Zhimei Qi, Itaru Honma and Haoshen Zhou

291

Hydrothermal Synthesis and characterization of mesoporous zirconia templated by triethanolamine Fu Ma, Jihong Sun, Hongjian Zhao, Yun Li and Shijie Luo

301

xvii

72.

73.

74.

75.

76.

77.

78.

79.

80.

The role of triethanolamine in the synthesis of mesostructured TiO2 by sol-gel method Feng Wang, Jihong Sun and Chongfang Ma

305

Nano-replication to mesoporous metal oxides using mesoporous silica as template Byung Guk So, Jeong Kuk Shon, Ji Ae Yu, Oh-Shim Joo and Ji Man Kim

309

A novel synthesis of manganese oxide nanotubes Li Tao, Chenggao Sun, Meilian Fan, Caijuan Huang, Hesheng Zhai, Hailong Wu and Zisheng Chao

313

Synthesis of well ordered crystalline TiO2 photocatalyst with enhanced stability and photoactivity Zhenfeng Bian, Jian Zhu and Hexing Li

317

Crystallization of stable mesoporous zirconia and ceria-zirconia Anil K. Sinha and Kenichirou Suzuki

323

Synthesis of mesoporous structures zinc sulfide by assembly of nanoparticles with block-copolymer as template Hongmei Ji, Jieming Cao, Jinsong Liu, Mingbo Zheng, Yongping Chen, Yulin Cao and Nongyue He

327

Surfactant-free Synthesis of mesoporous tin oxide with a crystalline wall Jieming Cao, Haitao Hou, Xianjia Ma, Mingbo Zheng and Jinsong Liu

331

Mesoporous crystals of metal oxides and their properties Calum Dickinson, Andrew Harrison, Jim A. Anderson and Wuzong Zhou

335

Synthesis and characterization of lanthanum oxide nanotubes using dendritic surfactant Li Tao, Chenggao Sun, Meilian Fan, Qi Liu, Caijuan Huang, Hesheng Zhai, Hailong Wu and Zisheng Chao

339

xviii

81.

82.

83.

84.

85.

Nanostructured SiC from preceramic polymer via replication of hard templates Jia Yan, Hao Wang, In-Kyung Sung, Kyung-Hoon Park, Anjie Wang, Xiao-dong Li and Dong-Pyo Kim

343

Gas-sensing properties of ordered mesoporous Co3O4 synthesized by replication of SBA-15 silica Thorsten Wagner, Jan Roggenbuck, Claus-Dieter Kohl, Michael Fröba and Michael Tiemann

347

Direct Synthesis of mesoporous spinel-type Zn-Al complex oxide with a crystalline framework Lu Zou, Feng Li, Xu Xiang, David G. Evans and Xue Duan

351

Visible light activated mesoporous TiO2-xNx nanocrystalline photocatalyst Zheng Jiang, Farhan Al-Shahrani, Tsung-Wu Lin, Yingying Cui and Tiancun Xiao

355

Mesoporous metal oxides and mixed oxides nanocasted from mesoporous vinylsilica and their applications in catalysis Yanqin Wang, Yangang Wang, Yun Guo, Yanglong Guo, Xiaohui Liu and Guanzhong Lu

361

IV. Mesoporous carbons 86.

87.

88.

89.

Surface functionalization of templated porous carbon materials Dan Yu, Zhiyong Wang, Nicholas S. Ergang and Andreas Stein

365

Rational control of the micro/mesoporosity of multimodally porous carbon monoliths synthesized by nanocasting Jan-Henrik Smått, An-Hui Lu, Stefan Backlund and Mika Lindén

369

Synthesis of mesoporous carbon frameworks with graphitic walls by secondary hard template method Renyuan Zhang, Bo Tu and Dongyuan Zhao

373

Porous carbons cast from meso- or nonporous silica nanoparticles Camila Ramos da Silva, Martin Wallau, Eduardo Prado Baston, Rita Karolinny Chaves de Lima and Ernesto A. Urquieta-González

377

xix

90.

91.

92.

93.

94.

95.

96.

97.

98.

Carbon fiber-templated growth of hierarchical analcime hollow fibers Xueying Chen, Zhiying Lou, Minghua Qiao, Kangnian Fan and Heyong He

381

Synthesis of mesoporous silica and mesoporous carbon using gelatin as organic template Chun-Han Hsu, Hong-Ping Lin, Chih-Yuan Tang and Ching-Yen Lin

385

A study on the Synthesis of mesoporous silica and carbon platelets with perpendicular nanochannels Yi-Qi Yeh, Gui-Min Teo, Bi-Chang Chen, Hong-Ping Lin, Chih-Yuan Tang and Chin-Yen Lin

389

Preparation of versatile silica/carbon nanocomposites via carbonization of ethyl-bridged periodic mesoporous organosilica Zhuxian Yang, Yongde Xia and Robert Mokaya

393

Ordered mesoporous carbon as new support for direct methanol fuel cell: controlling of microporosity and graphitic character Chanho Pak, Sang Hoon Joo, Dae Jong You, Hyung Ik Lee, Ji Man Kim, Hyuk Chang and Doyoung Seung

397

Direct sulfonation of ordered mesoporous carbon for catalyst support of direct methanol fuel cell Chanho Paka, Sang Hoon Joo, Dae Jong You, Ji Man Kim, Hyuk Chang and Doyoung Seung

401

Effect of chemically surface modified MWNTs on the mechanical and electrical properties of epoxy nanocomposites Joohyuk Park and Abu Bakar Bin Sulong

405

Synthesis of uniform carbon nanotubes by chemical vapor infiltration method using SBA-15 mesoporous silica as template An-Ya Lo, Shou-Heng Liu, Shing-Jong Huang, Huang-Kai Shen, Cheng-Tzu Kuo and Shang-Bin Liu

409

Synthesis of large pore mesoporous carbon using colloidal silica template Huachun Li and Shunai Che

413

xx

V. Functional Mesoporous Materials 99.

Study of mercury(II) binding to thiol-modified ordered mesoporous silicas by analytical and electrochemical analyses: influence of the pore structure and the functionalization process Fabrice Gaslain, Cyril Delacôte, Bénédicte Lebeau, Claire Marichal, Joël Patarin and Alain Walcarius

417

100. The effect of inorganic salt on the Synthesis of large-pore PMO with aromatic moieties in the framework Sung Soo Park, Booyoun An, Yunji Kang, Mina Park, Il Kim and Chang-Sik Ha

421

101. Bovine serum albumin adsorption in large pore amine functionalized mesoporous silica S. Z. Qiao, Haiying Zhang, Xufeng Zhou, Sandy Budihartono and G. Q. Lu

425

102. Effect of various templates on the formation of mesoporous benzene-silica hybrid material K.-F. Zhou, Q.-H. Xia, H.-B. Zhu, D. Hu and Z.-M. Liu

429

103. Synthesis of layered organosilica binding with self-assembled LB film Takayuki Chujo, Yu Gonda, Yasunori Oumi, Tsuneji Sano and Hideaki Yoshitake

433

104. Synthesis of highly ordered mesoporous benzene-silicas using PEO–PLGA–PEO triblock copolymers Eun-Bum Cho, Hyojung Kim and Dukjoon Kim

437

105. Tailoring cage-like organosilicas with multifunctional bridging and surface groups Rafal M. Grudzien, Bogna E. Grabicka, Donald J. Knobloch and Mietek Jaroniec

443

106. Synthesis and morphology of functionalized mesoporous ethanesilica Yaojun Wang, Yanqin Wang, Xiaohui Liu and Guanzhong Lu

447

xxi

107. Periodic mesoporous organosilicas: thermal stability and etherification of phenol Micha Rat, M. Hassan Zahedi-Niaki, Serge Kaliaguine and Do Trong-On

451

108. Highly efficient microwave-assisted asymmetric transfer hydrogenation with SBA-15-supported TsCHDA chiral ligands Myung-Jong Jin, M. S. Sarkar and Ji-Young Jung

455

109. Preparation of bimodal MCM-41 encapsulated Co(III)-porphyrin complex and its catalytic properties in cyclohexane oxidation Shijie Luo and Jihong Sun

459

110. Synthesis of optically active monoesters via enantioselective reaction catalyzed by heterometallic chiral (salen) co complex immobilized on acid sites of A1-MCM-41 Geon-Joong Kim, Chang-Kyo Shin and Rahul B. Kawthekar

463

111. Chiral (salen) cobalt complexes encapsulated in mesoporous mordenite as an enantioselective catalyst for phenolic ring opening of terminal epoxides Kwang-Yeon Lee, Young-Hee Lee, Chang-Kyo Shin and Geon-Joong Kim

467

112. Effect of surface functional groups on adsorption and release of bovine serum albumin on SBA-15 S.-W. Song, S.-P. Zhong, K. Hidajat and S. Kawi

471

113. Microstructure understanding of organic-inorganic hybrid mesoporous silica by SAXS Yanjun Gong, Zhihong Li and Tao Dou

475

114. Surface aminosilylated mesoporous SBA-15 with rare earth metal sandwiched polyoxometalates as heterogeneous catalyst Yan Zhou, Bin Yue, Renlie Bao, Min Gu and Heyong He

479

VI. Mesoporous zeolite-like materials 115. Characterization of nickel metal distribution in Ni/y-zeolite Dul-Sun Kim, Jung-hee Yoon, Jae-Suk Shin and Dong-keun Lee

483

xxii

116. Synthesis of MCM-22/MCM-41 composites with zeolite MCM-22 as precursor Li Yuping, Zhang Wei, Wang Xiaoli, Dou Tao and Xie Kechang

487

117. Micro-mesoporous composite molecular sieves with wormlike morphology prepared from zeolite beta Ying Zhang, Tao Dou, Qiang Li and Shanjiao Kang

491

118. Steam stable mesoporous silicalite-1 with semi-crystalline framework Xiong Li, Sun-Jin Kim and Wha-Seung Ahn

495

119. Synthesis of bimodal mesoporous material with the primary/ secondary structure of ZSM-5 as building unit Yong Niu and Jihong Sun

499

120. Synthesis of meso-structured silicalite-1 by combining solid phase crystallization and carbon templating Jia Wang and Marc-Olivier Coppens

503

121. Assembly of mesocellular silica foams from colloidal zeolite nanocrystals through template free process Yuxin Jia, Wei Han, Guoxing Xiong and Weishen Yang

507

122. Microwave assisted-direct Synthesis of highly ordered large pore functionalized mesoporous SBA Sujandi, Sang-Cheol Han, Dae-Soo Han and Sang-Eon Park

511

123. Template-free sol-gel synthesis of mesoporous materials with ZSM-5 structure walls Wei Han, Yuxin Jia, Guoxing Xiong and Weishen Yang

515

124. Facile low temperature synthesis of primary amine templated super-microporous aluminosilicates Graham Rance, Yongde Xia and Robert Mokaya

519

125. Synthesis of zeolitic mesoporous titanosilicate using mesoporous carbon as a hard template Haijiao Zhang, Yueming Liu, Mingyuan He and Peng Wu

523

xxiii

126. Synthesis of micro- and mesoporous ZSM-5 composites and their catalytic application in glycerol dehydration to acrolein Chunjiao Zhou, Caijuan Huang, Wengui Zhang, Hesheng Zhai, Hailong Wu and Zisheng Chao

527

127. Comparative time-resolved luminescence studies of Tb-ZSM-5 and Tb-MFI mesoporous materials C. Tiseanu, M. U. Kumke, V.I. Parvulescu, B. C. Gagea and J. A. Martens

531

128. Acylation of fatty acids with amino-alcohols on UL-MFI type materials M. Musteata, V. Musteata, A. Dinu, V.I. Parvulescu, V.T. Hoang, D. Trong-On and S. Kaliaguine

535

129. Creating mesopores in ZSM-5 for improving catalytic cracking of hydrocarbons Yingxu Wei, Fuxiang Chang, Yanli He, Shuanghe Meng, Yue Yang, Yue Qi and Zhongmin Liu

539

VII. Mesoporous films and morphology of mesoporous materials 130. Effect of surfactant on the morphology of Ti-MMM-2 mixed-phase materials Sean M. Solberg, Dharmesh Kumar and Christopher C. Landry

543

131. Chiral mesoporous silica tubules by achiral surfactant template Jingui Wang, Wenqiu Wang, Pingchuan Sun, Zhongyong Yuan and Tiehong Chen

547

132. Aspects of a novel method for the pore size analysis of thin silica films based on krypton adsorption at liquid argon temperature (87.3 k) Matthias Thommes, Norikazu Nishiyama and Shunsuke Tanaka 551 133. Dynamics of xenon adsorbed in organically modified silica thin films using hyperpolarized 129Xe 2D- exchange NMR M. Nader, F. Guenneau, C. Boissiere, D. Grosso, C. Sanchez and A. Gédéon

555

xxiv

134. Nanocrystal-micelle: a new building block for facile self-assembly and integration of 2, 3-dimensional functional nanostructures Hongyou Fan

559

135. Direct visualization of mesoporous structures in the framework of SBA-15 mesoporous films Jinlou Gu, Hangrong Chen, Xiongping Dong, Zhicheng Liu and Jianlin Shi

563

136. Preparation, texture and electrochemical properties of TiO2 films with highly ordered mesoporosity and controlled crystallinity D. Fattakhova Rohlfing, M. Wark, J. Rathousky, T. Brezesinski and B. Smarsly

569

137. Optimization of the silylation procedure of thin mesoporous SiO2 films with cationic trimethylaminopropylammonium groups Dina Fattakhova-Rohlfing, Michael Wark and Jiri Rathousky

573

138. Synthesis of transparent mesoporous aluminum organophosphonate films through triblock copolymer templating Tatsuo Kimura and Kazumi Kato

579

139. Electrical/mechanical properties of nanoporous thin films by using various sized cyclodextrins Jin-Heong Yim, Jong-Ki Jeon and Young-Kwon Park

583

140. Synthesis of MSU-1 silica particles with spherical morphology Kalidas Biswas, Soo-Hyun Jang, Wha-Seung Ahn, Yoon-Suk Baik and Won-Jo Cheong

587

141. Proton conductivity of cubic silica-based mesostructured monolithic membranes Liangming Xiong, Yong Yang, Hangrong Chen, Jianlin Shi and Masayuki Nogami

591

142. Vapor phase preparations of mesoporous silica thin films for ultra-low-k dielectrics Shunsuke Tanaka, Takanori Maruo, Norikazu Nishiyama, Korekazu Ueyama and Hugh W. Hillhouse

595

xxv

143. Synthesis of silica nanospheres with well-ordered mesopores assisted by amino acids Toshiyuki Yokoi, Marie Iwama, Tatsuya Okubo, Yasuhiro Sakamoto, Osamu Terasaki, Yoshihiro Kubota and Takashi Tatsumi

599

144. Size and morphology control in the Synthesis of SBA-15 Huanling Xie, Ranbo Yu, Dan Wang, Jianxi Yao, Xianran Xing and Wenguo Xu

603

145. Synthesis and characterization of mesostructured silica sphere particles with core space Jung-Sik Choi, Kyung-Ku Kang and Wha-Seung Ahn

607

146. Synthesis of highly ordered large pore mesoporous silica SBA-16 spheres Hongxiao Jin, Qingyin Wu, Chao Chen, Daliang Zhang and Wenqin Pang

611

147. Effects of the different amount of phosphoric acid on the resulting morphology of SBA-15 Yun Li, Jihong Sun, Fu Ma and Shijie Luo

617

148. Morphology control of SBA-15 in chiral organic acid media Shengrong Ye, Yueming Liu, Mingyuan He and Peng Wu

621

149. Synthesis of the mesoporous TiO2 films and their application to dye-sensitized solar cells Dong-Hyun Cha, Young-Suk Kim, Jia Hong Pan, Yoon Hee Lee and Wan In Lee

625

150. Formation mechanism of monodispersed mesoporous silica spheres and its application to the synthesis of core/shell particles Hiroshi Nozaki, Noritomo Suzuki, Tadashi Nakamura, Yuusuke Akimoto and Kazuhisa Yano

629

151. Controllable synthesis of cubic MCM-48 with different morphologies by using ternary surfactant templating route Lingdong Kong, Su Liu, Yi Wang, Xuewu Yan, Heyong He and Quanzhi Li

633

xxvi

VIII. Catalysis of mesoporous materials 152. Mesoporous silica hosts for polyenzymatic catalysis Anne Galarneau, Lai Truong Phuoc, Aude Falcimaigne, Gilbert Renard and François Fajula

637

153. Mesoporous silica-supported chiral norephedrine ligands for asymmetric transfer hydrogenation Myung-Jong Jin, M. S. Sarkar and Sang-Eon Park

643

154. Facile heterogenization of homogeneous ferrocene catalyst on SBA-16 David Raju Burri, Isak Rajjak Shaikh, Sang-Cheol Han and Sang-Eon Park

647

155. Naphthalene alkylation with i-PrOH over bimodal mesoporous catalysts containing alumina Fang Liu, Jihong Sun, Quansheng Liu and Haibo Jin

651

156. Synthesis and application of MCM-41 molecular sieves modified by lanthanum in oxidation of cyclohexane Wangcheng Zhan, Yanglong Guo, Yanqin Wang, Yun Guo and Guanzhong Lu

655

157. Microwave Synthesis of Fe-SBA-16 mesoporous silica and Friedel-Crafts type reaction Dae-Soo Han, Sujandi, Jeong-Boon Koo and Sang-Eon Park

659

158. Photocatalytic oxidation of phenylsulfonephthalein by hydrogen peroxide over Ti containing SBA-15 mesoporous materials Phuong T. Dang, Tuan A. Vu, Thang C. Dinh, Yen Hoang, Thang G. Vuong, Thang V. Hoang, Hoa K.T. Tran, Lan K. Le and Phu H. Nguyen

663

159. Influence of the catalyst on the formation and structure of bimodal mesopore silica Xiaozhong Wang, Wenhuai Li, Bing Zhong and Kechang Xie

667

160. Mesoporous zirconia with different pore size for Fischer-Tropsch Synthesis Yachun Liu, Jiangang Chen, Kegong Fang and Yuhan Sun

671

xxvii

161. Catalytic phenol hydroxylation over Cu-incorporated mesoporous materials Huili Tang, Yu Ren, Bin Yue, Shirun Yan and Heyong He

675

162. Alumina-promoted sulfated mesoporous zirconia and catalytic application in butane isomerization Chi-Chau Hwang, Jung-Hui Wang, She-Tin Wong and Chung-Yuan Mou

679

163. Reducibility of cobalt oxides over SBA-15 supported cobalt catalysts for Fischer-Tropsch synthesis Dae Jung Kim, Brian C. Dunn, Min Kang, Jae Eui Yie, Seong-Hyun Kim, Jenifer Gasser, Eric Fillerup, Louisa Hope-Weeks and Edward M. Eyring

685

164. Microencapsulation of heterocyclic carbene-pd complex in SBA-15 silica for heck reactions M. S. Sarkar, Ji-Young Jung and Myung-Jong Jin

689

165. Heterogeneous asymmetric transfer hydrogenation with mesoporous silica SBA-15-supported Ru-TsCHDA catalyst Ji-Young Jung, M. S. Sarkar and Myung-Jong Jin

693

166. Mesoporous silica-SBA-15 supported n-heterocyclic carbene-Pd complex for Suzuki coupling reaction Myung-Jong Jin and M. S. Sarkar

697

167. Selective a-alkylation of ketones with alcohols catalyzed by highly active mesoporous Pd/MgO-Al2O3 type basic solid derived from pd-supported MgAl-hydrotalcite Suman K. Jana, Yoshihiro Kubota and Takashi Tatsumi

701

168. Asymmetric dihydroxylation catalyzed by SBA-15 silica-supported bis-cinchona alkaloid M. S. Sarkar, Ji-Young Jung and Myung-Jong Jin

705

169. Mesoporous silica SBA-15-supported palladium catalyst for green Sonogashira coupling reactions Myung-Jong Jin, M. S. Sarkar, Dong-Hwan Lee and Ik-Mo Lee

709

xxviii

170. VO(acac)2 incorporated in mesoporous silica SBA-15-confined ionic liquid as a catalyst for epoxidation M. S. Sarkar, Ji-Young Jung and Myung-Jong Jin

713

171. Selective photocatalytic oxidation of methane into methanol on V-MCM-41 mesoporous molecular sieves Yun Hu, Yasuhito Nagai, Masaya Matsuoka and Masakazu Anpo

717

172. Hydrodesulfurization of dibenzothiophene and 4,6-dimethyldibenzothiophene over Ni-Mo catalysts supported by siliceous SBA-15 Jing Ren, Anjie Wang, Juan Tan, Guangwei Cao, Chang Liu, Yongtai Li, Mohong Lu and Yongkan Hu

721

173. Photocatalytic preferential oxidation of Co with O2 in the presence of H2 (photo- PROX) on Mo-MCM-41 at 293 K Masaya Matsuoka, Takashi Kamegawa and Masakazu Anpo

725

174. Influence of the location of Rh(0) particles within MCM-41 materials on the selectivity of hydrogenation reactions Maya Boutros, Franck Launay, Audrey Nowicki, Thomas Onfroy, Virginie Semmer-Herledan, Alain Roucoux and Antoine Gédéon

729

175. Platinum catalysts supported on SBA-15 for the selective catalytic reduction of lean NOx with propylene Kwang-Eun Jeong, Joo-Il Park and Son-Ki Ihm

733

176. Catalytic activity of dinuclear chiral salen complexes immobilized on modified SBA-15 Chang-Kyo Shin, Chul-Heng Ahn, Wenji Li and Geon-Joong Kim

737

177. Simultaneous separation and enantioselective hydrolysis reaction of epoxides in membrane system containing chiral polymer salen catalyst immobilized on MCM-41 Young-Hee Lee, Kwang-Yeon Lee, Chang-Kyo Shin, Sang-Han Kim and Geon-Joong Kim

741

178. Mesoporous silica MCM-41-supported norephedrine and ephedrine as heterogeneous chiral ligands in asymmetric catalysis Sang Han Kim, Chang kyo Shin, Jong Hyuk Seok, Choong Young Lee and Geon Joong Kim

745

xxix

179. Catalytic performance of Cu-MCM41 with high copper content for NO reduction by CO Yan Kong, Yanhua Zhang, Xiaoshu Wa, Jun Wang, Haiqin Wan, Lin Dong and Qijie Yan

749

180. Influence of iron content on the structure and catalytic activity for the hydroxylation phenol of Fe-MCM41 Cheng Wu, Yan Kong, Xingjie Xu, Jun Wang, Fei Gao, Lin Dong and Qijie Yan

755

181. Basic catalysis by surfactant containing MCM-41 Leandro Martins and Dilson Cardoso

761

182. Growth of carbon nanotubes with different inner diameter on mesoporous silica Lingxia Zhang, Jina Yan, Jianlin Shi, Lei Li, Zile Hua and Hangrong Chen

765

183. Selective hydrogenation of benzene over Ru/SBA-15 catalyst prepared by the “double solvents” impregnation method Juan Bu, Yan Pei, Pingjun Guo, Minghua Qiao, Shirun Yan and Kangnian Fan

769

184. Mesoporous calcined Mg-Al hydrotalcites as catalysts for synthesis of propylene glycol Gongde Wu, Xiaoli Wang, Junping Li, Ning Zhao, Wei Wei and Yuhan Sun

773

185. Application of Ti-containing mesoporous silica (single-site photocatalyst) and photo-assisted deposition (PAD) method for preparation of nano-sized Pt metal catalyst Hiromi Yamashita, Toshiaki Shimizu, Naoki Mimura, Makoto Shimada, Shuai Yuan, Kohsuke Mori, Tetsutaro Ohmichi, Iwao Katayama, Takao Sakata and Hirotaro Mori

777

186. Hydroisomerization and hydrocracking of long chain n-alkane and Fischer-Tropsch wax over bifunctional Pt-promoted Al-HMS catalysts Yanyong Liu, Toshiaki Hanaoka, Kazuhisa Murata and Kinya Sakanishi

781

xxx

187. Preparation and characterization of SBA-15 supported molybdenum nitride for NH3 decomposition Hongchao Liu, Hua Wang, Zhongmin Liu, Jianghan Shen and Ying Sun

787

188. Comparative study of the catalytic activity of Al-SBA-15 and Ga-SBA-15 materials in a-pinene isomerisation and oxidative cleavage of epoxides B. Jarry, F. Launay, J. P. Nogier and J. L. Bonardet

791

189. Mesoporous silica supported Ni catalysts for CO2 reforming of methane Shaobin Wang

795

190. SBA-15 mesoporous molecular sieve as an appropriate support for highly active HDS catalysts prepared using Mo and W heteropolyacids Lilia Lizama, Juan C. Amezcua, Ramón Reséndiz, Sergio Guzmán, Gustavo A. Fuentes and Tatiana Klimova 799 191. SBA-15 mesoporous molecular sieves doped with ZrO2 or TiO2 as supports for Mo HDS catalysts Oliver Y. Gutiérrez, Fernando Pérez, Cecilia Salcedo, Gustavo A. Fuentes, Manuel Aguilar, Xim Bokhimi and Tatiana Klimova

803

192. Isopropylation of naphthalene over mesostructured aluminosilicate nanoparticles with wormhole framework structures Shang-Ru Zhai, Chang-Sik Ha, Yong Liu, Hua-Yu Qiu, Dong Wu, Yu-Han Sun, Shao-Jun Wang and Bin Zhai

807

193. Adsorption desulfurization from gasoline by silver loaded on mesoporous aluminum oxide Wenzhong Shen, Xiangping Yang, Qingjie Guo, Yihong Liu and Yanru Song

811

xxxi

IX. Applications of mesoporous materials 194. Proton conduction of ordered mesoporous silica-methanesulfonic acid hybrids Yonggang Jin, Zhi Ping Xu, Shizhang Qiao, João C. Diniz da Costa and G.Q. Max Lu

817

195. Oligodeoxynucleotide molecule delivery by organically modified SBA-15 mesoporous materials Xi-chuan Cao, Zhuo-qi Zhang, Jian R. Lu and Michael W. Anderson

821

196. Release of guest molecules from modified mesoporous silica Magdalena Stempniewicz, Michael Rohwerder and Frank Marlow

825

197. Spherical siliceous mesocellular foam particles for high-speed size exclusion chromatography Yu Han, Su Seong Lee and Jackie Y. Ying

829

198. Synthesis of meso/macroporous SBA-15 and its application to VOCs’ adsorption Ji Sun Yun, Joo-Il Park, Kwang-Eun Jeong and Son-Ki Ihm

833

199. Novel hydrophobic mesostructured materials: synthesis and application for VOCs removal Thang C. Dinh, Yen Hoang, Thanh V. Ho, Phuong T. Dang, Nam H. T. Le, Hoa K. T. Tran, Hoa V. Nguyen, Tuan A. Vu and Phu H. Nguyen

837

200. Synthesis of silver nanowire/mesoporous silica composite as a highly active antiseptic Diequing Zhang, Ying Wan, Guisheng Li, Jing Zhang and Hexing Li

841

201. Preparation and conductivity of decatungstomolybdovanadogermanic heteropoly acid supported on mesoporous silica SBA-15, SBA-16, MCM-41 and MCM-48 Qingyin Wu, Hongxiao Jin, Wenqi Feng and Wenqin Pang

847

xxxii

202. Fabrication of highly dispersed Pt nanoparticles in tubular carbon mesoporous materials for hydrogen energy applications Shou-Heng Liu, Rong-Feng Lu, Shing-Jong Huang, An-Ya Lo, Wen-Hua Chen, Wen-Yueh Yu, Shu-Hua Chien and Shang-Bin Liu

853

203. Membranes with Ni, Mn-MCM-41 mesoporous molecular sieves and their applications for waste water purification Viorica Pârvulescu, Gabriela Roman, Simona Somacescu, Isabella Dascalu, Bujor Albu and Baolian Su

857

204. Hybrid mesoporous SC/SBA as a chemosensor for recognizing Cu2+ Ling Gao, Jianqiang Wang, Liying Shi, Li Huang, Ying Wang, Xiaoxing Fan, Tao Yu, Mei Zhu and Zhigang Zou

861

205. Aluminosilicate mesoporous MCM-41 for drug famotidine delivery Qunli Tang, Yao Xu, Dong Wu and Yuhan Sun

865

206. DNA delivery using polyethyleneimine (PEI) coated iron oxide-silica mesostructured particles Stuart C. McBain, Humphrey H. P. Yiu, Alicia J. El Haj and Jon Dobson

869

207. A new highly sensitive and selective nanosensor for Mercury (II) ions Noan Nivarlet, Samuel Martinquet and Baolian Su

873

208. SBA-15 functionalized by epoxy groups for immobilization of penicillin G acylase Yongjun Lü, Qiaoling Zhao, Yanglong Guo, Yanqin Wang, Yun Guo and Guanzhong Lu

877

209. Adsorptive desulfurization of diesel using metallic Nickel supported on SBA-15 as adsorbent Chang Hyun Ko, Jung Geun Park, Sang-Sup Han, Jong-Ho Park, Soon-Haeng Cho and Jong-Nam Kim

881

210. Highly hydrophobic mesoporous materials as matrix for gas chromatography separation of water-alcohols mixtures Lianxiu Guan, Junping Li, Dongjiang Yang, Xiuzhi Wang, Ning Zhao, Wei Wei and Yuhan Sun

885

xxxiii

211. Photoluminescence study of [Eu(bpy)2]3+ supported on mesoporous materials of different pore sizes Shuxun Ge, Nongyue He, Song Li, Jiqing Wang, Libo Nie and Hong Chen

889

212. Benzene sensors based on surface photo voltage of mesoporous organo-silica hybrid thin films Brian Yuliarto, Yoko Kumai, Itaru Honma, Shinji Inagaki and Haoshen Zhou

893

213. Lipase immobilization in ordered mesoporous materials Elías Serra, Álvaro Mayoral, Yasuhiro Sakamoto, Rosa M. Blanco and Isabel Díaz

897

214. Microwave Synthesis of Zr incorporated SBA-16 mesoporous silica as a catalyst for Meerwein-Ponndorf-Verley (MPV) reduction Nanzhe Jiang, Kwang-Min Choi, Sang-Cheol Han, Jeong-Boon Koo and Sang-Eon Park

901

215. One and three dimensional mesoporous carbon nitride molecular sieves with tunable pore diameters Ajayan Vinu, Toshiyuki Mori, Sunichi Hishita, Srinivasan Anandan, Veerappan Vaithilingam Balasubramanian and Katsuhiko Ariga

905

216. Synthesis of well-ordered carboxyl group functionalized mesoporous carbon using non-toxic oxidant, (NH4)2S2O8 Ajayan Vinu, Kazi Zahir Hossain, Sunichi Hishita, Toshiyuki Mori, Narasimhan Gokulakrishnan, Veerappan Vaithilingam Balasubramanian and Katsuhiko Ariga

909


Recent Progress in Mesostructured Materials D. Zhao, S. Qiu, Y. Tang and C. Yu (Editors) © 2007 Elsevier B.V. All rights reserved.

1

Synthesis of thick-walled SBA-15 in PEO27-PPO6r PEO27 template under relative low temperature and acidity Hailan Liua, Xiuguo Cuia*, Sik-Won Moonb and Wang-Cheol Zinb "Key Laboratory of Organism Functional Factors of the Changbai Mountain (Education Ministry of China), College of Engineering, Yanbian University, Yanji 133002, P. R. China h Dept. of Materials Engineering, Pohang University of Science and Technology, Pohang 790-390, Korea

Thick walled (7.7 nm) SBA-15 has been synthesized by using PEO27-PPO6r PEO27 (P104) as template under relative low temperature and acidity. SAXS, nitrogen sorption experiments and TEM have been utilized to characterize resultant materials. 1. Introduction The mesostructure of porous materials grown by surfactant templated processes is well established in pioneering work of Mobil's research group [1]. In view of the some applications such as catalytic cracking process as well as preparation of inverse replica materials through mesoporous template, wall thickness of mesoporous materials is a key feature that needs to be tuned. Much effort has been taken to control wall thickness by adjusting ratio of SiO2 and surfactant [2], acidity [3] and employing surfactant with ultra-long hydrophilic chains [4]. In hexagonal mesoporous materials, wall thickness (-6.4 nm) of SBA-15 obtained by PI 23 (PEO20-PPO70-PEO20) is larger than that of MCM-41, which result in well hydrothermal stability of SBA-15 [5]. However, further thickening of wall still remains as a challenge in the study of hexagonal mesoporous materials. Here, we present an easy method for preparation of thick walled SBA-15 (TSBA-15, 7.7 nm) in the presence of triblock copolymer, PI04 (PEO27-PPO6r PEO27), at relative low synthetic temperature and acidity. To the best of our

2

knowledge, to date there has been no report on wall thickness of SBA-15 exceeds 7 nm. 2. Experimental Section In a typical synthesis of T-SBA-15, 0.33 g of P104 (EO27-PO61-EO27, Mw=5160, BASF) were dissolved in 10 g of HC1 aqueous solution (2.5 g of H2O and 7.5 g of 2.5M HC1) by stirring at 45°C. Then, 0.7 ml of tetraethyl orthosilicate (TEOS, Aldrich) was added to the homogeneous solution. White precipitate was repeatedly washed with water and air-dried at 45°C for an additional 48 h, and then was calcined at 500°C for 8 h. In characterization of TSBA-15, synchrotron small angle X-ray scattering (SAXS) pattern was obtained on 3C2 beam line with CuKa radiation (wavelength, A,=0.1542 nm) in the Pohang Accelerator Laboratory, POSTECH, Korea. Nitrogen adsorption and desorption isotherms were measured at 77K on a Micromeritics ASAP2010 having an accelerated surface area and porometry system. Surface area was determined by the BET (Brunauer-Emmett-Teller) method. The pore size distribution (PSD) was calculated by the BJH (Barrett-Joymer-Halenda) method from the isotherm of adsorption branch. Transmission electron microscopy (TEM) image was achieved using a Hitachi S-4200 microscope operating at HOkV. 3. Results and Discussion

.04nm

o . 500

100

—

210

1

2

q(nm 1 )

3

100 0.0

D(illgitrom)

0.2

0.4

0.6

0.8

1.0

Relative pressure (p/p0)

Figure 1 SAXS pattern (a), nitrogen sorption isotherm (b) and the pore size distribution (inset of Fig lb) of T-SBA-15.

3

Figure la demonstrates that T-SBA-15 exhibits three well resolved 100, 200 and 210 reflections resulting from the P6mm hexagonal symmetry, and about 10 nm of first ^/-spacing, similar to that reported for SBA-15 from PI23 in the past [4]. The nitrogen sorption isotherm and pore size distribution (determined by using BJH model) are shown in Fig. lb and its inset. A clear type IV isotherm with a small Hi-type hysteresis was obtained, which is typical of mesoporous materials and is in good agreement with SBA-15 prepared from PI23. Furthermore, T-SBA-15 has BET surface area of 884m/g and mean pore size of 3.86 nm. Thus, wall thickness of T-SBA-15 that calculated by subtracting mean pore size from aQ (=2d]Oo/^3) is 7.73 nm, which is both larger than reported SBA-15 with 6.4 nm of wall thickness from P123 [4] and that with 4.1 nm from PI04 [6].

Figure 2 TEM image of T-SBA-15 in [100] (left) and [110] direction (right).

TEM images in two directions shown in Fig. 2 further verified the results of the SAXS measurement and the nitrogen adsorption and desorption experiments. The space between pore and its adjacent pore, and the silica wall thickness are observably larger than that of usual SBA-15, which favor the improvement of hydrothermal stability mesoporous materials and the controlling pore size of the inverse replica materials such as CMK-3. Generally, in case of nonionic block copolymer template, because the surfactant PI04 used here has larger EO chains than the surfactant PI23, thicker silica wall of SBA-15 is expected and observed in our samples. Furthermore, both low synthetic temperature and certain pH value range that is nearby the

4

isoelectric point of silica result in thick silica wall of mesoporous materials [3]. The synthetic temperature of SBA-15 from P104 is in range of 55-85°C within which SBA-15 with wall thickness of 4.1 nm can be prepared [6]. Here, our synthetic temperature is 45°C that more lower than that of the past report, which induce well hydrophilic property of amphiphilic block copolymer and the formation of thick silica wall framework. At the isoelectric point of silica, hydrolysis rate is minimum and condensation rate is maximum, which is one of the reasons for T-SBA-15. Although synthetic conditions are strictly restricted, we have successfully synthesized T-SBA-15 (wall thickness of 7.73 nm) at new synthetic temperature and relative low acidity in the presence of PI 04. 4. Conclusion In summary, at relative low synthetic temperature and acidity, thick silica wall SBA-15 has been prepared in the presence of P104 (EO27-PO61-EO27). Increasing and controlling of wall thickness are significant both for hydrothermal stability of mesoporous materials and structure tailoring of the inverse replica materials. 5. Acknowledgement This work was supported by National R & D Project of Nano-Science and Technology (Grant No. Ml-0214-00-0021) in Korea, NSFC (Grant No. 20061003, 50463002), EYTP of M. O. E. and JDYSP of Jilin Prov. in P. R. China. Cui wishes to thank to the Korea-China Young Scientist Exchange Program of KOSEF. 6. References [1] C. T. Kresge, M. E. Leonowicz, W. J. Roth, J. C. Vartuli and J. S. Beck, Nature, 359 (1992) 710. [2] M. Choi, W. Heo, F. Kleitz and R. Ryoo, Chem. Comm., (2003) 1340. [3] X. Cui, W.-C. Zin, W.-J. Cho and C.-S. Ha, Mater. Lett., 59 (2005) 2257. [4] L. Wang, J. Fan, B. Tian, H. Yang, C. Yu, B. Tu and D. Zhao, Micropor. Mesopor. Mater., 67 (2004) 135. [5] D. Zhao, Q. Huo, J. Feng, B. F. Chmelka and G. D. Stucky, J. Am. Chem. Soc., 120 (1998) 6024. [6] P. Kipemboi, A. Fogden, V. Alfredsson and K. FlodstrSm, Langmuir, 17 (2001) 5398.


5

Synthesis of tetrakaidecahedronal SBA-16 by acidity adjusting Xiuguo Cuia*, Sik-Won Moonb and Wang-Cheol Zinb " Laboratory of Advanced Functional Materials, College of Engineering, Yanbian University, Yanji 133002, P. R. China b Dept. of Materials Engineering, Pohang University of Science and Technology, Pohang 790-390, Korea

Tetrakaidecahedronal SBA-16 (cubic Im 3 m) has been synthesized in PEO106-PPO70-PEO106 ( F127 ) template solution without inorganic salt by adjusting acidity at low temperature. Due to the pH-dependence of mesoporous silica morphology, the shapes of resultant materials show an evolution from irregular sphere —» dodecahedron —> tetrakaidecahedron —> irregular shape as the acidity increases. 1. Introduction In the past decade, A new development is the discovery of crystal morphology of mesoporous materials that reveal well order both on the mesoscopic scale of porous structures and the macroscopic scale of particle shapes. Ryoo [1] first reported on truncated rhombic dodecahedral single crystal MCM-48 (cubic, Ia3d). Subsequently, cubic mesophase crystal materials with dodecaoctahedron shape (SBA-1, Pm3n) [2, 3], a large number of facets [4], square [5], truncated-cube (SBA-1, Pm3n) [5], large hierarchical structured mesoporous built single crystals [6], and hybrid mesostructures (cubic, Pm3n) with dodecahedral crystal-like morphology [7] were synthesized by using an ionic surfactant template. Compared to the ionic surfactant method, non-ionic block copolymer synthesis of crystal or crystal-like mesophase is more difficult due to its relative weak the intensity of interaction between surfactants and inorganic species. Zhao [8] reported the first synthesis_of rhombdodecahedron shaped SBA-16 mesoporous single crystals (cubic Im 3 m) in the presence of F108 triblock copolymer and inorganic salt. In this present, a new_ faceted mesoporous material, tetrakaidecahedronal SBA-16 silica (cubic Im 3 m) has

6

been firstly synthesized by adjusting acidity of F127 template solution without auxiliary agent. 2. Experimental Section In a typical synthesis of tetrakaidecahedronal SBA-16, 0.35 g of F127 (EO106-PO70-EO106) were dissolved in 10 g of HC1 aqueous solution (9.0ml of H2O and 1.0ml of 2MHC1) by stirring at 18°C. Then, 0.7 ml of tetraethyl orthosilicate (TEOS) was added to the homogeneous solution. White precipitated was repeatedly washed with water and air-dried at 50°C for an additional 48h, and then was calcined at 500°C for 8 h. In characterization of tetrakaidecahedronal SBA-16, synchrotron small angle X-ray scattering (SAXS) pattern was obtained on 3C2 beam line with CuKa radiation (wavelength, A,=0.1542 nm) in the Pohang Accelerator Laboratory, POSTECH, Korea. Nitrogen adsorption and desorption isotherms were measured at 77K on a Micromeritics ASAP2010 having an accelerated surface area and porometry system. Surface area was determined by the BET (Brunauer-Emmett-Teller) method. The pore size distribution (PSD) was calculated by the BJH (Barrett-Joymer-Halenda) method from the isotherm of adsorption branch. Scanning electron microscopy (SEM) images were taken using a JEOL JSM-6330F operating at an accelerating voltage of 15 keV. 3. Results and Discussion

200-

rTTTrTO

dV/dr

Mean PoreS ze » B.3nm

100

I

Radius(An jstrom) 0.2

0.4

0.6

0.8

Relative pressure (p/pj

Figure 1 SAXS pattern (a) and N2 sorption isotherm (b) of tetrakaidecahedronal SBA-16

Figure la demonstrates that resultant material exhibits three well resolved 110, 200 and 211 reflections resulting from the Im3m cubic symmetry, similar to that reported for SBA-16 from F108 [5] and F127 [9]. The correlation between the mesostructure and crystal morphology of tetrakaidecahedronal

7

SBA-16 can not be fully confirmed in this present due to insufficient data from SAXS pattern and HRTEM images. The nitrogen sorption isotherm shows two condensation steps at middle and high relative pressure, respectively (Fig lb). In the set of Fig lb, pore size distribution (determined by using BJH model) is narrow and bimodal (6.3 nm and 4.1 nm of mean pore sizes). Under condition of strong acid, dodecahedron SBA-16 has been synthesized by aid of inorganic salt. In our work, SEM images of resultant materials reveal that tetrakaidecahedron consists of two hexagon facets and twelve trapezia facets. External morphologies of mesoporous materials present irregular sphere, dodecahedron (Figure 2 left), tetrakaidecahedron (Figure 2 right) and irregular shape at various acidity of template solution. These changes are related to acidity range within which assembly between inorganic precursor and polymer template is well accurate, without which it is discordant.

(a)

(b)

Figure 2 SEM images of dodecahedronal, and tetrakaidecahedronal SBA-16 at various acidity. Left: template solution (lml H2O+9ml 2MHC1). Right: template solution (9 ml H2O + lml 2M HC1).

In the absence of auxiliary agent such as electrolyte and co-solvent, it is somewhat difficult to prepare crystal-like mesoporous material from nonionic polymer template. Tetrakaidecahedronal SBA-16 can be fabricated only in a narrow range of acidity and temperature. 4. Conclusion In this work, SBA-16 with a new external morphology, tetrakaidecahedronal has been synthesized in low acidity template solution without aid of auxiliary.

8

An external morphological evolvement from irregular sphere to dodecahedron, and then to tetrakaidecahedron, final to irregular shape with increasing acidity of F127 template solution. 5. Acknowledgement This work was supported by National R & D Project of Nano-Science and Technology (Grant No. Ml-0214-00-0021) in Korea, NSFC (Grant No. 20061003, 50463002), EYTP of M. O. E. and JDYSP of Jilin Prov. in P. R. China. Cui wishes to thank to the Korea-China Young Scientist Exchange Program of KOSEF. 6. References [1] J. M. Kim, S. K. Kim and R. Ryoo, Chem. Commun., (1998) 259. [2] S. Guan, S. Inagaki, T. Ohsuna and O. Terasai, J. Am. Chem. Soc., 122 (2000) 5660. [3] Sayari, S. Hamoudi, Y. Yang, I. L. Moudrakovski and J. R. Ripmeester, Chem. Mater., 12 (2000) 3857. [4] S. Che, Y. Sakamoto, O. Terasaki and T. Tatsumi, Chem. Mater., 13 (2001) 2237. [5] M. C. Chao, D. S. Wang, H. P. Lin and C. Y. Mou, J. Mater. Chem., 13 (2003) 2853. [6] Z. R. Tian, J. Liu, J. A. Voigt, B. Mckenzie and H. Xu, Angew. Chem., Int. Ed., 42 (2003) 413. [7] M. P. Kapoor and S. Inagaki, Chem. Mater., 14 (2002) 3509. [8] Yu, B. Tian, J. Fan, G. D. Stucky and D. Zhao, J. Am. Chem. Soc., 124 (2002) 4556. [9] W. Stevens, K. Lebeau, M. Mertens, G. V. Tendeloo, P. Cool and E. F. Vansant, J. Phys. Chem. B, 110(2006)9183.

Progress in in Mesostructured Materials Materials Recent Progress S. Qiu, Y. Tang and C. Yu (Editors) (Editors) D. Zhao, S. © 2007 2007 Elsevier Elsevier B.V. B.V. All All rights reserved. reserved.

9

In-situ X-ray diffraction study on the formation of a periodic mesoporous organosilica material Michael Tiemann,a Cilaine V. Teixeira,b Maximilian Cornelius,8 Jiirgen Morell,a Heinz Amenitsch,0 Mika Lindenb and Michael Frobaa "Institute of Inorganic and Analytical Chemistry, Justus Liebig University, HeinrichBuff-Ring 58, D-35392 Giessen, Germany b Department of Physical Chemistry, Abo Akademi University, Porthansgatan 3-5, FIN-20500 Turku, Finland c Institute of Biophysics and X-ray Structure Research, Austrian Academy of Sciences, Schmiedlstrafie 6, A-8042 Graz, Austria

1. Introduction Recently the synthesis of a new periodic mesoporous organosilica (PMO) material, including the preparation of the respective organosilane precursor, l,4-bis-((E)-2-(triethoxysilyl)vinyl)benzene (BTEVB), was reported simultaneously and independently by Cornelius etal. [1] and by Wang and Sayari [2]. The organic unit consists of an aromatic and an unsaturated component conjugated to each other. The PMO material exhibits cylindrical mesopores periodically arranged in a two-dimensional hexagonal p6mm symmetry as evidenced by X-ray diffraction (see below) and TEM. Nitrogen physisorption reveals typical mean pore diameters (BJH) and specific surface areas (BET) of 2.6 nm and 730 m2g'', respectively. Within the pore walls the organic units are aligned in a crystal-like fashion, similar to those in some phenylene- [3, 4], biphenylene [5], and ethylene-bridged PMOs [6]. For further details on the synthesis and structural properties of the products see reference 1. Characterization of the PMO material by X-ray diffraction yields two pieces of information. First, the low-angle region of the diffraction pattern shows peaks which correspond to the periodic two-dimensional hexagonal order of the mesopores. Second, the wide-angle region exhibits a series of equidistant reflections which are created by the periodic, crystal-like arrangement of the organic groups within the pore walls. These two sets of information obtained from a single X-ray diffraction experiment over the entire scattering region, i.e.

10 10

low angle and wide angle, make it possible to tackle the question whether or not the formation of crystal-like ordering in the pore walls occurs simultaneously with the generation of the periodically arranged mesopores [7]. 2. Experimental Section In-situ X-ray diffraction experiments were carried out at the Austrian SAXS beamline at the ELETTRA synchrotron source in Trieste, Italy, using a 2D CCD-detector. Prior to each measurement BTEVB was dispersed in an aqueous solution of octadecyltrimethylammonium chloride (OTAC1) and NaOH (BTEVB/OTACl/NaOH/H2= 1/1.4/11.9/660) and allowed to hydrolyze at room temperature for 24 h under vigorous stirring. A fraction of the homogeneous mixture was then transferred to an X-ray capillary. The sealed capillary was mounted in the sample holder where it was heated to 95 °C under constant rotation during the measurement. These experimental conditions correspond to those of the synthesis reported in reference 1. The diffraction patterns were corrected for variations in the primary intensity as well as for a background of the solvent. Positions and integrated intensities of the reflections were obtained by fitting Lorentzian profiles to the experimental data. 3. Results and Discussion Figure 1 shows the temporal evolution of the diffraction patterns during the PMO synthesis. The generally high intensity in the low-angle region is due to diffuse scattering from various objects, such as micellar aggregates. After ca. 50 minutes a low-angle Bragg reflection (s = 0.21 nm"1) is visible, corresponding to the formation of the periodic surfactant-organosilane mesophase. About simultaneously (see below) two additional Bragg reflections in the wide-angle region (s = 0.85 nm"1 and 1.70 nm"1) are detected which correspond to the periodic, crystal-like arrangement of the organic groups within the pore walls. The low-angle peak's integrated intensity is plotted as a function of the reaction time in Figure 2a. During the first 50 minutes the peak is not unambiguously distinguishable from diffuse scattering. The broad distribution of the data, especially after longer reaction times, is presumably caused by inhomogenities of the sample in the rotating capillary. However, extrapolation of the mean peak intensity towards zero suggests that the formation of the mesophase starts approximately at the onset of the measurement, i.e. at t = 0. Figure 2b shows the temporal evolution of the second wide-angle peak's intensity. (The second wide-angle peak was chosen instead of the first one because it has a higher signal-to-noise ratio.) The peak cannot be distinguished from noise at short reaction times, but extrapolation indicates that it has its origin at approximately t = 0. These findings indicate that both the formation of the mesophase and the local ordering in the walls occur simultaneously, i.e. in a

11 11

cooperative fashion. Similar results have been reported for the synthesis of a PMO material with a different organic unit [7].

0,2

0,4

0,6

0,8

1,0

1.2

2,0

s / nm"1

Figure 1: Temporal evolution of the X-ray diffraction pattern for the formation of a periodic mesoporous organosilica material. The peak at low-angle (a) corresponds to the periodic surfactant-organosilane mesophase; the peaks in the wide-angle region (b) characterize the periodic arrangement of the organic groups within the pore walls.

The d values of all three reflections remain approximately constant during the in-situ measurement. This is in contrast to the slight subsequent decrease which is frequently observed during the formation of mesostructured silica materials from precursors which are not organically modified [8-10]. However, in the in-situ measurements the low-angle reflection is located at a slightly larger d value (4.89 nm) than in the powder diffraction pattern of the final porous material after removal of the surfactant (4.72 nm [1]). This shift in the repeat distance by ca. 4 % is attributable to a shrinkage of the mesostructure due to additional condensation of the building units in the pore walls upon removal of the surfactant. For the wide-angle reflections no such difference between the in-situ measurements and the powder diffraction pattern is observed; in both cases the d values are 1.19 nm for the first peak and 0.60 nm for the second peak, respectively, indicating that the repeat distance in the regular arrangement of the organic units is widely inflexible.

12 12

60

120 180 time I minutes

240

Figure 2: Temporal evolution of the intensities of (a) the low-angle reflection and (b) the second wide-angle reflection. Extrapolation of both plots to zero suggests that both peaks start to evolve simultaneously at / = 0.

4. References [1] [2] [3] [4] [5] [6] [7]

M. Cornelius, F. Hoffmann and M. Froba, Chem. Mater., 17 (2005) 6674. Sayari and W. Wang, J. Am. Chem. Soc, 127 (2005) 12194. S. Inagaki, S. Guan, Y. Fukushima, T. Ohsuna and O. Terasaki, Nature, 416 (2002) 304. M. P. Kapoor, Q. Yang and S. Inagaki, Chem. Mater., 16 (2004) 1209. M. P. Kapoor, Q. Yang and S. Inagaki, J. Am. Chem. Soc, 124 (2002) 15176. J. Xia, W. Wang and R. Mokaya, J. Am. Chem. Soc, 127 (2005) 790. J. Morell, C. V. Teixeira, M. Cornelius, V. Rebbin, M. Tiemann, H. Amenitsch, M. Froba and M. Linden, Chem. Mater., 16 (2004) 5564. [8] P. Agren, M. Linden, J. B. Rosenholm, R. Schwarzenbacher, M. Kriechbaum, H. Amenitsch, P. Laggner, J. Blanchard and F. Schuth, J. Phys. Chem. B, 103 (1999) 5943. [9] M. Tiemann, V. Goletto, R. Blum, F. Babonneau, H. Amenitsch and M. Linden, Langmuir, 18(2002)10053. [10] K. FlodstrOm, C. V. Teixeira, H. Amenitsch, V. Alfredsson and M. Linden, Langmuir, 20 (2004) 4885.

Recent Progress in Mesostructured Materials D. Zhao, S. Qiu, Y. Tang and C. Yu (Editors) © 2007 Published by Elsevier B.V.

13 13

Is constant mean curvature a valid description for mesoporous materials? Michael W. Andersona, Philip J. Hughesa, Osamu Terasakib, Yasuhiro Sakamotob and Ken Brakke0 "School of Chemistry, The University of Manchester, Oxford Road, Manchester, Ml 3 9PL, UK b Structural Chemistry, Arrhenius Laboratory, Stockholm University, 10691 Stockholm, Sweden 'Mathematics Department, Susquehanna University, Selinsgrove PA 17870, USA

1. Introduction A detailed comparison is made between electrostatic potential density maps and surfaces of constant mean curvature for a variety of cubic mesoporous phases. We establish that the average iso-electron density surface near the wall of the mesoporous material is consistent, within experimental error, with a constant mean curvature surface. The deviation from zero mean curvature is different for different synthesis conditions and structures. On a short timescale surfactant mesophases in a water/surfactant system exhibit a boundary between the two phases which can be described in terms of sectional curvatures - usually either the mean curvature H= (ki+ k2)/2 or Gaussian curvature K = ki * k2, where kjand k2 are the maximum and minimum curvature at any given point on the surface. In a number of instances this surface has been considered to be minimal and periodic corresponding to zero mean curvature at every point (Luzzati et al 1996). This is similar to the surface formed by an open soap film suspended on a wire frame where the pressure is equal on both sides of the film and hence the mean curvature at every point is zero. Mesoporous inorganic phases templated by surfactant or block co-polymer mesophases make an interesting test of such theories. Although the system is more complex, and also there is some debate as to whether the structures are at thermodynamic equilibrium, there is the distinct advantage that the materials are solid and amenable to detailed investigation by electron crystallography. Consequently we have access to accurate electrostatic potential density maps which can be

14 14

matched with computed surfaces with known mean curvature (Anderson et al. 2005). The goal of this work is not only to establish the nature of the curvature but also to understand the formation mechanism. The results also have implications for natural inorganic structures which are templated by macromolecular organic assemblies. 2. Experimental section Electrostatic potential density maps were determined using electron crystallographic methods, described elsewhere (Anderson et al. 2004), which rely on data from a single particle and consequently are not contaminated by scattering from ill-formed material. Constant mean curvature surfaces are computed using a periodic lattice with pre-determined symmetry using the Surface Evolver programme (Brakke 1996). 3. Results and discussion Fig. 1 shows an example of AMS-8, synthesised with an anionic surfactant (Garcia-Bennett et al. 2004) both as an iso-electron density contour plot and as a constant mean curvature surface. The slices shown in Fig. 2 reveal that for this structure there is a very close fit at zero mean curvature. However, for SBA-1, SBA-6 and SBA-16 - all with cubic symmetry - a similar analysis reveals a constant mean curvature but not zero mean curvature. AMS-8

Equi-electrostatic potential surface

Zero mean curvature surface

Fig. 1 The structure of AMS-8 from both experimental electron crystallography and as an isomean curvature map determined using Surface Evolver.

The close approximation to a constant mean curvature surface suggests that the forces at the interface of the average silica surface with the mixed phase water/surfactant or water/polymer are relatively even. This in turn suggests a uniform interface. The four cubic mesophase systems studied all result from an

15 15

arrangement of high mean curvature micelles packed on a cubic lattice. The gaussian curvature of these micelles is positive. The resulting silica structures for three materials, SBA-1, SBA-6 and AMS-8, have constant but low mean curvature and also negative gaussian curvature. This suggests that the interface is not between the silica and organic agent but between silica and water. Only for SBA-16 does the mean curvature of the silica material become sufficiently high to suggest a closer interaction between silica and block co-polymer template.

Fig. 2 Slice of electrostatic potential density map for AMS-8, coloured contours are experimental and dotted line is computed for slices taken through the unit cell at z=0 and z=0.125.

Fig. 3 shows the gaussian curvature computed for AMS-8 and also SBA-16. The AMS-8 structure has already been shown to have constant mean curvature close to zero and as expected the gaussian curvature is negative everywhere, indicating a saddle-like surface. The gaussian curvature is most negative at the necks which join the cages. For SBA-16 the story is quite different. In this case the actual structure is far from zero mean curvature exhibiting a constant and positive mean curvature. As can be seen from Fig.3 the gaussian curvature over most of the surface is also strongly positive with negative gaussian curvature only at the rather narrow necks. This is consistent with the silica surface being much more closely bound to the block co-polymer templating agent. This is consistent with the prevailing conjecture that the end of the block co-polymer chains are embedded within the silica wall resulting in additional microporosity when the template is removed by calcination. Fig. 3 also shows the ideal zero mean curvature topology for the Im 3m structure which is often used to describe the related liquid crystal boby-centred cubic mesophase. This demonstrates how the specific interactions between the templating agent and the silica wall are crucial to define to final topology.

16 16

Fig. 3 Gaussian curvature for (a) AMS-8, (b) zero mean curvature ideal SBA-16 topology and (c) actual SBA-16 topology with positive mean curvature.

4. Summary This work demonstrates that, within experimental error, constant mean curvature is a valid description to describe the stucture of a variety of cubic mesoporous structures. The mean curvature is closest to zero for surfactant based preparations but large and positive for polymer based preparations. This indicates the difference in interfacial interactions between the two systems. 5. References [1] V. Luzzati, H. Delacroix and A.Gulik, The micellar cubic phases of lipid-containing systems: Analogies with foams, relations with the infinite periodic minimal surfaces, sharpness of the polar apolar partition. Journal De Physique II 6 (1996) 405. [2] M. W. Anderson, C. C. Egger, G. J. T. Tiddy, J. L. Casci and K. A. Brakke, A new minimal surface and the structure of mesoporous silicas. Angewandte Chemie-International Edition 44 (2005) 3243. [3] M. W. Anderson, T. Ohsuna, Y. Sakamoto, Z. Liu, A. Carlsson and O. Terasaki, Modern microscopy methods for the structural study of porous materials. Chemical Communications (2004) 907. [4] K. A. Brakke, The surface evolver and the stability of liquid surfaces. Philosophical Transactions of the Royal Society of London Series a-Mathematical Physical and Engineering Sciences 354 (1996) 2143. [5] A. E. Garcia-Bennett, O. Terasaki, S. Che and T. Tatsumi, Structural investigations of AMS-n mesoporous materials by transmission electron microscopy. Chemistry of Materials 16 (2004) 813.


17 17

Salt effect in the synthesis of highly ordered, extremely hydrothermal stable SBA-15 C. L. Li, Y.Q. Wang*, Y. L. Guo, X. H. Liu, Y. Guo and G. Z. Lu Lab for Advanced Materials, Research Institute of Industrial Catalysis, East China University of Science and Technology, Shanghai 200237, P. R. China

1. Introduction Since the discovery of MCM-41 by Mobil scientists in 1992 [1], ordered mesoporous silicate materials have attracted considerable attention for their potentially applications as catalyst supports, adsorbents and etc. Up to now, a serial of ordered mesoporous silica (M41S, SBA-2, 3, MSU, SBA-15, etc.) have been successfully synthesized. However, these materials have not been widely used in industry because of their relatively poor hydrothermal stability. Hydrothermal stability of mesoporous materials is an important property for future applications and much work has done to improve it. Normally, post-treatment with organosilane, incorporation of hetero-atoms, carbon propping and assembly of zeolite precursors with template were used to enhance the hydrothermal stability. Such as post-treatment of MCM-41 with methyl-chlorosilane has been used just at the discovery of M41S family [1]. Generally, increasing the aging temperature would be a good way to enhance the hydrolysis and condensation of silicon precursors, and finally improve the hydrothermal stability. Yan Y et al [2, 3] realized it by using fluorocarbon-hydrocarbon surfactant mixtures as templates. In our work, inorganic salt (NaCl) was used to assist the formation of highly ordered, extremely hydrothermal stable SBA-15. 2. Experimental Section The synthesis was done under 1.0 M HC1 solution, using the mixture of triblock copolymer P123 and semi-fluorinated surfactant FSO-100 as the template and inorganic salt (NaCl) as an assistant agent. Samples without addition of NaCl were synthesized with the similar procedure and the normal SBA-15 was also synthesized according to literature [4] for comparison.

18 18

The hydrothermal stability was investigated by treating samples in a closed bottle at 100°C for 300 h under static conditions. High-temperature steam test was carried out by exposing the samples to water vapor in N2 steam at 600°C for 6 h. The samples were characterized with small-angle XRD, TEM, N2 sorption and solid state 29 Si MAS NMR. 3. Results and Discussion The mesoporous structures were characterized by SXRD, TEM and N2 sorption. Fig. 1A shows the SXRD patterns of SBA-15 synthesized at 160 °C with and without NaCl. It can be seen clearly that the addition of NaCl remarkably enhances the ordering of mesostructure, this phenomena have been confirmed before [5-8]. Fig. IB gives the SXRD patterns of SBA-15 synthesized at various aging temperatures in the presence of NaCl. They clearly show 3-4 well-resolved reflections that can be indexed as 100, 110, 200 and 210 diffractions associated with the p6mm hexagonal symmetry. This is an indication of good long-range hexagonal ordering. It is interesting to note that with the increase of aging temperature, the diffraction intensity decreases slightly, but the positions have no obvious shift. It is different from that synthesized at relatively low temperatures [9], which showed that the temperature had a significant influence on the structural parameters. 100

B

Intensity

Intensity

A

11

110 200 210 O

140 C O

With NaCl

160 C

Without NaCl

180 C

3 4 2 2 2-Theta(degree)

O

5

1

3 4 2 2 2-Theta(degree)

5

Fig. 1 (A)SXRD patterns of SBA-15 synthesized at 160°C with and without NaCl, (B) SXRD of SBA-15 synthesized with the addition of NaCl at different temperature (140 -180 °C).

Fig. 2A is the SXRD patterns of SBA-15 after treating in boiling water for 300 h. Three peaks indexed as 100, 110 and 200 reflections of the mesostructure are obvious. There were no significant changes of the 20 positions, intensities and linewidths of diffraction peaks compared with that of calcined SBA-15, which indicates that the highly ordered mesostructures were still maintained after hydrothermal treatment. The SXRD patterns of steaming treated SBA-15 are displayed in Fig. 2B, the patterns also show a very intense 100 reflection and two

19 19 1 100 100

Hydrothermal treatment A: Hydrothermal

110 200

O 140OC;300h 140 C; 300 h

Intensity

Intensity

100 100

B: Steaming treatment

110200

O

160 C; 300 160OC; 300 h

O

140 C;steaming 66 h 140 O

160 C;steaming C;steaming6h 160 6h

O

180 C; 300 h C;300 1

2

3

4

O 180OC;steaming6h C;steaming 6 h 180

5

1

2

2-Theta(degree)

3

4

5

2-Theta(degree)

Fig. 2 (A) SXRD patterns of SB A-15 after treating in boiling water for 300 h, (B) after steaming at 600 °C for 6 h.

additional higher order reflections with lower intensity, indicating that the mesostructures weren't destroyed even under such severe conditions. These results demonstrate that the synthesized samples have remarkably hydrothermal stability. N2 sorption measurements showed that the BET surface area reduced a little bit after hydrothermal treatment, but narrow pore size distribution still maintained (unshown here), indicating that the ordered structures undestroyed, which is in accordance with the XRD measurement. The structural properties of the samples are summarized in Table 1. All the results demonstrate that the synthesized samples have good mesostructural ordering and remarkably hydrothermal stability. The extremely high hydrothermal stability of thus-synthesized SBA-15 was due to the high aging temperature as discussed by Han Y [2, 3]; and at the same time, inorganic salt, NaCl, also played a important role in the enhancement of the hydrolysis and condensation of silicon precursor. The latter was confirmed by solid Table 1. Structural properties of calcined and treated samples Sample

dioo

/nm S-140 S-140-H S-140-600 S-160 S-160-H S-160-600 S-180 S-180-H S-180-600

10.2 10.4

9.7 10.4 10.5

9.9 10.0 10.1 10.0

a0 /nm

/m

11.8 12.0 11.2 11.9 12.1 11.4 11.5 11.7 11.5

438 320 298 422 312 313 377 294 243

SBET 2

g"1

Dp /nm 7.4 7.5 6.5 7.3 7.5 7.3 6.8 7.6 7.0+14.7*

W /nm 4.4 4.5 4.7 4.6 4.6 4.1 4.7 4.1 4.5

Vp

SBET reduction

/cmV

/%

0.983 0.848 0.738 0.941 0.832 0.764 0.851 0.797 0.821

26.9 32.0 26.0 25.8 22.0 35.5

Note: a0: cell dimension; Dp: pore diameter; W: pore wall thickness; Vp: total pore volume. * Pores come from the aggregation of particles (void space).

20

state 29Si MAS NMR (unshown here). The ratio of Q4/Q3 in thus-synthesized SBA-15 is higher than that in the sample synthesized without NaCl addition and much higher than that in normal SBA-15. The high degree of condesation plays the most important role in enhancing the hydrothermal stability. 4. Conclusion

In conclusion, highly ordered and high hydrothermal stable SBA-15 have been synthesized in a one-step simple process. After treatment in boiling water or steaming, the ordering of the mesostructures hasn't destroyed. Such materials may have potential applications in catalysis and separation. 5. Acknowledgement This project was supported financially by the National Basic Research Program of China (No. 2004CB719500) and Commission of Science and Technology of Shanghai Municipality (04ZR14036, 05PJ14032), China. 6. References [1] J. S. Beck, J. C. Vartuli, W. J. Roth, M. E. Leonowicz, C. T. Kresge, K. D. Schmitt, C. T-W. Chu, D. H. Olson, E. W. Sheppard, S. B. McCullen, J. B. Higgins and J. L. Schlenker, J. Am. Chem. Soc. 114(1992)10834. [2] Y. Han, D. F. Li, L. Zhao, J. W. Song, X. Y. Yang, N. Li, Y. Di, C. J. Li, S. Wu, X. Z. Xu, X. J. Meng, K. F. Lin and F. S. Xiao, Angew. Chem. Int. Ed. 42(2003) 3633. [3] D. F. Li, Y. Han, J. W. Song, 1. Zhao, X. Z. Xu, Y. Di and F. S. Xiao, Chem. Euro. J. 10 (2004)5911. [4] D. Y. Zhao, J. L. Feng, Q. S. Huo, N. Melosh, G. H. Fredrickson, B. F. Chmelka and G. D. Stucky, Science, 279(1998)548. [5] C. Z. Yu, B. Z. Tia, J. Fan, G. D. Stucky and D. Y. Zhao, J. Am. Chem. Soc, 124(2002) 4556. [6] K. Flodstrom, V. Alfredsson andN. Kallrot, J. Am. Chem. Soc. 125(2003) 4402. [7] B. Lee, D. L. Lu, J. N. Kondo and K. Domen, J. Am. Chem. Soc. 124(2002)11256. [8] Y. Q. Wang, B. Zibrowius, C. M. Yang, B. Spliethoff and F. Schiith, Chem. Commun., (2004) 46. [9] X. J. Meng, Y. Di, L. Zhao, D. Z. Jiang, S. G. Li and F. S. Xiao, Chem. Mater., 16(2004) 5518.


21 21

Hydrocarbon templated sol-gel synthesis and characterizations of mesoporous silica xerogel Halina Misran3*, Mohd Ambar Yarmob and Ramesh Singh3 "College of Engineering, University Tenaga Nasional, Km 7, Jalan Kajang-Puchong 43009 Kajang, Selangor, Malaysia. School of Chemical Sciences and Food Technology, Universiti Kebangsaan Malaysia, 43600 Bangi, Selangor, Malaysia.

1. Introduction Porous silica materials are widely known for various applications from adsorbents, catalysis and as template to metal oxide [1-3]. In recent years, ordered mesoporous silica xerogels had gained considerable attention in various field due to the reduced production cost and improved properties. Recently, a low-cost attempt on producing nanosized perovskite, spinels and mesoporous carbon via silica xerogel templating route where the silica xerogel used had the structural characteristics similar to mesoporous silica materials were reported [4]. Microporosity, mesoporosity or both could be introduced in the silica xerogels by using quaternary surfactant and polystyrene spheres in a "one-pot" synthesis method [5]. General method of producing mesoporous silica xerogel employed the use of expensive and toxic surfactants as structure directing agents. Thus, a low-cost and environmental-friendly approach of producing mesoporous silica xerogel would be by terminally eliminating the use of surfactants in the synthesis procedure. In this study, we report on the attempt to produce silica xerogels with similar properties as MCM type silica materials using renewable resources of palm oil derived hydrocarbons in nanometer size oil-in-water droplets emulsion. In order to study the application of the silica xerogels as silica support materials, "one-pot" functionalization method using phenol-red were carried out and the resulting materials were characterized accordingly.

22

2. Experimental Section Silica xerogels were prepared by the hydrolysis and co-condensation of TEOS as silica precursor in a surfactant-less oil-in-water emulsion. In a typical synthesis procedure, oil phase were dispersed in a continuous phase containing co-solvent by ultrasonification. Then, TEOS was added dropwise to the solution mixture containing base catalyst and subjected to acoustic emulsification followed by stirring for 24 h. The final pH of the mixture was adjusted with acid until gelation occurred [7]. The gels were washed, filtered and dried followed by calcinations to obtain xerogels, hereafter denoted as ULSF6,ULSF-8 and ULSF-9. For functionalized silica xerogel materials, phenol red (PR) was diluted in alcohol and added to the solution mixture. The gel was solvent extracted, filtered and dried to obtain ULSF-10PR. Structural characterizations were done using nitrogen sorption on a Quantachrome NOVA 1200e at 77 K, SEM using LEO 1450VP at 20 kV, TEM using Hitachi Tecnai at 200 kV. 29Si and 13C were measured using Bruker AV400. 3. Results and Discussion The 13C CP NMR of as-synthesized xerogels as shown in Figure 1 exhibited strong signals at ca. 22 to 34 ppm were assigned to the alkyl groups in saturated alkanes [6]. The peaks were attributable to the carbon atom chains in fatty alcohols. These results suggested that the fatty alcohols play the role as structure directing agents during the synthesis. The resonance peaks observed at ca. 62 and 69 ppm were assigned to the carbon atoms in the methoxy groups. These signals were observed from the residues of short-chain alcohol used in the synthesis. A representative X-ray diffraction analysis of calcined silica #

F li e : H \: 3 1 C N M \R r1

* OCH

In t e n s it y ( a .u . )

OCH33 #

Si CH2 CH2 O OSiC OCH3 OCH

## * 80 80 8 0

7 0

#

* 6050 40 60 40 Chemical shift shift (ppm) (ppm) Chemical 6 0

5 0

4 0

3 0

# #

20 2 0

Fig. 1. 13 CCP NMR of as-synthesized xerogels.

1 0

20 20

40 40

220O θ(°)

60 60

Fig. 2 A representative XRD pattern.

xerogels as shown in Figure 2, exhibited a broad peak centered at ca. 20 = 22° suggesting that the materials were of amorphous nature. The absence of pronounce peaks at lower angle also indicated that the pores were of disordered

23

wormhole-like structure. Nitrogen adsorption isotherms of calcined samples are shown in Figure 3. With the exception of ULSF-9, all samples exhibited Type IVa isotherms in the IUPAC classification with narrow HI type hysteresis loops These results suggested the successful formation of mesoporous silica xerogels with open-ended tubular pores. The surface area estimated from the BET equation applied to the monolayer region of adsorption branches were at ca. 305 m /g to 600 m2/g as shown in Table 1. Silica xerogels prepared from decyl alcohols exhibited highest surface area at ca. 600 m2/g. This result was obtained due to the stability of the nanometer sized oil droplets in the oil-in-water emulsion formed from decyl alcohol. Thus, during the synthesis, more hydrolysis and condensation-polymerizations of anionic silicate oligomers could occur on the surface of the nanosized oil droplets giving rise to the morphology of spherical agglomerates as confirmed by SEM image in Figure 4. Pore volume estimated by the t-plot method also exhibited highest value of 1.5 mL/g for ULSF-9, sample prepared from decyl alcohol. SEM image of calcined sample as shown in Figure 4 exhibited fine globular units of spherical morphology. 800

0.5 Relative Pressure (P/Po)

0.2 0.4 0.6 0.8 Relative Pressure (P/Po)

1

Fig. 3. Nitrogen adsorption isotherms with the corresponding pore size distributions a) ULSF-8 b) ULSF-6. Table 1. Pore characteristics of calcined and solvent extracted silica xerogels. Sample Name

Type of fatty alcohols

Pore size (nm)c

Surface area (m2/g)a

Total pore volume (mL/g)b

ULSF-9

Decyl

17.4d

600

1.5

ULSF-6

Octyl

12.1

305

0.9

ULSF10-PR

Octyl

8.0

545

0.8

ULSF-8

Dodecyl

19.7

a

By BET method.

b

By t-plot method.

494 c

By BJH method

1.1 d

By DFT method.

The particle sizes observed were at ca. 5 nm) silicas [1]. However, mesoporous silicas with cubic symmetry are generally more difficult to prepare than their two dimensional (2-D) hexagonal counterparts (e.g. SBA-15) [2], and particularly, cage-like mesophases are often synthesized in a narrow range of synthesis conditions. 3-D materials are expected to be superior to materials with 1-D channels especially for applications related to adsorption, diffusion and host-guest interactions. Despite synthetic progress [3-7], methods for synthetic tailoring of structure, pore dimensions and pore topology remain to be improved. In addition, due to the cage-like pore structure, it is challenging to accurately determine the real size of the cages and pore windows. The present contribution introduces recent developments in the preparation and characterization of 3-D silica mesostructures consisting of large interconnected cage-like pores. The results are especially concerned with the modulation of pore dimension and pore shape of mesoporous Imhm silicas (SBA-16) [8,9]. 2. Experimental Section Large pore cage-like mesoporous silicas were synthesized with Pluronic F127 (EO106PO70EO106) as the structure-directing agent and TEOS as the silica source. The reactions were performed at low HC1 concentration (0.4 M) at 45°C for 24 h, followed by aging for 24 h at a temperature ranging from 45 to 130°C. nButanol was added to the mixture to act as a co-surfactant. The molar composition of the starting mixture was varied in the range 0.0035 F127:x TEOS:^ BuOH:0.91 HC1:117 H2O with x = 0.5-3, and y = 0-3, respectively. For template removal, the as-synthesized mesophases were either extracted at room temperature with HCl/ethanol followed by calcination at 550°C for 2 h, or

58

subjected to H2SO4 treatment. Briefly on the treatment, 2 g of the as-synthesized mesophase was stirred in H2SO4 (48 wt%) at 95°C for 24 h. The powder was further heated at 250°C in air for 3 h. Materials were characterized by nitrogen physisorption measurements at 77 K, argon physisorption measurements at 87 K, and powder X-ray diffraction (XRD). Physisorption data were evaluated using the Quantachrome Autosorb 1.52 software. 3. Results and Discussion The low acid concentration conditions employed enable the introduction of nbutanol as a phase-controlling agent [4,8] into the Si02-EOio6P070EOio6-H20 system, to provide tuning of the mesophase topology. Various silica mesophases with either facecentered cubic (fee) Fm3m, body-centered cubic (bec) Im3m or 2-D hexagonal [0.91,2.08| structures are generated depending on the TEOS/BuOH mole ratio in the starting synthesis mixture [8]. For TEOS/BuOH [1.52,1.34) ratios comprised between 2.29/0.15 and 0.91/2.08, the XRD peaks observed in the [2.29, 0.15] range of 2 theta = 0.6-2.5 are indexed to the 0.5 1.0 1.5 2.0 2.5 3.0 Im3m space group, as exemplified in Fig. 1. 28 (degrees) All the N2 isotherms of these silicas are type IV isotherms with a H2-type adsorption- Fig. 1 XRD patterns for cubic Iniim desorption hysteresis loop characteristic of SBA-16 silicas, prepared at the mesoporous materials with cage-like pores molar ratio of 0.0035 F127:* [3,10]. The structural parameters of these TEOSy BuOH:0.91 HC1:117 H2O, cubic Im3m silica materials are summarized with [x, y] as shown. in Table 1. Specific surface area (SOFT), total pore volume (FDFT), and micropore volume (Vmi volume for pore diameters < 2 nm) could be estimated using non-linear density functional theory method (NLDFT). The model used for the NLDFT evaluations is the recently developped kernel of isotherms of N2 adsorbed on silica with spherical pore geometry, using the adsorption branch [11]. The primary mesopore cage diameter is denoted $DFT and was estimated using the same NLDFT method.

59 Table 1 Physicochemical parameters derived from N2 sorption measurements performed at 77 K [TEOS, BuOH]

a

SOFT 2

1

SBET 2

1

VDFT 3

1

vmi 3

1

W X. '' spheres

"cylinders

fry]

(nm)

(m g )

(m g )

(cm g )

(cm g )

(nm)

(nm)

[2.29,0.15]

15.3

753

890

0.49

0.088

7.1

4.7

[1.88,0.68]

15.5

746

860

0.51

0.092

7.9

5.1

[1.52, 1.34]

15.1

767

810

0.51

0.116

8.2

5.4

[1.27, 1.61]

15.6

909

1050

0.72

0.090

8.9

6.3

[0.91, 2.08]

16.2

930

980

0.74

0.068

10.1

7.2

for the calcined SBA-16 samples with different TEOS/BuOH molar ratios (see text).

Our investigations reveal that the structural properties of the cubic Im3m mesoporous silicas can be tailored by simply adjusting the amounts of the silica source and co-surfactant in the synthesis mixture. A pronounced increase of the mesopore volume is observed with simultaneous decrease of the TEOS amount and increase of the butanol content. This behavior is also reflected on the dimension of the cages as illustrated by the evolution of the pore size distribution (Fig. 2). The pore size increases from 7.1 nm up to 10.1 nm with concurrent increase of butanol and decrease of the quantity of TEOS. Note that pore size analysis by NLDFT calculations based on a cylindrical pore model underestimates the pore dimensions by about 30%. Three population of pores are evidenced (Fig. 2): micropores around 1.4 nm (possibly noncomnecting), connecting windows centered around 3 nm, and the main large mesocages. Cubic mesoporous silicas prepared at low HC1 concentrations also exhibit distinct textural properties when the template is removed either by calcination or by a treatment with sulfuric acid. Particularly, the acid treatment allows for tailoring of the pore topology and seems to open access to uniform synthetic tuning of pore entrances instead of producing materials with distribution of entrance sizes.

2

4

6

8

10

12

" 16 1» 2° Pore diameter [nm]

Fig. 2 PSD for SBA-16 samples, calculated from the N2 sorption isotherms at 77 K using the NLDFT model based on spherical pores (dotted line). Solid line is the FFT smoothed

60

0.2

0.4 0.6 0.8 Relative pressure (P/PJ

0.2

0.4 0.6 0.8 Relative pressure (P/Po)

Fig. 3 Argon physisorption isotherms measured at 87 K on calcined and acid-treated SBA-16 (Si02-EO,o6P07oE0106-H20-butanol): (a) aged at 100 °C and (b) aged at 60 °C.

The acid-treated materials exhibit larger unit cell parameter and larger pore volume than those observed for the same materials after conventional calcination. The applied acid treatment can produce materials with pseudocylindrical mesopores (Fig. 3) while maintaining the overall cubic symmetry. However, pore size analyses performed with the respective NLDFT pore models suggest little influence of the treatment on the large mesopore diameter. 4. References [1] G. J. A. A. Soler-Illia, E. L. Crepaldi, D. Grosso and Sanchez, C, Curr. Opin. Colloid Interface Sci., 8 (2003) 109. [2] M. Choi, W. Heo, F. Kleitz and R. Ryoo, Chem. Commun., (2003) 1340. [3] F. Kleitz, D. Liu, G. M. Anilkumar, I. S. Park, L. A. Solovyov, A. N. Shmakov and R. Ryoo, J. Phys. Chem. B, 107 (2003) 14296. [4] F. Kleitz, L. A. Solovyov, G. M. Anilkumar, S. H. Choi and R. Ryoo, Chem. Commun., (2004)1536. [5] T.-W. Kim, R. Ryoo, M. Kruk, K. P. Gierszal, M. Jaroniec, S. Kamiya and O. Terasaki, J. Phys. Chem. B, 108 (2004) 11480. [6] J. Fan, C. Yu, F. Gao, J. Lei, B. Tian, L. Wang, Q. Luo, B. Tu, W. Zhou and D. Zhao, Angew. Chem. Int. Ed., 42 (2003) 3146. [7] J. Fan, et al. J. Am. Chem. Soc, 127 (2005) 10794. [8] F. Kleitz, T.-W. Kim and R. Ryoo, Langmuir, 22 (2006) 440. [9] C. M. Yang, W. Schmidt and F. Kleitz, J. Mater. Chem., 15 (2005) 5112. [10] P. I. Ravikovitch and A.V. Neimark, Langmuir, 18 (2002) 1550. [11] M. Thommes, B. Smarsly, M. Groenewolt, P. I. Ravikovitch and A. V. Neimark, Langmuir, 22 (2006) 756.


61 61

A novel method of mesostructured material architecture using DBD plasma on illite with nonexpandibility Myung Hun Kima, II Mo Kangb, Kiwoong Sungc, Bui Hoang Bacc, Jeong Hun Kimd, Yungoo Songc, Hi-Soo Moon0 and Su Dok Yie "Department of Chemistry, Yonsei University, Seoul 120-749, Korea Institute of Earth Atmosphere Astronmy, Yonsei University, Seoul 120-749, Korea c Department of Earth System Sciences, Yonsei University, Seoul 120-749, Korea Department of Ophtalmology, Seoul National UniversityHospital, Seoul lqO-744, Korea e Yong Koong Illite Company, Bokwang Building, Seoul 152-080, Korea

The mesostructured material architecture using hydroxyl groups derived from DBD plasma within illite structure has been successfully accomplished by hydrothermal conditions under between 353 and 373 K and pH=6 condition. 1. Introduction Illite has a three-sheet layer structure and non-expandibility with tightly held interlayer K+ balancing a high layer charge. The surface charge of illite layers, one Al3+ octahedral sheet sandwiched between two Si4+ tetrahedral sheets, is the permanent negative charge on the basal planes due to the isomorphic substitutions, Al3+ for Si4+ and Mg2+ or Fe3+ for Al3+. Additional polar sites, mainly octahedral Al-OH and tetrahedral Si-OH groups, are situated at the broken edges. These amphoteric sites are conditionally charged, and so variable charges can develop at the edges by direct H+ or OH" transfer from aqueous phase depending pH. The hydroxyl groups are active sites which tend to react with many polar organic compounds and various functional groups [1]. However, no attempt to generate effectively hydroxyl groups in illite is mentioned in literatures and the use for the hydroxyl groups has been published a few reports. Hence, in an effort to establish the importance of these groups, we refered to a noteworth paper reported by U. Kogelschatz et. al to generate a lot of hydroxyl groups on illite [2]. The author showed the ozone generated from the

62

dielectric-barrier discharge (DBD) plasma through the discharge gap between the electrodes was transformed into the hydroxyl groups on the amorphous silica. The purpose of present work gains a better understanding of the role of hydroxyl groups molded in DBD plasma treatment process on non-expandible illite and derives the mesostructured materials using these groups. 2. Experimental Section Illite was obtained from Yong Koong Illite Company. DBD plasma was treated for 0.5 and 1.0 min on illite under oxygen atmosphere, respectively. After that, the samples were refluxed with 0.5 N HC1 for 4 h, washed and dried at RT. The chemical composition of the gel solution is 1.5 CTMAC1: 2.0 Illite: 0.5 EtOH: 5000 H2O. All reactions carried out at 353 K and 373 K under pH = 6. Also, the products were denoted M-Ili(l) and M-Ili(2). The resultant solids were characterized by means of PXRD, TGA, TEM and nitrogen adsorption. 3. Results and Discussion The X-ray patterns in Fig. 1 show mesopore phases displaying peaks in the range of 0.78-90 nm with the interplanar spacing of 7.0-8.0 nm. MIli(l) and M-Ili(2) synthesized at 353 K and 373 K with plasma-treated illites exhibit one peak, respectively, but raw illite was not appeared any peaks at low q value. The results from XRD indicate that DBD plasma treatment causes the generation of specific active sites within illite structure and it derives the formation of pores in accordance with CTMA+ induction. In order to investigate the presence of the functional groups generated after DBD plasma treatment, FTIR analyses were carred out in the range 400-4000 cm"1. The band at 3752 cm"1 is due to the free silanol groups and the band at 3671 cm"1 represents the vibration of weakly interacting vicinal silanol groups. In addition, the band at 3650 cm"1 corresponds to Si-O-H stretching of

(i)

0.4

0.8

1.2

1.6

2.0

Fig. 1. Powder XRD patterns (I) of (a) Illite, (b) M-Ili(l) and (c) M-Ili(2) (inset: FTIR spectrum (II) of samples treated by DBD plasma with different time of (a) 0 min., (b) 0.5 min., and (c) 1 min.).

63

internal silanol groups and the band at 3627 cm"1 is attributed to OH vibration mode of hydrogen bonded hydroxyl groups between inter/intra illite layers. Actually, plasma-treated samples appeared to increase the band intensity of new hydroxyl groups than raw illite. This means that oxygen radicals formed from plasma treatment lead new functional hydroxyl groups in illite basal layers. The groups play an important role of the interaction between the CTMA+ as structure directing agent and the sheets of non-expandible illite to derive mesostructure materials. Representative N2 adsorption-desorption isotherm results are displayed in Table 1. The shapes of the isotherm for M-Ili series corresponded typical behavior of mesopore solids with partial micropore contribution in the lower relative Table 1. Specific surface area, mesopore and micropore volume of illite and M-Ili series.

Materials Illite M-Ili(l)

Total N2adsb (mL/g)

Micropore vol.0 (mL/g)

65

0.056

0.056

335

0.310

0.054

BET

Mesopore vol.0 (mL/g) 0.256

400 0.405 0.058 0.347 b From the linear t-plot at low P/Po. From the isotherm at low P/P0~0.55. °Total amount adsorbed minus micropore volume. a

pressure range and with mesopore volume saturation capacity of about 0.256 and 0.347 mL/g, respectively. The estimated BET surface areas are much larger than that for the parent illite. The pore volumes for M-Ili(l) and M- Ili(2) are lower than those of typically observed mesoporous solids. The results of the presented isotherms confirmed to form a novel mesostructured material by selfassembly of induced CTMA+and illite with new generated hydroxyl groups. This is consisted with the micrograph suggested by high resolution TEM in Fig. 2. The TEM image shows representative example of the material produced, all being essentially homogeneous. From upper results, authors suggest that after disintegration of the illite layers under specific pH condition and temperature, induced CTMA+ ions are bonded on the fragments surfaces of illite layers 50 nm with new hydroxyl groups as Fig. 3. And + then CTMA ions-illites are selfassembled as spherical shape to keep Fig. 2. TEM micrograph of M-Ili(2).

64

3k. Ci6TMA +

Illite

Fig. 3. Mechanisms of the mesostruct formation of illite with hydroxyl groups generated from DBD plasma treatment. thermo-dynamical stable state. This model implies that silanol groups (Si-OH) generated after DBD plasma treatment form hydrogen bondings with CTMA+ and they derive a novel porous material going with the micropores according to mesopore evolution process such as Fig. 3. 4. Conclusion This study introduces the architecture of a novel mesostructured material from illite with non-expandibility. The pores are formed from the interaction between structure directing agent, CTMA+, and new functional groups within illite sheets due to hydroxyl groups generated by oxygen radical emitted from DBD plasma. 5. Acknowledgement Financial supports of the Ministry of Science and Technology of Korea (Grant No. R01-2005-000-11039-0) and Yong Koong Illite Company are greatly acknowledged. 6. References [1] C. C. Liu and G. E. Maciel, The Fumed Silica Surface: A Study by NMR. J. Am. Chem. Soc. 118(1996)5103-5119. [2] U. Kogelschatz, B. Eliasson and W. Egli, From Ozone Generators to Flat Television Screens: History and Future Potential of Dielectric-Barrier Discharges. Pure Appl. Chem. 71 (1999) 1819-1828.

Progress in in Mesostructured Materials Recent Progress S. Qiu, Y. Tang and C. Yu (Editors) (Editors) D. Zhao, S. © 2007 2007 Elsevier Elsevier B.V. B.V. All All rights reserved. reserved.

65 65

Production of highly mesostructured SBA-15 silicas at pH around the PZC Alexandra Chaumonnot and Emmanuelle Trela IFP-Lyon, BP 3, 69390 Vernaison, France.

1. Introduction During the last few years, an increasing amount of mesostructured oxide materials with high specific surface area have been synthesized by a cooperative self-assembly mechanism between inorganic precursors and surfactant molecules or macromolecules under hydrothermal conditions [1, 2], Among them, mesostructured aluminosilicates present an obvious interest as heterogeneous catalysts and sorbents [3]. Much effort has therefore been devoted to the introduction of aluminum into silica frameworks [4]. A usual method to obtain Al-SBA-15 materials consists in adding an aluminum precursor into the silica gel prior to hydrothermal synthesis. Contrary to the preparation of SBA-15 silica, where pH is around 0, Al-SBA-15 is produced at a higher pH (just below the point of zero charge of silica, pH ~ 1.5) in order to limit the dissolution of a fraction of the aluminum precursor [5]. In this range of pH, a decrease in the level of mesostructuration is observed, even for pure SBA15 silica materials. Moreover, the presence of aluminum species reinforces this phenomenon. In preliminary works, we have found that the loss of structural organisation for pure SBA-15 silicas is due to the presence of amorphous and partially organised phases mixed with a well-organised phase. In this study, we describe and discuss the influence of the rate of hydrolysis (r = H2O mole number/Si mole number in the initial solution) of a conventional synthesis on the percentage of non-organized phases present in pure SBA-15 silicas. In fact, it is well reported in the literature that two aspects are essential to fine-tune the selfassembly and the construction of the inorganic framework: the reactivity of the inorganic precursors (hydrolysis and polymerization rate) and their interactions with the template to generate a well-defined organic-inorganic interface [2]. The rate of hydrolysis is closely related to the kinetics of polymerization. Therefore,

66

r is obviously one of the most critical experimental parameters which need to be precisely controlled in order to induce the mesostructuration process. 2. Experimental Section SBA-15 silica was synthesized according to literature procedures and used as a reference (So sample) [6]. Practically, 4 g of triblock poly(ethylene oxide)poly(propylene oxide)-poly(ethylene oxide) (EO20PO70EO20, Aldrich) were added to 150 mL of an aqueous HC1 solution at pH = 1.5 at 313 K. After stirring for 24 h, 9 mL of tetraethylorthosilicate (TEOS) were added at 313 K. The mixture was stirred for another 24 h and then heated at 373 K for 24 h under hydrothermal conditions. The reference rate of hydrolysis r was set at 217. The samples Si to S4 were obtained using similar setups with the following respective rates of hydrolysis: 54, 79, 108 and 434. The other experimental parameters were kept constant, particularly the weight ratio TEOS/ - All products were filtered, dried at 373 K and calcined at 823 K for 4 h with a heating rate of 120 K.h"1. N2 adsorption/desorption isotherms were recorded on a Micromeritics ASAP 2405 volumetric adsorption analyzer at 77 K. Samples were dried under a vacuum of 10"5 Torr for 12 h at 723 K. The specific surface area was determined by a modified BET method adapted to microporous/mesoporous solids [7]. The mesopore size distribution (Dmeso < 50 nm) and the cumulative surface area as a function of pore size were calculated by applying the BdB method to the N2 adsorption branch [8]. XRD data were collected on a PANalytical X'Pert Pro 9/20 diffractometer equipped with a copper X-ray target and an X'Celerator fast detector. Special attention was given to the sample preparation as reflexion Bragg Brentano geometry was used at a very low angular range (0.4 to 2.0°26). TEM images were obtained on a Jeol 2010 microscope. 3. Results and Discussion Fig. 1 shows the N2 adsorption/desorption isotherm and the evolution of the cumulative surface area as a function of pore size, obtained for the reference silica sample So. For P/Po > 0.6, this isotherm is characteristic of mesostructured solids with a narrow pore size distribution centered around 8 nm (type IV according to the IUPAC classification). The organized porosity is also confirmed by the small angle XRD data (not shown) typical of a 2D hexagonal mesostructure. Nevertheless, another porosity in the range of small mesopores is observed, characterized by a large pore size distribution centered around 5 nm. TEM analyses also show that the mesostructuration process was not complete. This leads to the production of an amorphous or partially organized phase in the reference sample, yielding this second porosity.

67

500

400

350

C u m u l a t i v e S m 2 .g -1

3

Volume adsorbed cm .g

-1

* 400

300

200

S0 -o-SO

300

250

200

150

100

50

100 0

- • - SS3 3

2

4

6

8

10

12

14

Pore size nm

0 0

0,1

0,2

0,3

0,4

0,5

0,6

0,7

0,8

0,9

1

P/Po

Fig. 1 N2 adsorption/desorption isotherms at 77 K and cumulative surface area as a function of pore size (inset) calculated for the adsorption branch (BdB method) for So et S3 samples.

By varying the hydrolysis rate between 54 to 434, we have shown that only a narrow window of r values leads to the mesostructuration process. In fact all products, except for S3 sample, are characterized by an amorphous or a partially organized phase (presence of some uniform porosity with an absence of organization) (Table 1). Table 1 Properties of the So to S4 samples. Sample

r

Structure

SO

217

A/PO/O mixture

460

242

218

5,0 - 7,9

SI

54

A/PO

517

339

178

5,8

S2

79

A/PO

494

314

180

5,5

S3

108

0

577

380

197

7,3

S4

434

A

495

113

382

5,4

S B ET

m2

/g

SBdB m /g

SBET " SedB m

/g

§ (nm)

A: amorphous; PO: partially organized; O: organized.

High rates of hydrolysis lead to an entirely amorphous solid (S4 sample), which is presumably due to a lack of interaction between the silica oligomers generated and the triblock copolymer macromolecules. The medium being more diluted than in the reference sample, we may assume that it induces the formation of smaller silica oligomers with probably non-hydrolyzed OEt groups at the surface. These species might not be able to undergo enough of the weak interactions that are necessary to activate the mesostructuration process. Reversely, excessively low values of r lead to pseudo-organized materials with a high percentage of amorphous or partially organized phases (Si and S2 samples). This could be explained by an excessive rate of polymerization of the inorganic precursors which prevents either the creation of an interface with the

68

organic micelles or the formation of these micelles. Finally, only values of r around 100 lead to a highly mesostructured silica (S3 sample, Fig. 1). 4. Conclusion We have shown that, in the case of SBA-15 silicas, the percentage of amorphous and partially organized phases, mixed with a highly mesostructured 2D hexagonal phase, clearly depends on the concentration of the precursors. In fact, a complete mesostructuration process can only be obtained for values of the rate of hydrolysis around 100. These new experimental data should pave the way towards the controlled synthesis of well-ordered Al-SBA-15. 5. References [1] J. S. Beck, J. C. Vartuli, W. J. Roth, M. E. Leonowicz, C. T. Kresge, K. D. Kresge, K. D. Schmitt, C. T.-W. Chu, D. H. Olson, E. W. Sheppard, S. B. McCullen, J. B. Higgins and J. L. Schlenker, J. Am. Chem. Soc, 114 (1992) 10834. [2] G. J. de A. A. Soler-Illia, C. Sanchez, B. Lebeau and J. Patarin, Chem. Rev., 102 (2002) 4093. [3] A. Corma, Chem. Rev., 97(1997)2373. [4] Luan, M.Hartmann, D. Zhao, W. Zhou and L. Kevan, Chem. Mater., 11 (1999) 1621. [5] S. Sumiya, Y. Oumi, T. Uozumi and T. Sano, J. Mater. Chem., 11 (2001) 1111. [6] Y.-H.Yue, A. Gedeon, J. L. Bonardet, J. B. d'Espinose and J. Fraissard, Stud. Surf. Sci. Catal., 130(2000)3035. [7] D. Zhao, J. Feng, Q. Huo, N. Melosh, G. H. Fredrickson, B. F. Chmelka and G. D. Stucky, Science, 279 (1998) 548. [8] P. Schneider, Applied Catalysis A:General, 129 (1995) 157. [9] A. J. Lecloux, J. Bronckart, F. Noville and J.-P. Pirard, Stud. Surf. Sci. Catal., 39 (1988) 233.

Recent Progress in Mesostructured Mesostructured Materials D. Zhao, S. Qiu, Y. Tang and C. Yu (Editors) © 2007 Elsevier B.V. All rights reserved.

69 69

Three-dimensional large pore cubic niobosilicates: direct synthesis and characterization IzabelaNowak*aand Mietek Jaroniecb "Faculty of Chemistry, A. Mickiewicz University, Grunwaldzka 6, PL-60-780 Poznan, Poland b Department of Chemistry, Kent State University, Kent, OH-44240 USA 1. Introduction

Since discovery of surfactant-templated silicas the pore range of structurally ordered materials has been extended from micropores (zeolites) to mesopores (2-50 nm). Ordered mesoporous silicas are amorphous frameworks of welldefined porous structures that impart strict shape-selective properties utilized to great advantage in separations and catalysis. For many applications three dimensional molecular sieves are desired because they provide an accessible pore volume to minimize (reactant, product) diffusion constraints. To take a full advantage of these mesostructures in catalysis, one should be able to incorporate transition metal species of desired catalytic activity and to control the sizes of cages and cage entrances. The polymeric templates provide great opportunities in the pore size and pore structure engineering [1], thus three kinds of triblock copolymers that generate cubic cage-like structures: SBA-1 (Pm3n), SBA-16 (Im3m), and FDU-1 (Fm3m) were chosen for this study. A comparative study of these mesostructures containing niobium species is presented. 2. Experimental Section NbSBA-1, NbSBA-16, and NbFDU-1 materials were prepared using tetraethyl orthosilicate (TEOS) from Aldrich and ammonium tris(oxalate) complex of niobium(V) (CBMM, Brazil) as silicon and niobium sources, respectively. The Si/Nb atomic ratio was kept 64. Three different block copolymers, i.e., Pluronics P85 (EO)26(PO)39(EO)26 and F127 (EO),06(PO)7o(EO)io6 from BASF and B50-6600 (EO)39(BO)47(EO)39 from Dow Chemicals,

70

were used for the synthesis of NbSBA-1, NbSBA-16, and NbFDU-1, respectively, in order to investigate the influence of the surfactant geometry on the mesostructure. The synthesis gel was subjected to a hydrothermal treatment by transferring it into polypropylene bottles and heating at 373 K for 48 h without stirring. The product was then filtered out, washed, dried and calcined at 813 K. The synthesis of NbFDU-1 was previously reported in [2], while the NbSBAland NbSBA-16 samples were prepared by using recipes provided in [3]. The structure was confirmed by X-ray diffraction (XRD), transmission and scanning electron microscopy (SEM and TEM), and nitrogen adsorption at 77 K. In addition, the incorporation of niobium species was investigated by UV-Vis Diffuse Reflectance (UV-Vis-DR) and Infrared (FTIR) spectroscopies. 3. Results and Discussion Textural/structural properties. The powder Xray diffraction patterns for the samples prepared using J2500 s different triblock copolymers showed characteristic n low angle diffraction peaks typical for SBA-1, SBA16, and FDU-1 structures. The well-resolved diffraction peaks of NbFDU-1 were assigned to cubic Fm3m symmetry group [2]. The XRD patterns for calcined NbSBA-16 shows a strong 110 peak at 20 = Nb-SBA-1 -0.8° with small shoulders, which could be arise from 200 (20 = 1.08°) and 220 (20 = 1.69°) reflections according to the Im3m symmetry group (Fig. 1). Also, quite intense reflections were observed at the low angle range of 2G = 0.5-1.5° for NbSBA-1, which Nb-SBA-ie" could be indexed as 110, 200, and 210 according to the Pm3n symmetry. According to these assignments, 0.8 1.6 1.2 0 the unit cell parameters for the NbSBA-1, NbSBA-16, 20, and FDU-1 mesostructures are equal to 14.5, 16.0, Fig. 1. XRD data for cubic and 23.5 nm, respectively. materials. The BET surface area for all niobium-containing materials studied was similar, over 900 m2g"1. The total pore volume of Nb-containing materials was between 0.6 and 1.0 cm3 g"1 with the highest value for NbFDU-1. The existence of micropores is obvious from Table 1 and it was also the biggest for FDU-1 structure. Fig. 2 shows a comparison of nitrogen adsorption isotherms for a series of cubic samples. The nitrogen adsorption-desorption isotherms obtained for calcined mesoporous niobio-silicates are type IV (Fig. 2) with visible capillary condensation step. As can be seen from Table 1 the mesopore widths are -6.9, 11.4, and 15.3 nm for NbSBA-1, NbSBA-16, and NbFDU-1, respectively. The minimal wall thickness for all samples studied, calculated according to relations provided in [4], was between 1 and 3 nm. The shape and closure of 200

O

Int ensity, a.u.

>1102um) 5.0 3.0 1.8

HaP(20-45nm)* 5.0 2.5 1.3

* prepared ex-situ

The F" retention was one order of magnitude greater for HaP/M41 than pure HaP (Bio-Rad) and greater than for nanometric HaP, see table 2. 4. Conclusion The method used for the host inclusion (not reported in literature) seems to be adequate, since the OH- groups of HaP were not blocked. The HaP was essentially located inside the mesopore channels. Furthermore, only HaP was formed and no K oxide and/or PO4" phases were detected by XRD. In the case of HaP (ex-situ), its lower crystal size favored the F" retention compared with the commercial one. M41 acts as a support to anchor the HaP nanocrystals, without exclude the possibility of the growth of few crystals of HaP in the external surface according to TEM images. 5. References [1] [2] [3] [4]

A. Laghzizil, N.Elhrech, O. Britel and O. Bouhaouss, J. Fluorine Chem. 101 (2000) 69. O. Anunziata,A. Beltramone and J. Cussa,Applied Catalysis A.General,270 (1-2) (2004) 77. O. Anunziata, L. Pierella, E. Lede and F. Requejo, Stud. Surf. Scie. Catal. 135 (2001). F. Chen, A.Shen, X-Jun Xu, R.Xu, F. Kooli, Micropor. Mesopor. Mater., 79 (2005) 85.

Progress in in Mesostructured Materials Recent Progress S. Qiu, Y. Tang and C. Yu (Editors) (Editors) D. Zhao, S. © 2007 2007 Elsevier Elsevier B.V. B.V. All All rights rights reserved. reserved.

81 81

Direct synthesis of cerium-incorporated SBA-15 mesoporous molecular sieves Qiguang Dai, Guoping Chen, Xingyi Wang* and Guanzhong Lu Laboratory for Advanced Materials, Research Institute of Industrial Catalysis, East China University of Science and Technology, Shanghai 200237, P.FLChina

Ce-SBA-15 mesoporous molecular sieves were synthesized by the two-step synthetic method in acid media. The obtained materials were characterized by small angle X-ray diffraction (SAXRD), transmission electron microscopy (TEM), N2 adsorption-desorption full isotherm and elemental analysis. Cerium has been incorporated into the framework position and walls of silica network of SBA-15. Additionally, the high catalytic activity of Ce-SBA-15 for trichloroethylene (TCE) combustion was observed. Keywords: Direct synthesis, SBA-15, Cerium incorporated 1. Introduction In the family of mesoporous molecular sieves, SBA-15 synthesized with triblock copolymer as a surfactant under strong acidic conditions exhibits larger pore sizes and thicker pore walls, compared with M41S. As it has been known, the pure-silica molecular sieves show almost no activity for catalytic reactions, and the active sites in the molecular sieves are always from heteroatoms. The hexagonal mesoporous SBA-15 has been synthesized at pH 0.0275 mol dm'3) dominated the shape of pores and the transition of mesostructure; while hydrogen ions had no effect on the transition. Due to the existence of lamellar mesostructure in resulting samples, H4 hysteresis loop occurred, no step appeared on the adsorption branch and the amount of N2 adsorbed reduced in N2 adsorption-desorption curves. 5. Acknowledgement This research is financially supported by the Key Project Foundation of the Ministry of Education of China (No: 105104), the Natural Science Foundation of China (No: 50572057, 50472069) and the Middle-aged and Youthful Excellent Scientist Encouragement Foundation of Shandong (No: 2005BS 11003). 6. References [1] C. T. Kresge, M. E. Leonowicz, W. J. Roth, J. C. Vartuli and J. S. Beck, Nature, 359(1992) 710. [2] Q. Huo, D. I.. Margolese and G. D. Stucky, Chem. Mater.8(1996) 1147. [3] S. Tolbert, H. Landry, C. C. Stucky, G. D. Chmelka, B. Norby, F. P. Hanson and J. C. A. Monnier, Chem. Mater. 13(2001) 2247. [4] K. W. Gallis, and C. C. Landry, Chem. Mater. 9 (1997) 2035. [5] S. Che, S. Lim, M. Kaneda, H. Yoshitake, O. Terasaki and T. J. Tatsumi, Am. Chem. Soc. 124(2002) 13962. [6] a) W.-J. Kim and S.-M. Yang, Langmuir, 16(2000) 4761. b) H.-P. Lin, S.-B. Liu, C.-Y. Mou and C.-Y. Tang, Chem. Commun. (1999) 583. [7] S. Bagshaw, A. E. Prouzet and T. J. Pinnavaia, Science 269 (1995) 1242. [8] K. S .W. Sing, D. H. R. Everett, A. Haul, W. L. Moscou, R. A. Pierotti, J. Rouquerol and T. Siemieniewska, Pure & Appl. Chem. 57(1985) 603.

Recent Progress Progress in in Mesostructured Mesostructured Materials Materials Recent D. Zhao, S. S. Qiu, Qiu, Y. Y. Tang and and C. C. Yu Yu (Editors) (Editors) D. © 2007 2007 Elsevier Elsevier B.V. B.V. All All rights rights reserved. reserved. ©

105 105

Structure characterization of mesostructured Silica nanowires formed in Porous Alumina membranes Baodian Yaoa'* and Ning Wangb " Department of Chemistry, Fudan University, Handan Road 220, Shanghai, 200433, China Department of Physics, the Hong Kong University of Science and Technology, Clear Water Bay, Hong Kong, China

1. Introduction Mesoporous silica [1] and anodic aluminum oxide (AAO) [2] porous membranes are two materials which have been widely employed as hosts in synthesizing ordered arrays of nanomaterials [3]. AAO membranes, characterized by one-dimensional regularly arranged, unidirectional parallel pores with uniform pore depth, are relatively easily prepared with pores of welldefined orientation over large areas. Mesoporous silica has smaller pore sizes than AAO and so may offer advantages in terms of quantum size effects and property control. Thus, the filling of mesoporous silica into AAO pores to form new hierarchical structures will make advantages of both materials as hosts in synthesizing other ordered arrays of nanomaterials. Of particular interest is the formation of silica-AAO composites in which the mesopores of the silica (such as MCM-41, SBA-15) are aligned parallel to the channels of the alumina framework. It is well-known that 2D hexagonal mesoporous silica films, say MCM-41, SBA-15 thin films, almost always contain pore channels oriented preferably along the substrates. In this regard, two possibilities of hexagonal pore alignment of mesoporous silica wires formed in a AAO membrane channel exist: one is alignment of the pores in longitudinal direction (columnar orientaion); the other is alignment of the pores in latitudinal direction (circular orientation). To date, studies on the confined assembly of silica-surfactant mesostructures within AAO membranes showed that pure columnar orientation is easily realized when ionic surfactants were used as the structure-directing agent [4-5]; in contrast, mesopores with the columnar and circular orientation usually

106 106

coexist in a membrane when nonionic surfactants were used as templates[5-9]. And it seemed that circular orientation was favored over the columnar ones in most cases [6-8], though single columnar orientation was once reported in the literature [9]. Apart from the mesopore orientations, the confined assembly of silica-surfactant often resulted in some unique mesostructures, such as concentric lamellar structured silica wires [6b]. And such unique silica mesostuctures are easily mistaken as 2D hexagonal silica wires with circular or columnar orientation, for concentric lamellar mesostructured silica wires will exhibit parallel stripes (side view) same to that of 2D hexagonal silica wires with columnar orientation, and exhibit concentric circles (plan view) same to that of 2D hexagonal silica wires with circular orientation. In this regard, conclusions in ref. [9-10] based on just side view TEM observations remain sceptical. Here we report on the structure characterization of mesostructured Silica nanowires formed within the pores of AAO by a sol-gel method from a SBA-15 precursor based on detailed TEM side view and plan view observation. 2. Experimental Section The mesoporous silica nanowires were prepared via a simple sol-gel and rotary evaporation method by using tetraethoxysilane (TEOS) as a silica source and triblock copolymer surfactants (BASF, Pluronic PI23) as the structuredirecting agent. Commercially available porous anodic alumina membranes (Whatman, Anodisc 25, pore diameter 200 nm, thickness 60 urn) were used as the substrate. A viscous silica sol and alumina membranes in a 50 ml beaker were sealed in a container and aged at 60°C for 12 h with (sample A) and without (sample B) the presence of 20 ml water, respectively. All the gelated samples were subsequently calcined at 500°C for 6 h (see ref. [7 ] for Detailed procedures). The mesostructures of the samples were investigated by Transmission Electron Microscopy (TEM) (a JEOL 2011 microscope operating at 200 kV). Plan view TEM samples were prepared by mechanical polishing followed by Argon ion milling. For the preparation of side view TEM samples, the AAO templates were first dissolved using the 5M HCl and silica NWs were collected by filtration. 3. Results and Discussion Figure 1 shows the typical TEM images of Sample A with clear structural characteristics. As can be seen from the plan view images (Figure la and b), most of the silica NWs consist of concentric circular features with a distorted core part and some of them are nearly completely composed of concentric circles (Figure lc). At the same time, hexagonal pore arrangements can be found in every silica wires in side view mode and Figure Id is the represent-

107 107

a

b

a

b

c

c d

d

e e

Figure 1 (Left). TEM images of sample A: (a) Low magnification, (b) and (c) High-resolution plan-view; (d) and (e) High-resolution side view. Scale bar: 1 OOnm.

Figure 2 (Right). TEM images of sample B: (a) Low magnification, (b) and (c) High-resolution planview; (d) and (e) High-resolution side view. Scale bar: 1 OOnm.

tative side view image. By combining the side view with plan view, we can conclude that silica NWs in sample A are of 2D hexagonal and exhibit a circular orientation. Figure le further confirms the circular orientation of mesopores, helix feature to some extent can also be observed. In sample B, for TEM plan view, most silica NWs have well hexagonally arranged pore cores surrounded by layered silica shells (see Figure 2a and b); for side view, parallel strips can be seen in Figure 2d and 2e. It should be noted here that images like Figure Id could not be found in sample B, which indicates that layers of Silica NWs in sample B, not like in sample A, have no further structure features, i.e. no pore exists. Thus, we can conclude that most silica NWs in sample B are composed of 2D hexagonally arranged pore cores with columnar orientation, which are wrapped by lamellar structured silica shells. In extreme cases, some silica NWs probably possess nearly 100% concentric lamellar mesostructure(part suggested by Figure 2c). The structural features of silica wires in sample B, in fact, should be regarded as the co-existence of a 2D hexagonal phase and a lamellar phase of mesoporous silica. Such two phase coexistence is often observed in the synthesis of mesoporous silica and can be easily controlled by process parameters, such as pH value, temperature [11], drying [12], and solvent evaporation [13]. The degree of polymerization of the Si precursor is believed to be one important factor in the phase evolution of mesoporous silica, which determines whether the rearrangement of surfactant can be happened during the synthesis processes [11]. In this regard, sample A may be regarded as the evolution product of sample B, whose polymerization of the Si precursor is not sufficient (for water is insufficient) and thus the rearrangement of surfactant is possible when additional water is provided in the case of sample A.

108 108

4. Conclusion Mesoporous silica NWs formed within the pores of porous alumina membranes have been detailedly charaterized by TEM. The mesostructures of as-prepared NWs can be readily controlled by varying the aging treatment. Two kinds of Silica NWs with nearly completely different structural features were thus obtained. When aged without water, silica NWs consisted of a 2D hexagonal pore core wrapped by a lamellar shell; when aged in the presence of water, 2D hexagonal mesoporous silica NWs with circular orientation were formed. The possible evolution suggested from Sample B to A would provide insight on the rational design and synthesis of mesoporous silica with special structural features. The work here also suggests strongly that both side view and plan view are indispensable in the characterization of mesoporous silica wires using TEM. 5. Acknowledgement This work was supported by the National Natural Science Foundation of China (20503006), Dr.Yao thanks the start-up funding from Fudan University. 6. References [1] B. Z. Tian, X. Y. Liu, H. F.Yang, S. H.Xie, C. Z. Yu, B. Tu, and D. Y. Zhao, Adv. Mater., 15(2003) 1370. [2] H. Masuda, H. Yamada, M. Satoh, H. Asoh, M. Nakao and T. Tamamura, Appl. Phys. Lett.,71(1997) 2770. [3] B. D. Yao and N. Wang, J. Phys. Chem. B, 105(2001)11395. [4] Yamaguchi, F. Uejo, T. Yoda, T. Uchida, Y. Tanamura, T. Yamashita and N. Teramae, Nature Materials. 3(2004) 337. [5] Platschek, N. Petkov and T. Bein, Angew. Chem. Int. Ed., 45(2006) 1134. [6] Z. L. Yang, Z. W. Niu,; X. Y. Cao, Z. Z. Yang, Y. F. Lu, Z. B. Hu and C. C. Han, Angew. Chem. Int. Ed., 42(2003) 4201; (b) D. H. Wang, R. Wang, Z. L. Yang, J. B. He, Z. Z. Yang and Y. F. Lu, Chem. Commun., ( 2005) 166. [7] Yao, D. Fleming, M. A. Morris and S. E. Lawrence, Chem. Mater., 16(2004) 4851. [8] Y. Y. Wu, G. S. Cheng, K. Katsov, S. W. Sides, J. F. Wang, J. Tang, G. H. Fredrickson, M. Moskovits and G. D. Stucky, Nature Mater., 3(2004) 816; (b) Y. Y. Wu, T. Livneh, Y. X. Zhang, G. S. Cheng, J. F. Wang, J. Tang, M. Moskovits and G. D. Stucky, Nano Lett., 4(2004) 2337. [9] Q. Y. Lu, F. Gao, S. Komarneni and T. E. Mallouk, J. Am. Chem. Soc, 126(2004) 8650. [10] W. P. Zhu, Y. C. Han and L. J. An, Microporous. Mesoporous Mater. 84(2005) 69. [11] C. Landry, S. H. Tolbert, K. W. Gallis, A. Monnier, G. D. Stucky, F. Norby and J. C. Hanson, Chem. Mater. 13(2001) 1600. [12] M. C. Liu, H. S. Shen and S. Cheng, Chem. Commun. (2002) 2854. [13] Grosso, F. Babonneau, G. A. A. Soler-Illia, P. A. Albouy and H. Amenitsch, Chem. Commun. (2002) 748.


109 109

CRISP and eMap: software for determining 3D pore structures of ordered mesoporous materials by electron crystallography H. Zhang3, T. Yub, P. Oleynikov0, D.Y. Zhaob, S. Hovmollerc and X. D. Zouc "Materials Science and Engineering, Central South University, 410083, Changsha, P. R. China Department of Chemistry, Fudan University, Shanghai 200433, P. R. China 'Structural Chemistry, Stockholm University, SE-106 91 Stockholm, Sweden

The software CRISP and eMap are developed for determining 3D pore structures of ordered mesoporous materials by electron crystallography. Here

they are demonstrated on the mesoporous material FDU-5 with the space group Ia3d. 1. Introduction Mesoporous materials with ordered pores are of great interests due to their applications in many areas. The structure of these highly ordered mesoporous materials can hardly be determined only from X-ray powder diffraction. Electron crystallography is the most powerful tool for determining the 3D pore structures of such materials [1]. We have developed software CRISP [2,3] and eMap [4] for determining 3D atomic structures of crystalline materials from HREM images [5]. The software is now extended and can be applied to 3D reconstruction of ordered mesoporous materialsÂn example is given for the mesoporous material FDU-5 with space group la 3d. 2. Experimental Section Synthesis of the cubic la 3d mesoporous silica FDU-5: in a typical synthesis, 1.00 g of P123 and 0.115 g of sodium dodecyl sulfate were dissolved in a mixture of 26.0 g water and 12.0 g of 2.0 M HC1 at 30°C. 2.08 g of tetraethyl orthosilicate (TEOS) was added to this solution under vigorous stirring. The solution was kept at 30°C for 24 h, and then transferred into a Teflon autoclave

110 110

and heated at 100°C for another 24 h. The precipitated solid was collected by filtration, washed with water, and dried in air at room temperature. The assynthesized powders were calcined in air at 550°C for 5 h to remove the template. N2 adsorption/desorption measurements were carried out at -196°C using a Micromeritics ASAP Tristar 3000 system. The samples were degassed at 180°C overnight on a vacuum line. The total pore volume of mesoporous silica was calculated to be 1.18 cm3g"', given by the single point amount adsorbed at a relative pressure of 0.99. Assuming a density of the silica wall of 2.20 gem"3, the fraction of pore volume corresponds to 72.2 %. Transmission electron microscopy was performed on a JEOL JEM-2000FX microscope operating at 200kV. Images were recorded either on films or with a KeenView CCD camera (Soft Imaging System, 1376 x 1032 pixels). The HREM image processing and 3D potential map calculation were performed using the software CRISP [2,3] and eMap [4]. 3. Results and Discussion HREM images of FDU-5 from three different zone axes of the same crystal were collected and the thinnest area were used for further image processing (Fig.l).

a

50 nm

b

50 nm

c

50 nm

Fig. 1 HREM images of FDU-5 taken along the (a) [111], (b) [001] and (c) [110] zone axes.

The images were processed using CRISP. The crystallographic image processing of the HREM image of FDU-5 taken along the [111] direction is shown in Fig. 2. First a Fourier transform was calculated from the thinnest area (512x512 pixels) of the crystal. The defocus value was determined either experimentally and/or from the Fourier transform of the image (-31000 A). The effects of the lens contrast transfer function were compensated for by CRISP (Fig. 2). Then the structure factor amplitude and phase of each reflection were extracted. Finally the symmetry of each projection was determined using CRISP (herep6m) and imposed onto the amplitudes and phases.

111 111

File

Edit

Tools

Are

CIP

ELD PhlDO

Statistics

Calculate

Options

Wind

DOO A Detocus (v]

p3nl p31n

i.l 26.2 2B.2 26.1

4.6 7.5 E.7 8.8

-

a=186 fi b=lSS & More

Try All

|

g=-l£0.0 Reline

1-31000 A

C Elliptic aproKimali ** Mathematical CTF

|

_

~a

Ia

| | [

Fig. 2 Crystallographic image processing of the HREM image taken along the [111] zone axis using CRISP. The effects of defocus and crystal tilt were compensated for. Table 1 Structure factors obtained by electron crystallography

hkl

112

022

004

123

024

233

224

044

134

Amplitudes

100.0

36.2

14.4

8.1

6.8

6.7

1.9

1.7

1.7

Phases(°)

0

0

0

180

180

0

0

0

180

Reflections from different zone axes were merged into a single set of reflections. Amplitudes of common reflections were used for scaling and the phases were changed according to the common origin. The merged structure factors are listed in Table 1. The data set was expanded according to the symmetry Ia3d and a 3D electrostatic potential map was calculated using eMap. The 3D pore structures were visualized using eMap (Fig. 3). The corresponding surface area and pore volume fraction were calculated simultaneously while the threshold value was changed.

112 112

a

b

c

Fig. 3 Reconstructed 3D electrostatic potential map by electron crystallography (a) FDU-5, (b) reconstructed from the data given by Sakamoto et al. (2004) and (c) FDU-5 using only 2 strongest reflections (211) and (220). The red side is towards the pores and green towards the walls. The mesopore structures are very similar in all 3 cases. However, the micropores are shown differently.

The 3D structure of FDU-5 reconstructed from the three zone axes (Fig. 3a) is similar to that reported by Sakamoto et al. [4] (Fig. 3b). The overall pore structure is accurately determined from only the two (!) strongest reflections (Fig. 3c). For detailed pore structures such as pore shapes and wall thickness, all reflections with significant amplitudes (>1.5% of the strongest reflection (112) are included, all with accurate relative amplitudes and phases. Correct determination of the contrast transfer function is essential for calculating correct amplitudes. The slight differences related to the micropores and wall thickness shown in Figs. 3a and b give an indication of the possible errors that may be generated. In order to detemine the exact sizes and shapes of the micropores, many and very accurate structure factors (amplitudes and phases) are needed. 4. References [1] Y. Sakamoto, T. W. Kim, R. Ryoo and O. Terasaki, Angew. Chem. Int. Ed. 43 (2004) 5231. [2] S. Hovmoller, Ultramicroscopy 41 (1992) 121. [3] Calidris, Image processing of electron micrographs (2005) http://www.calidris-em.com. [4] AnaliTEX, Computational crystallography with eMap (2005) http://www.analitex.com/Index.html. [5] X. D. Zou, Z. M. Mo, S. Hovmoller, X. Z. Li and K. H. Kuo, Acta. Cryst. A59 (2003) 526.


113 113

A mechanistic study on the degradation of highly ordered, non-ionic surfactant templated aluminosilicate mesoporous materials Al-CMI-1 in boiling water Alexandre Leonard and Bao-Lian Su* Laboratoire de Chimie des Materiaux Inorganiques (CMI), I.S.I.S, The University of Namur (FUNDP), 61, rue de Bruxelles, B-5000 Namur, Belgium

A detailed account of the evolution of aluminosilicate mesoporous materials in boiling water is described. After erosion of the surface silicate layer covering the inner side of the channel walls by hydrolysis, Al atoms become exposed and confer a remarkable resistance to these materials. 1. Introduction Aluminosilicate mesoporous molecular sieves have been conceived as complements to zeolites for cracking heavy gas-oil molecules. [1-3] Due to the number of potential applications in heterogeneous acid catalysis, many studies have been devoted to the synthesis, characterization and application in catalytic processes of aluminosilicate mesoporous materials. As a result, many different structures have been synthesized over recent years via several pathways such as post-synthesis grafting of Al-species, ion-exchange or direct co-condensation of both silica and alumina sources. [4-5] Different Al sources, Si/Al ratios, thermal treatment conditions, pH and surfactants have been used, which has in fine, led to a huge number of materials with similar or different properties. [6-9] Nonionic surfactants are ideal candidates for large-scale preparations because of their easy removal, their non-toxicity and biodegradability. [10] Al-CMI-1 materials, prepared via a non-ionic templating pathway, are characterized by hexagonal channel structures, pores of 3-4 nm and intra-framework Al atoms. Owing to the innumerous application possibilities, it is of crucial importance to have in hand the knowledge of the behaviour of such materials in aqueous media. Pure silica materials are commonly known to be rapidly hydrolyzed in

114 114

boiling water and we demonstrated a degradation-recovery phenomenon of textural properties with immersion time. [11] Aluminosilicate mesoporous sieves could however present a higher resistance. [12-14] The aim of this work was to investigate how Al-doped silica structures, obtained via non-ionic templating methods, behave in boiling water. The originality relies in the fact that the continuous evolution with time has been investigated, as thus far previous studies have only reported the changes after a certain period of time, e.g. 24 h. This could provide important information for the design of new highly efficient mesoporous aluminosilicate catalysts. 2. Experimental Section The aluminosilicate Al-CMI-1 materials have a hexagonal stacking of channels, specific surface areas exceeding 1100 m2/g, homogeneous pore sizes between 3 and 4 nm and the majority of Al atoms located in a tetrahedral environment, i.e. in framework positions. After complete removal of surfactant by solvent extraction, the materials were immersed in boiling water and samples were withdrawn after fixed periods of time ranging from 5 minutes to 97 h, dried and fully characterized. The techniques used for characterization included XRD (Siemens D5000), transmission electron microscopy (TEM, Philips Tecnai T10), scanning electron microscopy (SEM, Philips XL20), 27A1 NMR (Bruker 500) and nitrogen adsorption-desorption (Micromeritics Tristar 3000). 3. Results and Discussion The XRD patterns show that the structure seems to be globally destroyed immediately after immersion as all diffraction peaks disappear, suggesting a far more widespread degradation than in pure silica materials. Intact ordered zones can however still be seen by TEM, indicating that part of the framework resists the extreme conditions (Fig. 1A). The 27A1 NMR spectra show 2 peaks, one at 50 ppm for tetrahedral species, and one less intense signal at 0 ppm for octahedral Al species (extra-framework Al, EFAL) (Fig. IB).

A

J> B

1

52 ppm

-6 ppm

'-

97h 0h 0h

-200 -100 -200-10

0 100 100 200 8 27Al (ppm) (ppm) δ

Fig. 1 : TEM pictures and Al NMR spectra of Al-CMI-1 after different immersion times.

As the time immersed in boiling water is extended, the EFAL species seem to be washed out of the structure and no supplementary EFAL is created upon immersion. The morphology of the particles remains unchanged, thus the

115 115

f

>•

500

1200

A

400

0h 97h

300

2h

200 100 0,0 0,0

0,2 0,2 0,4 0,4 0,6 0,6 0,8 Relative pressure p/p0 p/p0

1,0

|

0

1000 1000 800 600

B

P o r e d i a m e t e r (n m )

600

S p e c i f i c s u r f a c e a r e a (m ² / g )

V o l u m e a d s o r b e d ( c m ³/g - S T P )

alterations occur on the interior walls of the channels, leaving the global structure unmodified. Same transformations occur in pure silica structures. [11] More striking changes occur from the textural point of view. The starting sample has a type IV isotherm with a steep adsorption branch and a homogeneous pore size distribution centred between 3 and 4 nm (Fig. 2A). Immediately after immersion, the shape of the isotherm tends towards type I, (microporous structure) with a sharp drop in specific surface area (Fig. 2B). This can also be observed for pure silica materials and could result from a partial hydrolysis at the inner surface of the channels, with hydrolyzed species obstructing the apertures. After 13-20 h, the shape of the isotherms tends towards that of mesoporous structures, the pore size increases again and the specific surface area reaches 90% of its initial value. No further changes occur for longer immersion times, except for a slight decrease in surface area, but its value still exceeds 800 m2/g after 97 h. The homogeneous mesopores reformed after 13-20 hours also remain unchanged even after 97 h (Fig. 2C). As reported for pure silica structures, the recovery of the starting textural characteristics could result from dissolution of the pore-blocking species, liberating the mesochannels. [11] The main difference of these structures compared to pure silica relies in the long-term transformation. In the present case, homogeneous pore sizes and high specific surface areas are maintained even for very long immersions, suggesting no further alteration of the framework, whereas the silica analogues completely collapse. Such higher resistance cannot be attributed to a protective AI2O3 layer as already suggested because octahedral Al species are absent in our samples (evidenced by 7A1 NMR measurements, Fig. IB). [15] Instead, we suggest that the Al atoms are not located at the surface of the channels but hidden in the thick walls separating adjacent mesopores. This is supported by the fact that we observed only weak interactions when adsorbing basic probe molecules. [16] The surface of the channels is thus constituted only of SiO2. 3.2

C

2.8 2.4 2.0

0 20 0 20 20 40 40 60 60 80 80 100 100 20 40 40 60 80 100 Immersion duration (hours)

Fig.2 : Nitrogen adsorption isotherms (A) and evolution of specific surface area (B) and pore diameter (C) as a function of immersion time in boiling water.

According to our previous study, the siloxane bonds are rapidly and irreversibly hydrolyzed by the attack of water molecules, thus explaining the rapid degradation upon immersion in boiling water. Then, when the pore-

116 116

blocking silica species are dissolved, the Al atoms become exposed on the surface of the channels. These freshly exposed Si-O-Al groups have a protective action by repelling the hydroxide anions that catalyze the hydrolysis of the framework. [17] For that reason, further collapse of the structure, observed for pure silica mesoporous materials, is prevented and the framework remains unaffected, even for very long immersion times in boiling water. These results show that the introduction of a trivalent heteroatom can considerably improve the resistance of a mesoporous framework. 4. Conclusion The characteristic amorphous wall composition of non-ionic surfactant templated Al-CMI-1 mesoporous materials confers a remarkable stability to boiling water, even after hydrolysis and dissolution of the silica interior coating of the channels. This synthetic pathway could be an interesting alternative approach compared to the steam-stable materials made of crystalline walls separating adjacent mesopores that are obtained via quite tedious syntheses. 5. References [1] C. T. Kresge, M. E. Leonowicz, W. J. Roth, J. C. Vartuli and J. S. Beck, Nature 359 (1992)710. [2] Corma, Chem. Rev., 97(1997)2373. [3] D. T. On, D. Desplantier-Giscard, C. Danumah and S. Kaliaguine, Appl. Catal. A : Gen., 253 (2003) 545. [4] E. M. Serwicka, R. Mokaya, J. Poltowicz and W. Jones, Chem. Phys. Chem., 10 (2002) 892. [5] S. K. Jana, H. Takahashi, M. Nakamura, M. Kaneko, R. Nishida, H. Shimizu, T. Kugita and S. Namba, Appl. Catal. A : Gen., 245 (2003) 33. [6] K. M. Reddy and C. Song, Catal. Today, 31 (1996) 137. [7] Z. Luan, C. F. Cheng, W. Zhou and J. Klinowski, J. Phys. Chem. B, 99 (1995) 1018. [8] S. K. Badamali, A. Sakthivel and P. Selvam, Catal. Today, 63 (2000) 291. [9] S. Biz and M. G. White, J. Phys. Chem. B, 103 (1999) 8432. [10] J. L. Blin, A. Leonard and B. L. Su, Chem. Mater., 13 (2001) 3542. [11] Leonard, J. L. Blin and B. L. Su, Coll. Surf. A : Physicochem. Eng. Aspects, 241 (2004)87. [12] S. Kawi and S. C. Shen, Mater. Lett. 42 (2000) 108. [13] Z. H. Luan, C. F. Cheng, H. He and J. Klinowsky, J. Phys. Chem. B, 99 (1995) 10590. [14] L.Y. Chen, S. Jaenicke and G. K. Chuah, Micropor. Mater., 12 (1997) 323. [15] R. Mokaya, Chem. Phys. Chem., 3 (2002) 360. [16] Leonard, N. Moniotte and B. L. Su, (2006) submitted for publication. [17] R. Mokaya, J. Phys. Chem. B, 104 (2000) 231.


117 117

Tailoring the phase and texture of mesoporous silica by using tetraethylenepentamine and ethanol MingBo Yue, Xin Dong and JianHua Zhu* Key Laboratory of Mesoscopic Chemistry, School of Chemistry and Chemical Engineering, Nanjing University, Nanjing 210093, China,-

1. Introduction Mesoporous systems with more effective interchannel accessibility are interesting candidates for many applications [1]. To improve interchannel transportation, a large amount of molecular sieves with bimodal pore system or bicontinuous network structure were synthesized [2,3]. To favor transition of a hexagonal phase to a cubic phase like MCM-48, many parameters are changed in the synthesis of MCM-41. For example, cosolvent additives such as alcohol have been reported in many variants [4,5]. However a few reports involve amine. Amine has not only the same function as aqueous ammonia to promote the hydrolysis and condensation of silica, but also more complex interaction with surfactants to modify the micelles [6]. Here we use tetraethylenepentamine (TEPA) and ethanol (EtOH) and adjust their molar ratios to transform MCM-41 into MCM-48, tailoring not only the phase but also the textural properties of obtained mesoporous material. 2. Experimental Section Mesostructure silica materials were prepared using a mixture of TEPA, EtOH and CTAB (cetyltrimethylammonium bromide) as a structure-directing mixture. The molar composition of the starting reaction mixture was varied in the range of 0.4CTAB/TEOS/xEtOH/yTEPA/314H2O, with x = 0-50, y = 0.3-4.5. In a typical preparation, 1.3 g CTAB was dissolved in 50 g distilled water and 20 g EtOH. After complete dissolution, 3.8 g TEPA was added at once. The solution was stirred at 298 K for 10 min and 1.84 g TEOS was added. This mixture was left under vigorous and constant stirring at 298 K for 24 h and then at 323 K for another 20 h. Subsequently, the mixture was aged at 373 K for 24 h under static

118 118

conditions. The resulting solid was recovered by filtration, washed with distilled water and dried in air. The template was removed by calcination at 823 K for 6 h in airflow and the sample denoted as MS-x-y, where x and y denote the molar ratio of EtOH and TEPA respectively. X-ray powder diffraction (XRD) patterns and N2 adsorption isotherms were taken to character the phase and textural properties of obtained mesoporous silica materials [7]. 3. Results and Discussion Figure 1A depicts the XRD patterns of surfactantQ_ H 03 free mesoporous silicas (MS-x-2.3 materials with varying EtOH moral ratio from 0 to 60), demonstrateing the crucial role of the EtOH concentration played in the formation of the 0.0 0.2 0.4 0.6 0.8 2Theta (degrees) Relative Pressure (P/P ) mesophase structure. Table 1 lists the textural properties Fig. 1. Powder XRD patterns (A), N2 adsorption-desorption of obtained mesoporous isotherm and pore size distribution (B) for the mesoporous silica materials. Figure IB silica MS-x-2.3. The molar ratio of EtOH (x) was varied at: illustrates nitrogen adsorp- a, (0), b (20), c (40), d (50), e (60). The isotherms of the were offset vertically b y l b , (200 cmVg); c, (400 tion isotherms and pore size samples 3 cm /g); d, (600 cm3/g); e, (800 cm3/g) respectively. distributions (PSDs) of these silica materials. From the evolution of the diffraction patterns, mesoporous phase varied from hexagonal P6mm to cubic laid as EtOH molar ratio increasing from 0 to 50; and with EtOH molar ratio further enhanced to 60, less ordered mesophase material formed. Without EtOH, the product of MCM-41 with ordered hexagonal pattern was obtained. When EtOH was added, it caused a phase transformation from MCM-41 to MCM-48. The surfactant packing parameter g = (V)/(ao)(l) modulates the self-assembly of the organic-inorganic structure and directs the phase of acquired mesoporous material [8]. The added EtOH penetrates into the surfactant micelles and increases the effective surfactant volume, raising the value of g and causing transformation from hexagonal phase to a cubic phase (Fig. 1A). However with the EtOH further increased, the value of g increased correspondingly and the cubic phase of the micelles transformed into lamellar phase [8]. So the material obtained at 60 molar ratio of EtOH has a less ordered structure than that obtained at 50 molar ratio of EtOH as shown in Fig. 1A. At first sight, the N2 adsorption isotherms (Fig. IB) is common with a sharp inflection to all these samples existing at P/Po = 0.28. This inflection is typical of a capillary condensation process and the P/Po value corresponds to a pore o

119 119

size of about 2.7 nm. However, sample MS-0-2.3 has an additional uncommon type-H4 hysteresis loop at P/Po between 0.5 and 1. Two kinds of hysteresis loop means bimodal pore in sample MS-0-2.3. There were two kinds of pore with narrow pore size distribution in sample Table 1. Textural properties of samples MS-x-y. sample MS-0-2.3 MS-20-2.3 MS-40-2.3 MS-50-2.3 MS-60-2.3 MS-20-0.3 MS-20-1.2 MS-20-4.5 MS-0-2.3

X

0 20 40 50 60 20 20 20 40

S B ET/(m 2 /g)

y 2.3 2.3 2.3 2.3 2.3 0.3 1.2 4.5 0.3

1133 1060

964 903 558 854 1009 1225

798

Vpore/CcmVg) 1.07

0.9 0.77

0.6 0.42 0.74 0.85 1.08 0.68

d/(nm) 2.83 3.68 2.67 3.75 2.43 2.84 2.96 2.73 2.67 2.65 3.71 2.74

Intensity (a.u.)

3

Volume Adsorbed (cm /g STP)

MS-0-2.3 (2.8 and 3.7 nm), and the pore around 3.7 nm disappeared with the further addition of EtOH. This variety of pore size and distribution is the result of surfactant micelles modified by TEPA and EtOH. As a polar molecule, EtOH or TEPA can change the micelle size and shape [6,9]. The first impact is to decrease the dielectric constant of water upon solubilization of EtOH. It is expected to result in a decrease of micelle aggregation number since the water becomes less water-like [9]. Other effects of EtOH and TEPA associate to their penetration in the micelles. This should increase the micelle size although not necessarily the aggregation number of the surfactant. So bimodal pore in sample MS-0-2.3 obtained with no addition of EtOH may be ascribed to two kinds of micelles coexistence in solution with different size. One directed the small pore (2.83 nm); another was enlarged micelle penetrated by TEPA that directed large pore (3.68 nm). Addition of EtOH promotes the solubilization of TEPA in solution so the larger pore B disappeared at EtOH molar A 1200 ratio 40 in sample MS-40d aa V _ 800 c 2.3. Besides, the addition b b of EtOH reduced micelle 400 a aggregation number and c 0 the micelle size decreased. As shown in Fig. IB and d d -400 V Table 1, the pore diameter 0.0 0.2 0.4 0.6 0.8 1.0 1.0 1 2 3 4 5 6 7 8 Relative Relative Pressure (P/P ) 2Theta (degrees) (degrees) of obtained samples decreased from 2.83 nm Fig.2. Powder XRD patterns (A), N2 adsorption(MS-0-2.3) consecutively, desorption isotherm and pore size distribution (B) for the mesoporous silica MS-20-y. The molar ratio of TEPA (y) achieving 2.67 nm (MS20-2.3) and 2.43 nm (MS- was varied at: a (0.3), b (1.2), c (2.3), d (4.5). The isotherms of the samples were offset vertically: b 40-2.3) at EtOH molar 3 3 ratio 20 and 40 respective- (200cm /g), c (400cm /g) and d (600cmVg). a b c d

5

10

Pore size / nm

0 0

120 120

3

Volume Adsorbed (cm /g STP)

Intensity (a.u.)

ly. However the further increased EtOH penetrated the micelle to enlarge the micelle size, the pore diameter increased to 2.84 nm at EtOH molar ratio 50 (MS-50-2.3). When the EtOH molar ratio increased to 60, the phase of micelles transformed from cubic into lamellar and the pore size distribution of obtained mesoporous material (MS-60-2.3) was broad. Figure 2 illustrate XRD patterns, N2 adsorption isotherm and pore size distribution for the silica materials (MS-20-y with varying TEPA moral ratio from 0.3 to 4.5). With constant molar ratio of EtOH (20), the role of TEPA on the structure of the mesoporous material was studied. Mesoporous phase varied from less ordered to well order hexagonal P6mm (Fig. 2A). At low molar ratio of TEPA, the rate of hydrolysis and condensation of TEOS was slow and less ordered mesoporus material was obtained. With the molar ratio of TEPA increased to 4.5, the sample MS-20-4.5 has not only well ordered hexagonal phase but also bimodal pore (as shown in Fig. 2B). The further increased TEPA penetrated into micelle of CTAB and formed larger size micelle which directed large size pore. Although both samples MS-0-2.3 and MS-20-4.5 have bimodal pore, but the TEPA molar ratio of in the prepare mixture is different. The TEPA molar ratio in the mixture to prepare MS-20-4.5 is 4.5, twice over MS-0-2.3. This can be ascribed to the solubilization of EtOH. When the concentration of TEPA is low in EtOH solution, 600 TEPA can be well dispersed B A a in the solution and there is 500 b only one kinds of micelle in 400 the solution. So there are a 300 one kinds of pore in the sample. However as the 200 molar ratio of EtOH b 100 increased to 40, the pore 1 2 3 4 5 6 7 8 0.0 0.2 0.4 0.6 0.8 1.0 1.0 size was controlled by Relative Pressure (P/P (P/P ) 2Theta (degrees) (degrees) TEPA concentration. Figure 3 indicts XRD Fig. 3. Powder XRD patterns (A), N adsorption-desorption patterns, N2 adsorption iso- isotherm and pore size distribution, 2for the mesostructured therm and pore size distri- silica materials MS-40-y. The molar ratio of TEPA (y) was butions of the silica mater- varied at: a (2.3) and b (0.3). ials (MS-40-y with varying TEPA moral ratio from 0.3 to 2.3). The evolution of diffraction patterns indicates that the sample has deviated the hexagonal P6mm phase (Fig. 3A). With the TEPA concentration increased from 0.3 to 2.3, the 29 values varied from 1.85 to 2.28. Both of them have IV type isotherms with the pore filling restricted to a narrow range of P/Po, which means a sharp pore distribution. However, hysteresis loop of sample MS-40-0.3 at a higher relative pressure than sample MS-40-2.3 indicates a different pore diameter. Sample MS-40-0.3 prepared with a lower concentration of TEPA has a larger pore diameter (2.74 nm) than sample MS-40-2.3 (2.43 nm). With constant EtOH concentration a b

5

10

Pore size / nm

0 0

121 121

(molar ratio 40), TEPA can be well dispersed in the solution. Following the increase of TEPA concentration, the dielectric constant of water and critical micelle concentration (CMC) of surfactants (CTAB) were reduced [6], so the micelle aggregation number decreased which results in the decrease of micelle and pore size. 4. Conclusion MCM-41 like material with bimodal pore and MCM-48 were prepared from this TEOS-CTAB-TEPA-water-ethanol system, and the textural properties such as pore diameter could be tailored by modifying the TEPA and EtOH molar ratio. 5. Acknowledgement NSF of China (20273031 and 20373024) and Analysis Center of Nanjing University financially support this investigation. 6. References [1] [2] [3] [4] [5] [6] [7] [8] [9]

C. F. Cheng, Z. Luan and J. Klinowski, Langmuir, 11 (1999) 2815. H. P. Lin, S. T. Wong and C. Y. Mou, J. Phys. Chem. B., 104 (2000) 8967. R. Ryoo, S. H. Joo and J. M. Kim, J. Phys. Chem. B, 103 (1999) 7435. A. Sayari, M. Kruk and M. Jaroniec, Adv. Mater., 10 (1998) 1376. S. Q. Liu, P. Cool and O. Collart, J. Phys. Chem. B, 107 (2003) 10405. B. Y. Jiang, J. Du and S. Q. Cheng, J. Disper. Sci. Technol, 24 (2003) 755. Y. M. Wang, Z. Y. Wu, L. Y. Shi and J. H. Zhu, Adv. Mater., 17 (2005) 323. Q. Huo, D. I. Margolese and G. D. Stucky, Chem. Mater., 8 (1996) 1147. R. Zana, Advances in Colloid and Interface Science, 57 (1995) 1.



123 123

Synthesis of mesoporous aluminosilicates via recrystallisation of pure silica MCM-41: A stepwise post-synthesis alumination route Robert Mokaya

School of Chemistry, University of Nottingham, University Park, Nottingham NG7 2RD, UK

Mesoporous aluminosilicates are prepared via post-synthesis alumination involving the recrystallisation of pure silica MCM-41 in which increasing proportions of the MCM-41 are aluminated depending on the amount of Al available in the recrystallisation gel. Varying the amount of Al enables a stepwise alumination of the Si-MCM-41 via the formation of an aluminosilicate layer on the inner surface of aluminated pore walls. The aluminosilicates have high surface area (800 - 100 m2/g) and pore volume (0.5 - 0.9 cm3/g), and the Al is incorporated into tetrahedral positions and generates significant acidity. 1. Introduction The synthesis of mesoporous aluminosilicates via direct mixed-gel synthesis results in materials with a uniform spatial distribution of Al [1, 2]. Increasing the amount of Al in the synthesis gel generally results in a uniform increase in the content of Al throughout the entire sample [1, 2]. Here, we describe the post-synthesis alumination of pure silica MCM-41 in which increasing proportions of the MCM-41 are aluminated depending on the amount of Al available in the synthesis gel [3]. The step-wise alumination occurs during a recrystallisation process in which calcined pure silica MCM-41 is used as 'silica source' in the presence of surfactant molecules and an Al source. During the recrystallisation process calcined pure silica MCM-41 particles act as seeds for further silica or aluminosilica deposition [4]. This allows the preparation of acidic mesoporous aluminosilica from a recrystallisation gel comprising of calcined pure silica MCM-41, templating surfactant and Al source.

124 124

2. Experimental, Results and Discussion The recrystallisation of Si-MCM-41 was as follows; tetramethylammonium hydroxide (TMAOH) and cetyltrimethylammonium bromide (CTAB) were dissolved in distilled water by stirring at 35°C. Calcined pure silica Si-MCM-41 and the required amount of Al (as aluminium isopropoxide) were then added to the template solution under stirring for 1 h. After further stirring for 1 h the resulting gel was aged for 20 h at room temperature and then transferred to a teflon-lined autoclave and heated at 150°C for 48 h. The solid product was obtained by filtration, washed with distilled water, dried in air at room temperature and calcined in air at 550°C for 8 h. The samples were designated A1-MCM41-X, where x is the recrystallisation gel Si/Al ratio. As shown in Fig. 1, the parent Si-MCM-41 exhibits an XRD pattern typical of well ordered MCM-41 [5]. The XRD patterns of recrystallised samples prepared at gel Si/Al ratios of 80, 40 and 20 exhibit two low angle peaks; the original 100 peak (i.e., retained from Si-MCM-41) and a new peak at slightly higher 26 values (i.e., lower basal spacing). The intensity of the new peak gradually increases, and at a gel Si/Al ratio < 10, the original basal peak is absent and only the new peak is observed. We propose that the new peak is due nits)

Pure silica Si-MCM-41 f

h Pure silica Si-MCM-41

Si/Al = 80

W1000

_j

rbitr;

Si/Al = 80

A

-5-

~800

Si/Al = 40 Si/Al = 20

(0

-A

c

Si/Al = 10 Si/Al = 5

0

2

f•o

20tdegfees?

10

I OG00 to ^400

>

200 0.0

0.2

0.4

0.6

0.8

1.0

Partial pressure (P/Po)

to aluminated Al-MCM-41, which increases in proportion at higher recrystallisation gel Al contents. At a gel Si/Al ratio < 10, there is enough Al to aluminate all the Si-MCM-41 and therefore only the new peak is observed. The presence of the original peak for samples recrystallised at a Si/Al gel ratio of 80, 40 and 20 implies that a portion of these samples remains essentially nonaluminated and retains the characteristics of the parent Si-MCM-41 material. Fig. 1. Powder XRD patterns and nitrogen sorption isotherms of pure silica Si-MCM-41 and recrystallised Al-MCM-41 samples prepared from gels with varying amounts of Al. The amount of Al is indicated by the Si/Al ratio.

The nitrogen sorption isotherms in Fig. 1 clearly show two capillary condensation (pore filling) steps for the 'partially' aluminated samples (prepared at Si/Al = 80, 40 and 20). We attribute the first step (at lower partial pressure) to the filling of 'aluminated pores' and the second step to the filling of

125 125

pure silica, i.e. 'non-aluminated pores'. The second pore filling step in the partially aluminated samples occurs at the same partial pressure as the filling of pores in the parent Si-MCM-41. This indicates that the pore size of the nonaluminated pores in 'partially' aluminated samples remains unchanged. The textural properties of the samples are summarised in Table 1. The basal spacing of the non-aluminated portion remains unchanged at ca. 43 A, which is similar to that of the pure silica Si-MCM-41. The basal spacing of the aluminated portion gradually decreases at higher Al content from 40.1 to 33.5 A. The surface area and pore volume generally decrease with the extent of alumination.The apparent Al content (Table 1) is higher than expected for samples prepared at gel Si/Al ratio = 80, 40 and 20. This is consistent with the proposal that only part of the Si-MCM-41 is aluminated. The Al content approaches the expected value as the extent of alumination increases, i.e. as the proportion of aluminated material increases, the measured Si/Al ratio becomes more representative of the gel ratio. At gel Si/Al = 10 or 5, the Al content is very close to the expected values; the samples are fully aluminated and essentially homogeneous with respect to spatial distribution of Al. Incorporation of Al onto the silica framework of the aluminated samples was confirmed by 27 Al MAS NMR analysis in Fig. 2. The spectra, of calcined samples, exhibit resonances at 55 and 0 ppm arising from tetrahedral (framework) and octahedrally coordinated (non-framework) Al respectively. From the spectra we estimate that ca. 80% of the Al in the samples (except for A1-MCM41-5 with ca. 65%) is in tetrahedral framework positions. This is consistent with the acidity data in Table 1. The acid content of medium to strong acid sites (obtained via temperature programmed desorption of cyclohexylamine-containing samples after thermally treated at 250°C [6]) increases at higher Al content. Table 1. Elemental composition and textural properties of pure silica Si-MCM-41 and recrystallised Al-MCM-41 samples prepared from gels with varying amounts of Al Sample

Si/Al ratio

basal ((sf1Oo) spacing

(A) Si-MCM-41 A1-MCM41-80 A1-MCM41-40 A1-MCM41-20 A1-MCM41-10 A1-MCM41-5

40.1 28.1 16.9 8.8 5.8

42.8 43.2; 40.1 43.0; 39.7 42.8; 38.2 37.6 33.5

surface area (m2/e) 1017 995 922 840 785 878

pore volume (cnrVg) 0.91 0.87 0.78 0.62 0.53 0.51

acidity (mmol/e) 0.15 0.25 0.39 0.64 0.81

This study shows that well ordered mesoporous aluminosilcates may be prepared via stepwise alumination during recrystallisation pure silica MCM-41 in the presence of discrete amounts of Al. The proportion of aluminated MCM41 increases with the amount of Al in the recrystallisation gel and beyond a

126 126

100

i 50

-50

-100

5AI

Fig. 2. 2IA\ MAS NMR of calcined Al-MCM-41 samples

certain gel Si/Al ratio the whole MCM-41 sample is aluminated. Varying the amount of Al therefore controls the extent of alumination and enables a stepwise alumination of the Si-MCM-41. Alumination of the pure silica MCM41 is thought to occur via the formation of an aluminosilicate layer on the inner surface of the pore walls. Our findings suggest that it is possible to fully aluminate a portion of the pores of a pure silica MCM-41 before alumination of other pores has started. The ability to vary the spatial distribution of Al (or other heteroatoms) in such a manner may find use in the preparation of composite materials and may open new opportunities for selective molecular engineering within the internal surface of mesoporous silicas and aluminosilicas. 3. References [1] S. Biz and M. L. Occelli, Catal. Rev.-Sci. Eng., 40 (1998) 329. [2] (a) A. Sayari, Chem. Mater., 8 (1996) 1840. (b) M. T. Janicke, C. C. Landry, S. C. Christiansen, S. Birtalan, G. D. Stucky and B. F. Chmelka, Chem. Mater., 11 (1999) 1342. [3] R. Mokaya, Chem. Commun., (2000) 1541. [4] (a) R. Mokaya, W. Zhou and W. Jones, J. Mater. Chem., 10 (2000) 1139. (b) R. Mokaya, J. Mater. Chem., 12 (2002) 3027. (c) Y. Xia and R. Mokaya, J. Mater. Chem., 13 (2003) 3112. (d) R. Mokaya, Adv. Mater., 12 (2000) 1681. (e) R. Mokaya, W. Zhou and W. Jones, Chem. Commun., (1999) 51. [5] J. Y. Ying, C. P. Mehnert and M. S. Wong, Angew. Chem. Int. Ed., 38 (1999) 56. [6] R. Mokaya, W. Jones, S. Moreno and G. Poncelet, Catal. Lett., 49 (1997) 87.


127 127

One-pot synthesis of ionic liquid functionalized SBA-15 mesoporous silicas Yong Liua, Jiajian Peng a , Shangru Zhaib, Ningya Yuc, Meijiang Lia, Jianjiang Mao a , Huayu Qiu^*, Jianxiong Jianga and Guoqiao Laf'*

"Key Laboratory of Organosilicon Chemistry and Material Technology of Ministry of Education, Hangzhou Teachers College, Hangzhou 310012, China Department of Chemical Engineering and Materials, Dalian Institute of Light Industry, Dalian 116034, China 'Institute of Catalysis and Synthesis, and Key Laboratory of Chemical Biology and Traditional Chinese Medicine Research of Ministry of Education, Hunan Normal University, Changsha 410081, China

l-Methyl-3-w-propyl-imidazolium chloride (MPImCl) and ./V-propylpyridinium chloride (PPyCl) ionic liquid functionalized SBA-15 mesoporous materials were sucessfully synthesized through the co-condensation of tetraethoxysilane (TEOS) with l-methyl-3-(triethoxysilyl propyl)-imidazolium chloride (MTESPImCl) and 3-(triethoxysilyl propyl)- pyridinium chloride (TESPPyCl) using EO20PO70EO20 (Pluronic PI23) as surfactant. These organicinorganic hybrid materials may have potential applications in heterogeneous catalysis reactions. 1. Introduction Since the discovery of mesoporous materials in the early 1990s [1], surfacefunctionalized mesoporous materials have attracted great interests due to the combination of unique physico-chemical properties of the parent counterparts (high surface area, uniform pore structure, high adsorption capacity and relative stable framework, etc.) [2-5] with the introduced functional groups, that is, surface-functionalized ones provide distinct properties such as better compatibility and abilities to further graft other reactive complexes. Of the two functionalizing strategies, post-grafting and co-condensation, the latter is often preferred because it offers more uniform surface coverage, higher loading and simpler synthesis steps [6].

128 128

Ionic liquids (ILs), known as novel environmental benign media, have attracted great interests in the last two decades since they can serve not only as favorable media for catalysis [7] but also as green catalyst themselves in many reactions such as Knoevenagel condensation [8], cycloaddition [9] and Biginelli reaction'101. However, in some cases separation of product is still a problem since the miscibility of ionic liquids with some products and reactants. Thus, immobilization of ionic liquids on solid based materials is of particular interest. Recently, several groups have reported the synthesis of ionic liquids immobilized solid hetergenous catalyst [11-13]. It's noteworthy that Mehnert et al. found that ionic liquid functionalized solid could act as support for rhodium which was used as catalyst in hydroformylation reactions [14,15]. However, silica gel were used in most reports and stduies on ordered ionic liquids functionalized mesoporous materials are still quite rare [16,17]. Herein, we report the one-pot synthesis of MPImCl and PPyCl ionic liquid functionalized SBA-15 mesoporous materials which may be used as catalyst or support for heterogeneous catalysts. 2. Experimental Section All reagents were of analytical grade and used as received. MTESPImCl and TESPPyCl were synthesized through the reaction between 1methylimidazole or pyridine and y-chloropropyl triethoxysilane at 120°C for 24 h. The synthesis procedures of ionic liquid functionalized SBA-15 mesoporous materials were similar to those of other functionalized mesoporous silica[18]. Under the direction of PI23, TEOS was allowed to pre-hydrolyzed for specific times and then MTESPImCl was added, followed by hydrothermal treatment in favor of the formation of mesoporous structure. Template was removed from the as-synthesized material by washing with ethanol under reflux for 24 h. X-ray powder diffraction (XRD) data were acquired on a Rigaku D/max 2500V/PC X-ray diffractometer with Cu Ka radiation. IR spectra were taken with a Nicolet 700 FT-IR spectrometer. Nitrogen adsorption and desorption isotherms were measured using a Quantacrome Autosorb-1 system at 77 K. Elemental analysis were performed on an Elementar Vario EC III C/H/N/O/S element analyzer. 3. Results and Discussion Fig 1 gives XRD patterns of MPImCl functionalized SBA-15 with different MPlmCl/(MPImCl + TEOS) ratios with different TEOS prehydrolysis times. With a TEOS prehydrolysis time of 40 min, the produts differed from highlyordered SBA-15 to nearly amorphous materials as MPImCl content increased from 0 to 15%. When TEOS prehydrolysis time was prolonged to 4 h, the regularity of pore structure (MPImCl content 15%) was greatly improved. This could be explained by that MPImCl might perturbe the self-assembly of

129 129

Fig 1 XRD patterns of MPImCl functionalized SBA-15 with different prehydrolysis times and MPImCl ratios: (a) 0.10, 4 h, (b) 0, 0 , (c) 0.05, 0.1540 min, (d) 0.10, 40 min, (e) 0.15, 40 min.

Fig 2 XRD patterns of PPyCl functionalized SBA-15 with different PPyCl ratios prehydrolyzed for 4 h: (a) 0.05, (b) 0.10, (c)

surfactant micelles and longer TEOS prehydrolysis time could faver the formation of highly ordered mesoporous structures, as also observed in the synthesis of other organic functionalized mesoporous materials [18]. As PPyCl functionalized SBA-15 materials were concerned, however, mesopores were less ordered at high PPyCl loading amounts even if the prehydrolysis time was as long as 4 h (Fig 2 ) . N2 adsorption - desorption was carried out to supply further infor- IL ratio SBET Dp Loading vn mation about the physical properties , 0/ . 2 (m-.2/g) (cm7g) (nm) (mmol/g) of the ionic liquid functionalized 0 688 0.937 6.21 0 SBA-15 materials. As shown in Table 1, surface areas, pore volIm5" 482 0.849 0.512 6.18 umes and pore diameters of the ImlO" 400 0.564 5.13 0.943 products all decreased as ionic 0.221 1.322 143 3.62 liquid content increased from 0 to I m l 5 " 15%, which could be attributed to ImlO* 529 0.996 0.653 6.15 the increasing distribution of ionic 0.569 Py5* 558 0.997 8.04 liquid moieties in the interior meso504 0.986 0.901 8.03 pore surfaces. With longer pre- Py 10* hydrolysis time, products, especial- P y l 5 * 5.74 1.409 368 0.755 ly PPyCl functionalized ones displayed much higher surface areas Table 1 N2 adsorption-desorption and elemental and larger pore diameters, which is analysis results of IL-SBA materialsa: TEOS prein consistent with XRD results. hydrolysis time 40 min; b: TEOS pre-hydrolysis Elemental analysis results indicated time 4 h that the loading amounts of MPImCl and PPyCl functionalized SBA-15 were comparable and increased with the raise of IL contents in the initial mixture. IR spectra in Figure 3 convinced

130 130

\

\

smi tabce

the vibrations of imidazolium cation ring (1575 cm 1 ) and pyridium cation ring (1490 cm"1), confirming the successful incorporation of IL moieties in the mesopores. In summary, ionic liquid functionalized SBA-15 mesoporous materials were synthesized through a one-pot cocondensation route, resulting in novel organic-inorganic hybrid materials with forth-coming applications in heterogeneous catalysis.

i

\

/

/^"

b

1/ y

)

— \ \

/

ro I—

\ 4000

3000

2000

1000

Wavenumber (cm1)

Fig 3 IR spectra of (a) MPImCl and (b) PpyCl functionalized SBA-15

4. References [1] C. T. Kresge, M. E. Vartuli, W. J. Roth, J. C. Vartuli and J. S. Beck, Nature, 359 (1992) 710. [2] A. Sayari and S. Hamoudi, Chem. Mater., 13 (2001) 3151-3168. [3] A. Corma, Chem. Rev., 97 (1997) 2373. [4] S. R. Zhai, J. L. Zheng, X. E. Shi, Y. Zhang, L. Y. Dai, Y. K. Shan, M. Y. He, D. Wu and Y. H. Sun, Catal. Today, 93/95 (2004) 675. [5] N. Y. Yu, Y. J. Gong, D. Wu, Y. H. Sun, Q. Luo, W. Y. Liu and F. Deng, Micropor. Mesopor. Mater., 72 (2004) 25. [6] M. Kruk, T. Asefa, M. Jaroniec and G. A. Ozin, J. Am. Chem. Soc., 124 (2002) 6383. [7] J. Dupont, R. F. Souza and P. A. Z. Suarez, Chem. Rev., 102 (2002) 3667. [8] D. C. Forbe, A. M. Law and D. W. Morrison, Tetrahedron. Lett., 47 (2006) 1669. [9] J. J. Peng and Y. Q. Deng, New J. Chem., 25 (2001) 639. [10] J. J. Peng and Y. Q. Deng, Tetrahedron. Lett., 42 (2001) 403. [11] K. Qiao, H. Hagiwara and C. Yokoyama, J. Mol. Catal. A: Chem., 246 (2006) 65. [12] P. Kumar, W. Vermeiren, J. P. Dath and W. F. Hoelderch, Appl. Cataly. A: General, in press. [13] M. Gruttadauria, S. Riela, P. L. Meo, F. D'Anna and R. Noto, Tetrahedron. Lett., 45 (2004) 6113. [14] C. P. Mehnert, R. A. Cook, N. C. Dispenziere and M. Afeworki, J. Am. Chem. Soc, 124 (2002) 12932. [15] C. P. Mehnert, E. J. Mozeleski and R. A. Cook, Chem. Commun., (2002) 3010. [16] M. H. Valkenberg, C. Castro and W. F. Hoelderch, Green Chem., 4 (2002) 88. [17] B. Gadenne, P. Hesemann and J. J. E. Moreau, Chem. Commun., (2004) 1768. [18] D. Margolese, J. A. Melero, S. C. Christiansen, B. F., Chmelka and G. D. Stucky, Chem. Mater., 12(2000)2448.


131 131

Preparation of novel mesostructured Titaniumpillared hydrotalcite Myung Hun Kima, Seok-Heung Jangb, Youngho Leec, II Mo Kangd, Yungoo Song6, Myongsoo Leea, Jin-Won Parkb and William Jonesf "Department of Chemistry, Yonsei University, Seoul 120-749, Korea Department of Chemical Engineering, Yonsei University, Seoul 120-749, Korea 'Technology Support Division, KICET, Seoul 153-801, Korea Institute of Earth Atmosphere Astronmy, Yonsei University, Seoul 120-749, Korea "Department of Earth System Sciences, Yonsei University, Seoul 120-749, Korea •^Department of Chemistry, University of Cambridge, Cambridge, CB2 1EW, UK

Novel mesostructured titanium-pillared materials with 300-550 m2/g surface area and 11.0-14.0 nm pore were successfully prepared from hydrotalcite(HTlc). 1. Introduction The considerable efforts have been invested in the design of new pores from materials with lamellar structure for the applications of shape-selective adsorption and support in catalyst and material chemistry by various intercalation procedures [1]. Layered materials consisting of stacked sheets can be easily functionalized by the host-guest interaction in the interlayer region. Among layered solids, hydrotalcite-type anionic clays (HTlcs) have been interested in as host materials. Generally, the hydrotalcite-like solids are described the empirical formula [M2+1.xM3+x(OH)2][(Am")x/m-nH2O], abbreviated hereafter as [M2+-M3+-A] where x may vary from 0.17 to 0.33. A represents the m-valent anion necessary to compensate for the net positive charge [2]. Based on these properties, the intercalation of specific elements into such HTlcs is also particular importance in the architecture of novel materials with various pore sizes. The aim of this study is fabricated the mesostructured titanium-pillared HTlc (Ti-HTlc) with different pore size, pore volume, and BET surface area by the intercalation of titanium chain anions, -(Ti-O-Ti)n-, into the gallery space of

132 132

HTlc through host-guest interaction, where TiO6 octahedra run along perpendicular direction with two layers. 2. Experimental Section Titanium chain anions were prepared by reaction of TBOT with basic solution of pH= 12 in stainless steel bomb at 393 K for 24 h. Also HTlc host powder was calcinated to get carbonated free solid at 823 K for 12 h. Ti-HTlcs were constructed by intercalation method starting with the addition of titanum chain anions into host powder, HTlc, under pH = 10.0, 11.0 and 12.0 conditions at 393 K for 24 h. The chemical composition of reactants is consited of host powder, titanium chain anions, and water in 1:0.7:5600 mole ratio. The obtained samples after being filtered off and washed with water were refluxed in acetone at 373 K for 24 h in order to decompose organic species in the interlayer. The resulting materials after reflux in acetone are designated as Ti-HTlc(l), TiHTlc(2) and Ti-HTlc(3), respectively. 3. Results and Discussion Fig. 1 shows the XRD patterns of the mesostructured Ti-HTlcs prepared from pH values of 10.0, 11.0, ,0.45 and 12.0, respectively. All products in the range of about 0.4-1.6 nm"1 ,0.49 exhibit common features of mesoA.0.52 structured material with pores between 11.0 and 14.0 nm consisting \ of pillars. Assuming a thickness of 0.48 nm for the HTlc layer, the newly formed spaces were approxi(c) mately 10.5-13.5 nm, compared with a carbonate HTlc gallery 10.58 \ (b) height of 0.28 nm. Among the products, Ti-HTlc(3) obtained at pH (a) =12 appeared in the largest mesostructured titanium-pillared HTlc. 0.4 0.8 1.2 1.6 The TEM image of Ti-HTlc [3] in q (nm"') Fig. 2 reveals that the pores newly constructed by pillars are about 13 F i g , P o w d e r X R D p a t t e m s o f (a) T i . H T l c ( 1 ) ; nm. Therefore, this result agreed (b ) Ti-HTlc(2) and (c) Ti-HTlc(3). with that of the XRD indicating the mesostructured presence forming new frameworks by intercalating titanium anion chains into HTlc. To the best of our knowledge, this is the first time to i

133 133

obtain the uniform mesoporous HTlc using the intercalation of inorganic anion chains under the basic condition (i.e. pH = 12).

50n

m 50 nm *•

'

-

-

•

•

.

"**!

Fig. 2. TEM micrograph of Ti-HTlc(3).

Furthermore, table 1 provides the basic physical properties of all samples analyzed using N2 adsorption-desorption isotherms. The values for Ti-HTlc series correspond the typical mesostructured solids with mesopore volume saturation capacity between 0.26 and 0.46 mL/g. All samples also have high BET surface areas of 300-550 m2/g and pore sizes of 10.0-13.0 nm. But the reason with the smaller values than those of the typical mesoporous silicas is assumed partial disordering due to the intercalation of the titanium anion chains Table 1. Pore size and specific surface area of HTlc and Ti-HTlc series.

Materials

Pore size (nm)

0.3

HTlc Ti-HTlc(l)

10.6

Ti-HTlc(2)

11.7

Ti-HTlc(3)

13.6

SBET" 2

(m /g)

90 300 360 550

Total amount N2 adsb (mL/g) 0.08 0.26 0.31 0.46

"From the linear ?-plot at low P/Po. *From the isotherm at low P/Pf=0.5

Also the presence and nature of specific vibration bands in HTlc and Ti-HTlcs were investigated with FTIR spectroscopy. The band at 1108 cm"1 is caused by the Ti-O-Ti units, and the decrease of band intensity at 1377 cm'1 assigning vibration mode of CO32" from Fig. 3b to 3d indicates the different pillaring degrees of the titanium anion chains into HTlc. Such bands suggest that TiC>6

134 134

octahedra are linked together with formation of liner .. -O-Ti-O-Ti-Ochains in the perpendicular plane within HTlc structure.

(d)

4000

3000

2000

1000

W avenum b e r (nm " ' ) Fig. 3 FTIR spectra of (a) HTlc, (b) TiHTlc(l), (c) Ti-HTlc(2) and (d) Ti-HTlc (3).

4. Conclusion This paper provides the new approach for the architecture of mesostructured materials from hydrotalcite by the intercalation reaction at specific pH. 5. Acknowledgement We are grateful to the Ministry of Science and Technology of Korea (Grant No. R01-2005-000-11039-0) and 21c Eco-Mat Technology Company for financial support. 6. References [1] G A. Graham, K. H. Robin and R. F. Kevin. A structural consideration of kanemite, octosilicate, magadiite and kenyaite. J. Mater. Chem. 7 (1997) 681-687. [2] V. Rives and M. A. Ulibarri. Layered double hydroxides (LDH) intercalated with metal coordination compounds and oxometalates. Coord. Chem. Rev. 181 (1999) 61-120.


135 135

Synthesis, characterization and catalytic activity of Titania and Vanadium grafted and substituted on mesoporous silicas T. Williams3, J. N. Beltramini*" and G. Q. Lub "ARC Centre for Functional Nanomaterials,The University of Queensland, Brisbane, Queensland, AUSTRALIA. ''Department of Chemical Engineering, University of Delaware, USA

The catalytic properties of mesoporous silica catalysts with titanium (Ti) and vanadium (V) loadings between 0.5 and 6 wt %, surface areas around 1300m2/g and synthesized using the isomorphous substitution (IS) and molecular designed dispersion (MDD) techniques were tested using toluene as a model VOC in a fixed bed reactor at temperatures between 300 to 550°C. The different behaviour of the Ti and V-HMS catalysts were explained in terms of the location and the total number of Ti and V actives species located on the surface of the HMS. Activation energies calculations support this view. 1. Introduction MCMs and HMSs mesoporous materials are very promising catalyst supports since they are capable of transforming much larger or bulky molecules than their microporous counterparts [1]. This novel class of silica-based materials are characterized by a regular arrangement of uniform mesopores [2]. Several pathways have been reported in recent years for the assembly of mesoporous molecular sieves [3]. The molecular designed dispersion technique (MDD), a very promising technique for creating metal oxide catalysts consists of the irreversible adsorption of metal acetylacetonate complexes onto a silica support followed by decomposition to yield the supported metal oxide catalyst. This study focuses on the adsorption and thermolysis of titanium acetylacetonate and vanadium acetylacetonate respectively onto hexagonal mesoporous silica using MDD technique. The physical, chemical and oxidative

136 136

catalytic properties obtained by the MDD method are then compared to those obtained by the simpler isomorphous substitution (IS) pathway. 2. Experimental Section For the MDD method TiO(acac)2 and VO(acac)2 crystals were used as the Ti and V sources respectively. Once totally dissolved, dry HMS was added to the reaction vessel. After the reaction the silica was filtered and then dried under vacuum. The dry solid was then calcined at 450°C. The HMS catalyst support was synthesized via the neutral templating mechanism [4]. The IS of TiHMS and VHMS were similar to that of HMS except that titanium or vanadium solutions were respectively added drop wise after the addition of TEOS. BET surface area, pore volume, pore size and PSD were calculated. Powder X-ray diffraction (XRD), UV-vis diffuse reflectance spectroscopic, pyridine TPD and TEM were performed on all samples. Ti and V content were determined by chemical analysis. The catalytic activity tests were carried out at atmospheric pressure in a continuous flow, fixed-bed quartz tube micro-reactor loaded with 0.05 g of calcined catalyst using toluene as reactant with a concentration of 1000 ppm and operating between 300 and 550°C. The reaction products were analysed using two Shimadzu GC-17A gas chromatographs equipped with a 30 m DB-5 capillary column connected to a FID and a 30 ft Porapak Q packed column connected to a TCD. 3. Results and Discussion The MDD and IS techniques both result in mesoporous silicas with pore volumes between 0.6 and 1.0 cc/g and high surface areas around 1000 m2/g. For comparison the physical properties of all synthesized Ti and V-HMS samples are listed elsewhere [4-5]. The IS technique is limited in the amount of titanium or vanadium which can be incorporated, (~4 wt %). In contrast, the MDD exceeds 14 wt%. The MDD method however allows much greater control of the physical properties of the final product than the IS. This is because any parent silica support material with the desired physical properties can first be chosen. The subsequent addition of the metal oxide acid sites via the molecular designed dispersion method has very little effect on the parent silica's physical structure. A linear relationship between the amount of metal acetylacetonate complex used during synthesis and the amount of metal incorporated onto the silica surface was also observed. This is a very desirable property and will allow for the design of the Ti- and V-HMS catalysts with the desired metal content. Energy dispersive spectra and UV-vis spectra of TiHMS and V-HMS show that the metal sites are not evenly dispersed over the surface of the material. However using the IS technique the addition of Ti and V sources to the synthesis gel can significantly change the properties of Ti- and V-HMS materials. Results on Table 1 using samples with similar textural

137 137

porosity and close mesoporous volume showed that meanwhile MDD method give rise to a great proportion of 5 and 6 coordinated Ti sites with greater energy of desorption, the IS method gives rise mainly to 4 coordinated Ti sites. V-HMS catalysts prepared by IS results showed a great proportion of isolated tetrahedra at Si/V molar ratio greater than 50. As bulk V content increases the pro-portion of polymeric vanadium species grows as more V is incur-porated into the HMS framework. Table 1: Identification and Quantification of Titanium sites by UV-vis Isomorphous Substitution

Ti Wt %

4 coordinated peaks (% area of spectra)

5 and 6 coordinated peaks (% area of spectra)

Molecular Designed Dispersion

Ti Wt%

4 coordinated peaks (% area of spectra)

5 and 6 coordinated peaks (% area of spectra)

Ti-HMS4[50] 1.20 44 10 90 56 Ti-HMS4[100] 2.29 64 13 87 36 Ti-HMS4[200] 75Ti-HMS3 2.10 3.25 24 76 29 71 75Ti-HMS4 Ti-HMS6[50] 1.155 1.89 70 30 70 30 Ti-HMS6[100] 2.112 75Ti-HMS5 1.35 24 76 43 57 Ti-HMS6[200] 2.998 75Ti-HMS6 1.11 24 76 70 30 35Ti-HMS2 5.06 Ti-HMS7[50] 0.64 17 30 70 83 Ti-HMS7[100] 2.109 35Ti-HMS3 4.61 82 28 72 18 3.199 35Ti-HMS4 5.11 Ti-HMS7[200] 22 79 30 70 35Ti-HMS5 4.22 35 65 35Ti-HMS6 4.49 32 68 Pyridine-TPD results demonstrated that the bulk V content has very little effect on the energy of desorption of the hydrogen-bonded SiOH groups while increasing V content has more pronounced effect on the free SiOH energy of desorption. Activation energies for toluene conversion were calculated assuming first order kinetics [5]. Ti -HMS catalysts synthesized via MDD have lower activation enery that their counterparts synthesiz-ed by IS as can be seen in Table 2. On MDD catalysts Ti atoms are exclusively located on the surface of the silica and therefore are more accessible to the toluene feed lowering the activation energy. Conversion of toluene over Ti-HMS results in total oxidation with detectable products such as: CO, CO2 and H2O. Figure 1 compares effect of Ti loading on toluene conversion samples synthesized using IS and MDD. 75Ti-HMSl

2.10

75Ti-HMS2

2.09

Table 2: Activation Energies for Toluene Oxidation over MDD/IS Ti-HMS Catalysts Synthesized via MDD 3.25TiHMS-0.13 3.20TiHMS-0.60 3.00TiHMS-1.30 1.16TiHMS-1.32 2.11TiHMS-1.37 3.00TiHMS-1.30

E Toluene (kJ/mol) 4.1 1.5 5.9 6.7 5.1 5.9

Catalysts Synthesized via IS 4.61TiHMS-0.75 2.10TiHMS-0.84 4.49TiHMS-0.10 2.09TiHMS-0.35

E Toluene (kJ/mol) 29.1 80.2 35.5 52.1

138 138 — • — i_irnHMS-i_33 -O 2.11T1HMS-1.37 —T— 3.DCmHM&1.30

*

f

I

4.49TiHM50.10

O

4.61TIHMSD.75

v—

2.10TiHM50.84

-J^J/ (a)

—V

-* '

(b) TsmpsraturaCC)

Figure 1: Toluene conversion on Ti-HMS synthesized by (a) IS (b) MDD

In contrast, it can be seen from Figure 2 that the conversion of toluene over VHMS catalysts synthesized by IS results in only partial oxidation with carbon oxides, benzene, benzaldehyde and water as the main reaction products. However V-HMS synthesized by MDD favours only total oxidation to CO and CO2 as no benzaldehide was found. This can be explained in terms of the location and the number of vanadium active species on the surface of the HMS.

S so-

25D

••"O 111 Benzaldshvde Yield

Yield (%)

60 -

3DD

350

4CO

453

SOD

Temperature t°C)

55D

6DD

Temperature (°C)

(a)

(b) (b) Figure 2: Toluene conversion on V-HMS synthesized by (a) MDD, (b) IS

4. Acknowledgment The authors wishes to acknowledge the financial assistance of the ARC Centre for Functional Nanomaterials during the preparation of this work. 5. References [1] J. S. Reddy, R. Kumar and P. Ratnasamy, Appl. Catal, 58 (1990) LI. [2] C. T. Krege, M. E. Leonowicz, W. J. Roth, J. C. Vartuli and J. S. Bech, Nature, 359 (1992) 710. [3] C. Y. Chen, H.X. Li and ME. Davis, Micropor Mater, 2 (1993) 17. [4] T. Williams, J. Beltramini and G. Q. Lu, Microp. Mesop Mat., 88 (2006) 91. [5] T. Williams, J. Beltramini and G. Q. Lu, J. Env. Eng., 130 (2004) 356.


139 139

Synthesis and characterization of B- and Ti-MCM36 Se-Young Kima, Gon Seob and Wha-Seung Ahna* "Department of Chemical Engineering, Inha University, Inchon, 402-751, Korea b School of Applied Chemical Engineering, Chonnam National University, Gwangju, 500-757, Korea

B- and Ti-containing MCM-36 materials were prepared from MCM-22 type precursors by surfactant swelling followed by silica pillaring. Their structural evolution was investigated by XRD, BET surface area measurements, and UVvis spectroscopy. Catalytic performance data on 1-hexene epoxidation probe reaction demonstrated superior performance of Ti-MCM-36 over TS-1 and TiMCM-22. 1. Introduction MCM-36 is a pillared molecular sieve, which contains micropores inside its crystalline layers and mesopores in the interlayer space. Mesoporous region is created by expansion of MCM-22 lamellar structure and insertion of polymeric silica pillars. MCM-36 has high specific surface area and good accessibility for relatively large molecules and its catalytic application in refinery processes are well documented [1]. Ti-containing MCM-36 is a titanosilicate with isolated tetrahedral Ti sites in the framework, and is expected to function as a partial oxidation catalyst using H2O2 as an oxidant. Ti-MCM-36 with zeolytic layers may demonstrate better catalytic performance over Ti-MCM-41 with amorphous wall structure. Ti-MCM-36 is typically prepared from B-containing MCM-22. In this study, structural evolution of these B- and Ti-MCM-36 structures from MCM-22 precursors was investigated in a systematic manner. 2. Experimental Section B-MCM-22 precursor was initially prepared following the synthesis method reported by Millini et al. [2], and Ti-MCM-22 was synthesized both by direct

140 140

hydrothermal synthesis [3] and post synthesis method [4] reported using Bcontaining MCM-22 as a starting material. Preliminary work indicated that the post-synthesis scheme is a better synthesis approach. To be specific, B-MCM22 precursor was treated with 6 M HNO3 and this treatment was repeated three times to remove boron completely. Afterwards, it was mixed with H2O, piperidine(PI), tetrabutyl orthotitanate(TBOT) with molar composition of 1.0 SiO2 : 0.03 TiO2 : 1.0 PI : 19 H2O. The mixture was heated in a Teflon stainless-steel autoclave at 448 K for 7 days. Ti-MCM-22 precursor prepared was treated with 2M HNO3 to remove octahedral Ti species detrimental to catalytic epoxidation reaction. B- and Ti- MCM-36 were prepared based on the synthesis protocol for AlMCM-36 reported by He et al. [1]. Swelling process was carried out by refluxing a mixture of B- or Ti-MCM-22(P) : 4 CTMAC1 : 1.2 TPAOH, followed by mixing the product obtained with TEOS at a weight ratio of 1:5 for pillaring, and the mixture was heated at 353 K for 25 h in nitrogen atmosphere. After filtration and drying, hydrolysis was carried out in water at 413 K for 6 h. Finally, B- and Ti-MCM-36 were obtained by calcination at 723 K for 3 h in nitrogen and at 812 K for 6 h in air (heating rate of 2 K/min). The crystallinity of the samples prepared was measured by X-ray diffraction using Ni-filtered CuKa radiation (Philips, PW-1700) and the specific surface area and average pore diameters were determined by N2 adsorption-desorption using a Micromeretics ASAP 2000 automatic analyzer. UV-visible spectra were measured on a Varian cary-3E double beam spectrometer using SiO2 as a reference. Catalytic performance of Ti-MCM-36 was investigated by 1-hexene epoxidation with H2O2 oxidant. 3. Results and Discussion Structural evolution of MCM-36 from MCM-22 precursor was shown in Fig. 1. MCM-22 has MWW lamellar structure and swelling step using surfactant expands interlayer distance of MCM-22 precursor. Finally, mesoporous region was formed after pillaring step using polymeric silica.

Mesopore Mesopore

Pillaring

MCM-22 MCM-22 precursor

Swollen material MCM-36Swollen material

Fig.l. Schematic representation of MCM-36 structure.

MCM-36

141 141

The XRD patterns of the various MCM-22 and MCM-36 materials are compared in Fig. 2. The pattern of B-MCM-22 precursor was characterized by 001 and 002 peaks at 20 = 3-7° due to its c-axis. Deboronated MCM-22 with 6 M HNO3 created linkages of lamellar structures, which is reflected by the disappearance of 001 and 002 peaks in XRD. Ti-MCM-22 precursor showed the same XRD pattern as B-MCM-22 precursor due to restored MWW lamellar phase. Ti-MCM-36 showed a characteristic new peak at 26 = 1-2° indicating expansion of distance between sheets and subsequent formation of mesopores. The XRD pattern of B-MCM-36 is virtually identical to that of Ti-MCM-36. 400 400-r 300 200 100

10

20

30

Fig.2. XRD pattern of materials; (a) as-syn B-MCM-22, (b) acid treated B-MCM-22, (c) as- synTi-MCM-22, (d) Ti-MCM-22, (e) Ti-MCM-36.

40

0 0.0

0.2

0.4

0.6

0.8

1.0 1.0

Fig.3. N2 adsorption isotherms of • Ti-MCM-22,0 B-MCM-22 • Ti-MCM-36, D B-MCM-36.

ABS

The N2 adsorption isotherm of B- and Ti-MCM-22 in Fig. 3 is of type I due to the microporous nature of the materials, whereas the isotherms of B- and TiMCM-36 are of type IV with hysteresis loop at p/po= 0.4 for capillary condensation due to the presence of mesopores. While (a) BET surface areas of B-MCM-22 and TiMCM-22 were 234 and 471 m2/g, B- and Ti-MCM-36 showed substantially increase(b) ed surface area of 520 and 674 m2/g, respectively. Ti-substituted materials show large pore volume and surface area than Bcontaining counterparts due to acid 200 300 400 500 600 washing treatment. 300 500 200 UV-visible spectra of Ti-MCM-36 samWavelength/nm Wavelength/nm ples are shown in Fig. 4. Absorption band Fig 4. UV-vis spectra of (a) calcined Ti- of Ti-MCM-36 prepared with Ti-MCM-22 MCM-36 and (b) Ti-MCM-36 using precursor without acid washing produced acid treated MCM-22 precursor. both 220 nm peak corresponding to the

142 142

catalytically active tetrahedral sites as well as 260 nm peak corresponding to detrimental octahedral Ti species. On the other hand, Ti-MCM-36 prepared with acid treated Ti-MCM-22 precursor showed enhanced 220 nm band and most of the octahedral Ti species was found successfully removed. Table 1 compares the catalytic activity and selectivity of Ti-MCM-36 with other Ti containing catalysts. Ti-MCM-36 exhibited higher conversion than either that of Ti-MCM-22 or TS-1, which is believed to be a consequence of reactant molecules having easier access to Ti sites in the framework due to swelling/pillaring. It is known that 1-hexene epoxidation is strongly influenced by diffusion [5]. To evaluate the potential adverse effect of boron remained in Ti-MCM-36, B-MCM-36 is also tested for n-octane cracking reaction and virtually no conversion was observed, demonstrating negligible side reaction due to very weak acidity. 4. Acknowledgement This work was supported by Korea Research Foundation Grant (KRF-2003 041-D00181). 5. References [1] Y. J. He, G. S. Nivarthy, F. Eder, K. Seshan and J. A. Lercher, Micropor. Mesopor. Mater., 25 (1998) 207. [2] R. Millini, G. Perego, W. O. Parker, Jr., G. Bellussi and L. Carluccio, Microporous Materials, 4 (1995) 221. [3] P. Wu, T. Tatsumi, T. Komatsu and T. Yashima, J. Phys. Chem. B, 105 (2001) 2897. [4] P. Wu and T. Tatsumi, Chem. Commun., 10 (2002) 1026. [5] W. J. Kim, T. J. Kim, W. S. Ahn, Y. J. Lee and K. B.Yoon, Catalysis Letters, 91 (2003) 123.


143 143

Delamination and intercalation of layered aluminophosphate with [AI2P3O12]3" stoichiometry by a controlled two-step method Chen Wang, Ying Li, Weiming Hua,* Yinghong Yue* and Zi Gao Department of Chemistry and Shanghai Key Laboratory of Molecular Catalysis and Innovative Materials, Fudan University, Shanghai 200433, China.

1. Introduction Numerous microporous aluminophosphates with non-unity Al/P ratios have been synthesized using solvothermal method [1]. Among them 2-D layered aluminophosphates are of particular interest because of their potential application in separation, catalysis or as functional materials. Delamination and intercalation of these layered compounds are critical for the above application. However, they are more difficult to bring about than those of ordinary layered metal phosphates due to the instability of the microporous sheets and their strong interaction with the protonized organic ammonium cations [2]. We have succeeded in delaminating and intercalation of the layered aluminophosphates with [A13P4O]6]3 stoichiometry by aromatic amine using a novel controlled twostep method [3], in which delamination and intercalation processes proceed separately and sequentially under different controlled conditions, so that the dielectric constant and the pH value of the medium in these two steps can be varied to suit a wider variety of intercalating agents and to guarantee the success of exfoliation and reassembly of the aluminophosphate. [Al2P3Oi0(OH)2] [C6NH8] (A1P) is another kind of aluminophosphate which is prepared from a butanol system using 4-methylpyridine as a template [4]. Its 2-D network is constructed of alternating aluminum units (A1O4 and A1O5) and phosphorous units (PO4, PO3(OH) and PO2(=O)(OH)) and featured by a series of edgesharing bridged-6MRs and zigzag 4MRs arranged in alternative rows. The inorganic sheets are held together through the H-bondings between the two layers as well as the H-bondings between the organic template and the layer. Here, the delamination and intercalation of A1P by C4-Ci6 alkylamines using the two-step method are studied.

144 144

2. Experimental Section A1P was synthesized following the procedure described in the literature [4]. For delamination, A1P (200 mg) was placed in 20 ml of the buffer solution, stirred at ambient temperature continuously. The delaminated A1P was separated by centrifugation and then added into 20 ml of ethanol/water mixture with a calculated amount of alkylamine, stirred for 1 d, and the final product was obtained by centrifugation. XRD patterns were recorded on a Rigaku D/MAX-FLA diffractometer, and SEM images were attained with a Philips XL-30 scanning electron microscope. 3. Results and Discussion The delamination of A1P was carried out in solutions at different pH and different Na+ concentration, and the observations of the systems by XRD were summarized Table 1. The results show that the delamination process would be facilitated in the solution with high pH value and high Na+ concentration but would be slowed down by adding phosphate or phosphonates to the solution. This is consistent with the previous observations in delamination of similar materials [3, 5]. Table 1. Time for complete delamination of A1P in the different solutions . . Solution o

1 2 3 4 5 6 7 8

„ er. . Buffer pair _ H3BO3/NaH2BO3 NaHCO3/Na2CO3 NaHCO3/Na2CO3 Na2HPO4/Na3PO4 Na2HPO4/Na3PO4 Na2HPO4/Na3PO4 Na2HPO4/Na3PO4 Na2HPO4/Na3PO4

,, , pH value 9 10 11 11 12 12 12 12

Concentration of + .. , ..,,. Na cation (mol/1) 0.30 0.30 0.30 0.30 0.30 0.45 0.60 0.75

x.

Time for complete , . . .. ,,, delamination (h) — 14 5 16 10 5 5 5

The intercalation of the delaminated A1P with C4-Ci6 alkylamine in the different water/ethanol solution at pH of 6 was studied. The results are given in Table 2. It can be seen that in the solution of alkylamine with short chain such as butylamine and pentylamine, the intercalation only takes place in pure ethanol, namely in solution with low dielectric constants. A pure phase of butylamine intercalate with d-spacing of 1.22 nm and pentylamine intercalate with d-spacing of 1.33 nm are formed, respectively. As the water/ethanol ratio of the solution is increased, no trace of intercalate was observed. This is quite similar with our previous result in preparing the benzylatnine and aniline intercalates, which shows that low dielectric constant is necessary for ressembly of the intercalates . But in the solution of alkylamine with carbon atoms bigger

145 145

than 6, the results are quite different. Pure phase of intercalation can be obtained in the both solutions with high or low dielectric constants. For example, in the solution of hexadecylamine, which has been proved very difficult to be intercalated into the layer of A1P by one-port method because of its large size and low solubility, an intercalate with a d-spacing of 3.14 nm can be obtained in the pure ethanol. The amount of this new phase decreases with an increase of water/ethanol ratio of the solution while another phase with a d-spacing of 3.75 nm appears. This new intercalate finally becomes a pure phase with d-spacing of 4.07 nm in pure water solution and the solution with water/ethanol ratio of 3:1, namely in solution with high dielectric constants. The different phenomena observed in the intercalation process of low chain alkylamine and high chain alkylamine may come from the different interaction between the intercalated alkylamine and the solvent, which deserves further studies. Table 2 Intercalation of A1P with various alkylamines in different solutions

\ .

W/E

Amin&\^ ^ \ Butylamine pentylamine Hexylamine Octylminae Dodyclyamine Hexadyclmine

Interlayer spacing (nm) Pure water — — 2.01 2.50 3.05 4.07

3:1

1:1

1:3

— — 2.01 2.50 3.05 4.07

— — — 2.41 3.05 3.75+3.14

— — — — 3.05+2.38 3.75+3.14

Pure ethanol 1.22 1.33 1.46

1.70

2.38 3.14

The phase transition associated with the dielectric constants of the solution is probably caused by a different arrangement of alkylamine molecules in the interlayer region. At lower dielectric constants, the stronger interaction between the protonized amine and the oxygen atom of the layer forces the amine to tilt a smaller angle with respect to the layer plane and reduces the interlayer distance. Similar results are obtained in the solution of hexylamine, octylamine and dodecylamine. The packing of the alkyl chains in the interlayer region of the saturated intercalates can be obtained by plotting the interlayer spacing against the number of carbon atoms in the alkyl group. The interlayer spacing of saturated intercalates obtained in pure water and pure ethanol increases linearly with a slope of 0.198 nm/CH2 and 0.160 nm/CH2, respectively, which are both larger than 0.127 nm/CH2 for an all-trans fully extended alkyl chain but smaller than two. This means that the alkyl chains in both saturated intercalates should be arranged as bilayers in the interlayer region, tilted with angles of Sin'1 (0.198/2 x 0.127) = 51.2° and SinÔ.Ô^ x 0.127) = 39.0° with respect to the layer plane, respectively. The calculated result is closed to the value of the similar intercalates obtained by one-port method [6].

146 146

The SEM images of and the octylamine intercalate, which is selected as the representation, are shown in Fig. 1. The original A1P is composed of large regular thin plate-like crystals with the size about 6 x 15 x 0.1 um [6]. The platelike crystals break into small thin flakes through hydrolysis of the Al-O-P bonds, and these small thin flakes reassembly new crystals with more irregular morphology compared with original one. There is a bit difference in morphology between the intercalates obtained in pure water and in pure ethanol. The morphology of the saturated intercalate obtained in pure ethanol shows more evident characteristic of rosette-like crystal aggregates.

Fig. 1 SEM images of octylamine intercalates obtained in pure water (left) and pure ethanol (right)

4. References [1] [2] [3] [4]

J. H. Yu and R. R. Xu, Ace. Chem. Res., 36 (2003) 481. L. Peng, J. Yu, J. Li, Y. Li and R. Xu, Chem. Mater., 17 (2005) 2101. C. Wang, W. M. Hua, Y. H. Yue and Z. Gao, Micro. Meso. Mater., 84 (2005) 297. J. Yu, K. Sugiyama, K. Hiraga, N. Togashi, O. Terasaki, Y. Tanaka, S. Nakata, S. Qiu and R. Xu, Chem. Mater., 10 (1998) 3636. [5] D. M. Kaschak, S. A. Johnson, D. E. Hooks, H. N. Kim, M. D. Ward and T. E. Mallouk, J. Am. Chem. Soc, 120 (1998) 10887. [6] Q. Huang, W. Wang, Y. H. Yue, W. M. Hua and Z. Gao, Chem. J. Chin. Univ., 25 (2004) 2065.


147 147

Novel synthesis method of mesoporous MoSiOx Yanying Zheng,a'b Tao Dou,a* Aijun Duan,a Zhen Zhaoa and Shanjiao Kanga "The Key Laboratory of Catalysis, China University of Petroleum, Beijing, 102249; Basal Science Department, Beijing University of Agriculture, Beijing, 102206;

1. Introduction Mesoporous materials possess advantages as very high specific surface areas and large pore size which qualify them talent material as catalysts especially for bulky molecules treatment. Mo species are important active components and insertion of Mo in silica-based mesostructure have attracted extensive attention. Conventional post-synthesis methods have limitation of low Mo loading which implies possible low activity of catalyst. Recently, In-situ preparation strategies are adopted and mainly focus on preparation in acidic media [1,2] among which Bregeault and coworkers [3,4] have established an effective modification mode and reached an ultra high loading of Mo and W with Si/Mo mole ratio of 25, which is equivalent to Mo loading of 4.6 wt%. Whereas assembling in alkaline medium favors further incorporation of secondary metal ion as Ni2+ through reaction of precipitation, Viswanathan's group [5] had reached Mo loading of 0.1 wt% in weak alkaline medium and Ziolet's group [6] had reached Mo loading of 0.00045 wt% at pH level of 11 respectively. To overcome disadvantages of low Mo loading and low Mo usage, efficient processes for incorporation of Mo in basic media are worth of further investigation. This paper presents a novel in-situ method for synthesis of mesoporous MoSiOx composite in strong caustic medium with acetylacetone (HAcac) introduced, through approaches established, Mo loading of 6.7 wt% have been reached, which is a bit higher than that reported by Bregeault [3,4] in acidic media and much higher than that reported in basic medium [5,6]. The work dedicates to the effects explanations of HAcac on MoSiOx preparation and the characteristics of MoSiOx discussion also.

148 148

2. Experimental Section 2.1. Synthesis MCM-48 was prepared according to procedures described by D. Kumar and coworkers [7]. Mesoporous HAcac-silica was prepared according to the same method but with introduction of HAcac before aqueous ammonia adding. Mesoporous MoSiOx and SiO2 were prepared according to formula as follow: 1.00 TEOS (tetraethyl orthosilicate): x Mo: 2.16 NaOH: 0.13 CTMAB (cetyltrimethyl-ammonium bromide): 107 H2O: 3.56 HAcac with adding sequence of NaOH, (NH4)6Mo7O24.4H2O, HAcac, CTMAB, and TEOS. The mixture was agitated for 3 h and aged for 3-7 days; the resulting solid was filtered and washed, then dried at 373 K for 6 h and calcined at 823 K for 6 hr. 2.2. Characterization techniques XRD (Rigaku D/max 2000), N2 adsorption/desorption (ASAP 2020), TEM (Hitachi-9000) and SEM (Oxford S-36) were used for materials detection. 3. Results and Discussion 3.1. Effects of HAcac The effects of HAcac on mesostructure were studied through com-parison of MCM-48 and HAcac-silica firstly. XRD patterns (Figure 1) of calcined samples show that the 100 diffraction strength of HAcac-silica are higher than or equivalent to that of MCM-48 with dramatic shift toward the lower 2 theta degree with proper amount of HAcac, which indicate 2 3 4 5 2theta /deg. that HAcac contribute to enlargement of pore size without unwanted reduction of Figure 1. XRD patterns of MCM-48 and HAcac-silicas with different mesostructure order. amount of HAcac (xlO~2mol): a. 0; The morphologies of mesoporous MCM-48 and HAcac-silica were investigated by HRTEM shown in Figure 2. The results prove that the pore size of HAcac-silica were much larger than those of MCM-48, which are consistent with analysis of XRD results of Figure 1. Besides pore size enlarging impaction confirmed above, HAcac displays even greater significance in preparation procedures because condensation or precipitation of hydrolysate of TEOS is inhibited when pH level is higher than 14. Synthesis of SiOx show that with no HAcac adding the mixture keeps homogenous when stirred for more than 3 h; while deposition emerging within

149 149

20 min with 0.0195 mol of HAcac and increased amount of HAcac result in decreased condensation time. Synthesis of MoSiOx verifies the promotion effect also. (b)

(a)

(c)

Figure 2. TEM images of MCM-48 (a). HAcac-silica (b) and MoSiOx (c) with scale bars 20nm

3.2. Characteristics ofMoSiOx

-1

(b)

(a )

1.6

(b)

3

Intensity /cps

11800 800

Pore Volume /(cm .g )

Figure 3 shows the XRD patterns of MoSiOx with Mo loading of 3.3 wt%. Lower angle XRD spectrum reveals the characteristics of mesoporous material; and wider angle spectrum inserted reveals no peak of ordered crystal, which indicates that there have no MoOx in the material, or MoOx is highly dispersed with particle size within 30A beyond the detection limitation of XRD even when Mo loading is as high as 6.7 wt%. 9.4 wt% Mo loading result in color change from milk-white to light-blue, despite the mesostructure feature maintained crystal MoO3 is detectable with XRD. SEM results of MoSiOx reveal that the average particle size of spheral MoSiOx is about 200nm, much smaller than that of MCM-48 of 0.5 ~ 2u.m prepared by D. Kumar [11], the results explains the dispersion feature of XRD 100 patterns also. 1200 5

600

20

40

60

80

0 1

2

33

2 th e ta /d e g. 2theta /deg.

44

Figure 3. XRD patterns of MoSiOx (with wider 2theta range 5-75 ° inserted)

5

1.2 0.8

(a)

0.4 0.0 -5

20 00 55 10 Pore Diameter /nm

15

20

Figure 4. Pore size distribution of (a) MCM-48 and (b) MoSiOx (3.3

The HRTEM morphology of MoSiOx shown in Figure 2 is similar to that of HAcac-silica, which suggest that proper amount of Mo insertion brings no dramatic effects on physical features. But excessive Mo loading will reduce order of pore arrangement or even destroy the mesostructure. The maximum Mo loading is 9.4 wt% and the limitation of Mo raw material added is 3 g. Results of Nitrogen adsorption-desorption were summed up in Table 1. The variables claim that the physical features will be affected by HAcac adding and Mo loading, increased amount of Mo loading result in shrinking of surface area,

150 150

diminishing of the pore size and the pore volume. The pore size distributions in Figure 4 show that MoSiOx possesses uniform pore size, which imply that proper amount of Mo loading and HAcac adding have no effect on pore order. Table 1.

Results of N 2 adsorption-desorption

Sample

BET surface area / m2.g"'

BJH pore size / nm

Pore volume / cm'.g"1

MCM-48

1589

2.5

1.02

MoSiOx (3.3 wt%)

966

4.8

1.50

MoSiOx (5.4 wt%)

868

3.7

0.95

The nice features qualify MoSiOx talent catalyst for bulky chemicals processing as hydrodesulfurization (HDS). HDS conversion of diesel on MoSiOx with 3.3 wt% Mo content is 80%, which is a bit higher than that of Y-AI2O3 with the same Mo loading, the remained sulfides are mainly multi-alkyl substituted especially of 4, 6-alkyl substituted naphthalene components. 4. Conclusion The paper presents an original method for MoSiOx synthesis in strong caustic medium with HAcac introduced. Through method established, Mo loading of MoSiOx is higher than or equivalent to the reported best and much higher than those prepared in basic media. Promoting precipitation and enlarging pore size qualify HAcac significant additive in the present method, and its effects on insertion of other transitional metal species are under investigation. 5. Acknowledgment Acknowledge for supporting of NSFC project (No. 20406012), National Basic Research Program of China(2004 CB 217806) and CNPC project (05E7019). 6. References [1] Z. Zhang, J. Suo, X. Zhang and S. Li, Chem. Commun, 2 (1998) 241. [2] F. Somma and G. Strukul, J. Catal., 227 (2004) 344. [3] J. Y. Piquemal, J. M. Manoli, P. Beaunier, A. Ensuque, P. Tougne, A. P. Legrand and J. M. Bregeault, Micropor. Mesopor. Mater., 29 (1999) 291. [4] J. Y. Piquemal, E. Briot, G. Chottard, P. Tougne, J. M. Manoli and J. M. Bregeault, Micropor. Mesopor. Mater., 58 (2003) 279 [5] R. K. Rana and B. Viswanathan, Catal. Lett. 52 (1998) 25. [6] M. Zioleka, I. Nowaka, B. Kilos, I. Sobczak, P. Decyk, M. Trejda and J. C. Voltab, J. Phys. Chem. Solids. 65 (2004) 571. [7] D. Kumar, and K. Schumacher, et al. Colloid. Surf. A: Physicochem. Eng. Aspects 187-188(2001) 109.


151 151

Birch templated synthesis of macro-mesoporous silica material for sustained drug delivery Huiming Lin a , Fengyu Qu a>b, Shiying Huang a , Guangshan Z h u a and Shilun Qiu a '

State Key Laboratory for Inorganic Synthesis and Preparative Chemistry, Jilin University, Changchun 130023, China Chemistry Department of Harbin Normal University, Harbin, 150025, China.

The hierarchical porous silica material with the structure of macropore and ordered hexagonal mesopore was prepared using birch as hard template and PI23 as soft template, respectively. The products remain the morphology and the macropore structure of birch and the wall was replaced by ordered mesoporous silica. The hierarchical porous silica was characterized by scanning electron microscope, powder x-ray diffraction, transmission electron microscope and nitrogen adsorption/desorption. The drug store and controlledrelease using the products as drug carrier have been investigated. Ibuprofen (IBU) was employed as a model drug and the release profiles showed that the hierarchical porous material can be served as a sustained drug delivery system. 1. Introduction Recently, several groups have tried to use biological templates to synthesize hierarchical porous materials with two or more level and complex morphologies [1]. This kind of materials may improve diffusion and transport of large molecular through the macropores and channels; meanwhile high surface areas and large pore volumes provided by meso-pore may be beneficial to larger loading amount of guest molecules [2, 3]. Compared to the artificial templates, biological templates have the characteristics of low-cost, abundant, renewable, environmental friendly and inherent complex structure, which make it possible to synthesize materials with unique multilevel structures and complex morphologies [4-6]. Liu and co-workers reported the mineralization of wood tissue which can form a silica replica with the cellular structures of poplar and pine [7]. 3D

152 152

microscale metallic materials exhibited elaborately detailed and nanometerscale features have been synthesized using diatom as template by direct fabrication method [8]. Synthesized porous micron-sized particles of silica, calcium carbonate, and calcium phosphate with complex morphologies employed pollen grains as direct template have been reported by Mann and coworks [9]. Ogasawara et al. proposed that cuttlebone P-chitin with macroscopic porosity can be used as a highly organized organic template to prepare analogous silica-polysaccharide with 3-D interconnected box structures [10]In this paper, Bio-template (birch) and surfactant PI23 were employed as dual template to synthesize hierarchical porous material. The morphology of the birch has been remained perfectly and the macro-mesopore structure has been obtained. Additionaly, Ibuprofen delivery profiles had been studied by using this hierarchical porous material as drug carrier. 2. Experimental Section The hierarchical porous silica material with the structure of macropore and ordered hexagonal mesopore was prepared using birch as hard template and PI23 as soft template respectively under acidic system. In a typical procedure, 0.9 g P123 was dissolved in the mixed solution of 10 g EtOH, 0.1 g hydrochloric acidic (2 M HC1) solution and 0.8 g deionized water. To above mixture, 2.08 g TEOS was added under stirring. After stirring 2 h at room temperature, several pieces of birch were soaked in the solution and kept at 60°C for 3 days in unsealed polythene container. Finally, the samples were taken out from the solution, air dried and calcined at 550°C for 6 h in room air. The loading of the drug was carried out by immersing the sample (217 mg) in a hexane solution of IBU (10 mL, 0.1 M) and stirred for 2 h at room temperature. The IBU-loaded sample was separated from the solution by vacuum filtration, and dried at room temperature. The loading amount was determined by UV/VIS spectrophotometry. The drug-loaded sample was compressed into a tablet with a diameter of 10 mm and a thick of 0.5 mm. The release rate was obtained by soaking the drug tablets in a solution of simulated intestinal fluid (pH = 6.8 aqueous) maintained at 37°C. At predetermined time intervals, samples (3 mL) were withdrew and immediately replaced with an equal volume of solvent to keep the volume constant. These samples were filtered (0.45 um), diluted, and analyzed for BIU content at 221nm using a GBC-10/20 UV/VIS spectrophotometer. Powder XRD data was collected on a SIEMENSD5005 diffractometer with CuK a radiation at 40 kV and 30 mA. The nitrogen adsorption/desorption, surface areas, and median pore diameters were measured using a Micromeritics ASAP 2010M sorptometer. Before measurement at 77 K, the samples were degassed at 373 K. for 12 h. Specific surface areas and pore size distributions were calculated using the Brunauer-Emmett-Teller (BET) and Barrett-JoynerHalenda (BJH) model from the adsorption branch, respectively. UV-VIS spectra

153 153

were taken on a Lambda 20 spectrophotometer. SEM Micrographs were performed using JEOL-JSM-6300 operating at an accelerating voltage of 2030 kV. TEM image was recorded on JEOL 2010 F and Philips CM200 FEG with an acceleration voltage of 20 kV. 3. Results and Discussion Fig.l shows low angle X-ray diffraction (XRD) pattern for hierarchical porous material using PI23 and birch as templates, which exhibits a strong diffraction peak at 29 = 0.9, indicating that the ordered mesopore structure have been obtained. The morphologies of the bio-template (birch) and the sample the sample 0 11 2 2 3 4 5 6 calcined are revealed by SEM. Fig. 2a, 2 Theta 2b shows that the birch has tubular cross structure, and the di-ameter of the tube is ca. lum. The hierarchical pore material Fig. 1 Low-angle of XRD of birch with surfactant after calcination has re-mained the birch morphologies completely. It can be observed clear-ly that the size of the macro-pore is ca. 1 um from the SEM image (Fig. 2c). The nitrogen adsorption/desorption isotherms and corresponding pore size distribution of the sample are shown in Fig. 3. It yields a type IV isotherm with HI-type hysteresis, which is a typical c characteristic of mesoporous material with hexagonal cylindrical channel. Compared with common mesoporous material (SBA-15) synthesized at similar condition, the BET surface areas (293.85 m2g"'), and pore volumes (0.4835 cm3g"1) decreased somewhat, which may be due to the existing of macropore. The pore Fig. 2 SEM image of birch (a, b), surfactantdiameter is about 5.2 nm, calculating templated birch sample after calcination (c) from the BJH method of mesopore size analysis to the adsorption branch of the nitrogen isotherm. TEM image shows that the sample still possesses ordered hexagonal mesoporous structure (Fig. 4). The pore size observes from image is about 5.5 nm, which is consistent with the results of XRD and nitrogen adsorption/desorption.

a

; \ .r

Vfj/fj',':

-1

a

3

L 300 300 3. 250

1 200 200 8 150 150 t 100 100 | >

-1 3

Volume Adsorbed (cm g )

_ 350

Volume Adorbed (cm g )

154 154

1.6 1.4 1.2 1.0 0.8 0.6 0.4 0.2 0.0 -0.2

0

10

20

30

40

50

Pore Size (nm)

50 50 0 0

0.0

0.2

0.4

0.6

0.8

1.0 1.0

Relative Pressure (p/p ) (p/p0 0

Fig. 3 Nitrogen adsorption-desorption isothem Fig. 4 TEM image of birch with surfactant and mesopore distribution of the samples after calcination

The cumulative release rate is shown in Fig. 5. The diagram clearly proves the system exhibits sustained-release profile. Only 10 wt% of IBU released within 1 h, and it took 8 and 28 h to reach 40 wt% and 60 wt% drug releasing. Compared to the releasing rate of IBU from SBA-15 (Fig. 6), the release rate of IBU from the hierarchical porous material has more sustained releasing behavior. 60 60

•

•

M

40 40

/

30 30

/

20 20

1010

£

0 0

i 0 0

10 10

100 100 90 90 80 80 70 ? 70 60 60 50 50 ; DC 40 40 (0 30 30 aQ0>> 20 20 DC 10 10 Release Ra te (wt%) ate(\

Release R ate (wt%) Rate

fi

B

50 50

20 20

30 30

40 40

50 50

Time(h) Time (h)

Fig. 5 release rate of IBU from the hierarchical porous material

/

. 1 0 0

10 10

20 20

30 30

40 40

50 50

Tim e (h) Time(h)

Fig. 6 release rate of IBU from pure SBA-15

This may be due to the delivery of the drug from hierarchical porous carrier may take two steps: (i) drug released from mesopore to the macropore; (ii) drug released from macropore to the outside. As the drug releasing from mesopore to macropore, the macroporous structure played a role of alleviator, which slowed the release rate of the drug. The concentration of the drug may have a homeostasis between the macropore and releasing media. Consequently, the drug could not release completely, and the final release amount could only reach 60 wt %.

155 155

4. Conclusion We have demonstrated a feasibility method to synthesize hierarchical porous silica material with the structure of ordered hexagonal mesopore and macropore, using PI23 and birch as templates. The structure and morphology of birch have been replicated perfectly. And the material has sustained drug delivery profile. 5. Acknowledgement This work was supported by the National Natural Science Foundation of China (Grant Nos. 20571030, 20531030, 29873017 and 20101004), and the State Basic Research Project (G2000077507 and 2003CB615802). 6. References [1] [2] [3] [4] [5] [6] [7] [8] [9] [10]

Z. Y. Yuan, B. L. Su and J. Mater. Chem., 16(2006)663. N. Stachoqiak, A. Bershteyn, E. Tzatzalo and D. J. Trvine, Adv. Mater., 17 (2005) 399. P. Sepulveda, J. R. Jones and L. L. Hecfh, J. Bio. Mater. Research, 59 (2002) 340. J. Zhang, S. A. Davis and S. Mann, chem. commun., (2000) 781. V. Valtchev, M. Smaihi and L. Vidal, Argew. Chem. Int. Ed., 42 (2003) 2782. F. C. Meldrum and R. Seshadri, Chem. Commun., 29 (2000). Y. S. Shin, J. Liu and G. J. Exarchos, Adv. Mater., 137 (2001) 29. E. K. Payne, N. L. Rosi and C. A. Mirkin, Angrew. Chem. Int. Ed., 44 (2005) 5064. S. R. Hall, H. Boleger and S. Mann, Chem. Commun., (2003)2784. W. Ogasawara, W. Shenton and S. Mann, Chem. Mater., 12 (2000) 2835.



157 157

Synthesis of metal-doped mesoporous silica by spray drying and their adsorption properties of water vapor Akira Endo *, Yuki Inagi, Satoko Fujisaki, Takuji Yamamoto, Takao Ohmori and Masaru Nakaiwa National Institute of Advanced Industrial Science and Technology (A 1ST), Research Institute for Innovation in Sustainable Chemistry Tsukuba Central 5, 1-1-1 Higashi, Tsukuba, Ibaraki 305-8565, Japan.

1. Introduction Ordered mesoporous silicate(MPS) templated by surfactant molecular assemblies have been attracted much attention because of their potential applications as catalysts, adsorbents, molecular sieves, sensors, etc. [1] The Evaporation Induced Self Assembly (EISA) technique is one of the most promising process for the large scale synthesis of ordered mesoporous materials, because of some advantages over the hydrothermal synthesis such as short synthesis time, easiness of controlling silica/metal ratio, possibility of continuous synthesis etc. Some reports on the synthesis of ordered mesoporous materials using spray-drying process, which is a kind of EISA process, have been published, reporting the synthesis conditions and their influence on the porous structure and morphology [2-5]. However, there is no paper describing the metal incorporation into silica network, which is important for the practical application of MPS materials. For example, Bruinsma reported the possibility of Al into silica network by spray-drying [2]. However, the Al was not retained after calcination to remove the templates. In the present study, metal-doped MPS with hexagonal array of cylindrical pores were synthesized by spraydrying using ethanol as a solvent and their water adsorption were investigated. 2. Experimental Section TEOS and C,,TAC (« = 10 - 18) were dissolved into ethanol, where n represents the number of carbon atoms composing the alkyl chain of

158 158

alkyltrimethylammonium chloride (C«TAC). After HC1 aqueous solution (10"3 M) and metal source(ZrO(NO3)2 • 2H2O and A1(NO3)3' 9H2O) was added to the mixture, obtained solution was stirred at room temperature for 1 hour to hydrolyze the TEOS. The typical molar ratio of the starting solution was 1 0.95 TEOS : 0 - 0.05 metal : 0.2 CnTAC : 10 EtOH : 1.8 X 10'4 HC1 : 10 H 2 O. The solution was then transferred to a round-bottom flask and evaporated using a vacuum rotary evaporator at 70 hPa for 0.7-1 h. Then, the solution was spray dried using the spray dryer GS310 (Yamato Kagaku Co. Ltd.). The inlet temperature was 433 K and the gas pressure was 0.075 MPa. The resulting solid, a silica-surfactant composite, was calcined at 873 K for 5 h to remove the surfactant. XRD and nitrogen adsorption/desorption measurements were carried out for the characterization of the metal-doped mesoporous silicas. XRD measurements were performed using a Rigaku Miniflex diffractometer (Cu/Ka radiation, operated at 40 kV and 30 mA). The nitrogen adsorption/desorption isotherm was measured using Belsorp-mini, fully automatic adsorption isotherm measuring equipment (manufactured by BEL Japan, Inc.). The pre-treatment was carried out at 573 K for 5 h under a nitrogen atmosphere. The state of metal incorporated into silica network was investigated by XPS measuremt using Shimadzu ESCA-1000). The acid sites of metal-doped samples was measured by temperature programmed NH 3 desorption (NH3-TPD) using BELCAT(manufactured by BEL Japan, Inc.). 3. Results and Discussion

Intensity / a.u.

All the samples except the 5% Aldoped sample were obtained in the 5% Zr shape of dried powder after the spray-drying. The 5% Al-doped 5% Al sample was not sufficiently dried in our experimental condition described 1% Zr above and resulted in relative large particle size. The XRD patterns of pure silica and Al and Zr-doped 1% Al mesoporous silica tem-plated by pure silica Ci6TAC are shown in Fig. 1. The diffraction peaks indicate that the 2θ /degree 2θ/degree samples have periodic mesostructure with hexagonal array, although the Fig. 1 The XRD patterns of metal-doped peaks of metal-doped samples MPS powder synthesized by spray-drying. broaden-ed with increasing the Al and Zr amount. The same results were obtain-ed for the other samples templated by the different surfactants, although it is not described here. We confirmed the metal incorporation into the silica network by SEM/EDX and XPS measurements. The state of metal species for all samples was not metallic 2

4

6

8

10

159 159

but oxidized. For example, the O Is XPS of 1%-Zr-doped sample can be attributed to two types of oxygen, Si-O-Si(533.0eV) and Si-O-Zr(531.1eV) [6]. From the N2 adsorption measuremts at 77K, the BET surface area(SBET) of all samples are over 1150 m2/g. The most common pore size(dp) for the metaldoped mesoporous silicas decreased with increasing the metal amount. The pore structural parameters are summarized in Table 1. Table 1 Porous properties of synthesized mesoporous silica

Metal

Sample (mol%)

Zr Zr Al Al

dioo

dp

(nm) 3.85 3.38 3.27 3.34 3.07

(nm) 3.40 2.92 2.66 2.91 2.37

vP (ml/g) 0.90 0.75 0.64 0.75 0.58

dw (nm) 1.05 0.99 1.12 0.95 1.17

SBET

(m2/g) 1154 1155 1176 1178 1286

Amount of adsorbed water / gig

-1

0.7

0.6

(a) pure silica

(b) 1% Al

(c) 1% Zr

0.5

0.4

0.3

0.2

0.1

0.0 0.0

0.2

0.4

0.6

0.8

0.0

0.2

0.4

0.6

0.8

0.0

0.2

0.4

0.6

0.8

1.0

Relative Humidity Humidity / Relative

Fig. 2 Adsorption/desorption isotherms of water vapor : (a) pure silica, (b)l% Al-doped silica, (c) 1% Zr-doped silica; before ( • )and after(#) the water vapor treatment at 373 K for 24 h.

The water adsorption isotherms at 298K were measured using a Belsorp 18-3, fully automatic adsorption isotherm measurement instruments (manufactured by BEL Japan, Inc.). The pre-treatment was carried out at 573 K for the first measurement and 413 K for the second measurement for 8 h under a pressure of 2 Pa. For evaluating the durability of the samples, the synthesized silicas were not exposed to water directly, but rather were exposed to water vapor in an autoclave at 373 K for 24 h. After this water vapor treatment, the adsorption characteristics of the samples were examined. Fig. 2 shows the water adsorption isotherms before and after the steam treatment for 1%-metal-deoped samples. The shape of adsorption/desorption isotherms for 5%-metal-doped samples (not shown here) were almost identical.

160 160

The shapes of all the water adsorption isotherms were Type V of IUPAC classification with a hysteresis loop. The metal-doped samples adsorbed more water at the lower relative humidity region and the relative pressure where the steep increase in the amount of adsorbed water due to the capillary condensation occurred at lower relative humidity region, compared to the pure silica sample. The existence of acid sites, which influence the surface hydrophilic/hydrophobic properties, on the pore surface for the metal-doped samples was confirmed by the NH3-TPD measurement. This indicates the metal-doped samples posses a stronger hydrophilic nature than the pure silica sample. The pore structure of pure silica (Figure 2(a)) collapsed during the steam treatment, decreasing the BET surface area andthe capillary condensation observed before the steam treatment disappeared. On the other hand, no significant change was observed in the shape of adsorption isotherms of the metal-doped mesoporous silicas(Figure 2(b) and (c)) after the steam treatment, indicating an increase in the stability of these materials in the presence of water vapor. These results clearly show the successful incorporation of metal atoms into silica network, although the incorporation mechanism should be investigated. 4. Conclusion Highly ordered, metal-doped MPSs were successfully synthesized by spraydrying. This synthesis method can easily introduce metals into silica materials in comparison with a hydrothermal synthesis, and can be easily scaled-up as required. The metal-doped samples showed more hydrophilic properties at a lower relative humidity and higher durability towered water vapor. The water adsorption/desorption isotherms, XPS and NH3-TPD measuemts indicated, ithe successful incorporation of Al and Zr atoms into silicate network. This method also can be applied for the synthesis of other kinds of metal-doped MPSs, if an appropriate metal source is used. 5. References [1] C. T. Kresge, M. E. Leonowicz, W. J. Roth, J. C. Vartuli and J. S. Beck, Nature, 359 (1992) 710.

[2] P. J. Bruinsma, A. Y. Kim, J. Liu and S. Baskaran, Chem. Mater., 10 (1997) 2507. [3] N. Baccile, D. Grosso, C. Sanchez and J. Mater. Chem., 13 (2003) 3011. [4] N. Andersson, P. C. A. Alberius, J. S. Pedersen and L. Bergstrom, Micropor. Mesopor. Mater., 72 (2004) 175. [5] B. Alonso, C. Clinard, D. Durand, E. Veron and D. Massiot, Chem.Commun., (2005) 1746. [6] D. J. Jones, J. Jimenez-Jimenez, A. Jimenez-Lopez, P. Marireles-Torres, P. Oliverra-Pastor, E. Rodriguez-Castellon and J. Roziere, Chem.Commun., (1997) 431.


161 161

Structural characterization and systematic gas adsorption studies on a series of novel ordered mesoporous silica materials with 3D cubic Ia-3d structure (KIT-6) Freddy Kleitz*a, Chia-Min Yangb and Matthias Thommes*0 "Universite Laval, Department of Chemistry, Quebec G1K 7P4, Canada, Department of Chemistry, National Tsing-Hua University, Hsinchu, Taiwan. ''Quantachrome Instruments, 1900 Corporate Drive, Boynton Beach, FL 33426

We present the results of systematic gas adsorption experiments and an advanced structural characterization of novel ordered mesoporous silica materials with 3-D cubic Ia-3d structure (KIT-6). The pore condensation and hysteresis behavior of nitrogen (at 77.4 K) and argon (at 77.4 and 87.3 K) was studied in KIT-6 materials of different porosities and various mean pore diameters (ranging from ~ 5 nm up to 12 nm). We compare further the sorption and phase behavior of nitrogen and argon confined to this 3D cubic porous system with their behaviour in pseudo-ID pore systems (e.g. SBA-15 silica). Our results also shed light on the extent to which the so-called single pore model can be used for the pore size analysis of materials consisting of ordered pore networks. 1. Introduction Recently, a novel type of large-pore mesoporous silica with a cubic Ia-3d structure was synthesized by using a blend of triblock copolymer Pluronic PI23 and H-butanol as a structure-directing mixture [1,2]. This mesoporous silica material is composed of two interwoven mesoporous networks similar to MCM48, but can be synthesized with much larger mean pore diameters. In addition to potential applications in catalysis, adsorption, separation etc, these novel silica materials have the potential to serve as model substances for evaluating the details of the adsorption and phase behaviour of fluids in highly ordered pore

162 162

networks. Even though a lot of progress was achieved in the understanding of the sorption and phase behaviour of fluids in materials consisting of single pores (e.g. MCM-41) [ref. 3 and references therein], the investigation of pore condensation and hysteresis in pore networks is still under investigation [3,4]. To address this problem we performed, in addition to a structural characterization (by various techniques including XRD and gas adsorption), systematic gas adsorption experiments of pure fluids in a series of highly ordered mesoporous 3D silica materials of different porosities and mean pore size. 2. Materials and Experimental The mesostructured silica materials were prepared according to refs. [1,2] using Pluronic PI23 (EO20PO70EO20) and «-butanol as a structure-directing mixture, with TEOS as the silica source. This method has the advantage of being simple and highly reproducible in large quantities. The molar composition of the starting reaction mixture is TEOS/P123/HCl/H2O/BuOH = 1/0.017/1.83/195/1.31 in mole ratio. The reaction temperature is fixed at 35°C for 24 hours and the hydrothermal aging temperature varied from 50 to 130°C for 24 hours more. For comparison, different 2-D hexagonal SBA-15 samples were synthesized following the method proposed by Choi et al. [5]. Powder Xray diffractograms of the calcined samples were recorded on a Stoe STADI P 99 X-ray diffractometer in reflection geometry (MPI fur Kohlenforschung, Miilheim, Germany). High resolution nitrogen (77.4 K) and argon (77.4 K, and 87.3 K) adsorption/desorption isotherm measurements were performed with an Autosorb-I-MP adsorption instrument (Quantachrome Instruments, Boynton Beach, FL) in the relative pressure range from 1 x 10"6 to 1. 3. Results and Discussion In this study, we report (i) results of the structural characterization and (ii) a systematic study of pore condensation and hysteresis phenomena in a series of highly ordered mesoporous 3-D silica materials of different porosities and various mean pore diameters (ranging from ca. 5 nm up to 12 nm). In this short paper we can only present some characteristic results; extensive data are presented in [6]. The XRD patterns of the cubic mesoporous materials indicate excellent structural order with the symmetry being commensurate with the body-centred cubic Ia-3d space group. Fig. la illustrates the XRD pattern measured for a sample synthesized with the hydrothermal step performed at 130°C for 24 hours. The exact assignment to the Ia-3d symmetry for the materials was confirmed by transmission electron microscopy and is reported elsewhere [1,7]. Importantly, highly resolved XRD patterns as well as electron microscopy studies suggest no structural distortion. The unit cell size, calculateed from the 211 reflexion of the cubic Ia-3d phase, is measured to be 24.1 nm

163 163

for the calcined material prepared with aging at 130°C. This is a value substantially larger than the unit cell parameter of other cubic analogues (e.g. MCM-48 [8]). The high degree of structural order of this material is also demonstrated in the gas adsorption data. Some characteristic adsorption results for a Ia-3d material with a (mode) pore diameter of ~ 10 nm (aged at temperatures above 100°C) are shown in Figures 1-2. Figure l(b) reveals argon and nitrogen adsorption data at 77.4 K for Ia-3d silica obtained at 130°C. The high degree of order for this sample is clearly evident from the almost vertical adsorption/desorption branches of the HI hysteresis loop. Figure 2(a) shows an argon sorption isotherm obtained over a wide range of rel. pressures, i.e. 10"6 to 1, sensing the micro-, meso- and macropore ranges of this sample. The argon (87 K) and nitrogen (77 K) isoherms were used to calculate the pore size distribution with proper NLDFT methods, and in both cases, the NLDFT equilibrium transition kernel was applied to the desorption data. 1200

130°C Inte nsi ty ( a.u.)

Volume [cm3 g-1] STP

1000

I

Nitrogen at 77.35 K Argon at 77.35 K

800

600

400

200

1.0

1.5

2.0 2 theta (°)

2.5

3.0

0 0

0.2

0.4

0.6

0.8

1

Relative Pressure P/P0

Fig. l(a) Powder XRD pattern of the Ia3d KIT-6 silica sample prepared with aging at 130°C. (b) Nitrogen and argon adsorption at 77.35 K on this Ia-3d silica.

The argon and nitrogen pore size distribution curves agree very well as clearly revealed in Fig. 2(b). Moreover, the NLDFT mode pore diameter of 10.13 nm (calculated from the nitrogen desorption branch) is in very good agreement with the pore diameter (10.05 nm) obtained by using a geometrical model based on unit cell (unit cell: 24.1 nm), and wall thickness (2 nm) parameters as derived from the XRD data [9].

164 164 0.25

1200

Argon adsorption at 87.3 K Argonadsorptionat87.3 K Argon desorption at 87.3 K Argondesorptionat87.3 K

Dv(d)[cm3/Å/g]

Volume [cm3 g-1] STP

720

g 480 4S0-

0.15

0.1

0.05

240

0

Nitrogen (77 K) • NLDFT NLDFTNitrogen (77K) Argon (87 K) • NLDFT NLDFTArgon (87K)

0.2

960

5 10-5

5 10-4

5 10-3

5 10-2


5 10-1

5 100

0 5

25

45

65

85 105 105 125 125 Pore Diameter [Å]

145 145

165 165

185 185

205

Fig. 2 (a) Semilogarithmic plot of an argon adsorption/desorption at 87.3 K on Ia-3d silica (aged at 130°C) measured over a wide rel. pressure range from 10"6 to 1 (b) NLDFT pore size distributions from argon (87 K) and nitrogen (77 K).

The good agreement between the pore size data obtained with the NLDFT method and the geometrical approach indicates that the independent pore model (which has been confirmed for pseudo 1 -D pore systems such as MCM-41 and SBA-15) appears also to be applicable to this KIT-6 sample. However, a detailed study on a series of KIT-6 and SBA-15 silica's (pore diameter range from ca. 5 to 12 nm) suggests that there are differences in the hysteresis behavior of SBA-15 and KIT-6 materials in the pore diameter range < 9 nm. The hysteresis loop for KIT-6 is slightly (but clearly detectable) narrower as compared to appropriate SBA-15 samples. These differences in the width of hysteresis between SBA-15 and KIT-6 vanish for pore diameters > 9 nm. Details of these results and their interpretation are described elsewhere [6]. 4. References [1] F. Kleitz, S. H. Choi and R. Ryoo, Chem. Commun. (2003) 2136. [2] T.-W. Kim, F. Kleitz, B. Paul and R. Ryoo, J. Am. Chem. Soc. 127 (2005) 7601. [3] M.Thommes, in Nanoporous Materials; Science and Engineering; G. Q. Lu, X. S. Zhao, Eds.; Imperial College Press: London, U.K., (2004) 317. [4] M. Thommes, B.Smarsly, M.Groenewolt, P. I. Ravikovitch and A. V. Neimark, Langmuir 22(2006) 756. [5] M. Choi, W. Heo, F. Kleitz and R. Ryoo, Chem. Commun. (2003) 1340. [6] F. Kleitz, C. M. Yang and M. Thommes, manuscript in preparation, (2006). [7] Y. Sakamoto, T. W. Kim, R. Ryoo and O. Terasaki, Angew. Chem. Int. Ed. 2004,43, 5231. [8] M. S.Morey, A. Davidson and G. D. Stucky, J. Porous Mater. 5 (1998) 195. [9] XRD modeling was performed according to L. A. Solovyov, et al. J. Phys. Chem. B, 109(2005)3233.


165 165

Synthesis and characterization of mesoporous MCM-41 silica with thick wall and high hydrothermal stability under mild base solution Chi-Feng Cheng,* Po-Wen Cheng , Shu-Hsien Chou, Hsu-Hsuan Cheng and Hwa Kwang Yak Department of Chemistry, Center ofNanotechnology and R&D Center for Membrance and Technology, Chung Yuan Christian University, 200, Chung Pei Rd., Chung Li, Taiwan 32023, China

Abstract Siliceous MCM-41 mesoporous materials with wall thickness up to 36 A could be prepared at 165°C for 7 days under mild basic solution. More than 85% of surface area for these materials was retained even after hydrothermal treatment in boiling water inside autoclave for 14 days. A reasonable model explaining formation of thicker MCM-41 wall, not enlarging pore channel, is proposed. Thermal restructuring process under mild basic condition favors the silica redeposition on silica wall and building up thicker wall. 1. Introduction Low hydrothermal stability restricts practical applications of mesoporous molecular sieve MCM-41. The introduction of Al on the surface or into the framework of MCM-41 results in the remarkable improvement of hydrothermal stability of MCM-41 [1]. The most promising method for improving the hydrothermal stability of aluminosilicate mesoporous materials was using the aluminosilicate zeolitic nanoclusters as a raw material to build up mesostructure [2-5]» However, the improvement of mesoporous silica hydrothermal stability is still developing. Thermal and hydrothermal stabilities of a wide range of mesoporous silica have been studied by Cassiers et al. [6] They concluded that the thermal and hydrothermal stability were strongly related to the wall thickness. Ryoo et al. [7] considered that the wall-thickening approach appears to be the simplest one among these techniques, but no completely synthetic strategies have yet been found for systematic control of the wall thickness. Here, we report that the wall

166 166

thickness can be controlled systematically up to 36.1 A simply by increasing crystallization time to 1 ~ 7 days at 150 ~ 180°C at mild basic condition. 2. Experimental Section The siliceous MCM-41 was prepared as follows. Tetramethylammonium hydroxide (TMAOH) and cetyltrimethylammonium bromide (CTABr) were added to deionized water with stirring at room temperature. Fumed silica was added to the solution with stirring and then aged for 24 h at room temperature. The final gel of composition 1 SiO2: 0.19 TMAOH : 0.27 CTABr : 40 H2O was transferred to a Telflon-lined stainless steel autoclaves at 150 ~ 180°C for 1 ~ 7 days. The reaction product was filtered, washed with distilled water, dried in air at 110°C and calcined at 550°C for 8 h. Hydrothermal stability of the MCM-41 was studied by mixing 0.5 g of calcined samples with 50 g of deionized water, sealing in the closed glass bottles and heating at 100°C for 1 ~ 28 days. The parent samples without hydrothermal treatment are designated MCM-x-yd where x, y respectively are the crystallization temperatures at °C unit and time in days. Samples after hydrothermal treatment for z days are designated MCMx-yd-zd. These materials were characterized by XRD, N2 adsorption/desorption measurement, TEM, solid state NMR and TGA. 3. Results and Discussion Previous studies [8] have shown that the di0o spacing increased sharply when crystallization time increased from 1 to 48 h at 165°C. XRD patterns of sample crystallized for 2 days show a very intense (100) diffraction peak and four additional 110, 200, 210, 300 peaks. This suggests that MCM-165-2d sample has a long ordering of hexagonal pore arrays. However, the d\Oo spacing increases slightly from 58.1 to 61.4 A when crystallization time increases from 2 to 7 days. When the crystallization time increases gradually from 2 to 7 days, 110, 200 diffraction peaks of samples are gradually weakening and 210, 300 peaks progressively disappear (not shown). N2 sorption isotherms of above all samples without hydrothermal treatment exhibit a sharp adsorption/desorption hysteresis (not shown) and indicate that all samples possess good structural ordering and a narrow pore size distribution. Corresponding results are summarized in Table 1. It is shown that the increase of wall thickness results from a slight increase of unit cell and gradual decrease of pore size. Wall thickness increases systematically from 23.3 to 36.1 A as a result of increasing crystallization time from 1 to 7 days at 165°C at the expense of decrease of surface area and pore volume. It is probably that more silica source is used to build thick wall instead of high surface area and pore volume. To our best knowledge, the 36.1 A wall thickness of siliceous MCM-41 reported herein has not been described before. It is also noticed that surface MCM-41 with the wall thickness of 36.1 A prepared at 165°C for 7 days shows outstanding hydrothermal stability as compared to those prepared at 180 and 150°C for one or two days from the X-ray data in Fig. 1. Relative XRD

167 167

intensity of MCM-41 synthesized for different time at 165°C after hydrothermal treatment for 1 to 28 days and relative surface area of those samples are shown in Fig. 2. MCM-165-7d after 7 days of hydrothermal treatment at 100°C reserves 62% of 100 X-ray peak intensity and 90% of surface area as compared to original MCM-165-7d in Fig. 2. After further hydrothermal treatment for two weeks, MCM-165-7d-14d still has 52% of 100 X-ray peak intensity and 90%of surface area. The sharp hysteresis loop of adsorption/desorption and narrow pore size distribution for MCM-165-7d-14d illustrate that most mesostructure of calcined MCM-41 with ultra-thick wall is retained even after hydrothermal treatment at 100°C for 14 days (not shown). However, mesostructure of MCM165-7d after 3 or 4 weeks of hydrothermal treatment is disintegrated gradually. It is interesting that 26 % of 100 X-ray peak intensity is retained but the surface area is only 6.6 m2/g for MCM-165-7d-28d .

MCM-165-7d-7d

1.0 1.0

1.0 01.0

0.8

0.8

0.6

0.6 rO.eg

0.4

0.4 0.4 0

(0

(0

MCM-165-7d-14d

SUf

Intensity (A.U.)

T-

m /z = 12 m /z = 28 m /z = 44

i

1600

1200 1200

m /z m /z m /z m /z

= = = =

14 26 29 30

400 •

0

0

100

200

300

400

500

74.3 ppm

(a)

"I

1 163 ppm

600

19.3 ppm

72.0 ppm 69.1 ppm 9.1 p p m 66.2 66.2 p pppm m

62.3 ppm

49 ppm pm

Signal (U.A.)

(b) (b)

(c) (c)

(d)

(e) (e)

J|| '

[CH22CHCH CHCH33O]m O]m

[

CH22CH CH22 O]nn CH22 CH2 [CH 2 OH

HOCH HOCH2CH2OH 2CH2OH

O=CHOCH2CH2O

200

150

OCH3

[CH22CHCH33O]m O]m

100

50

0

4. Conclusion The above results lead to a better understanding of the combustion mechanism of the template in the MMS. N2 sorption and 13C NMR experiments

193 193

of these materials calcined at different temperatures showed that larger mesopores are first emptied followed by intrawall porosity. Further on going studies will investigate the relation between the SBA-15 porosity and the template combustion pattern. 5. References [1] D. Zhao, J. Feng, Q. Huo, N. Melosh, G. H. Fredrickson, B. F. Chmelka and G. D. Stucky, Science 279 (1998) 548. [2] D. Zhao, Q. Huo, J. Feng, B.F. Chmelka and G.D. Stucky, J. Am. Chem. Soc. 120 (1998) 6024. [3] G. Buchel, R. Denoyel, P. L. Llewellyn and J. Rouquerol, J. Mater. Chem. 11 (2001) 589. [4] M.TJ. Keene, R. Denoyel and P.L. Llewellyn Chem. Commun. (1998) 2203. [5] R. van Grieken, G. Calleja, G. D. Stucky, J. A. Melero, R. A. Garcia and J. Iglesias, Langmuir 19 (2003) 3966. [6] S. Kawi and M. W. Lai, Chem. Commun. (1998) 1407. [7] B. Tian, X. Liu, C. Yu, F. Gao, Q. Luo, S. Xie, B. Tu and D. Zhao Chem. Commun. (2002) 1186. [8] C.-M. Yang, B. Zibrowius, W. Schmidt and F. Schuth, Chem. Mater. 16 (2004) 2918. [9] C.-M. Yang, B. Zibrowius, W. Schmidt and F. Schuth, Chem. Mater. 15 (2003) 3739. [10] M. Kruk, M. Jaroniec, C. H. Ko and R. Ryoo, Chem. Mater. 12 (2000) 1961. [11] C.-Y. Chen, H.-X. Li and M.E. Davis Microporous Mater. 2 (1993) 17. [12] A.G.S. Prado and C. Airoldi J. Mater. Chem. 12 (2002) 3823. [13] R. Mokaya and W. Jones, J. Mater. Chem. 8 (1998) 2819. [14] S. Hitz and R. Prins, J. Catal. 168 (1997) 194. [15] F. Kleitz, W. Schmidt and F. Schuth, Micropor. Mesopor. Mater. 65 (2003) 1. [16] M. Jaroniec, M. Kruk and J. P. Oliver, Langmuir 15 (1999) 5410. [17] C. Decker and J. Marchal, Die Makromolekulare Chemie 166 (1973)117.



195 195

Evolution of mesoporosity and microporosity of SBA-15 during a treatment with sulfuric acid Anja Rumpleckera, Bodo Zibrowiusa, Wolfgang Schmidt3 Chia-Min Yangb and Ferdi Schiith3 "Max-Planck-Institut fur Kohlenforschung, 45470, Mulheim an der Ruhr, Germany, Deptartment of Chemistry, National Tsing Hua University, Hsinchu, 30013 Taiwan

1. Introduction SBA-15 type materials are prepared by cooperative self-assembly of silica and micelles of a triblock copolymer as structure directing agent, which is afterwards removed either by calcination, microwave digestion, solvent extraction, or supercritical fluid extraction. The synthesis of SBA-15 type materials offers great potential for fine-tuning pore dimensions, pore structures and particle morphology which can be achieved by adjusting solution composition, pH, reaction time and temperature. However, selective access to only one of the pore systems remains a challenging task. Such a bimodal, microporous and mesoporous structure is of special interest for applications in various fields, such as in catalysis, in delivery and release techniques, in adsorption and separation processes. Hence, a better understanding of stepwise vacation of mesopores and micropores in SBA-15 type materials prepared at different conditions is of high importance. 2. Experimental Section The SBA-15 silica materials used were synthesized according to the methods described in literature [1,2]. A hydrochloric acid (HC1) solution of the triblock copolymer was prepared and tetraethoxysilane (TEOS) was added after complete dissolution. The molar composition was 1 TEOS : 191 H2O : 0.017 P123 : x HC1, varying systematically the concentration of HC1 (0.3 mol L"1 < x < 1.7 mol L"'). The mixture was stirred at 35 °C and hydrothermally treated at 90 °C. After filtration of the solid was dried at 90 °C. Samples were designated as Sx-48-y, where x stands for the sample number and y stands for drying

196 196

duration in hours. Samples designated as Sx-48-yA were washed with acetone prior to the drying. The influence of HC1 concentration, of acetone washing, and of the drying time on the properties of the material obtained after treating the as-synthesized SB A-15 with H2SO4 (48 %) at 95 °C for 24 h were examined. The materials were characterized by nitrogen physisorption, thermogravimetrydifferential thermal analysis coupled with mass spectrometry, powder X-ray diffraction, 13C CP/MAS NMR and 29Si MAS NMR spectroscopy. 3. Results and Discussion Due to the strong influence on surface properties, mesopore size distribution and the ordered structure itself, the template removal is generally one of the most important steps during the preparation of mesoporous ordered materials. Recently, a procedure for the stepwise removal of the triblock copolymer template Pluronic PI23 has been developed for mesoporous SBA-15 type materials, which is based on the use of concentrated aqueous solutions of sulfuric acid [3]. The method is based on ether cleavage, which happens selectively in the easily accessible mesopores. Afterwards the micropores blocked by poly(ethylene oxide) fractions of the block copolymer template can be made accessible by a calcination at 250 °C. The nitrogen physisorption isotherms and t-plots of two SBA-15 batches prepared at different HC1 concentrations are reported in Figure 1. The structure directing agent was removed by a treatment with H2SO4 and, in comparison to that, by a calcination at 540°C. Sample SI was prepared at low concentration (0.3 mol L"1) of HC1 during the synthesis as described previously by Choi et al [2]. Sample S2 was prepared at high concentration of HC1 (1.7 mol L"1), which corresponds to the conditions described in the original literature of Zhao et al [1]. In all cases, the isotherms are of type-IV with a clear HI-type hysteresis loop, typical of materials with a constant cross section. As described in literature, the isotherms and t-plots of the calcined samples indicate comparable textural properties of both SBA-15 materials using different synthetic approaches [2]. Nevertheless, the isotherms and the t-plots of the SBA-15 samples treated with H2SO4 strongly differ from each other. This clearly suggests different distributions of mesopore volumes and micropore volumes for SBA-15 materials which were prepared with low concentration (0.3 mol L"') and high concentration (1.7 mol L"1) of HC1 during the synthesis. The t-plot in Figure 1 illustrate that only for the latter a post-synthesis treatment with H2SO4 leads to a stepwise vacation of mesopores and micropores. For SBA-15 materials prepared at substantially reduced acid concentrations (SI) a selective removal of only the poly(propylene oxide) fraction of the triblock copolymer template was not possible under any of the conditions applied. The results indicate that the synthesis procedure of SBA-15 has a strong influence on mesopore sizes and micropore sizes after a template removal using acid extraction methods. Therefore, we systematically studied the influence of

197 197

0.2

0.4 0.6 0.8 relative pressures p/p

1.0

0.2

0.4 0.6 0.8 relative pressure p/p

1.0

Figure 1: N2 isotherms and t-plots (inserts) of calcined SBA-15 (filled symbols) and of SBA-15 treated with 48wt % H2SO4 (open symbols); SBA-15 prepared with 0.3 mol I/ 1 HC1 (SI, I) and SBA-15 prepared with 1.7 mol L 1 HC1 (S2,11).

the HC1 concentration (0.3 mol L"1 < x < 1.7 mol L"1) at otherwise fixed molar composition of the synthesis. Furthermore, we analyzed the influence of the drying procedure of SBA-15, prepared at different HC1 concentrations, on the results of a post-synthesis treatment with H2SO4. Figure 2 shows the nitrogen isotherms and the t-plots of acid treated samples of one batch of SBA-15 prepared at low concentration of HC1 (0.3 mol L"1) after the as-made material was dried for 10, 20 or 40 h, respectively. One part of the as-made material was washed with acetone after filtering and lateron dried as described above.

0.0

0.2

0.4

0.6

0.

rel. pressures p/p 0

1.0

0.2

0.4

0.6 0.1

rel. pressures p/p 0

1.0

- • - S 3 48 40 -O-S34840A 0.2 0.4 0.6 0.8 1.0 rel. pressures p/p 0

Figure 2: N2 isotherms and t-plots (inserts) of SBA-15 treated with 48 wt % H2SO4 after different drying times. Open symbols indicate the experimental results for samples washed with acetone prior to drying.

The isotherms of the sample S3-48-10 and the acetone washed S3-48-10A differ strongly in the shape of the hysteresis loop. Therefore, it can be assumed that acetone washing of a freshly prepared as-made material can influence

198 198

mesopore shapes in case of SB A-15 prepared at low concentrations of HCl. For both materials, a treatment with the H2SO4 solution also vacates the micropores. After a longer drying (40 h) of the as-made material, the difference of the textural properties for acid treated samples becomes significantly smaller. Here, washing the as-made material with acetone does not lead to different pore size distributions. The inserts in Figure 2 show that acetone washing and extended drying times facilitate a selective vacation of only the mesopores. 4. Conclusion This study concerns in particular the stepwise vacation of mesopores and micropores using a treatment with H2SO4. Comparing SBA-15 materials prepared at different concentrations of HCl, we conclude that the mesopore and micropore size distribution after a treatment with H2SO4 depends strongly on the HCl concentration during the synthesis of the as-made SBA-15. An acid treatment of as-made SB A-15 prepared at substantially lower concentrations of HCl (0.3 mol L'1) does not necessarily lead to a selective vacation of the mesopores. For such samples the post-synthesis steps are the key factors influencing the mesopore and micropore size distribution. An extended drying period in combination with acetone washing leads to selective vacation of the mesopores. We suggest, that the evolution of mesopores and micropores during acid extraction depends on the degree of condensation of the silica which is influenced both by acid concentration during synthesis and by the drying procedure. 5. References [1] D. Zhao, Q. Huo, J. Feng, B. F. Chmelka and G.D.Stucky, J. Am. Chem. Soc, 120 (1998) 6024. [2] M. Choi, W. Heo, F. Kleitz and R. Ryoo, Chem. Commun. (2003) 1340. [3] C. M.Yang, B. Zibrowius, W. Schmidt and F. Schlith, Chem. Mater. 16 (2004) 2918.

Materials Recent Progress in Mesostructured Materials (Editors) D. Zhao, S. Qiu, Y. Tang and C. Yu (Editors) © 2007 2007 Published Published by Elsevier Elsevier B.V. B.V.

199 199

Framework modification and acidity enhancement of zirconium-containing mesoporous materials Lifang Chena, Xiaolong Zhoub'\ Luis E. Norena3, Guoxian Yub, Chenglie Lib and Jin-An Wang0* "Departamento de Ciencias Bdsicas, Universidad Autonoma Metropolitana-A, Av. San Pablo 180, Col. Reynosa-Tamaulipas, 02200 Mexico D.F., Mexico. Petroleum Processing Research Center, East China University of Science and Technology, 200237Shanghai, P. R. China c Labor atorio de Catdlisis y Materiales, SEPI-ESIQIE, Instituto Politecnico Nacional, Col. Zacatenco, 07738 Mexico D.F., Mexico

Zirconium-modified mesoporous molecular sieves with different Si/Zr molar ratios were synthesized through a surfactant templating route. In situ FTIR characterization shows that surfactant strongly interacts with the solid matrix, and its complete removal could be achieved at 400 °C. The structural ordering, textural properties and surface acidity of the resultant materials vary with the Si/Zr molar ratio. The incorporation of zirconium greatly increases not only the number of both Lewis and Bronsted acid sites but also the acid strength. 1. Introduction Zirconium based materials with large surface areas synthesized by sol-gel and non-ions surfactant synthesis routes show interesting catalytic properties in Fischer-Tropsch synthesis and alcohol dehydration [1-4]. Aiming to developing new acid catalytic materials with enhanced acidity and improved accessibility, this work reports synthesis of Zr-containing mesoporous molecular sieves through a cationic surfactant templated pathway. The removal of the clogged surfactant from the solids, textural properties, crystalline structure, zirconium incorporation and surface acidity of the resultant solids were studied by in situ Fourier transform infrared spectroscopy (FTIR), N2-physisorption isotherms, Xray diffraction (XRD), 29Si MAS-NMR, atomic absorption spectroscopic analysis (AAS) and W-visible spectroscopy and in situ FTIR spectroscopy of pyridine adsorption techniques.

200

2. Materials Synthesis The mesoporous materials were prepared by adding 0.6 g of fumed silica into 5.4 g of 45% tetrabutylammonium hydroxide aqueous solution with vigorous stirring for 5 min to form a transparent gel. And then 12 g of cetyltrimethylammonium chloride (25 wt% solution in water) were added into the above gel with agitation. Afterwards, 1 g of fumed silica was immediately added into the above mixture followed by vigorous agitation for approximately 15 min. The final step consisted of adding a given amount of zirconium-npropoxide (70% in propanol). The amount of zirconium-n-propoxide depends on the required Si/Zr mole ratio (Si/Zr = 25, 15, 8 and 4). For example, for a typical synthesis leading to a Si/Zr =15 solid, 0.77 ml of zirconium-n-propoxide were added. The mixture was sealed in a Teflon bottle and heated at 100 °C for 48 h. The resultant white solid was filtered and washed, and then dried at 80 °C for 24 hrs. The dried solid was calcined at 600 °C for 6 hrs in air with a flow rate of 60 ml/min. The actual Si/Zr molar ratio in the obtained materials determined by AAS technique was reported in Table 1. 3. Results and Discussion The features of the in situ FTIR spectra of the samples with various Si/Zr ratios are very similar. As an example, a set of FTIR spectra of the as-made sample with a Si/Zr = 4 are shown in Figure 1. At 25 °C, the IR spectrum consists of a broad band between 3700 and 3000 cm"1, which is due to water adsorbed on the sample surface, and two peaks at 2950 and 2850 cm"1, which are assigned to the stretching vibrations of C-H bonds in hydrocarbons (vCH3as and vCH2as), i.e., herein the surfactant [5]. In the C-H deformation vibrations region, several bands at approximately 1480 and 1371 cm"1, arise from vibrations of the bending modes (scissoring and rocking vibrations) of the C-H bonds. Below 1250 cm", the bands are mainly produced by the fundamental vibrations of the Si-O-Si (1231, 791, 575 cm"1) and Si-O-Zr (960 cm"1) bonds within the framework. Increasing temperature results in water desorption and surfactant removal. It is noted that a peak appears around 3710 cm"1 at 200 °C and it gradually shifts towards a higher energy position with temperature increasing, which is assigned to silanol groups linked to the framework. At 400 °C, the disappearance of the group bands at 2800-3000 cm"1 and at 1485 cm'1 strongly indicates complete removal of the clogged surfactant from the solid. The XRD patterns of the as-made samples show four peaks indexed to the (100), (110) (200) and (210) planes of a typical MCM-41 structure with hexagonal arrangement (not shown). After calcination at 600 °C, the (100) peak loses its sharpness and some peaks disappear, indicating that the ordered structure, in some degree, becomes into wormhole-like arrangements, particularly in the solid with high zirconium content. The mean pore diameter, increases from 2.16 nm to 2.53, 2.93 and 3.69 nm and the surface area decreases

201

from 1113.9 m2/g to 680.6, 654.8 and 668.1 m2/g when the Si/Zr molar ratio varies from 25 to 15, 8 and 4, respectively. 4

3

Q

Q 2

Q

300 °C

200 °C

Si/Zr =25

Intensity (a.u.)

Absorbance (a.u.)

400 °C

Si/Zr=15

100 °C

Si/Zr=8 Si/Zr=4

25 °C

4000 3500 3000 2500 2000 1500 1000 1000 500 500 -1 Wavenumbers (cm-1 ) )

Figure 1. A set of in situ FTIR spectra of the samples with different Si/Zr molar ratios.

-80

-90

-100 -110 -120 -130 -140 -150 δ5 (ppm) (ppm)

Figure 2.29Si MAS-NMR spectra of the samples with different Si/Zr molar ratios.

The 29rSi MAS-NMR spectra of the samples calcined at 600 °C are shown in Figure 2. Each spectrum consists of three main components with chemical shifts at ca. -92 ppm (Q2), -103 ppm (Q3) and -115 ppm (Q4) silicon nuclei. All the samples show (Q +Q2)/Q4 value bigger than 0.49 that corresponds to pure SiMCM-41 solid. The UV-vis profiles exhibit a single band around 201 nm attributable to a charge-transfer from oxygen to an isolated Zr (IV) ion in a tetrahedral environment [6]. The peak intensity of the zirconium-containing sample significantly increases with the zirconium content which significantly differs from the pure Si-MCM-41 sample where no clear band is observed in the given range. Both, 29Si NMR and UV-vis characterization results, confirm that zirconium ions are, indeed, homogeneously incorporated within the framework of the mesoporous materials and they occupy the isolated tetrahedral sites. Both Lewis (L) and BrQnsted (B) acid sites are formed on all the samples as characterized by the formation of the pyridine adsorption bands around 1450 cm'1 (L), 1590 cm"1 (L) and 1540 cm"1 (B). As the Si/Zr molar ratio decreases from 25 to 15, 8 and 4, the B acid sites remarkably increase from 11 to 14, 70 and 142 \imo\lg (Table 1). The total acid sites (T) in all the Zr-modified materials are almost two times greater than that of the pure Si-MCM-41 on which no B acid sites but only 658 umol/g Lewis acid sites are formed. The creation of B acid sites in the zirconium modified mesoporous materials is assumed to be related to the strong polarization of Si4+—O--Zr4+ linkages [7]. When the small Si4+ ions are replaced by large Zr4+ ions in the framework of the solid, the electron density around Si is changed due to a charge unbalance or a local structural deformation resulting from the introduction of Zr4+ ions into the

202

vicinity of the hydroxyls carrying silicon, which may activate the SiO-H bond, favoring the release of the proton. Table 1. Acid properties of the Zr-modified samples

Si/Zr (nominal) Si/Zr (AAS) B (|4.mol/g) L (umol/g) oo(Si-MCM-41) 25 15 8 4

25.4 14.8 8.1 4.3

0 11 14 70 142

658 1045 1165 1217 1134

T (fimol/g) 658 1056 1179 1287 1276

4. Conclusion (1) Zirconium incorporation within the framework increases the pore diameter but diminishes the surface area and the pore volume; (2) The structural regularity of the resultant solids can be improved or reduced, depending on the Si/Zr molar ratio; (3) Zirconium incorporation greatly promotes the formation of Bronsted acid sites, and significantly enhances the acid strength and doubly increases the population of the total acid sites compared to the pure Si-MCM-41. 5. Acknowledgment L. F. Chen thanks the scholarship granted by CONACyT-Mexico for her doctoral study. The financial support from the projects CONACyT (Mexico)NSF (China) (No. J 110.426/2005), CGPI-IPN-2006067 and China 973-Project (No. 2004CB720603) are appreciated. The authors thank to Dr. P. Salas and Dr. J. Navarrete for their technical assistances. 6. References [1] [2] [3] [4] [5] [6] [7]

K. Tanabe and T. Yamaguchi, Catal. Today, 20 (1994) 185. J. Walendziewski, B. Pniak and B. Malinowska, Chem. Eng. J., 95 (2003) 113. M. Wei, K. Okabe, H. Arakawa and Y. Teraoka, Catal. Commun., 5 (2004) 597. Q. Zhuang and J. M. Miller, Appl. Catal. A, 209 (2001) L1-L6. V. Ivanov, E. Zausa, Y. Ben Taarit and N. Essayem, Appl. Catal. A, 256 (2003) 225. M. S. Morey, G. D. Stucky, S. Schwarz and M. Froba, J. Phys. Chem. B., 103 (1999) 2037. J. A. Anderson, C. Fergusson, I. Rodriguez-Ramos and A. Guerrero-Ruiz, J. Catal., 192 (2000) 344.

Materials Recent Progress in Mesostructured Materials (Editors) D. Zhao, S. Qiu, Y. Tang and C. Yu (Editors) © 2007 2007 Elsevier Elsevier B.V. All All rights rights reserved. reserved.

203 203

Pulsed field gradient NMR studies of n-hexane diffusion in MCM-41 materials Ziad Adem,a Flavien Guenneau,a Marie-Anne Springuel-Huet,a Juliette Blanchardb and Antoine Gedeona "Laboratoire Systemes Interfaciaux a I 'Echelle Nanometrique, Laboratoire de Reactivite des Surfaces, Universite Pierre et Marie Curie, 4 place Jussieu, 75252 Paris Cedex 05 (France)

1. Introduction The knowledge of transport properties in heterogeneous catalysis is of important interest since the selectivity and the activity depend significantly on diffusion. Pulsed Field Gradient (PFG) NMR has proved to be a valuable tool to probe the intracrystalline diffusion of molecules adsorbed in microporous solids [1]. This technique can also be used to study the diffusion in mesoporous materials, such as MCM-41 [2]. In this case, the root mean square displacement of the diffusing molecules during the observation time A is usually larger than the particle diameter and the purely intracrystalline diffusivity Dintra can only be attained using a "two region" model involving the intra- and interparticle spaces [13]In this work we use PFG NMR to study the influence of the pore diameter, the hydrophobicity of the pore surface and the adsorbate concentration on the intraparticle diffusion of n-hexane in MCM-41 solids. 2. Experimental Section The MCM-41 materials were prepared according to the procedure proposed by Ryoo et al [4] using various alkyltrimethylammonium (from C12 to C18) as surfactants to obtain materials referred as MCM-Cxx, with different pore diameters. The calcinations were performed under air flow at 823 K or 1273 K for 6 h. The characteristics of the samples are given in Table 1. The adsorption isotherms at 295 K of n-hexane were measured and a known amount (expressed in percentage of the saturation loading) was subsequently adsorbed at

204

equilibrium. The NMR experiments were run on a Bruker DSX spectrometer operating at a proton frequency of 300 MHz. The Bruker DiffiO probe delivers a maximum gradient value of 12 T.m"1 along the Bo direction. We used the stimulated echo variant of the spin echo pulse sequence to take advantage of the long relaxation time Ti. 3. Results and Discussion 0

20

40

60

80

0 -0.5

ln ( Ψ )

-1 -1.5 -2 -2.5 -3 -3.5

gradient strength (Gauss.cm-1)

Fig.l. Echo attenuation ( f ) versus the gradient strength (g) for MCM41-C14 at various observation times. (•, 3.5ms); (A, 4ms); (*, 4.5ms); (+, 5ms); (-, 5.5ms); ( • , 6ms); ( • , 6.5ms); ( • , 7ms). Experimental parameters are indicated by symbols and solid curves represent model fits.

Examples of the signal attenuation Q¥) versus the gradient strength are depicted on Fig. 1 for different observation times A. Those curves were fitted using the "two-region" equation introduced by Karger et al. [1, 3] in order to extract the effective diffusion coefficient of n-hexane inside the mesopores. In this approximation the guest molecule can diffuse in the void space between MCM-41 particles (i.e. interparticle space), region 1, or within the MCM-41 channels (i.e. intraparticle space), region 2. Therefore, the echo attenuation is given by: P\D\

<J 1

3

0)

205

where pi denotes the relative number of molecules in the interparticle space. Dl and D2 are the diffusion coefficients for the two regions, 1 and 2, respectively. T2 is the mean lifetime of the diffusing molecule inside the MCM-41 particles, y the gyromagnetic ratio (yH = 2.67x108 T s-1), g the gradient strength, 8 is the gradient pulse duration. The effective observation time A was chosen in the range of 2.5 ms to 8 ms. The variation of D2 with the square-root of A follows a linear trend (Fig. 2). 2 −1 D2 (m (m2.s 1)

2 D2 (m (m2.s−11)

1.6E-09

1.E-09 1.E-09

1.4E-09 1.2E-09 9.E-10

1.0E-09 8.0E-10

8.E-10

6.0E-10 0

0.02 0.04 0.06 0.08 Δ

1/2

0.1

1/2

(s )

Fig.2. Effective diffusion coefficient versus observation time for MCM41-C14 at two relative concentrations. (O, 40%; D, 90%)

0 50 100 100 concentration (% of max. loading) loading)

Fig.3. Effective diffusion coefficient versus relative concentration of n-hexane in MCM41C14

This is a clear sign of the existence of some restricted diffusion and can be rationalized following the theoretical treatment of Mitra et al [5] for a totally reflecting interface: 3

D2(A) - DinSm - 4

^

The extrapolation of the straight line to A=0 gives us the genuine intracrystalline diffusion coefficient Djntra (Table 1). Figure 3 shows the intracristalline diffusion coefficient versus different pore fillings of n-hexane in MCM-C14. The intracrystalline diffusivity decreases when the amount of nhexane is increased, as previously observed [6], approaching a constant value in the vicinity of the condensation region of the adsorption isotherm. Three different diffusivities exist within the pores corresponding to three regions of diffusion: D s , surface diffusion, Dinter, diffusion between the adsorbed layer and the internal void space and D)jq, liquid-phase diffusion [6]. The measured diffusion coefficient (Table 1) may then be considered as the sum of three components. In spite of a pore diameter similar to that of MCM-C12 and MCMC14 the diffusivity measured for MCM-C16 calcined at 1273 K, which presents

206

a more hydrophobic surface, is much higher. The surface diffusion seems to be an important contribution to the overall diffusion. Table 1: Textural characteristics of the MCM-41 materials determined fromN2 adsorption and the intracrystalline diffusion coefficients of n-hexane (at 40 and 90 % of the saturation loading) measured by PFG NMR

0a(A)

Materials

eb(A)

V^cmV)

Diffusion coefficient (m2.s ') 40%

90%

MCM-C18(823K)

44

6.2

1.04

4.41 xlO 9

1.14xlO"9

MCM-C16 (823 K)

40

6.5

0.94

2.89xlO"9

1.17xlO"9

MCM-C14 (823 K)

36

6.5

0.85

9.95x10"'°

8.50xl0"10

MCM-C12 (823 K)

32

7.2

0.70

5.07x10"'°

3.69x10"'°

MCM-C16 (1273 K)

34

8.2

0.66

1.23x10""

8.92x10"'°

a

b

c

pore diameter, wall thickness, mesoporous volume.

4. Conclusion Intracrystalline diffusion measurements of n-hexane in MCM-41 materials with different pore sizes have been carried out by PFG NMR. The results show that the diffusivities are found to be increasing with pore diameter. However, it seems that the pore diameter is not the only factor affecting the diffusion coefficient. Calcination at high temperature (1273 K) clearly shows that the surface state induces an increase in the intraparticle diffusion coefficient. 5. References [1] J. Karger and D. M. Ruthven Diffusion in zeolites and other microporous solids; Wiley Interscience, 1992. [2] E. W. Hansen et al, Micropor. Mesopor. Mater. 22 (1998) 309-320 ; F. Courivaud et al, Micropor. Mesopor. Mater. 35-36 (2000) 327-339 ; F. Stallmach et al, Micropor. Mesopor. Mater. 44-45 (2001) 745-753; F. Stallmach et al, J. Am. Chem. Soc. 122 (2000) 9237-9242. [3] J. Karger, Ad. Colloid Interface Sci. 23 (1985) 129. [4] R. Ryoo et al, Stud. Surf. Sci. Catal. 117 (1998) 151-158; J. M. Kim et al, J. Phys. Chem. B 103 (1999) 6200-6205;S. Jun et al, Micropor. Mesopor. Mater. 41 (2000), 119-127. [5] P. Mitra et al, Phys. Rev. B 47 (1993) 8565-8574; L. Latour et al, J. Magn. Reson. A 101 (1993), 342-346. [6] F. Courivaud et al., Micropor. Mesopor. Mater. 37 (2000), 223-232.


207 207

TEM Studies of Bicontinuous Cubic Mesoporous Crystals Yasuhiro Sakamotoa, Chuanbo Gaob, Shunai Cheb and Osamu Terasakia "Structural Chemistry, Arrhenius Laboratory, Stockholm University, 10691 Stockholm, Sweden School of Chemistry and Chemical Technology, State Key Laboratory of Composite Materials, Shanghai Jiao Tong University, 800 Dongchuan Road, Shanghai 200240, China

1. Introduction There are several bicontinuous cubic structures observed in water-surfactant system. The three most well known bicontinuous cubic structures are mathematically described by gyroid minimal surface (G-surface), double diamond minimal surface (D-surface) and primitive minimal surface (P-surface), which have zero mean curvature and belong to Ia-3d (called Q230 in watersurfactant system), Pn-3m (Q224) and lm-3m (Q229) space group, respectively (Figure 1). All the structures are uniquely composed of two interpenetrating, but non-intersecting, domains separated by these surfaces, which are located in the middle of the surfactant bilayer in surfactant rich system. Structural transformation between these bicontinuous cubic structures has been attributed to small temperature or composition changes. Their transition enthalpy is much smaller than that of bicontinuous-hexagonal transition and lamellarbicontinuous transition [1, 2]. Topologically, the three minimal surfaces are related to each other through Bonnet transformation. In 1992, scientists in Mobil corporation discovered one of the bicontinuous cubic structures, MCM-48, with Ia-3d symmetry in surfactant templated silica mesophase [3]. MCM-48 has two independent mesopores, which are divided by silica wall formed on G-surface [4]. The surface of silica wall and mesopore is well described by a constant mean curvature surface. Since its bicontinuous mesoporous crystal was found as a chemically and thermally stable solid inorganic material, it has attracted a lot of attentions from various fields. Especially, this cubic bicontinuous silica mesoporous crystal has been recently expected to be useful medium for the rational design of biocompatible materials

208

for encapsulation, controlled release and uptake, and delivery of drugs and bioactive components [5, 6]. Recently we have succeeded in synthesizing a new bicontinuous cubic Pn-3m mesoporous crystal, AMS-10, and solving its structure [7]. The silica wall structure is formed on a D-surface. Whilst many new mesoporous structures have been prepared, AMS-10 is the first newly discovered bicontinuous structure since MCM-48 was found more than ten years ago.

Figure 1. Typical minimal surfaces, (a) G, (b) D, and (c) P-surfaces.

2. Experimental Section This new mesoporous crystal, AMS-10, was synthesized using anionic surfactant 7V-myristoyl-L-glutamic acid (Ci4GluA) as a template and iVtrimethoxylsilylpropyl-Af,Af,AMximehylammonium chloride (TMAPS) as a costructure-directing agent (CSDA) under the condition which NaOH was added in to control the neutralization degree of the surfactant [7]. The structure was characterized by transmission electron microscopy (TEM) and its threedimensional (3D) structure was reconstructed based on electron crystallography method [8]. High resolution TEM (HRTEM) was performed with a JEOL JEM3010 microscope operating at 300 kV (Cs = 0.6 mm, Point resolution 1.7 A). Images were recorded with a CCD camera (MultiScan model 794, Gatan, 1024 x 1024 pixels, pixel size 24 x 24 |im) at 50,000 - 80,000 magnification under low-dose conditions. 3. Results and Discussion The space group of AMS-10 was determined to be Pn-3m based on reflection conditions obtained from Fourier diffractograms of HRTEM images and electron diffraction patterns (Figure 2), although Pn-3 is another candidate from the conditions. The unit cell parameter as derived from XRD pattern is a = 9.6 nm. The 3D electrostatic potential distribution was unquestionably constructed

209

by an inverse Fourier transform of the structure factors, which were extracted from HRTEM images after a correction of contrast transfer function. Based on this 3D electrostatic potential distribution, direct information on the detailed structures of mesoporous crystal AMS-10 was obtained. The main conclusion is that AMS-10 has a bicontinuous cubic structure where the silica wall follows the minimal D-surface. The crystal has two interpenetrating pore systems without intersections. This is the same situation as MCM-48 with Ia-3d symmetry. However, each pore network has four connected nodes (Figure 3b) at the special position with the -43m site symmetry, while in MCM-48, G-surface, three connected nodes (Figure 3a) are at the positions with 32 site symmetry. For reference, P-surface, which has not yet been discovered in silica mesoporous crystals, has six connected nodes (Figure 3c).

mm:.

Figure 2. TEM images of AMS-10 with their Fourier diffractograms. Taken along (a) [100], (b) [110], and (c) [111] directions.

Figure 3. Network connectivity of the (a) G, (b) D, and (c) P-surface. For silica mesoporous crystals these are pore networks.

210

4. References [1] S. T. Hyde, S. Andersson, B. Ericsson and K. Larsson, Z Kristtallogr., 168 (1984) 213. [2] S. T. Hyde, in Handbook of Applied Surface and Colloid Chemistry. Edited by Krister Holmberg, John Wiley & Sons, Ltd 2001, Chapter 16 . [3] J. S. Beck, J. C. Vartuli, W. J. Roth, M. E. Leonowicz, C. T. Kresge, K. D. Schmitt, C. TW. Chu, D. H. Olson, E. W. Sheppard, S. B. McCullen, J. B. Higgins and J. L. Schlenkert, J. Am. Chem. Soc, 114 (1992) 10834. [4] A. Carlsson, M. Kaneda, Y. Sakamoto, O. Terasaki, R. Ryoo and S. H. Joo, J. Electron Microsc, 48 (1999) 795. [5] M. Vallet-Regi, A. Ramila, R. P. Del Real and J. Perez-Pariente, Chem. Mater., 13 (2001) 308. [6] I. Izquierdo-Barba, A. Martines, A. L. Doadrio, J. Perez-Pariente and M. Vallet-Regi, Eur. J. Pharm. Sci., 26 (2005) 365. [7] C. Gao, Y. Sakamoto, K. Sakamoto, O. Terasaki and S. Che, Angew. Chem. Int. Ed., 45 (2006) 4295. [8] Y. Sakamoto, M. Kaneda, O. Terasaki, D. Zhao, J. M. Kim, G. D. Stucky, H. J. Shin and R. Ryoo, Nature, 408 (2000) 449.


211 211

Characterization of vesicular mesostructured silica synthesized under alkaline conditions Cheng Chi, Bo Wang, Wei Shan, Yahong Zhang and Yi Tang* Department of Chemistry and Shanghai Key Laboratory of Molecular Catalysis and Innovative Materials, Fudan University, Shanghai 200433 (P. R. China)

1. Introduction Ordered mesostructured silica has attracted considerable attention in many different areas, such as catalysis, adsorption and separation. Among the various structural types, MCM-41 is one of the most extensively studied mesostructured silica especially in its application in catalysis [1-10]. Many different micronscale morphologies of MCM-41 have been reported by Ozin's group [6-8]. These products were typically prepared by controlling the hydrolysis of tetraethyl orthosilicate (TEOS) under an acidic synthesis condition. A liquid crystal defect mechanism was proposed by Ozin's group to explain these enigmatic curved morphologies [8]. Recently, we reported a series of MCM-41 type vesicular mesostructured silica (VMS) with a rich diversity of micron-scale topologies [10], which was prepared by using the hydrolysis of ester to drive the assembly of silicate and surfactant in an alkaline system [9]. A comparison between VMS and the traditional vesicles suggests that the formation of vesicular structure is a micron-scale self-assembly behavior of MCM-41 mesostructured silica. In this work, the VMS prepared at different reactant concentrations were further systematically characterized by means of thermogravimetric analysis, nitrogen sorption and electron microscopy. 2. Experimental Section The VMS was prepared in a sodium silicate (SS)-cetyltrimethylammionium bromide (CTAB)-ethyl acetate (EA)-water system, as shown in reference [10]. To clearly observe the vesicular structure of VMS, an ammonium treatment was carried out using a diluted ammonium solution (1 wt%) at 80°C overnight. For comparison, a silica gel was also synthesized under the same condition but

212

without adding the surfactant. The thermogravimetric-differential thermal analysis (TG-DTA) was performed on a Rigaku Thermoflex instrument. The samples were heated at a rate of 10 K min"1 from 300 K to 900 K in an air flow. Prior to TG-DTG and DTA experiment the sample was dried at 350 K for 24 h until the mass became constant. Scanning electron microscopy (SEM) and transmission electron microscopy (TEM) images were obtained on Philips XL 30 and JEOL JEM-2010, respectively. Nitrogen sorption isotherms were measured using a Micromeritics TriStar 3000 system. Before the sorption measurement, the samples were degassed at 200 °C for about 3 h. 3. Results and Discussion (a)

In order to get a better understanding of the TG-DTA result of the VMS sample, we made a comparison between VMS and the silica gel. Figure 1 shows that the TG-DTA profiles of VMS ranging from 300 K to 900 K are quite different from those of the silica gel. The broad peak within the temperature range 350-450 K in the TG-DTA of silica gel corresponds to the water desorption and the condensation of silanol, which leads to a weight loss of ca 8 wt%. Similarly, the VMS also has a weight loss step beginning at ca 400K, induced by the silanol condensation. However, a larger weight loss peak could be identified above 450 K. Since no obvious exothermic effect was detected from the DTA result, this peak should be ascribed to the surfactant fragmentation/evaporation within the nano-pores of VMS [11, 12]. Another relatively smaller peak at ca 620 K could be observed in the DTG, which has a strong exothermic effect. It should be Temperature/ K induced by the oxidation of surfactant or its Figure 1. TG-DTG curves for fragments at such a high temperature [11,12]. VMS (a), silica gel (b) and DTA When the VMS sample was heated up to curves for both samples (c). 900 K, only the pure silica remains, therefore, the silica content of the VMS could be estimated from its residue weight after calcination at high temperature. It is found by measuring more than 30 samples that the silica content of VMS is ca 45-55 wt%. We further made a comparison between the amount of silica in the VMS product and the silicate sodium we used during the synthesis process. Interestingly, we found that more than 90% of the silicate source transferred into the VMS product within the experimental 300

400

500

600

213

ranges of CTAB and EA concentrations (see figure 2). This result indicates that the surfactant is over-amounted in the synthesis of VMS, as compared to the silicate source. In other words, the over-amounted "soft template" during the self-assembly of vesicular MCM-41 should be an important factor for the formation of ordered 2D hexagonal mesostructure. Insufficient surfactants would lead to the formation of small amorphous silica particles. Our further study shows that amount of the CTAB also plays a role in controlling the dimension of the product. The detailed result will be reported elsewhere. The pore structures of VMS were characterized by nitrogen sorption isotherms. Figure 3 demonstrate a large hysteresis loop at the relative pressure of 0.8-1.0, 0.4 0.6 0.8 Relative pressure (p/p ) corresponding to a large quantity of nonMCM-41 pores in the VMS product. Because Figure 2. Silica yields of VMS of the existence of large pores, such material prepared at different concen-trations was ever considered to be bimodal of CATB and EA (molar ratio, 4.07 SS: x CTAB; y EA: 1,000 H2O). mesoporous silica in the literature [9]. However, we found in this work that these large pores would decrease after a simple hydrothermal treatment in a diluted ammonium solution at 80°C, while the MCM-41 mesopores were well retained. The TEM images of the ammonium-treated VMS exhibit obviously enlarged cavities (Figure 4), suggesting that the non-MCM-41 pores mainly exist in the amorphous phase inside the vesicular structure. (Figure 4f) Figure 3. Nitrogen sorption isotherms Conversely, the MCM-41 pores mainly exist of VMS (molar ratio, 4.07 SS: 1.82 in the shell part of VMS, which could be CTAB; 13.3 EA: 1,000 H2O) before identified in Figure 4d. The assembly process (I) and after (11,111) ammonium leading to the formation of such hybrid pores treatment. Curves I and II were moved in VMS was further discussed as below. up 800 and 400 cm3/g respectively. During the synthesis process various vesicular structures with MCM-41-type mesostructures are formed in the aqueous solution, which is driven by the self-assembly behavior of the silicatesurfactant complexes [10]. However, owing to the closed vesicular structures, some intermediate species (i.e. silicate anion and cationic surfactant) would possibly be encapsulated in the large cavity of VMS. During the recovery process of VMS from the synthesis solution, a fast precipitation might occur to the encapsulated species inside the vesicular structure. It would result in 0

EA (mol /1.000 H;O)

214

unordered silicate-surfactant aggregates with relatively large pores. However, these encapsulated aggregates could be easy to be removed by diluted alkali solution due to the weak interaction between surfactants and silicates. 4. Conclusion Vesicular MCM-41 was further systematically characterized by means of thermogravimetric analysis, nitrogen sorption and electron microscopy. The TG-DTA result of VMS is similar to that of the conventional MCM-41 product [10,11]. The further analysis of the silica yield revealed that more than 90% of the silicate Figure 4. SEM and TEM images of source transferred into the VMS product during VMS (molar ratio, 4.07 SS: x the self-assembly process, and an over-amount CTAB; y EA: 1,000 H2O) before of surfactant is critical to the formation of (a,c,d) and after (b,e,f) ammonium ordered 2D hexagonal mesostructure. Moreover, treatment the combination of the nitrogen sorption and TEM results showed that the nonMCM-41 pores mainly exist in the center of VMS while the MCM-41 pores exist in the shell part. 5. References [1] C. T. Kresge, M. E. Leonowicz, W. J. Roth, J. C. Vartuli and J. S. Beck, Nature 359(1992) 710. [2] A. Firouzi, D. Kumar, L. M. Bull, T. Besier, P. Sieger, Q. Huo, S. A. Walker, J.A. Zasadzinski, C. Glinka, J. Nicol, D. Margolese, G. D. Stucky and B. F. Chmelka, Science, 267(1995)1138. [3] A. Monnier, F. Schuth, Q. Huo, D. Kumar, D. Margolese, R. S. Maxwell, G. D. Stucky, M. Krishnamurty, P. Petroff, A. Firouzi, M. Janicke and B. F. Chmelka, Science, 261(1993) 1299. [4] H. P. Lin and C. Y. Mou, Science, 273(1996) 765. [5] H. P. Lin, Y. R. Cheng and C. Y. Mou, Chem. Mater., 10(1998) 3772. [6] H. Yang, N. Coombs and G. A. Ozin, Nature, 386(1997) 692. [7] H. Yang, G. A. Ozin and C. T. Kresge, Adv. Mater., 10(1998) 883. [8] S. M. Yang, H. Yang, N. Coombs, I. Sokolov, C. T. Kresge and G. A. Ozin, Adv. Mater., 11(1999)52. [9] G. Schulz-Ekloff, J. Rathousky and A. Zukal, Inter. J. Inorg. Mater., 1(1999) 97. [10] B. Wang, W. Shan, Y. H. Zhang, J. C. Xia, W. L. Yang, Z. Gao and Y. Tang, Adv. Mater., 17(2005) 578. [11] A. S. Araujo and M. Jaroniec, Thermochimi. Acta 363(2000) 175. [12] J. Goworekl, A. Borowka, R. Zaleski and R. Kusak J. Therm. Anal. Cal., 79(2005) 555.


215 215

Zirconium species created within the mesopores of MCM-41 and NbMCM-41 Joanna Goscianska and Maria Ziolek* Adam Mickiewicz University, Faculty of Chemistry, Grunwaldzka 6, PL-60-780 Poznan, Poland

1. Introduction The synthesis and characterization of nanoscale siiicides with potential application in nanotechnology is of a great interest in the development of new materials used in modern technology. The most often used techniques for their preparation is the sputtering method to deposit metal layers for contacts or in the self-aligned silicidation process. As Mo and Ti systems were widely investigated less work has been done on the Zr/Si materials for contacts [1]. The generation of zirconium siiicides could base on the silicon treating with Zr source because Zr readily removes native oxide layers existing at the Zr-Si interfaces (ZrO2 has a larger negative heat of formation than that of SiO2). The formation of silicide is accounted for by a reaction mechanism involving a reaction of ZrO2 with SiO [2]. This feature led us to an idea of the creation of zirconium siiicides in the mesoporous silicate and niobosilicate MCM-41 type materials. The undertaken study faced two basic challenges. First - finding the possibility for the zirconium silicide formation in MCM-41 materials. Second diagnosing the role of Nb in the creation of Zr species towards the formation of the effective ZrNbMCM-41 support for platinum. Pt/ZrNbMCM-41 would be addressed to NSR (NO storage reduction) process. NbMCM-41 was chosen as a matrix for Zr because Nb is an excellent NO storage species [3] and one could expect that the admission of Zr improves both the thermal stability and spillover effect. These issues play an important role in the creation of catalysts for NOx removal from exhaust gases from lean fuel burn engines. Therefore, the studies reported in this paper give the fundamentals for the further preparation of the threefold system (Pt, Zr, Nb) intended to the NOx reduction.

216 216

2. Experimental Section MCM-41 was synthesized following the procedure reported originally by Kresge at al. [4] i.e. by the hydrothermal method from sodium silicate (27% SiO2in 14% NaOH; Aldrich) and cetyltrimethylammonium chloride (25 wt. % in water; Aldrich) as a template. Ammonium complex of niobium(V) trisoxalate solution (CBMM, Brazil) and zirconium dinitrate oxide- ZrO(NO3)2 (Alfa Aesar) were used when mono or bimetallic silicates were produced. The Si/T atomic ratio (T=Nb and/or Zr) in the gels was 128. NbMCM-41 was also impregnated with zirconium salt. The prepared materials were characterized by XRD (TUR62 diffractometer, CuKot radiation), nitrogen sorption (Micrometrics 2010) SEM, TEM (JEOL 2000 electron microscope), UV-VIS (VARIAN CARY 300 Scan), 29Si NMR (Bruker Avance 300dmx spectrometer operating at 59.62 MHz), TG/DSC (TG Setaram SetSysl2 thermobalance, in air or nitrogen, heating ramp 5 K min"1), and FTIR (Bruker FTIR Vector 22, the samples dispersed in KBr pellets). 3. Results and Discussion Table 1. Texture parameters of the catalysts and UV-VIS results. Mesopore Catalyst

d1Oo

ao, nm

-'D'

Wall thickness,

UV-VIS bands, nm

BJHads. PSD, nm

MCM-41

3.65

4.21

1323

3.11

1.25

-

ZrMCM-41

3.26

3.77

1019

2.56

1.33

230, 250 (overlapped)

NbMCM-41

3.87

4.47

1047

2.88

1.73

218

ZrNbMCM-41

3.87

4.47

1015

2.64

1.96

230, 250 (shoulder)

Zr/NbMCM-41* 3.81

4.40

994

2.83

1.70

218, 230 (overlapped)

* - Zr impregnated sample, **- t = ao - D/l.05

XRD patterns (Fig. 1A) as well as nitrogen adsorption isotherms and TEM images confirmed the hexagonal, well ordered arrangement of mesopores in all studied samples. Nitrogen adsorption isotherms of all the materials studied are of type IV according to the IUPAC classification. The significantly increase of adsorption in p/p0 = 0.9-1 for NbMCM-41 and Zr/NbMCM-41 samples indicates the presence of macroporosity, which is less visible in the case of ZrMCM-41 sample and does not occur in ZrNbMCM-41. Texture parameters of the prepared materials shown in Table 1 indicate the significant influence of niobium content on the unit cell (ao) and dioo parameters, whereas Zr admission during the synthesis does not change these values and the

217

impregnation of NbMCM-41 with zirconium salt slightly decreases both features. Interestingly, Zr introduced together with Nb species leads to the diminishing of the mesopore diameter by the increase of wall thickness. The question arises whether zirconium is located inside the skeleton or in the extra framework position. UV-VIS result (Table 1) for ZrNbMCM41 indicates the A B presence of the 31,76 band at 230 nm with a wide 2rO (211) shoulder at ~ 250 45,46 nm. The first one, ZrSi(321) ZrO (140) which is not 66.19 75,28 a exactly at the a £• same position as b described in the c ; literature [5,6] for 2 nanoparticles which quickly formed. A third porosity can be found inside these nanoparticles. New experiments were carried out with several alkoxides (Ti(OR)4, A1(OR)3, Y(OR)3, Nb(OR)5, Ta(OR)5). Similar to the polymerization of Zr(OC3H7)4, hierchically bimodal porous structures were also obtained for the above mentioned alkoxides, but the macropores diameters, meso- and micropores sizes, surface areas and porous volumes were influenced by the type of inorganic precursor. 4. Conclusion In conclusion, the spontaneous pathway for the formation of hierarchical meso- (or micro) macroporous zirconium oxide has been studied. Their formation seems to be based on the synergy between the polymerisation kinetics of the inorganic precursors and the hydrodynamic flow of the solvent. The comprehension of this self-formation strategy should open exciting avenues for the fabrication of new classes of nanostructured porous materials. 5. References [1] [2] [3] [4] [5] [6] [7] [8] [9] [10]

Z. Zhong, Y. Yin, B. Gates and Y. Xia, Adv. Mater. 72(2000)206. B. T. Holland, C. F. Blanford and A. Stein, Science 281(1998)538. D. M. Antonelli, Microporous Mesoporous Mater. 33(1999)209. J. L. Blin, A. Leonard, L. Gigot, Z. Y. Yuan, A. Vantomme, A. K. Cheetham and B. L. Su, Angew. Chem. Intl. Ed. 42(2003)2872. Vantomme, Z. Y. Yuan and B. L. Su, New. J. Chem. 28(2004)1083. Z. Y.Yuan, T. Z. Ren, A. Vantomme and B. L. Su, Chem.Mater. 16(2004)5096. T. Z. Ren, Z. Y. Yuan and B. L. Su, Chem.Comm. (2004) 2730. Leonard and B. L. Su, Chem. Comm. (2004)1674. Z. Y.Yuan and B. L. Su, J. Mater. Chem. 16(2006)663. Collins, D. Carriazo, S. A. Davis and S.Mann, Chem.Comm. (2004)568.


239 239

Synthesis and characteristics of hierarchically porous zirconia-based composite oxides Hangrong Chen, Jianlin Shi* and Dongsheng Yan State Key Lab of High Performance Ceramics and Superfine Microstructures, Shanghai Institute of Ceramics, Chinese Academy of Sciences, Shanghai 200050, China

High surface area and thermally stable hierarchically porous zirconia-based composite materials with crystallized framework has been synthesized in a facile process templated from composite surfactants. XRD, nitrogen adsorption analysis, FESEM, FETEM, and EDX were used for the structural characterizations. 1. Introduction Hierarchically porous materials occur widely in nature, and have attracted significant attention owing to their unique properties. The pore sizes of such materials varied from Angstroms to nanometers to microns in one composite material, i.e., several different degrees of porosity incorporated into one body can play important roles in the practical applications, such as catalysis, adsorption, separation, chemical sensors, etc [1-4]. Various synthesitic pathways, including exo-templating and endo-templating strategies have been developed to create porous and high-surface-area inorganic materials. The exo-templates, such as polystyrene latex spheres, emulsions or vesicles can be used to produce a controlled three-dimensionally interconnected macroporosity, and the endotemplates, such as nonionic block copolymer macromolecular can be used to create the mesoscale porosity, and the oligomers, the individual polymers can produce the micropores. In our privious work, a novel hierarchical pure zirconia material with ordered pores-structures and well-crystallized framework has been synthesized by a facile process templated from composite surfactants of an amphiphilic poly block copolymer combined with nonionic alkyl-PEO surfactant [5]. Here, we study the different effects of other elements incorporation, such as titatium and cerium, on the pore structures of hierarchical zirconia.

240

2. Experimental Section In a typical preparation, a 18 wt% micellar solution of Pluronic P-123(BASF) and/or Brij56 [Ci6(EO)i0] (Aldrich) was prepared by dissolving P123 and/or Brij56 with a weight ratio of 1:1.2 in 50mL distilled water at the room temperature under stirring for more than 3 hours. An appropriate amount of zirconium propoxide [Zr(OC3H7)4] and titanium isopropoxide or inorganic cerium source were dropped into the above solution to give the surfactants. After further stirring for lh, the mixture was transferred into a Teflon-lined autoclave and heated at 1 1 0 - 130°C for 24 h. The product was calcined at 500°C for 6 h to remove the surfactant species. 3. Results and Discussion Figure 1A shows the representative FE-SEM image of the as synthesized hierarchically porous titanium doped zirconia, which exhibits macroscopic network structure with a uniformly distributed array of macropores of 200-400 nm in diameter. After calcined at 500°C, the macroporous structure almost remains unchanged (not shown here). Typical TEM image of the calcined sample shown in figure IB reveals that such titanium doped zirconia nanoparticles in the framework of macroporous structure consist of the uniformly distributed nanocrystallites and worm-like mesopores. A clear EDX spectrum shown in figure 2A confirms that about 10 wt% titanium has been incorporated into zirconia framework. Further study indicates that up to 30 wt% titanium can be doped into zironia with maintaining the most of hierarchically macro-mesoporous structures.

A

B

Figure 1 Typical FE-SEM image (A) and TEM image as well as its corresponding electron diffraction patterns (inset) (B) of titanium doped hierarchical porous zirconia after calcined at 723K.

241 350

A

0.12

Pore Volume/cm /g

f

3

Zr

*

0.08

3

V olume A sorbed/(cm /g) Volume Addsor

250 250

y

4.8nm

0.06

0.04

0.02

200

L

_ 0.00 0

10

20

30

40

50

60

70

80

Pore Diameter/nm

8

CPS/a.u.

O

C

B ,

2.2nm 0.10

—. 300 300cn

Zr

150

100 100

Ti Ti 0

5

50

Zr

* 10

15

0.0

20

0.2

Energy/keV

0.4

0.6

0.8

1.0

Relative Pressure(P/P Pressure(P/P) Relative ) 0

Figure 2 (A) EDX spectrum corresponding to the area of figure IB, (B) N2 adsorption-desorption isotherms and the BJH pore size distribution (inset) of the as-prepared sample (* is the Cu element).

The nitrogen adsorption-desorption isotherms of the as-prepared hierarchical titanium doped zirconia sample shown in figure 2B, can be attributed to type IV. For the as-prepared sample, a high BET surface area of 300 m2/g with the total pore volume of 0.44 cm /g is obtained from this material. Two narrow peaks in the BJH pore-size distribution curve are centred on 2.2 nm and 4.8nm. After calcination at 773K for 6h, the BET surface area distinctively decreases to 81m2/g because of the increased material density induced by the crystallization of zirconia framework. However, relative to the lower surface area, the total pore volume still remains as high as 0.19 m2/g, indicative of high thermal stability. B

A

a---CeZr500 b---Zr500 b—--Zr500

Intensity/a.u.

...

'en

I

b

20nm

a 10

20

30

40

50

60

70

80

2 Theta

Figure 3 (A) TEM and FE-SEM (inset, up-left) images of hierarchical porous ceria-zirconia composite after calcined at 773K, (B) XRD patterns of pure porous zirconia and ceria loaded porous zircona after calcination at 773 K.

Figure 3 A shows the typical TEM image and the FE-SEM image of the calcined cerium doped zirconia sample. The macrostructure tends to be

242

destroyed with the increased amount of cerium, which is different from titanium incorporation. In our experiments, less than 10 at% cerium can be incorporated into zirconia lattices, and at the same time, the hierarchically macromesoporous structures can be retained. Nevertheless, higher cerium/zirconium ratio of nanocrystalline ceria-zirconia solid solution with only mesoporous structure can be well obtained. Inorporation of cerium can effectively inhibit the phase transformation of pure zirconia under the high thermal treatments, which can be seen from figure 3B. After calcined at 773K, pure zirconia shows the monoclinic phase, while, cerium doped zirconia maintains the stable cubic phase. Such hierarchical ceria/zirconia nanocomposite can be interestingly used as novel three-way mobile exhausted catalyst. 4. Conclusion In conclusion, high surface area and thermally stable hierarchically porous zirconia-based composite materials has been successfully synthesized. This novel hierarchically porous composite, such as titanium doped porous zirconia, shows a well-defined ordered macroporous structure and a very uniform mesoporous pore size distribution. Both the mesoporous structure and the macroporous structures can be maintained, after calcination at 773K, indicative of high thermal stability. However, there seems to exist different effects of titanium and cerium incorporation on the thermal stability and pore structures of the prepared hierarchically porous zirconium oxide owing to their different atomic diameters. Either Ti or Ce incorporation can effectly inhibit the phase transformation of pure zirconia at 773K. 5. Acknowledgement We gratefully acknowledge the financial support from Shanghai Nanospecial Project with Contract 0552nm030 and Qiming Star Project with Contract 05QMX145 8. 6. References [1] A. Corma, P. Atienzer, H. Garcia and J.-Y. Chane-Ching, Nature, 3 (2004) 394. [2] Y. S. Shin, J. Liu, L.-Q. Wang, Z. Nie, W. D. Samuels, G. E. Fryxell and G. J. Exarhos, Angew. Chem. Int. ed., 39 (2000) 2702. [3] W. Deng, M. W. Toepke and B. H. Shanks, Adv. Func. Mater., 13 (2003) 61. [4] J. -L. Blin, A. Lenoard, Z.-Y. Yuan, L. Gigot, A. Vantomme, A. K. Cheetham and B.-L. Su., Angew. Chem. Int. Ed., 42 (2003) 2872. [5] H. R. Chen, J. L.Gu, J. L.Shi, Z. C. Liu, J. H. Gao M. L. Ruan and D. S. Yan, Adv.Mater., 17(2005)2010.


243 243

Synthesis of ordered mesoporous zinc oxide obtained by dry gel nanocasting from the mesoporous carbon CMK-3 Helwig H. Thiel,a Pablo Cascales de Paza,a Martin Hartmannb and Stefan Ernst a * " Department of Chemistry, Chemical Technology, Kaiserslautern University of Technology, Erwin-Schrodinger-Str. 54, 67663 Kaiserslautern, Germany b Department of Physics, Advanced Materials Science, University of Augsburg, Universitdtsstr. 1, 86154 Augsburg, Germany

1. Introduction The main application of zinc oxide in industrial processes is as an activator for the vulcanization accelerator in the manufacture of natural and synthetic rubber [1, 2]. ZnO is also used as pigment in colors and surface coatings, in Pharmaceuticals or in the cosmetic industry and, last but not least, as catalyst in, e.g., the synthesis of methanol. In many of its applications, an important property is the specific surface area of ZnO. Two ways have been proposed for the preparation of zinc oxide with high specific surface area. The first possibility is the synthesis of zinc oxide nanoparticles [3, 4]. But there are still problems with the handling of the small particles during the preparation or the use as catalyst. Small particles are difficult to recover from their "mother liquor" and they will cause high pressure drop in a fixed-bed reactor if used as such. The second method of preparing zinc oxide with a large specific surface area is the direct synthesis of mesoporous zinc oxide as prepared by Jiu et al. [5] and Jaramillo et al. [6] with a disordered pore system. Here we report our attempts to synthesize mesoporous zinc oxide with an ordered pore system using a carbon replica method. 2. Experimental Section Mesoporous SBA-15 silica [7] and CMK-3 carbon [8] were obtained as described previously. In a typical synthesis of mesoporous zinc oxide, 0.5 g of

244 244

CMK-3 was mixed with 1 g zinc nitrate hexahydrate (Aldrich) in a mortar and afterwards heated up in air to 75°C for 6 h. Due to its relatively low melting point (46°C), the solid zinc nitrate melts during heating and is sucked by capillary forces into the pores of CMK-3 without the necessity of any further pretreatment. This impregnation sequence has been repeated four times. Finally, the composite was heated to 600°C in air with a constant heating rate of 5°C-min" in order to burn-off the CMK-3 template. 3. Results and Discussion Figure 1 (left) shows the powder XRD patterns of the obtained mesoporous zinc oxide in comparison to those of the templates SBA-15 and CMK-3. In Fig. 1 E and D, the high-angle region of mesoporous ZnO is compared to bulk ZnO. Both ZnO samples show the five signals that are significant for ZnO crystallized in a wurtzite-structure. The low-angle regions of the XRD patterns confirms that CMK-3 is a good replica of SBA-15, since both show the (100), (110) and (200) reflections, while the XRD reflections of mesoporous zinc oxide are somewhat broadened. Nevertheless, the three reflections observed confirm the structural order of the obtained mesoporous ZnO. To characterize the textural properties of mesoporous zinc oxide, nitrogen adsorption at 77 K was measured. The observed isotherms are depicted in Fig. 2. They are of type IV (IUPAC classification) with a hysteresis loop close

,1

CD) 30

11 40 50 29 / degree

60

Figure 1 Left side: low-angle powder XRD patterns of SBA-15 silica (A), CMK-3 carbon (B) and the mesoporous zinc oxide (C). Right side: high-angle powder XRD patterns of bulk zinc oxide (D) and mesoporous zinc oxide (E). The XRD patterns were recorded using a SIEMENS D5005 X-ray diffractometer with CuKa radiation, 30 kV, 20 mA, counting time: 5 s and steps of 0.01 ° (left) or 0.05° (right), respectively.

to type HI. These are typical findings for mesoporous solids. The observed somewhat broad hysteresis loop of type HI (not vertical and almost parallel isotherm sections [9]) indicates that the long-range order of the pore system is disturbed to some extent. The structural properties of SBA-15 and CMK-3 are

245

in good agreement with literature data. The significant difference in specific surface area (1125 m2-g"' vs. 85 m2-g"') and specific pore volume (1.17 cm^g"1 -3 -1 vs. 0.11 cm -g" ) between CMK-3 and mesoporous zinc oxide can be explained 140

2 Relative pressure p N /p N

0

4

6

1

10

Pore diameter / nm

at least in part with the difference in the densities of both materials: the density Figure 2 Nitrogen physisorption on mesoporous zinc oxide recorded using a Quantachrome Autosorb-1 sorption analyzer. Left: nitrogen isotherms at 77 K (o adsorption, D desorption). Right: pore size distribution calculated from the desorption branch employing the BJH method.

of bulk zinc oxide is ca. 2.7 times higher than the density of amorphous carbon. The low specific pore volume of mesoporous zinc oxide is tentatively explained by some sintering of the material during calcination. Fig. 3 shows the results of simultaneous TGA/DTG/DTA/MS (thermogravimetry/differential TG/differential thermal analysis/mass spectrometry) for a sample consisting of 0.5 g CMK-3 which was impregnated with 2 g zinc nitrate hexahydrate. The observed total weight loss amounts to 63 %. At low 7 6 >5 =M

J22 fa , tsi uU

W-l -2 -3

100 200 300 400 500 600 700 T/°C

100 200 300 400 500 600 700 T/°C

Figure 3 TG-DTA analysis (left) coupled with mass spectrometry (right) of CMK-3 impregnated with zinc nitrate. The measurement was performed in an air flow with a heating rate of 2 K per minute on a Setaram-Setsys-16/MS (Balzers Quadstar 422) instrument.

temperatures (20°C to ca. 120°C) an endothermic weight loss of 29% due to the desorption of water is observed. The water comes from both, physically adsorbed and chemically combined H2O. Three further weight losses are

246

detected at ca. 120-150°C (8 wt.-%), ca. 150 to 195°C (12 wt.-%) and ca. 195 to 230°C (2 wt.-%). From the corresponding mass spectra these three weight losses can be attributed to the decomposition of zinc nitrate hexahydrate to nitrogen oxides, water and, of course, zinc oxide. Finally, at temperatures between 230°C and 400°C, the occluded carbon material from the CMK-3 template is burnt-off with the concomitant formation of CO2 (weight loss ca. 11%). An additional TGA/DTA analysis (in air) and FT-IR spectroscopic analysis of the mesoporous zinc oxide obtained in the described manner were used to ascertain that carbon-containing matter was completely removed by the calcination procedure described above. The combustion of neat CMK-3 typically starts at temperatures around 460°C. Hence, the zinc oxide present in the composite material probably acts as an oxidation catalyst leading to reduced combustion temperatures. 4. Conclusion In summary, we have synthesized highly ordered mesoporous zinc oxide with a thermal stability of at least 600°C, using a new "dry" nanocasting route employing CMK-3 as the template. Further investigations on this preparation strategy are currently underway and will be reported in a forthcoming paper. 5. Acknowledgment Financial support by Deutsche Forschungsgemeinschaft and Fonds der Chemischen Industrie is gratefully acknowledged. 6. References [1] G. Pfaff in R. Dittmeyer, W. Keim, G. Kreysa and A. Oberholz (eds.) Winnacker • Kuchler Chemische Technik, Wiley-VCH, Weinheim (2004) 314. [2] G. Heideman, R. N. Datta, J. W. M. Noordermeer and B. van Baarle, Rubber Chemistry and Technology, 77 (2004) 512. [3] Z. L. Wang, J. Phys.: Condens. Matter, 16 (2004) R829. [4] A. M. Khalil and S. Kolboe, Surf. Technol., 18 (1983) 249. [5] J. Jiu, K. Kurumada and M. Tanigaki, Mater. Chem. Phys., 81 (2003) 93. [6] T. F. Jaramillo, S.-H. Baeck, A. Kleiman-Shwarsctein and E. W. McFarland, Macromol. Rapid Commun., 25 (2004) 297. [7] M. Hartmann and A. Vinu, Langmuir, 18 (2002) 8010. [8] M. Hartmann, A. Vinu and G. Chandrasekar, Chem. Mater., 17 (2005) 829. [9] S. J. Gregg and K. S. W. Sing (eds.), Adsorption, Surface Area and Porosity, Academic Press Inc., London, (1982) 287.

Progress in in Mesostructured Materials Recent Progress S. Qiu, Y. Tang and C. Yu (Editors) (Editors) D. Zhao, S. © 2007 2007 Published Published by Elsevier Elsevier B.V. B.V.

247 247

Synthesis of mesostructured TiO2 through selfassembly of nanocrystals of rutile Wenfu YantHc, Zuojiang Li and Sheng Dai*

Chemical Sciences Division, Oak Ridge National Laboratory, Oak Ridge, Tennessee, 37831-6201. Present address: State Key Laboratory of Inorganic Synthesis and Preparative Chemistry, College of Chemistry, Jilin University, Changchun, 130012, P. R. China

Uniform microspheres of mesoporous titania with a worm-like structure and controlled nanocrystalline framework have been prepared by a simple procedure of the self-assembly of rutile TiO2 nanoparticles based on surfactant (EO) 20 (PPO)70-(EO)2o (PI23) in a nonaqueous system. The crystalline mesoporous TiO2 was characterized by X-ray diffraction (XRD), scanning electron microscopy (SEM), and N2 adsorption/desorption measurements. 1. Introduction Since the first discovery of M41S family of ordered mesoporous silicate and aluminosilicate materials with uniformly sized pores and high surface areas through use of amphilic template-directing methods in 1992 [1], there have been extensive research activities aimed at synthesizing tailored mesoporous silica for catalysis, separation, and nanostructure fabrications [2]. Recently, this approach has been extended to synthesize transition-metal oxides, which have wider applications because of their unique optical, electronic, and magnetic properties [3-6]. Among mesoporous transition-metal oxides, titanium dioxide (titania) is attractive because of its excellent performance in photocatalytic reactions. Titania exists in three naturally occurring polymorphs: anatase, rutile, and brookite. Under ambient conditions, rutile is the most stable phase in bulk forms. However, thermodynamic stability is dependent on particle sizes and at particle diameters below ca. 14 nm, anatase is more stable than rutile [7, 8]. To date, many different synthesis strategies have been developed to synthesize nonsilica mesoporous materials with frameworks composed of transition metal oxides, oxophosphates and oxosulfates, sulfides, and metals [9, 10]. Among the

248

synthesis strategies developed so far, the evaporation-induced self-assembly (EISA) method is one of the most promising methodologies [11] and has already proven to be very efficient for preparing organized thin films of inorganic materials via organic surfactant micelles as templates. By employing this method, mesoporous transition-metal oxide powders (including TiO2, ZrO2, A12O3, SnO2, Nb2O5, WO3, and mixed oxides) with 2D-hexagonal or cubic structures were successfully prepared. Mesoporous anatase thin films and powders were prepared through this technique from TiCl4 or other titanium precursors and surfactants [12]. Crystallization of initial amrorphous TiO2 takes place at high temperature (350-550°C) and is always accompanied by considerable shrinkage of the corresponding mesostructures. Higher temperature treatment can eventually lead to a complete collapsing of the mesopore structures because of extensive growth of anatase nanocrystals [6, 1319]. Accordingly, the studies on the preparation of mesoporous rutile TiO2 are rare [13, 20, 21]. The reported preparation of mesoporous titania with a rutile crystalline structure involves hydrolysis of either TiOCl2 or T1CI4 in the presence of surfactants. The previous study indicates that the mesoporous rutile titania exhibits a good photocatalytic activity for gas-phase photo-oxidation of a mixture of benzene and methanol [21]. In this paper, we present the synthesis and characterization of mesoporous TiO2 with a wormlike structure and controlled crystalline framework through self-assembly of rutile nanocrystals in the presence of triethyl phosphate for formation of a glassy phosphate phase, which acts as a "glue" among the rutile nanocrystals and stabilizes the resultant framework [17]. 2. Experimental Section 2.1. Synthesis The detailed synthesis protocol of the nanosized rutile particles has been given previously [22]. In a typical synthesis, 5 g of PI23 was dissolved in 60 g of anhydrous ethanol (200 proof) in the presence of 35 mL concentrated HC1 at ambient temperature under vigorous stirring. The mixture was continually stirred for 2 h. Meanwhile, 40 mL of deionized water was sonicated by employing a direct immersion titanium horn (Sonics and Materials, VCX-750, 20 kHz, and starting power 100 W) followed by the injection of 5 mL of titanium tetrachloride (Aldrich). The mixture was further sonicated continuously for 40 minutes and sonication was conducted without cooling. The resulted solution containing the nanosized rutile particles (seeds) was mixed with preprepared P123-ethanol-HCl solution followed by the addition of 5 mL triethyl phosphate ((C2H5O)3PO, Aldrich). After further stirring for 20 hours, the mixture was transferred to glass Petri dishes and left to dry

249

under ambient conditions for 7 days. The resultant product was calcined in air at 500°C for 6 h to remove the surfactant molecules (heating rate: 2.2. Characterization Powder XRD data were collected via a Siemens D5005 diffractometer with CuKa radiation (X = 1.5418 A). A Philips XL-30 field emission SEM operated at 15 kV and an HITACH HD-2000 STEM operated at 200 kV were used to carry out SEM analyses. N2 adsorption/desorption measurements for both nanosized rutile and the resulted mesoporous TiC>2 were conducted on a Micromeritics Gemini system. 3. Results and Discussion Powder XRD patterns of separately prepared nanosized titania seeds and the resultant titania microspheres (not shown) revealed the characteristic feature of the rutile structure. The weak and broad diffraction peaks result from the very small size of crystals in nano-scale. The SEM image of nanosized titania seeds in Figure 1 shows that the particle size of the sonicated rutile nanocrystals is approximately 10 nm and these nanoparticles aggregate Figure 1 SEM image of nanosized titania seeds. together to form bigger assemblies. It is believed that the inter-particles mesopores are responsible for the hysteresis loop observed in the N2 adsorption isotherm (Figure 2). Figure 3 shows a representative SEM image of the uniform • microspheres of the resulted mesoporous titania. The resulted spherical TiO2 particles exhibited a characteristic feature of mesoporous materials, which was confirmed by a typical type IV N2 adsorptiondesorption curve, as shown in Figure Figure 2 N2 adsorption isotherm of 4. A hysteresis loop with a sloping sonicated rutile.

250

adsorption branch and a relatively sharp steep desorption branch is observed at relative pressure (P/Po) range of 0.40.8. This observation is consistent with the assertion that the mesopores formed by the surfactant-assisted assembly of the rutile TiO2 nanoparticles have similar entrance pore sizes. The BET surface area is about 39.98 m2/g measured by Micromeritics Gemini 2375. The high magnification SEM image of a mesoporous TiO2 microphere in 02 0.4 0.6 Figure 5 reveals the same structural Relative Pressure, P/Pn feature. Compared to the previously Figure 4 N2 adsorption isotherm of the reported mesostructured titania [6, 12resulting micropheres of mesoporous titania. 19], the material described here is

Figure 3 SEM image of the resulting micropheres of mesoporous titania.

Figure 5 High magnification SEM image of a microphere of mesoporous titania.

expected to be more stable because of the formation of the phosphate glassy phase induced by the addition of triethyl phosphate. 4. Conclusion In summary, a simple synthetic approach to generate thermally stable mesostructured titania micropheres with a crystalline framework of rutile was reported. The additive of triethyl phosphate played an important role in stabilizing the resultant mesostructured titania. The material was characterized by XRD, SEM, and N2 adsorption/desorption measurements.

251

5. Acknowledgment This work was supported by the Office of Basic Energy Sciences, U.S. Department of Energy (DOE). The Oak Ridge National Laboratory (ORNL) is managed by UT-Battelle, LLC, for the U.S. DOE under Contract DE-AC0500OR22725. This research was supported in part by an appointment for W.Y. to the Oak Ridge National Laboratory Postdoctoral Research Associates Program administered jointly by the Oak Ridge Institute for Science and Education and Oak Ridge National Laboratory. 6. References [1] C. T. Kresge, M. E. Leonowicz, W. J. Roth, J. C. Vartuli and J. S. Beck. Nature 359 (1992) 710. [2] G. J. D. Soler-illia, C. Sanchez, B. Lebeau and J. Patarin. Chem. Rev. 102 (2002) 4093. [3] D. M. Antonelli and J. Y. Ying. Chem. Mater. 8 (1996) 874. [4] P. D. Yang, D. Y. Zhao, D. I. Margolese, B. F. Chmelka and G. D. Stucky. Nature 396 (1998)152. [5] E. L. Crepaldi, G. Soler-Illia, A. Bouchara, D. Grosso, D. Durand and C. Sanchez. Angew. Chem.-Int. Edit. 42 (2003) 347. [6] S. Y. Choi, M. Mamak, N. Coombs, N. Chopra and G. A. Ozin. Adv. Funct. Mater. 14 (2004)335. [7] H. Z. Zhang and J. F. Banfield. J. Mater. Chem. 8 (1998) 2073. [8] H. Z. Zhang and J. F. Banfield. J. Phys. Chem. B 104 (2000) 3481. [9] A. Sayari and P. Liu. Microporous Mater. 12 (1997) 149. [10] F. Schuth. Chem. Mater. 13 (2001) 3184. [11] C. J. Brinker, Y. F. Lu, A. Sellinger and H. Y. Fan. Adv. Mater. 11 (1999) 579. [12] P. C. A. Alberius, K. L. Frindell, R. C. Hayward, E. J. Kramer, G. D. Stucky and B. F. Chmelka. Chem. Mater. 14 (2002) 3284. [13] H. M. Luo, C. Wang and Y. S. Yan. Chem. Mater. 15 (2003) 3841. [14] E. L. Crepaldi, G. Soler-Illia, D. Grosso, F. Cagnol, F. Ribot and C. Sanchez. J. Am. Chem. Soc. 125 (2003) 9770. [15] H. Shibata, T. Ogura, T. Mukai, T. Ohkubo, H. Sakai and M. Abe. J. Am. Chem. Soc. 127 (2005) 16396. [16] Y. Zhou and M. Antonietti. J. Am. Chem. Soc. 125 (2003) 14960. [17] D. L. Li, H. S. Zhou and I. Honma. Nature Mater. 3 (2004) 65. [18] J. M. Du, Z. M. Liu, Z. H. Li, B. X. Han, Y. Huang and Y. N. Gao. Microporous Mesoporous Mater. 83 (2005) 19. [19] T. Sreethawong, Y. Yamada, T. Kobayashi and S. Yoshikawa. J. Mol. Catal. A-Chem. 241(2005) 23. [20] V. Samuel, P. Muthukumar, S. P. Gaikwad, S. R.Dhage and V.Ravi. Mater. Lett. 58 (2004) 2514. [21] Y. Z. Li, N. H. Lee, E. G. Lee, J. S. Song and S. J. Kim. Chem. Phys. Lett. 389 (2004) 124. W. F. Yan, B. Chen, S. M. Mahurin, V. Schwartz, D. R. Mullins, A. R. Lupini, J. Pennycook, S. Dai and S. H. Overbury. J. Phys. Chem. B 109 (2005) 10676.



253 253

Synthesis of a lamellar mesostructured calcium phosphate using hexadecylamine as a structuredirecting agent in the ethanol/water solvent system Nobuaki Ikawaa, Yasunori Oumia, Tatsuo Kimurab, Takuji Ikeda0 and Tsuneji Sano a* "Department of Applied Chemistry, Graduate School of Engineering, Hiroshima University, Higashi-Hiroshima 739-8527, Japan. b Advanced Manufacturing Research Institute, National Institute of Advanced Industrial Science and Technology (AIST), Shimoshidami, Moriyama-ku, Nagoya 463-8560, Japan. 'Research Center for Compact Chemical Process, AIST, Tohoku, Nigatake, Miyaginoku, Sendai 983-8551, Japan.

Control of solubility and crystallization properties of calcium phosphate species in the mixed solvent of ethanol and water led to the successful preparation of a novel lamellar mesostructured calcium phosphate in the presence of w-hexadecylamine. The formation of the lamellar mesostructured calcium phosphate was strongly dependent upon EtOH/H2O and solvent/H3PO4 ratios in the starting gel. 1. Introduction A wide variety of mesostructured and mesoporous metal oxides and phosphates can be prepared by using various surfactants as structure-directing agents (SDAs) [1-4]. Metal species are connected by oxygen atoms in their frameworks through covalent bonds. Although calcium phosphate has attractive much attension as biocompatible materials, there have been few reports on mesostructural control of calcium phosphate by using surfactants as SDAs [5-8]. Calcium and phosphate species are strongly interacted each other through electrostatic interaction, which prevents from interacting between calcium phosphate species and surfactant molecules, and calcium phosphate species are crystallized. Therefore, it is difficult to obtain mesostructured calcium phosphates through surfactant templating. In this study, solubility and

254

crystallization properties of calcium phosphate species were controlled according to the synthetic conditions such as EtOH/H2O and solvent/H3PO4 ratios and then a novel lamellar mesostructured calcium phosphate was prepared by using «-hexadecylamine in the ethanol/water system. 2. Experimental Section A lamellar mesostructured calcium phosphate was prepared by using phosphoric acid (85% H3PO4) and calcium acetate monohydrate (Ca(CH3COO)2H2O) in the presence of w-hexadecylamine (C16H33NH2). Ci6H33NH2 (2.41 g) and 85% H3PO4 (1.15 g) were added to a mixed solvent of EtOH (18.4 g) and H2O (6.6 g). After stirring at room temperature for 1 h, Ca(CH3COO)2 • H2O (1.76 g) and aqueous solution of ammonia (25% NH3 aq.) (0.34 g) were introduced into the surfactant solution. The mixture was stirred vigorously for 15 min and then kept at room temperature for 120 h statically. The solid product was filtered, washed with ethanol, and then air-dried. 3. Results and Discussion

001

The XRD pattern of the product showed three well-resolved peaks assignable to (001), (002) and (003) reflections of a lamellar phase with the d]Oo spacing of 4.4 nm (Figure 1).

002

J

hkl 001 002 003

A 4

d /nm 4.4 2.3 1.5

en oo

A 6 28 I

10

12

Figure 1. XRD pattern and TEM image of the lamellar mesostructured calcium phosphate,

the clear striped patterns were observed in the TEM image of the product and the repeat distance of the striped patterns was ca. 4.1 nm. On the basis of the results, mesostructural ordering of the product is considered to be lamellar. 3IP MAS NMR and ICP-AES measurements were carried out to investigate the framework of the product. The 31P MAS NMR spectrum showed two peaks at 0.5 ppm and 3.4 ppm. The Ca/P molar ratio of the product was 1.0. The organic content of the product was measured by CHN analysis. The product contained 36.1 mass % of carbon atoms, 7.9 mass % of hydrogen atoms and 2.6 mass %

255

of nitrogen atoms (C: H: N=16.1: 42.1: 1.0). The composition of the product is calculated to be 2.34CaO • 1.17P2O5 • C,6H33NH2 from the results by elemental analyses. Yuan et al. reported the possibility to synthesize the lamellar mesostructured calcium phosphate. However, they cannot show the direct evidence such as TEM image for the formation of a lamellar phase [9]. Thermal analysis (TG/DTA), FT-IR and 13C CP/MAS NMR were conducted to investigate thermal stability of the lamellar mesostructured calcium phosphate and conformation of alkyl chain in the surfactant molecules. The major mass loss in the TG/DTA curve occurred below 150°C and between 150 and 500°C. It seems that the mass loss 4000 3000 2000 1000 below 150°C is due to H2O desorption. Wavenumber / cnT! Burning of the surfactant molecules Figure 2. FT-IR spectrum of the lamellar started at around 220°C and the mass mesostructured calcium phosphate. loss between 150 and 500°C was ca. 48.5 mass %. The peak corresponding to -CN group as well as the peaks corresponding to -CH 3 and -CH 2 - groups were respectively observed at 1070 cm"1 and 2900-3000 cm"1 in the FT-IR spectrum (Figure 2). The 13C CP/MAS NMR spectrum exhibited a large peak at around 33 ppm with a small peak at around 15 ppm. The main peak at around 33 ppm is assigned to all-trans methylene (-CH 2 -) groups of the surfactant molecules. The chemical shift is typical of those observed for alkylammonium type surfactants in lamellar mesostructured materials. Effects of the synthtic conditions such as EtOH/H2O and solvent/H3PO4 (solvent = EtOH + H2O) ratios were investigated when both of the Ca/P and Ci6H33NH2/H3PO4 molar ratios in the starting mixtures were fixed at 1/1. The results are listed in Table 1. Brushite (CaHPO4 • 2H2O) known as one of crystalline calcium phosphates was mainly obtained when EtOH was not used as a solvent. The formation of brushite can be suppressed with an increase in the EtOH/H2O ratio and a lamellar mesostructured calcium phosphate (MCP) was obtained without byproducts at the EtOH/H2O ratio of 50/50 mol %. The EtOH/H2O mixed solvent system is useful for controlling crystallization of calcium phosphate species, leading to the successful formation of the lamellar mesostructured calcium phosphate. When the EtOH/H2O ratio was increased further, unreacted Ca source and lamellar hexadecylammonium phosphate salt ([C16H33NH3+][H2PO4"], HAP) were recovered without the formation of MCP because the solubility of Ca species is low in EtOH. No mesostructured calcium phosphate can be obtained without H2O because Ca species are not solubilized and then hardly reacted with phosphate species. A crystalline calcium phosphate such as monetite (CaHPO4) was formed at higher higher temperatures (50100°C).

256

The synthesis of the lamellar mesostructured calcium phosphate were also conducted by changing the solvent/H3PO4 ratio in the starting mixture with the EtOH/H2O ratio of 50/50 mol%. The crystallinity of the lamellar mesostructured calcium phosphate increased with the solvent/H3PO4 ratio. A pure lamellar mesostructured calcium phosphate can be obtained at the ratio of 80. When the ratio was higher than 120, brushite was also formed as byproduct. Table 1. Synthetic conditions and characteristics of lamellar mesostructured calcium phosphates. Starting mixture

Product

EtOH/H2O ratio

Solvent/H3PO4 ratio

Phase

t/ooi /

0/100

40

Brushite, HAP

—

25/75

40

Brushite, MCP

(4.4)

50/50

40

MCP

4.4

75/25

40

MCP (Ca source)

4.4

96/4

40

HAP (Ca source)

—

50/50

80

MCP

4.4

50/50

120

MCP, Brushite

4.4

n m

4. Conclusion A lamellar mesostructured calcium phosphate was successfully prepared by using «-hexadecylamine as a surfactant. Control of the solubility and crystallization of calcium sources and calcium phosphate species was found to be important for synthesizing mesostructured calcium phosphate. This is the first example of surfactant-templated mesostructured calcium phosphates whose frameworks are constructed through ionic bonds, being very important as model systems for biomimetic materials design such as bone and teeth. 5. References [1] F. Schtith, Chem. Mater., 13 (2001) 3184. [2] G. J. de A. A. Soler-Illia, C. Sanchez, B. Lebeau and J. Patarin, Chem. Rev., 102 (2002) 4093. [3] C. Yu, B. Tian and D. Zhao, Curr. Opin. Solid State Mater. Sci., 8 (2003) 191. [4] T. Kimura, Microporous Mesoporous Mater., 77 (2005) 97. [5] M. J. Larsen, A. Thorsen and S. J. Jensen, Calcif Tissue Int., 37 (1985) 189. [6] G. A. Ozin, N. Varaksa, N. Coombs, J. E. Davies, D. D. Perovic and M. Ziliox, J.Mater. Chem., 7(1997)1601. [7] J. Yao, W. Tjandra, Y. Chen, K. Tarn, J. Ma and B. Soh, J. Mater. Chem., 13 (2003) 3053. [8] J. Anderson, S. Areva, B. Spliethoff and M. Linden, Biomaterials, 26 (2005) 6827. [9] Z. Y. Yuan, J. Q. Liu, L. M. Peng and B. L. Su, Lamgmuir, 18 (2002) 2450.

257


Formation of Pt nanowires in mesoporous materials and SiO2 nanotubes Inga Bannat and Michael Wark Institute of Physical Chemistry and Electrochemistry, Leibniz University of Hannover, Callinstr. 3-3A, D-30167 Hannover, Germany

1. Introduction The synthesis of nanowires in different host structures has attracted extensive interest because of their structural, electronic and optical properties which are governed by the anisotropy and differ greatly from the bulk properties of the materials [1]. Furthermore, nanowire core-shell structures are studied as "nanocables" in nanoelectronics [2]. Mesoporous hosts are a perfect matrix for a stabilization of nanowires; the preparation and orientational studies on Pt nanowires in MCM-41 and MCM-48 have been studied for years [3-6]. In our study we compare the formation of Pt nanowires and their orientation in four different host systems. Basing on the approach of Terasaki et al. [3] we synthesized Pt nanowires via an introduction of Pt2+ ions by wetimpregnation in different mesoporous SiO2 hosts (MCM-41, SBA-15) or ionexchange in Al/Si-SBA-15 and subsequent reduction with H2. Scheme 1: Illustration of the formation of In an additional approach Pt Pt-doped SiO2 NTs by the metal salt NF nanowires were in-situ created in thin template method [7]. SiC>2 nanotubes (NTs). Here fibers of the Pt salt [Pt(NH3)4](HCO3)2 are used as templating structures for the sol-gel based synthesis of oxide NTs (Scheme 1) [7]. Continuous Pt nanowires are formed in thin NTs after reduction of the Pt salt template in air. Template nanofiber

sol-gel technique

Tet raethy lortho s i I i cate (TEOS)

258

2. Experimental Section 2.1. Pt nanowires in pre-formed mesoporous hosts Si-MCM-41 was synthesized directly in autoclavable polypropylene bottles with CTABr and Na2SiO3 following a procedure reported by Rathousky et al. [8], in which the homo-geneous precipitation of Si-MCM-41 is induced at 307 K by the addition of EtAc and subsequent hydrothermal treatment. Si-SBA15 and Al/Si-SBA-15 were prepared with Pluronic P 123 according to Zhang et al. [9] from tetraethyl orthosilicate (TEOS) and aluminium isopropoxide by aging at 313 K for 16 h and hydrothermal treatment at 373 K for 48 h. The resulting solid products were recovered by filtration, washing with water and calcination at 873 K in air for 6 h. In order to form the Pt nanowires, the mesoporous materials were impregnated repeatedly for 24 h with an aqueous solution of [Pt(NH3)4](NO3)2 (max. 0,1 wt %). After the removal of the solvent, the samples were reduced under H2 atmosphere for 1 h at 873 K. Extracted Pt nanowires were obtained by removing the silica framework with an aqueous HF solution. The study of Pt nanowires is often complicated by SiC>2 gel remaining from the host during the extraction and enhancing agglomeration. The effect is more pronounced the lower the degree of wires. 2.2. In-situformation ofPt nanowires in SiO2 NTs [7] In a first step nanofibers of the templating Pt salt [Pt(NH3)4](HCO3)2 were precipitated with ethanol from an ammonia containing aqueous solution. The system was kept in an ice bath for at least 5 min. Subsequently, 14 uL TEOS were added to the mixture under continuous stirring and finally more ethanol were injected rapidly. After 4 h template-filled SiO2 NTs were achieved and calcined at 773 K for 5 h. High resolution (scanning) transmission electron microscopy (HR(S)TEM) was carried out on a Jeol JEM-21 OOF electron microscope. 3. Results and Discussion Fig. 1 A-C shows high resolution STEM and TEM micrographs of Si-MCM41, Si-SBA-15 and Al/Si-SBA-15 samples after impregnation with the Pt precursor and subsequent reduction. For the different host materials, all possessing a well-ordered channel structure, different degrees of pore filling and formation of nanowires were observed. In Si-MCM-41 Pt nanowires are formed exclusively in the straight channels (Fig. 1 A). The wires are very uniform and their lengths vary from several tens to several hundreds of nanometers (Fig. 1 D). Their maximum diameter of 3.8 nm, deduced from HRTEM micrographs, is almost of the same value as the Si-MCM-41 channel to channel distance of

259

4.0 ± 0.2 nm obtained from XRD and TEM. Thicker (8 nm) but shorter (2050 nm) and quite irregular nanowires were received with Al-SBA-15 as host material (Fig. 1 C, F). This seems to be related to diffusion problems in the pores which are more pronounced in SBA-15 systems since in the wider pores (diameter of about 8 nm) more Pt precursors must be transported to form the

50 Fig. 1: HRSTEM and HRTEM micrographs of Pt nanowires and nanoparticles in mesoporous materials (A-C) and extracted Pt nanowires (D-F); host systems: (A,D) Si-MCM-41, (B,E) SiSBA-15, (C,F) Al/Si-SBA-15

Fig. 2 STEM micrographs of Pt nanowires in the inner void of thin SiO,NTs

Fig. 3: HRTEM micrographs of Pt wires extracted from Si-MCM-41 (A-B) and SiO2NTs (C-D)

wires. In the case of Si-SBA15 only Pt nanoparticles were formed (Fig. 1 B, E). They exhibits sizes of about 8 nm in accordance to the channel pores. Compared to Al/SiSBA-15, Si-SBA-15 with its electroneutral structure lacks of ion exchange capacity. Therefore, the [Pt(NH 3 ) 4 r ion incorporation is not attracted by coulomb forces and much less Pt precursor diffuse into the pores of SiSBA-15 so that only some small particles can be formed. Pt nanowires in thin SiO2 NTs, formed during heat treatment in air by an autoreduction of the templating [Pt(NH3)4](HCO3)2 nanofibers in the interior of the tube,

260

exhibit diameters of 15-35 nm and wire lengths up to 500 nm. Although the growth of the Pt nanowires in thickness is, in contrast to the situation in the SiMCM-41 or SBA-15 channels, not restricted by the pore geometry, in the about 100 nm wide NTs the Pt particles align to almost continuous but thin nanowires. Fig. 2 shows that the Pt nanowires are either formed by a line-up of individual Pt nanoparticles (A) or consist of one long crystalline segment (B). Forces between the Pt nucleation seeds as well as to the walls seem to support the wire formation. In thicker NTs these forces get weaker and less nanowires but more individual particles are found [7]. The Pt nanowires, observed in Si-MCM-41 and in SiO2 nanotubes, were studied in respect of their orientation in the host systems. High resolution TEM (HRTEM) micrographs of the Pt wires, extracted from Si-MCM-41, show that they consist of single-crystalline Pt segments (Fig. 3). The (111) and (200) planes of Pt, which crystallize in a face-centered cubic structure, were observed to lie parallel to the channels of the MCM-41. This suggests in agreement to findings of Yang et al. and Liu et al. [4, 5], that the nanowires preferentially grow in [110] direction. Although the pore channels are much wider equal results were received with the Pt nanowires extracted from SiC>2 NTs, indicating that this growth orientation is highly preferred for Pt independent of the host structures. 4. Conclusion Uniform Pt nanowires with lenghts up to several hundreds of nanometers were synthesized by two synthesis strategies. One strategy used mesoporous materials as matrix for the formation of the wires. Thus, we received Pt nanowire lenghts up to 200 nm and diameters in accordance to the pore diameters of the mesoporous materials. The other strategy used a metal salt as template to create Pt nanowires of about 500 nm and diameters of 15-35 nm in SiO2 NTs. In both cases the Pt nanowires grow in [110] direction independent of the pore geometries of the host system. 5. References [1] [2] [3] [4] [5] [6] [7] [8] [9]

Y. Wang, K. Takahashi, H. Shang and G. Cao, J. Phys. Chem. B, 109 (2005) 3085. Y. Cui and C. M. Lieber, Science, 291 (2001) 851. O. Terasaki, Z. Liu, T. Ohsuna, H. Shin and R. Ryoo, Microsc. Microanal, 8 (2002) 35. C.-M. Yang, H.-S. Sheu and K.-J. Chao, Adv. Funct. Mater., 12 (2002) 143. Z. Liu, Y. Sakamoto, T. Ohsuna, K. Hiraga, O. Terasaki, C. H. Ko, H. J. Shin and R. Ryoo, Angew. Chem., 112 (2000) 3237. X. Guo, C. Yang, P. Liu, M. Cheng and K. Chao, Cryst. Growth & Design, 5 (2004) 33. L. Ren and M. Wark, Chem. Mater., 17 (2005) 5928. J. Rathousky, M. Zukalova and J. Had, Collect. Czech. Chem. Soc, 120 (1998) 6024. F. Zhang, Y. Yan, H. Yang, C. Yu, B. Tu and D. Zhao, J. Phys. Chem. B 109 (2005) 8723.


261 261

Synthesis of Pd nanoparticles in La-doped mesoporous titania with polycrystalline framework Shuai Yuana, Qiao R. Shenga, Jin L. Zhanga*, Feng Chen8, Masakazu Anpob and Wei L. Daic a

Lab for Advanced Materials and Institute of Fine Chemicals, East China University of Science and Technology, 130 Meilong Road, Shanghai 200237, P. R. China; b Department of Applied Chemistry, Graduate School of Engineering, Osaka Prefecture University, 1-1 Gakuen-cho, Sakai, Osaka 599-8531, Japan;' Department of Chemistry, Fudan University, 200433, P. R. China

A simple synthetic method to prepare highly dispersed Pd nanoparticles in La-doped mesoporous titania with polycrystalline framework by coassembly and photoreduction is reported. The mesoporous materials were characterized by low angle and wide angle X-ray diffraction (XRD), transmission electron microscope (TEM), high-resolution transmission electron microscopy (HRTEM). 1. Introduction Noble metals, such as Pt, Pd and Au, are widely used in the fields of organic synthesis, petrochemistry, etc. Anchoring noble metal nanoparticles or clusters in zeolites can combine the advantages of nanoparticles and micropores [1]. However, the micropore sizes less than 2 nm restrict applications with the participation of macromolecules. The discovery of mesoporous materials provided a new kind of hosts to load nanoparticles with high dispersity [2]. The combination of noble metal nanoparticles with well ordered mesoporous materials is of interest in the field of catalysis, separation and sensors [3]. The substrates not only provide sites for nanoparticles, but also have great effects on catalytic activities. TiO2 is a kind of transition metal oxide having different

262

crystalline structures. Pd loaded on different crystalline titania have various catalytic activity and selectivity. To introduce Pd nanoparticles into rare earth doped mesoporous titania with highly crystallized walls and long-range ordered mesopores may bring more excellent properties in the redox reactions. However, it is difficult to introduce metal nanoparticles into mesopores by traditional impregnation methods, because they tend to deposit richly on outer surface of mesoporous materials. Moreover it is difficult to control the loading amount by impregnation. In here, a simple method is reported to synthesize highly dispersed Pd nanoparticles in La-doped mesoporous titania with crystallized walls by photoreducing PdO in-situ at room temperature. 2. Experimental Section 2.1. Experimental procedure In the synthesis process, Pluronic P-123 was dissolved in BuOH under vigorous stirring for 30min. Then the required content of La(NO3)3*6H2O and Ti(OBu)4 were added into the P-123 solution, followed by stirring for an additional 60 min. In a test-tube PdCl2 was dissolved in dilute hydrochloric acid (23.8 wt%). Then, the solution was added dropwise to the above mixture under stirring and ultrasonic treatment. The temperature of ultrasonic cell was kept at 298 K. The molar ratio of Pd: La: P-123: HC1: H2O: BuOH: Ti was kept 0.005: 0.01: 0.025: 1: 6.5: 6.5: 1. After 30 min, the transparent sol was transferred from the reactor to an open Petri dish. After aging at 298 K for 4 day, 413 K for 2h and then 473 K for 2h, the cracked-free thin layer was calcined at 673 K for lh in airflow. The brown powder, notated as PdO/MT, was divided into two portions. One portion was dispersed in aqueous solution of ethanol (1: 1, v/v), then illuminated at room temperature by UV light for 0.5 h after saturated by N2 for 20 min. The black product was notated as Pd(P)/MT. The other portion was reduced in H2 (99.99%) flow at 473 K for 4 h. H2 flow was stopped until the sample was cooled down to room temperature. The black product was notated as Pd(H)/MT. 2.2. Characterization X-ray diffraction (XRD) patterns of all samples were collected in 6-26 mode using Rigaku D/MAX-2550 diffractometer. The sample morphology was observed under transmission electron microscopy (TEM) and high-resolution transmission electron microscopy (HRTEM) on a 2100 JEOL microscope using

263

copper grids. The instrument employed for XPS studies was Perkin Elmer PHI 5000C ESCA System with Al Ka radiation operated at 250 W. 3. Results and Discussion In Figure 1, the appearance of low-angle diffraction peaks indicates that mesoporous order was preserved after calcination. Illumination by UV light in aqueous solution of ethanol or calcination in H2 flow did no damage to the mesostructure. From wide-angle XRD patterns, a series of peaks for anatase can be observed. Previous works confirmed that the walls consisted of anatase nanocrystals [4]. No characteristic peaks belonging to PdO appear after calcination. PdO may be amorphous or very small and highly dispersed. Otherwise, the presence of a very small amount of PdO would display characteristic peaks in the wide-angle XRD pattern. Because Pd2+ ion has larger size than Ti4+ ion, it is difficult for Pd2+ to be doped in the lattice of anatase. The PdO may exist on the outer surface, inner surface of mesoporous titania, or in the gaps between anatase nanoparticles. After thermal reduction by hydrogen at 473 K for 4 h, two peaks belonging to Pd (111) planes and (200) planes emerge. However, there is only one weak peak belonging to Pd (111) planes for Pd(P)/MT, which attributes to smaller metal particle size and higher dispersion. The inference is also verified by the following TEM images.

b 2 3 4 5 2-Theta (degree)

I 6 20

30 40 50 2-Theta (degree)

60

Figure 1. Low-angle XRD patterns (left) and wide-angle XRD patterns (right) for Pd(P)/MT (a), Pd(H)/MT (b) and PdO/MT (c).

264

• • :5Onin,

,

•

.

•

Figure 2. TEM and HRTEM images of Pd(P)/MT (a, c) and Pd(H)/MT (b, d)

TEM and HRTEM images are shown in Figure 2. The mesoporous titania matrix has long-range order and polycrystalline framework. There is no obvious agglomerate Pd particles in the mesopores of Pd(P)/MT (Figure 2a). Illuminated by UV light, PdO was reduced in-situ by photo-generated electrons avoiding high temperature in the presence of ethanol as photo-generated holes captor. In contrast, some larger Pd nanoparticles can be observed in the TEM image for Pd(H)/MT (Figure 2b). Pd nanoparticles grew in the mesopores, but the size was restricted by the pore diameter. Before reduction, the sintering of PdO should be slow because of the strong chemical interaction with titania by forming Pd-O-Ti. After reduction, Pd will agglomerate to reduce surface energy. High temperature will accelerate the agglomeration of Pd. From the HRTEM image of Pd(P)/MT(Figure 2c), anatase (101) planes with d= 0.35 nm and Pd (111) planes with d= 0.22 nm can be observed. From the HRTEM image of Pd(H)/MT(Figure 2d), anatase (101) planes with d = 0.35 nm and Pd (200) planes with d= 0.19 nm can be observed. The Pd nanoparticles prepared by photoreduction are smaller than by hydrogen reduction at high temperature, which agree well with XRD analysis. The valence states of palladium were analyzed by XPS spectra. Palladium only has one chemical state in Pd(P)/MT, which indicates the reduction was complete. The dispersion and the particles size of Pd° will affect the Pd 3d5/2 binding energy values greatly. The Pd° 3d5/2 binding energy of Pd(P)/MT is

265 265

335.8 eV, 0.2 eV higher than that of Pd(H)/MT, which may be due to higher dispersion and smaller size of Pd nanoparticles. In contrast, two chemical states of palladium can be distinguished in the XPS spectra for Pd(H)/MT. Pd 3d5/2 binding energies of 335.6 eV and 337.6 eV are attributed to highly dispersed Pd° and Pd2+, respectively [5, 6], By quantitative analysis, there is about 14% residual PdO. 4. Conclusion A simple method is reported to synthesize highly dispersed Pd nanoparticles in La-doped mesoporous titania with crystallized walls by photoreducing PdO in-situ at room temperature. The loading amount of Pd is easy to control, because there is no loss of Pd in such process. Compared with reduction by H2, photoreduction is highly efficient and complete with high dispersion, which profits from the polycrystalline framework of mesoporous titania. 5. Acknowledgment This work has been supported by National Basic Research Program of China (2004CB719500), Shanghai Nanotechnology Promotion Centre (0452nm010, 0552nm019 ), and National Nature Science Foundation of China (20577009). 6. References [1] J. G. Kim; S. K. Ihm, J. Y. Lee and R. Ryoo, J. Phys. Chem. 95 (1991) 8546. [2] C. T. Kresge, M. E. Leonowicz, W. J. Roth, J. C. Vartuli and J. S. Beck, Nature 359 (1992) 710. [3] R. C. Hayward, P. Alberius-Henning, B. F. Chmelka and G. D. Stucky, Microporous Mesoporous Mater. 44 (2001) 619. [4] S. Yuan, Q. Sheng, J. Zhang, F. Chen, M. Anpo and Q. Zhang, Microporous Mesoporous Mater. 79(2005)93. [5] I. Yuranov, L. Kiwi-Minsker, P. Buffat and A. Renken, Chem. Mater. 16 (2004) 760. [6] K. Sun, W. Lu, M. Wang and X. Xu, Appl. Catal. A 268 (2004) 107.


Recent Progress in Mesostructured Mesostructured Materials D. Zhao, S. Qiu, Y. Tang and C. Yu (Editors) © 2007 Published by Elsevier B.V.

267 267

Fabrication of metal oxide nanowires templated by SBA-15 with adsorption-precipitation method Renlie Bao, Kun Jiao, Heyong He, Jihua Zhuang and Bin Yue* Department of Chemistry and Shanghai Key Laboratory of Molecular Catalysis and Innovative Materials, Fudan University, Shanghai 200433, PR China.

1. Introduction One-dimensional (ID) nanostructured metal oxide materials have aroused current interest due to their exceptional properties and potential applications in many areas, such as electronics, miniaturized devices and catalysis [1-3]. Nanowires have been successfully synthesized by various methods, e.g. laser ablation, electroless deposition, thermal decomposition, cation exchange, selected-control reaction, chemical vapor deposition, arc discharge and conventional template-assisted solution phase growth. Recently, highly ordered silica mesoporous materials, have opened a new pathway for confined growth of nanowires inside the mesopores. SBA-15 is an ideal template for incorporation of precursors and formation of desired nanowires owing to its large surface area, variable pore size, regular pore system, and high thermal and hydrothermal stability [4]. ID nanowire and 3D nanowire array metal oxides have been successfully synthesized [5-7]. In this work a novel method called "adsorption-precipitation" was adopted to prepare Cr2O3, MnOx, NiO, and CO3O4 nanowires using SBA-15 as the template. The formation of these nanowires was monitored by XRD, TG-DTA, TEM and SAED. 2. Experimental Section SBA-15 was synthesized according to literature method [4]. In the adsorption-precipitation route, SBA-15 was refluxed in an aqueous solution containing certain amount of CrCl3-6H2O (MnCl2-4H2O, NiCl2-6H2O and Co(NO3)2-6H2O) overnight, and dried to remove the solvent. The resulting material was put in a flow of ammonia for 12 h at room temperature, then treated at 200°C for 5 h. The Cr2O3/SBA-15 (MnOx/SBA-15, NiO/SBA-15 and

268

CO3O4/SBA-I5) was obtained after calcination for 5 h at 550°C. To get different fillings, repeated adsorption of precursor was performed. The SBA-15 template of all samples was eliminated by 10% (v/v) HF aqueous solution. X-ray diffraction (XRD) was carried out on a Rigaku D/MAX-IIA diffractometer. Thermogravimetric (TG) analysis and differential thermal analysis (DTA) were performed on a Perkin-Elmer TGA7/DTA7 thermal analyzer in air atmosphere. The transmission electron microscopic (TEM) and selected area electron diffraction (SAED) images were taken on a JEOL JEM2010 transmission electron microscope.

ts

30

40

024

104 110 006 113

20

116

Cr O /SBA-15 Cr2O /SBA-15 2 33

012

Intensity

110 2 00

Intensity

100

3. Results and Discussion

50

(b)

60

SBA-15

(a) Cr22O33/SBA-15 (c) 1.0 1.0

2.0

3.0

4.0

5.0

6.0

2 theta (deg.) (deg.)

Fig. 1. The XRD patterns of (a) SBA-15 in the small angle region, (b) Cr2O3/SBA-15 in the large angle region, and (c) Cr2O3/SBA-15 in the small angle region.

The typical XRD patterns (Fig. 1) of Cr2O3/SBA-15 shows the (100) diffraction of hexagonal SBA-15 in the small angle region moved toward high angle in comparison with the parent SBA-15, indicating the shrinkage of silica framework after formation of metal oxide in the channels of SBA-15. In the large angle region the phase of Cr2O3 (JCPDS No. 38-1479) was observed. For the other metal oxide inside SBA-15, they exhibit the similar diffractions in the small angle region. The XRD patterns in the large angle region show that Mn3O4 (JCPDS No. 24-0734) and Mn2O3 (JCPDS No. 41-1442), NiO (JCPDS No. 44-1159) and Co3O4 (JCPDS No. 78-1970) formed in MnOx/SBA-15, NiO/SBA-15 and Co3O4/SBA-15, respectively. Therefore, the nanostructured crystalline metal oxides are formed inside SBA-15 after calcination. The TEM image of Cr2O3 sample (Fig. 2) shows nanowire morphology and SAED reveals their crystalline character. Moreover, it can be found that the diameter of Cr2O3 nanowires is in the region of 7-8 nm, indicating the replication of the mesopores of SBA-15. The improving of order and

269 269

crystallinity of CO3O4 nanowires can be achieved by increasing precursor fillings (Fig. 3). The morphology of MnOx, NiO and Co3O4 nanowires are similar to that of Cr2O3 nanowires (Fig. 2 and Fig. 3) ~|

Fig. 2. TEM image (a), HRTEM image (b), and SAED of Cr2O3 nanowires.

Fig. 3. The TEM images of Co3O4 samples impregnated (a) once, (b) twice and (c) three times; HRTEM images of (d) MnOx and (e) NiO.

The typical TG-DTA curves of Co(NO3)2-6H2O and Co(NO3)2/SBA-15 are shown in Fig. 4. It is noticeable that Co(NC>3)2 in SBA-15 channels decomposed to oxide completely at 200°C, indicating the decomposition of the nitrate in the mesopores occurred at lower temperature in comparison with the bulk sample. To investigate the formation of crystalline CO3O4 nanowires, the impregnated samples were pretreated at 40-150°C prior to calcination at 550°C. It is found that the order of Co3O4 nanowires was improved with increasing pretreatment temperature but not higher than 150°C, preferentially around the nitrate melting point. The similar results are also observed in the other samples. Therefore, we suggest a possible route for the formation of metal oxide nanowires from their nitrates as follow: when the precursor is pretreated below 150°C, the fusible nitrate with high fluidness gathers together in SBA-15 channels through capillary action, then the precursor undergoes the decomposition and crystallization to form metal oxide nanowires at higher temperatures. If the pretreatment temperature is higher than 150°C, the nitrate precursor may decompose to dispersed amorphous oxide particles before aggregation of nitrate in SBA-15 channels. Thus, the difficult mass transfer at higher temperature results in the formation of separated metal oxide nanowires and the decrease of the order of the nanowires.

270 100

(a) (a)

Weight% (%)

80 70 60

Co(NO33)22/SBA-15 /SBA-15

50 40

Co(NO3)2-6H2O

30

(b)

8

Delta T Endo Down (oC)

90

Co(NO3)2-6H2O

6 o

200 C 200°C 4

Co(NO3)2/SBA-15 2

0

o

250 C 250°C

-2

-4

20 100

200

300

400 o

Temperature (°C) ( C) Temperature

500

100 100

200 200

300 300

400 400

500 500

600

o

Temperature Temperature (°C) ( C)

Fig. 4. (a) TG and (b) DTA curves of Co(NO3)2-6H2O and Co(NO3)2/SBA-15.

4. Conclusion Cr2O3, MnOx, NiO, and CO3O4 nanowires have been successfully prepared with the adsorption-precipitation method using SBA-15 as the template. 5. Acknowledgement This work is supported by the National Basic Research Program of China (2003CB615807), the NSF of China (20371013, 20421303) and the Shanghai Science and Technology Committee (05DZ22313). 6. References [1] [2] [3] [4]

Y. Zhang, A. Kolmakov, S. Chretien, H. Metiu and M. Moskovits, Nano Lett. 4 (2004) 403. S. F. Yin, B. Q. Xu, C. F. Ng and C. T. Au, Appl. Catal. B: Environ. 48 (2004) 237. S. C. Laha and R. Ryoo, Chem. Commun. 17 (2003) 2138. D. Y. Zhao, J. L. Feng, Q. S. Huo, N. Melosh, G. H. Fredrickson, B. F. Chmelka and G. D. Stucky, Science 279 (1998) 548. [5] K. K. Zhu, B. Yue, W. Z. Zhou and H. Y. He, Chem. Commun. 1 (2003) 98. [6] F. Jiao, B. Yue, K. K. Zhu, D. Y. Zhao and H.Y. He, Chem. Lett. 32 (2003) 770. [7] K. K. Zhu, H. Y. He, S. H. Xie, X. Zhang, W. Z. Zhou, S. L. Jin and B. Yue, Chem. Phys. Lett., 377(2003)317.


271 271

Facile synthesis of hierarchically structured titanium phosphate with bimodal wormhole-like mesopores and macropores Hailong Fei, Xiaoquan Zhou, Pingchuan Sun, Zhongyong Yuan and Tiehong Chen* College of Chemistry, Department of Materials Chemistry, Key Laboratory of Functional Polymer Materials ofMOE, Nankai University, Tianjin, 300071, P.R. China

A facile template-free approach has been proposed to synthesize macroporous titanium phosphate with adjustable bimodal worm-like mesopores. Characterizations including SEM, TEM, FT-IR, N2 adsorption and MAS NMR have been performed. The results showed that phosphorus was incorporated into the framework in the form of Ti-O-P bonds. Bimodal worm-like mesoporores within the macropores formed by the crosslink of the blocks were identified in the range of 2.4 to 6.7 nm. 1. Introduction Titanium phosphates can be used not only as ion-exchange regents, but also as catalysts for the liquid partial oxidation [1]. Therefore, great attention has been paid to synthesize novel organically templated titanium phosphates with mixed valences and 2-D layers [2, 3], ordered mesopores [4] , high surface area [5] or crystalline inorganic framework [6]. Uniform titanium phosphate nanotubes [7] and ultrathin Ti (HPO4)2 film [8] were also fabricated. Recently, Yuan et al prepared mesoporous titanium phosphate with adjustable bimodal macropores via changing the concentration of surfactants [9]. Here we synthesized macroporous titanium phosphate with adjustable bimodal mesopores in a simple way without any surfactants. It is possible that the coeffects of n-butanol and phosphoric acid promote the formation of hierarchical titanium phosphate.

272

2. Experimental Section In a typical process, the mixture of titanium n-butoxide (TBT) and n-butanol with certain molar ratio was added dropwise to 30 ml 0.1M phosphoric acid solution under stirring at room temperature. After stirring for another 2 h, the obtained mixture was transferred into a teflonlined autoclave and aged at 80°C for 24 h. The product was filtered, washed with water, dried at 60°C for 12 h and calcined at 500°C for 2 h. All the samples were denoted as R-d or R-c, where R denotes as the molar ratio of n-butanol to TBT, d denotes as-synthesized and dried sample, c denotes calcined sample.. Infrared data were recorded on a Bruker Vector 22 spectrometer. 31P NMR was carried out by a Varian Infinityplus 400 MHz solid NMR spectrometer with H3PO4 at 0 ppm. N2 adsorption and desorption isotherms were determined on a Micromeritics Tristar 3000 system and pore size distribution was calculated by adsorption branch data. Nitrogen pore volumes were determined at P/Po=0.993. Micropore volumes were determined by the t-plot analysis. Scanning electron microscopy (SEM) was performed on a Philips XL-20 at 15 keV. Transmission electron microscopy (TEM) was carried out on a Philips Tecnai F20 electron microscopy instrument. 3. Results and Discussion

Transmittanee [%]

The FT-IR spectrum (Figure 1A ) clarified that phosphorus was mainly incorporated into the as-synthesized and calcined materials in the form of Ti-OP bonds, which is proved by the Ti-O-P framework vibration at 1034 cm"1 and the stretching frequency of P-0 bonds at 1383 cm"1 [10, 11], The deduction A ^

B

1 34 -O-P

/

j

V/

I .

1383 I'-O

J V

\

4000 3500 3000 2500 2000 1500 1000

Wavenumber cm"1

a

500

Figure. 1 FT-IR spectrum (A) and 31P MAS NMR spectra (B) of 2d (a), 2c (b).

above was further verified by 31P MAS NMR spectra (See Figure.lB). A wide peak appeared at -8.6 ppm for 2-d (Figure.lB-a) due to different phosphor environment [5]. The chemical shifts of (H2PO4)\ (HPO4)2', PO4 were reported around -10, -20, -30 ppm respectively [12]. The chemical shift of 2-c

273

Q -o

0.0 0.2 0.4 0.6 0.8 1.0 1.0 •^•__n Relative pressure (P/P00) 0

5

10 10 15 15 20 25 30 35 40 45 50

Pore diameter (nm)

-1

2c 11.5c 27.5c

3

b

3 -1

2d 11.5d 27.5d

dV/dD(cm g nm )

3 -1

-1

dV/dD(cm g nm )

3

Adsorption volume (cm /g)

a

Adsorbed volume (cm /g)

(Figure. lB-b) moved toward to -12.1 ppm caused by the effect of hydrogen bonding or deprotonation (Figure IB) [13].

0.0

0.2

0.4

0.6

0.8

1.0

Relative pressure (P/P0)

0

5 10 10 15 15 20 25 30 35 35 40 45 50 50

Pore diameter (nm)

Figure. 2 N 2 adsorption-desorption isotherms and BJH pore size distribution curves (outside) a) as-synthesized, b) calcined materials. Table 1 The physical sorption properties and pore parameters of as-prepared and calcined titanium phosphate materials of different molar ratio of n-butanol to TBT.

Mesopore Mesopore * micro II (nm) I (nm) (crnVg) 6.3 0.010 2-d 315 0.576 2.6 0.541 0.014 2-c 218 8.3 0.760 2.4 6.2 0.017 11.5-d 391 8.3 0.005 11.5-c 156 0.395 0.984 27.5-d 436 4.5 6.7 0.016 0.584 1.7 9.0 0.006 27.5-c 188 Figure 2 shows N2 adsorption-desorption isotherms and corresponding BJH pore size distributions(inset) of as-synthesized and calcined materials (The results were listed in Table 1). Figure 2a exhibits classical type IV isotherms with type H3 hysteresis loop and bimodal mesopore distributions(denoted as mesopore I and mesopore II). Mesopore I can be enlarged via enhancing the ratio of n-butanol (See Table land Figure. 2a). After calcination mesopore I almost disappeared and the pore size of mesopore II was increased. Therefore, Sample

SBET

(m 2 /g)

'pore

(cm 3 /g)

Figure.3 Morphologies of samples a) SEM image of 2d, b) TEM image of 2d, c) TEM image of 2c.

274

the calcined samples (Figure. 2b) show type IV isotherms with hysteresis loops of type HI (P/Po= 0.5 to 0.8). Uneven macropores on large blocks are shown in the SEM photo (Figure. 3a). Transmission electronic spectroscopy (TEM) was also performed to characterize the as-synthesized and calcined materials (n-butanol/TBT = 2). As displayed in Figure 3 a, the as-synthesized sample consists of cross-linked particles of 200-400 nm. Each particle is mesoporous and the space between the cross-linked particles corresponds to macropores. For the calcined sample (Figure 3 c) the mesopores are more clearly shown, in accord with the larger pore size from the N2 adsorption measurements. 4. Conclusion Macroporous titanium phosphates with adjustable bimodal worm-like mesopores were synthesized in the presence of n-butanol and phosphoric acid. The amount of n-butanol exerted a great influence on the pore size distribution and BET surface area .This kind of titanium phosphates with hierarchical pores is promising materials for catalysis, separation and material science. 5. Acknowledgement This work was supported by National Science Foundation of China (Grants No. 20373029, 20233030), and joint-research fund of Nankai University and Tianjin University on Nano-sciences. 6. References [1] [2] [3] [4] [5]

[6] [7] [8] [9] [10] [11] [12] [13]

A. Bhaumik and S. Inagaki, J. Am. Chem. Soc, 123 (2001) 691. Y. N. Zhao, G. S. Zhu, X. L. Jiao, W. Liu and W. Q Pang, J. Mater. Chem., 10 (2000) 463. C. Serre, S. Ekambaram, G. Ferey and S. C. Sevov, Chem. Mater., 12 (2000) 444. J. Blanchard, F. SchUth, P. Trens and M. Hudson, Micropor. Mesopor. Mater., 39 (2000) 163. D. J. Jones, G. Aptel, M. Brandhorst, M. Jacquin, J. Jimenez-Jimenez, Antonio. JimenezL6pez, Pedro. Maireles-Torres, I. Piwonski, E. Roziere-Castellon, and J. Roziere, J. Mater. Chem., 10(2000) 1957. Z. L. Yin, Y. Sakamoto, J. H. Yu, S. X. Sun, O. Terasaki, and R. R. Xu, J. Am. Chem. Soc.,126 (2004) 8882. Q. F.Wang, L. Zhong, J. Q. Sun, and J. C Shen, Chem. Mater., 17 (2005) 3563. G. S. Li, L. P. Li, B. G. Juliana and B. F.Woodfield, J. Am. Chem. Soc. ,127 (2005) 8659. R. Z. Ren, Z. Y.Yuan, A. Azioune and B. L. Su, Langmuir., 22 (2006) 3886. G. S. Li, L. P. Li, B. G. Juliana and B. F.Woodfield, J. Am. Chem. Soc. ,127 (2005) 8659. S. K. Samantaray and K. Parida, J. Molarcular Catalysis A: Chemical, 176 (2001) 151. H. Nakayama, T. Eguchi, N. Nakamura, S. Yamaguchi, M. Danjyoc and M. Tsuhakoc, J. Mater Chem., 7 (1997) 1063. Y. J. Li and M. S. Whitttingham, Solid State Ionics, 63 (1993) 391.


275 275

Synthesis of mesoporous alumina using anionic, nonionic and cationic surfactants Jagadish C. Ray,a Kwang-Seok You,b Ji-Whan Ahn,b and Wha-Seung Ahna* "Department of Chemical Engineering, Inha University, Incheon 402-751, Korea. Korea Institute ofGeoscience and Mineral Resource, Daejeon 305-350, Korea.

A series of mesoporous alumina was prepared based on literature recipes using anionic, non-ionic and cationic surfactants with aluminum tri-secbutoxide in organic solvents with controlled amount of water and in aqueous solution using a complexing agent at room temperature to 100°C. The materials obtained demonstrated physicochemical properties in the order of cationic > non-ionic > anionic surfactant system with respect to surface area, thermal stability and porosity. Mesoporous alumina with enhanced textual properties (506 m2/g, 0.83 cnrVg) and thermal stability to 700°C was prepared with cetyltrimethylammonium bromide in substrate composition of Al:surfactant: H2O: sec-butanol = 1.0 : 0.3: 2.0 : 15. 1. Introduction Many attempts have been made to synthesize mesoporous alumina through surfactant templating because of its potential applications in catalysis and adsorption. Thermally unstable lamellar and hexagonal aluminas have been produced using sodium dodecyl phosphate and sulphate, respectively. Carboxylate templating tends to give microporous material and carboxylic acids also give the materials having pore size distribution centered on 2.0 nm [1]. Non-ionics in aqueous [2] and in organic [3] solvent produced wormhole type materials with lower surface area. Cationics in aqueous medium resulted in a soft gel [4] but in non-aqueous hydrothermal synthesis produced a hard gel [5], both leading to wormhole-structured alumina. In this work, we tried to verify the representative recipes for mesoporous alumina to evaluate their reproducibility and their individual merits in physicochemical properties of the product. We optimized the best process selected by making an improvement in

276

substrate choice or in composition to make a mesophase alumina with improved textural properties and enhanced thermal stability. 2. Experimental Section Aluminum tri-sec-butoxide (ASB), lauric acid (LA), Pluronic 64L (PL) [(PEO)i3(PPO)3o(PEO)13], and cetyltrimethylammoniumbromide (CTAB), secbutanol (SB), n-propanol (NP), triethanolamine (TEA) are used in the synthesis. Several synthesis models for synthesis of mesoporous alumina were compared: anionic [1], non-ionic [3] and cationic [4, 5]. The materials are characterized by XRD using DMAX 2500(Rigaku), N2 adsorption analysis using ASAP 2000 and TEM (Philips CM 200). All the samples are prepared in essence according to the protocol given in the references. 3. Results and Discussion The summary of the synthesis conditions and the corresponding results are given in Table 1. Sample 1 is prepared using LA in n-propanol, 2 is prepared using PL in sec-butanol, 3 is prepared using CTAB in aqueous solution using a complexing agent, TEA. Samples 4 and 5 are prepared using CTAB in secbutanol. Table 1. Summary of the experimental conditions and the results obtained Alsource

surfactant

1

ASB

LA

2

ASB

PL

3

ASB

CTAB

4

ASB

5

ASB

No.

Mol ratio

Temp.

Al:surf.:H20:solvent

(°C)

1 0 0 3 -3 0-25 0 (NP)

100

surface

pore

pore

area

diameter

volume

(m 2 /g)

W

Ref.

(cc/g)

412

42

0.44

46 5

49

057

60

437

3. 8

0.42

4

CTAB 1.0:0.5:2.0:10 0 (SB)

100

475

5.9

0.67

5

CTAB 1.0:0.3:2.0:15.0 (SB)

100

506

6.5

0.83

5

1.0:0.1:2.0:25.0

1

Small angle XRD patterns of the calcined samples (sample No. 1, 2 and 5) with wide-angle reflections are displayed in Fig. 1. The single peak in each case indicates the uniformity of the pores without long-range order having y-alumina pore walls. Upon calcinations at higher temperatures, y-phase peaks are amplified. The differences in small angle XRD intensities are also reflected in

277

surface area and pore volume; the higher the peak, the higher were the surface

IIntensity ntensity ((a a. u.)

25000 20000

( c) 0(c) \

ST

\ ( b)

15000

bed aamount mount (cc/g, STP) A dsorrbed Adso

30000

\\ \

% o

V

( c) ( b)

10000

( aa)) 5000 5000( ( a)

20

40

60

80 80

fl0

2

4 6 Two theta (degree)

8

Fig.l Small angle XRD patterns of the samples calcined at 500°C for 4 h (a) sample 1, (b) sample 2, and (c) sample 5. Inset: Wide angle reflections.

10

0.0 0.0

0.2

0.4

0.6

0.8

1.0

Relative Pressure (P/Po)

Fig.2 Nitrogen adsorption-desorption isotherms of the calcined samples 1

area and pore volume of the alumina. Sample 3 showed no small angle peak, but mosopores were confirmed by TEM. Sample 4 using the original recipe [5] gave the lower intensity peak (not shown) but small adjustment in the substrate composition (sample 5) produced significantly improved small angle XRD peak intensity. The N2 adsorption-desorption isotherms of all the materials are portrayed in Fig. 2. The isotherms are all similar and belong to Type IV with a final saturation plateau together with well-defined hysteresis loops indicating capillary condensation in the mesopores. TEM micrographs of the samples are shown in Fig. 3, which are essentially wormhole structures characteristic to mesoporous alumina. Sample 4 is very similar to 5 and omitted. Sample 1 and 3 are inferior to others as they have smaller pore volumes (Table 1) and 3 have no small angle XRD peak indicating lack of uniformity of pores and sample 1 gives smaller intensity peak for calcined material. As-syn sample 1 had a well-defined XRD peak but after calcination, the intensity of the peak decreased and even disappeared in some cases indicating the instability of the mesostructure during removal of surfactant. Recipe of sample 3 appears good because of delaying hydrolysis rate due to complex formation of TEA with ASB prior to hydrolysis but it has two major problems; pore heterogeneity indicated by absence of XRD peak and the possibility of re-formation of the complex of hydrolyzed product resulting in lower yield. Recipe for synthesizing sample 2 could be made at room temperature but the reproducibility and yield are poor probably due to uncontrolled low temperature synthesis.

278

The recipe of sample 4 was found superior to others as it is stable thermally at 500 °C retaining the small angle peak with higher surface area and retaining the surface area ~35O m2/g up to calcination at 700°C. This recipe is further improved by lowering the amount of CTAB and increasing the amount of solvent, which would help to distribute the surfactant molecules evenly and make easy migration of substrate molecules to form the well organized material of uniform porosity (sample 5). It is also improved by changing the solvent from 1-butanol to sec-butanol to facilitate the establishment of the equilibrium during hydrolysis, which is expected to lower the rate of hydrolysis to organize the structure according to the following reaction. A1-[O-CH(CH3)-CH2-CH3]3 + 2H2O •-> A1OOH + 3CH3-CH2-CH(CH3)-OH According to the reaction, formation of boehmite is indicated and XRD of the as-synthesized sample also confirmed it (not shown), but upon calcination it transforms to y-alumina. In short, mesoporous alumina obtained using ASB, CTAB and water in sec-butanol with the mole ratio 1.0:0.3: 2.0: 15.0 is the best among the competing procedures because of its higher BET surface area and pore volume, good reproducibility and thermal stability.

M i

•

20 nm__..

_

1

2 composite. The c) prepared at 800 °C shrinkage decreased with increasing TiO2 loading. SEM images of the TiO2 monolith showed three-dimensional TiO2 frameworks with continuous macropores (Fig.3 (a)). High magnification SEM image of the monolith showed that the pores were in the range of 30 nm -15 um although some degree of local collapse and disorganization of the structure was observed. It is proved that hierarchical TiO2 monoliths with macro/mesopores were successfully produced by using CA as the template. The TiO2 monoliths showed structure features indicating the assembly of particles around the organic membrane structure. A direct replica or inverse copy of the membrane is not seen, as complete filling of the membrane pores with particles was not acquired. Instead, coating of the membrane material gives TiO2 monolith having a porous structure with pores of different diameters originating from the pores in the original template and the new pores 100 200 300 400 500 600 700 800 900 1000 Temperature (°C) obtained on removal of the template. The pore size of the structure varies in the range of 30 Fig.4. TG-DTA curve of the TiO2/CA composite nm~15 um. The minimum time required to impregnate the organic template (at room temperature without external shaking or stirring) and obtained the stable inorganic structure is 2 h. XRD confirmed that the TiO2 monoliths consist of crystalline TiO2 (anatase) suggesting that TiC>2 particles didn't transform to rutile during the heat treatment. It could be possible to prepare rutile hierarchical monoliths if the composite is heated over 800°C (Fig.3 (c)). Most of organic fragment was removed from the TiO2 monoliths after heating at 500°C since only broad peaks corresponding to Ti-O, OH and H2O bonds were evident in the IR spectrum of the TiO2 monoliths. TG -DTA curves (Fig. 4) indicated that complete removal of the C A template after 100

90 70 60

Exotherm.

Weight (%)

80

50 40 30 20 10

0

100 200 300 400 500 600 700 800 900 1000 o

Temperature ( C)

286

the calcination at 500°C. The percentage weight losses associated are 4.5 % with a small endothermic peak (< 200°C water) and 90% with large exothermic peaks Fig. 5. SEM images of the TiO2 monolith with high TiO2 loading (200°C -500°C). The a) and b) at the high magnification residual weight (5.5 mass %) corre-sponds to TiO2 loaded onto the CA surface. By decreasing the concentration of the sols an overall thinning of the walls and increased shrinkage were observed. This revealed that dilution of the dispersions led to insufficient coating. If the concentration of the sols was too low, no TiO2 monolith could be obtained. On the other hand, the pores size depended on the TiC>2 loading. Increasing the concentration of the sols could increase the TiC>2 loading, which produced monolith with smaller openings and thicker walls (Fig. 5). 4. Conclusion To summarize, hierarchical TiO2 monoliths with macro/mesopores were successfully produced by using CA as the template. After calcination at 500°C for 6 h, CA template could be complete removed. The final pore size and structure of the as-synthesized monolith were strongly dependent on the TiC>2 loading. 5. Acknowledgement The work is supported by the National Natural Science Foundation of China (20401015, 50574082). 6. References [1] [2] [3] [4] [5] [6] [7] [8]

O'Regan and M. Gratzel, Nature, 353 (1991) 737. A. Fujishima and K. Honda, Nature, 238 (1972) 37. B. Oregan, D. T. Schwartz, S. M. Zakeeruddin, M. Gratzel, Adv. Mater, 12 (2000) 1263. S. Nagaoka, Y. Hamasaki, S. Ishihara, M. Nagata, K. Iio, C. Nagasawa and H. Ihara, J. Mo.lCata.lA, 177(2002)255. B. J. Zhang, S. A. Davis and S. Mann, Chem. Mater, 14 (2002) 1369. R. A. Caruso and M. Antonietti,. Adv. Funct. Mater, 12 (2000), 307. R. A. Caruso and D. G. Shchukin, Chem. Mater, 16 (2004) 2287. H. Zhang, G. C. Hardy, Y. Z. Khimyak, M. J. Rosseinsky and A. I. Cooper, Chem. Mater, 16(2004)4245.


287 287

Template-free synthesis of hierarchical mesoporous alumina-based materials with uniform channel-like macrostructures Tie-Zhen Rena, Zhong-Yong Yuanb* and Bao-Lian Sua>* "Laboratory of Inorganic Materials Chemistry, The University ofNamur (FUNDP), 61 rue de Brnxelles, B-5000 Namur, Belgium. b Department of Materials Chemistry, Nankai University, Tianjin 300071, P.R. China.

1. Introduction Although several methods of surfactant-templating have been developed to prepare mesoporous alumina materials [1], it is still a challenge to develop one facile and effective method to synthesize mesoporous alumina with controllable crystalline phase, high crystallinity, hierarchical porosity and large surface area. Practical applications require mesoporous materials having hierarchical pore structures at different length scales in order to achieve highly organized functions, since the introduction of secondary larger pores can improve remarkably the activity of mesoporous catalysts due to the enhanced mass transport and reduced diffusion limitation [2]. Bimodal macro-mesoporous aluminum oxide [3, 4] and silica-alumina [5, 6] materials have thus recently been prepared in the presence of one single surfactant without needing colloid crystals or emulsion droplets for the formation of macropores. Their synthesis was based on a self-assembly process by the hydrolysis of the metal alkoxide droplets in a surfactant solution, and the synthesized materials exhibited a parallel-arrayed macrochannel structure. Herein we report the facile preparation of hierarchically mesoporous-macroporous aluminum oxide, alumina-silica, and phosphated aluminum oxide materials without using any templates. 2. Experimental Section In a typical synthesis, aluminum seobutoxide, or a mixture of aluminum secbutoxide and tetraethoxysilane with different Al/Si ratio (denoted as AlnSim for Al/Si ratio of nlm), was added drop-wise into a H2SO4 aqueous solution (pH=2)

288

under slow stirring. For the synthesis of phosphated materials, a mixed solution of Na2HPO4 and H3PO4 solution was used for the hydrolysis of aluminum secbutoxide with phosphate/aluminum molar ratio of 1/2 or 2/2 (denoted as PiAl2 or P2AI2, respectively).The obtained mixture was separated into two parts: one was transferred to a Teflon-lined autoclave and heated statically at 80°C for 24 h, and another was directly filtered, washed and dried at 60°C for comparison. 3. Results and Discussion 3.1. Meso-macroporous alumina and alumina-silica SEM and TEM images reveal that the obtained aluminum oxide samples, either non-autoclaved or autoclaved, presented a dual pore system of mesopores and macropores, indicating that the meso-macroporous aluminum oxide materials can be spontaneously formed by direct hydrolysis of aluminum secbutoxide in the diluted acid solution. The particles are made of tubular macrochannels with openings from 0.5 to 2 urn, separated by wormhole-like disordered mesopores (Fig. 1). The regularity in size of macrochannels is demonstrated by the cross-section observed by TEM. The walls separating the macrochannels of nonautoclaved aluminum oxide sample are amorphous, while the autoclaved sample frameworks are composed of fibrous nanoparticles of crystalline boehmite phase with a scaffold-like array of hierarchical ordering [3]. The similar macroporous structures were also observed in the synthesized AlnSim samples (Fig. 1). However, almost no fibrous nanoparticle assembly of macroporous frameworks was seen in the meso-macroporous AlnSim, but only disordered wormhole-like mesostructures. This is due to the crystalline phase modification of the autoclaved AlnSim from boehmite to amorphous phase with the increase of the silica content in the samples. Very weak and broad XRD peaks in the autoclaved Al7Sij might still be assigned to boehmite, whereas the non-crystalline or amorphous features were presented in the i5 and AljSi7. All the N2 adsorption -desorption isotherms, whatever nonautoclaved or autoclaved, pure alumina or alumina-silica, are of type IV, indicative of Fig. 1. (a) SEM and (b,c) TEM images of autoclaved aluminum oxide; (d) SEM image of autoclaved Al3Si7; (e) TEM image of

mesoporosity ^ with average pore size o f 3 -

autoclaved Al7Si3; (f) SEM image of autoclaved P,A12.

5 n m . The surface areas

289 289

of nonautoclaved and autoclaved aluminas are 320 and 430 m2/g respectively, while the autoclaved alumina-silica samples gave larger BET surface areas and pore volumes than the pure aluminas. The pore sizes of Al«Sim samples decrease with the increase of the content of silica. The textural and structural properties were modified by the introduction of the secondary oxide (silica). 27 A1NMR spectra of the meso-macroporous aluminum oxides contained only one single signal of six-coordinate Al species. Both six- and four-coordinated Al signals were seen in chemical shift ranges of 0 - 5 ppm and 5 5 - 6 0 ppm respectively in the synthesized AlnSim, and the intensity of the six-coordinated Al signal decreased with the increase of the silica content, accompanying with the increase of the intensity of the four-coordinated Al signal. This suggests that Al has partly been incorporated in the tetrahedral network with the formation of Al-O-Si bonds in Al«Sim. The Si MAS NMR spectrum of Al^Siz shows a broad peak that could be deconvoluted into three resonance lines at ~ -109 (shoulder), -102 (main) and -93 ppm (shoulder), assignable to Si(OAl), Si(lAl) and Si(2Al) respectively. The broadness of the signals indicates the random distribution of Si(Al)-0 units with different structures. The resonance lines shift to the range of-85 to -98 ppm for Alj-Sij, and to the range of-82 to -90 ppm for Al7Sij, accompanying with the decrease of the line intensities. This means that a downfield shift of the resonance position occurs with increasing Al/Si ratio, indicating a decreasing number of'pure' SiO2-rich domains (Q4). 3.2. Meso-macroporous phosphated alumina Phosphation has been determined to enhance the surface acidity of alumina remarkably, leading to the improved catalytic activities of the resultant phosphated alumina catalysts in several acid-catalyzed reactions [7]. The hydrolysis/polycondensation of aluminum seobutoxide in the mixed solution of Na2HPO4 and H3PO4 led to the formation of hierarchically phosphated mesomacroporous aluminum oxides. The macroporous structures are uniform with the sizes of 0.5 - 1.8 \xm, and the macropore walls are composed of small interconnected PA1 particles. The macrochannels are mainly of one-dimensional orientation, parallel each other, perforative through almost the whole particle, which are similar with the case of pure aluminas shown in Fig. 1. The XRD patterns revealed that the nonautoclaved PA1 samples are amorphous, while the autoclaved PAls exhibit diffraction lines of crystalline boehmite phase, though the crystallinity is lower than the autoclaved pure alumina. Direct phosphation and autoclaving take significant roles in not only the macroporosity but also the textural properties of the resultant PA1 samples. The N2 adsorption isotherms of PAls, both nonautoclaved and autoclaved, are of classical type IV with a hysteresis loop of type H2. The autoclaved PAls have higher surface areas than nonautoclaved ones (-370 m2/g vs. 270 m2/g), and smaller BJH-pore sizes (4.3 - 5 nm vs. 2.4 - 2.7 nm) with narrower pore size distributions. The surface stoichiometry characterization, performed by XPS,

290 290

indicated that the Al/P ratios of the PA1 samples are in the range of 8 - 13, regardless of whether the P/Al ratio of the initial gel was 1:2 or 2:2, which indicates stable phosphation by a similar quantity of phosphorus. Most of the detected P atoms may be on the surface of aluminum (oxyhydr)oxide particles, but mainly link with Al via O in the form of P-O-Al, which is further confirmed by FT-IR and solid-state 27A1 and 3 1 P NMR spectroscopy (Fig. 2). Most of the Al atoms exist in an octahedral coordination. Moreover, further work has also revealed that the synthesized hierarchical PA1 exhibited remarkably high thermal stability (at least 800°C), possessing large quantity of surface hydroxyl groups and acid sites, which may attract much interest for practical applications including catalysis. 4. Conclusion Hierarchically meso-macroporous aluminabased materials have been prepared by a template-free self-assembly process. The synthesized pure aluminum oxides, aluminasilicas and phosphated aluminum oxides possess a uniform channel-like macroporous structure with disordered mesopores in the walls. Direct phosphation led to the incorporation of phosphorus into the aluminum (oxyhydr)oxide framework by the Al-O-P bonds, which may attract much interest for practical applications including catalysis. 5. Acknowledgement

27

Al

(b) (a) 31

P

(b) (a) 100

50

0 0

(ppm) δδ(ppm)

-50 -50

-100

Fig. 2. 27 A1 and 3 1 P NMR spectra of (a) non-autoclaved and (b) autoclaved PiAl2

This work was supported by the Belgian Government PAI-IUAP-01/5 project, theNSFC (No. 20473041) and the 973 program (No. 2003CB615801) of China. 6. References [1] [2] [3] [4] [5] [6] [7]

J. Cejka, Appl. Cata!. A 254 (2003) 327-338, and the references therein. Z.-Y. Yuan and B.-L. Su, J. Mater. Chem. 16 (2006) 663-677. T. Z. Ren, Z. Y. Yuan and B. L. Su, Langmuir 20 (2004) 1531-1534. W. H. Deng, M. W. Toepke and B. H. Shanks, Adv. Funct. Mater. 13 (2003) 61-65. A. Leonard, J. L. Blin and B. L. Su, Chem. Commun. (2003) 2568-2569. Z. Y. Yuan, T. Z. Ren, A. Vantomme and B. L. Su, Chem. Mater. 16 (2004) 5096-5106. Z. Y. Yuan, T. Z. Ren, A. Azioune, J. J. Pireaux and B. L. Su, Chem. Mater. 18 (2006) 1753-1767.


291 291

Mesostructured powder of tungsten oxidesurfactant compound: influence of calcination on the material's structure Zhi-mei Qia, Itaru Honmab and Haoshen Zhou,a,b» a

PRESTO, Japan Science and Technology Agency, 4-1-8 Honocho, Kawaguchi, Saitama 332-0012, Japan. Energy Technology Institute, National Institute of Advanced Industrial Science and Technology, 1-1-1 Umezono, Tsukuba, Ibaraki 305-8568, Japan.

1. Introduction Tungsten oxide with multiple crystal phases has potential applications as an important functional material for catalysis, photoelectrode, electrochromic device, and chemical sensors [1-6]. These applications have been a tremendous driving force in the field of tungsten-oxide-based materials research and engineering. A great number of reports in this field are now available. Recently, much effort has been focused on synthesis of mesostructured and mesoporous tungsten oxides in order to improve the functional properties of the materials [311]. Mesostructured and mesoporous thin films of tungsten oxides are generally fabricated by the sol-gel triblock copolymer templating technique [6, 7]. For preparing mesostructured and mesoporous powder of tungsten-oxide-based compounds, cationic surfactants such as cetyltrimethylammonium chloride (CTAC) and bromide (CTAB) were used, which enable hydrothermal reaction with tungstic acid or salt precursors [9-11]. As-synthesized mesostructured tungsten oxide-based compounds have been well characterized by a lamellar mesostructure and a 3-dimensional periodical array of Keggin clusters [9-11]. Nevertheless, a detailed investigation into the influence of calcination on the structural properties of mesostructured tungsten-oxide-based compounds is absent. As a matter of fact, materials directly synthesized from liquid solution generally have many structural defects and a poor hydrothermal stability. Therefore, as-synthesized materials need to be treated at high temperatures, to remove the structural defects and to improve their hydrothermal stability. In the present study, we first synthesized tungsten-oxide-based compound powder by

292

precipitation reaction of peroxopolytungstic acid (PTA) with CTAC in aqueous solution and then carried out calcination of the compound powder under different conditions. The experimental results indicate that the as-synthesized PTA/CTAC compound contains a lamellar mesostructure but lacks a periodical arrangement of PTA polyanions. Calcination of the as-synthesized compound in air at 200°C not only enhanced the order degree of the lamellar mesostructure but also resulted in the formation of crystalline inorganic layers via reaction of tungsten oxides with trimethylamine gas N(CH3)3 that was produced by CTAC decomposition. When the calcination temperature exceeds 250°C, the lamellar mesostructure of the material collapses. Calcination in air at 400°C of the assynthesized compound produces conventional monoclinic-phase WO3 powder without containing the mesoporous mesostructure. The two-step calcination, first in air at 200°C and then in nitrogen at 400°C, resulted in the black powder of carbon-modified, cubic-phase crystalline WO3 particles with a preferred orientation normal to the (100) plane of the cubic structure. 2. Experimental Section PTA, a highly soluble amorphous mineral acid containing 12 tungsten atoms per molecule [12], is often used for fabrication of sol-gel thin film by dip coating or spin coating [7, 13-15]. We prepared the PTA powder by reaction of H2WO4 with H2O2 according to the previous work [7]. After dissolving a given amount of the self-synthesized PTA powder in 100 ml of deionized water, an aqueous solution of ionic surfactant (/. e., 0.2 M CTAC) was slowly added in the PTA solution under vigorous stirring, which resulted in white precipitate. The precipitate was sufficiently rinsed with deionized water until chlorine ions could not be detected in the waste filtrate by titration with aqueous AgNO3 solution. After drying at 70°C for 5 h, the white precipitate turned yellow. The dried sample was grinded into powder and then calcined at different temperatures and in different atmospheres. The as-synthesized and calcined powder samples were characterized by x-ray diffractometry (XRD, MacScience, Cu-Ka irradiation, A, = 1.5406 A), transmission electron microscopy (TEM, JEOS 1200EX, 200kV accelerating voltage), Raman spectroscopy (irradiation wavelength of 532 nm), and TG-DTA technique. 3. Results and Discussion Fig. 1, (a) and (b) show small-angle XRD patterns of the dried powder sample and that calcined in air at 200°C. Pattern (a) for the dried sample exhibits two peaks at 29 = 2.42° and 4.82°, which can be indexed as (100) and (200). It indicates that the as-synthesized PTA/CTAC compound powder has a lamellar mesostructure with a spacing of d = 36.5A that is very close to d = 35A for the mesostructured salt (H^WnCôXCÎioN^ synthesized by Stein and coworkers [10]. They observed the 3D ordered arrangement of Keggin ions in

293

their salt in addition to the inorganic-organic lamellar mesostructure. However, the lack of other peaks in (a) suggests that in the present PTA/CTAC compound PTA polyanions are ordered only in one dimension. The powder sample changed its color from yellow into brown after calcination in air at 200°C for 6.5 h. A gaseous substance with 2theta (dee) an intense ammonia smell was Fig. 1. Small-angle XRD patterns of (a) the asreleased from the furnace synthesized PTA/CTAC compound powder and (b) during the course of calcination. the powder calcined in air at 200 °C for 6.5 h. The gas proved to be trimethylamine (N(CH3)3, responsible for the smell of rotting fish) that arises from dissociation of amine groups from CTAC cations. Beck and coworkers also observed the release of trimethylamine at ~ 200°C when they used a similar cationic surfactant for preparing MCM-41 mesoporous silica [16]. Fig. 1, (b) displays XRD pattern of the calcined sample. The (100) and (200) peaks move to 29 = 3.68° and 7.27°, marking that the lamellar mesostructure of the material is stable at 200°C. Calcination induces a large decrease of the spacing from d = 36.50 A to 24.00 A. An increase of the peak intensity suggests that calcination also results in an enhanced order degree of the material's lamellar mesostructure. The preservation of the lamellar mesostructure at 200°C implies that the organic layers consisting of alky 1 chains (~ 20 A in length) of CTAC molecules are safe at this temperature. With the lamellar mesostructural model shown in Fig. 2 Inorganic layerSurfactant layer — Amine group —-

Fig. 2. Schematic explanation of the calcination induced changes in the lamellar mesostructure of the PTA/CTAC compound (a is the tilt angle between the inorganic layer and the alkyl chains of the CTAC surfactant, d is the spacing of the lamellar mesostructure).

[17], removal of -N(CH3)3 groups (~ 4 A in size) from the surfactant layers would cause a decrease of < 8 A in the spacing of the lamellar mesostructure. It is therefore estimated that shrinkage of the inorganic layers and reduction of the

294

tilt angle a between the alkyl chains and the inorganic layer, both induced by calcination, lead to a decrease of > 4.5 A in the spacing of the sample's lamellar mesophase. It is interesting to observe a new peak at 26 ~ 9.22° in Fig. 1, (b). This peak does not belong to the lamellar mesostructure but arises from the lattice diffraction (d ~ 9.57 A), revealing crystallization at 200°C of the inorganic layers of the mesostructured material. According to McMonagle et al, who synthesized the crystalline (NtL^PWnCô by exposure of H3PW1204o to ammonia gas at 190°C [18], it is most likely that the crystalline inorganic layers of the mesostructured material under investigation is a tungsten oxide-trimethylamine compound that could be formed via reaction of tungsten oxide with trimethylamine gas released from the surfactant layers. By carefully searching the JCPDS cards, the crystalline inorganic layers of the mesostructured sample were determined to be a compound referred to as tungsten oxide tetramethyl ammonium hydrate [(CHs^N^WCvLSFÔ (JCPDS card No. 31-1966, its three largest spacings are d = 12.20, 9.62 and 9.09 A, respectively.). There are three reasons to support this determination. The first reason is that the lattice diffraction peak with d = 12.20 A is identical in position with the (200) peak for the lamellar mesostructure of the material. In this case, the peak observed at 20 = 7.27° for the calcined powder sample should include two contributions: the lattice and mesostructure diffractions. The second reason is that d = 9.62 A is very close to d ~ 9.57 A. The last reason is that the right-side broadening of the peak at 26 ~ 9.22° could be ascribed to overlapping of two lattice diffraction peaks with d= 9.62 A and d= 9.09 A. Fig. 3, (a), (b) and (c) are the XRD patterns for the samples calcined at different conditions, (a) for the sample calcined in air at 250°C does not clearly show peaks at smaller angles, giving a sign of collapse of the lamellar mesostructure. The number of peaks at higher angles increases in (a), revealing improvement of crystallization of the sample. The peak at 20 = 10.32° corresponds to d = 8.55 A that is smaller than d ~ 9.57 A for the sample calcined at 200°C. Fig. 3. XRD patterns of the powder samples Moreover, the other high-angle calcined at different conditions (a. in air at 250 peaks in (a) are different in °C; b. in air at 400 °C; c: first in air at 200 °C for 5 position from those given in the h and then in nitrogen at 400 °C for 4 h.) JCPDS card 31-1966. Thus, a crystal-phase change for the sample most likely occurred when the calcination temperature was increased from 200°C to 250°C. Calcination of the sample at 250°C may lead to a new material because we did not find from the JCPDS

295

cards a known material whose XRD a pattern matches (a). Increasing the calcination temperature up to 400 °C causes the compound to become a conventional monoclinic-phase WO3 powder, as evidenced by Fig. 3(b). All metastable intermediates disappeared at 400°C. To try to transform the mesostructured PTA/CTAC compound into mesopor-ous tungsten oxide, the b powder sample calcined in air at 200°C underwent the second-step treatment in nitrogen at 400°C. After the second-step calcination, the sample turned its color from brown to black, attributable to the presence of carbon in the sample due to an incomplete combustion of c the CTAC surfactant. Fig. 3 (c) shows the XRD pattern for the sample calcined in two steps. Pattern (c) presents two peaks at 20 = 23.64 and 48.21°C, corresponding to d = 3.760 and 1.886 A. These spacing values are in excellent agreement with those for the (200) and (400) planes of the cubic-phase Fig 4 T E M i m a g e s o f (a) t h e as.synthesized WO3 reported by Sidle et al (JCPDS PTA/CTAC compound powder, (b) the card No. 46-1096: d200 = 3.761 A power calcined in air at 200°C and (c) that and (^400 = 1.878 A) [19]. The XRD calcined first in air at 200°C and then in peaks from the other crystal planes nitrogen at 400°C. Inserts (a) and (b) in (c) of the cubic Structure were not are magnified views of the selected areas. detected for the sample, revealing that the two-step calcination causes the WO3 particles to crystallize along the preferred orientation being normal to the (100) plane of the cubic phase. Note that the XRD peak for the (100) plane of the cubic structure cannot be observed. Growth of crystalline WO3 particles along the other directions in the cubic structure is prohibited, which should be attributed to the dimensional limitation by the lamellar mesostructure contained in the precursor material. The diffraction peaks at smaller angles are absent in (c), indicating that the cubic-phase WO3 particles do not contain the ordered mesoporous structure. However, the TEM investigations indicate that the stepby-step calcined sample contains a wormhole-like mesoporous structure with very small pore diameters (< 1 nm). The above XRD data show that the

296 296

mesostructured PTA/CTAC compound is quite sensitive to the calcination temperature and atmosphere. Fig. 4, (a), (b) and (c) show TEM images of the different powder samples, (a) for the as-synthesized compound powder presents the channel arrays with a spacing of d = 32 A. A reduction in spacing in contrast with d = 36.5 A determined by XRD arises from heating of the sample by electron beam irradiation, (b) for the sample calcined at 200°C indicates that the straight channel array has a spacing of d = 23 A, being very close to d - 24 A measured by XRD. It is clear that the calcined sample is not sensitive to the electron beam irradiation as compared with the as-synthesized one, suggesting a good hydrothermal stability of the calcined sample. Comparison between two images (a) and (b) confirms that after calcination at 200°C the lamellar mesostructure of the sample was indeed improved in its long-range order degree. The selectedarea electron diffraction (SAED) pattern shown in the insert in (b) reveals an amorphous structure despite the fact that the powder sample has become crystalline at 200°C. This is so because the lattice spacing of d ~ 9.57 A determined from the XRD pattern (Fig. 1, b) of the same sample is too large to be clearly observed in the SAED pattern. From the magnified image (another insert in b), the lattice fringes are ambiguously seen in each channel. Fig. 4 (c) displays the TEM image for the sample calcined in two steps (in air at 200°C and then in N2 at 400°C). From this image both a wormhole-like mesoporous structure with a pore diameter of ~ 1 nm and the lattice fringes can be seen. The insert (a) and (b) are the magnified views of the corresponding areas in the image (c). The insert (a) clearly shows the lattice fringes with d = 3.59 A, arising from diffraction of the (200) plane of the cubic-phase WO3. The lack of a wormhole-like mesoporous structure in the insert HDD 1300 (a) implies that crystallization of Wavenumber (cm' ) WO3 is disadvantageous to the „. . _ . , . . ° . ._ . Fig. 5. Raman spectra of seven powder samples mesopore formation. A magnified (a pTA . b P T A / C T A C c o m p o u n d ; c, d , e md f view of the wormhole-like mesop- c o r r e s p o n d i n g t0 t h e p o w d e r s a r n p i e s c a i c i n e d in orous Structure is shown in the air at 200, 250, 300 and 400 °C, respectively; g. insert (b) where the lattice fringes the sample calcined first in air at 200 °C and then were not seen. From this indication in nitrogen at 400 °C.) a conclusion could be derived that during the thermal treatment in nitrogen at 400°C the carbon residue produced by the incomplete decomposition of CTAC is attached to the tiny clusters of tungsten oxide to prevent crystallization of tungsten oxide and consequently 1

297 297

lead to the carbon-modified mesoporous tungsten oxide powder. Our group also prepared the carbon-modified ordered mesoporous silica powder by calcination in nitrogen of the mesostructured silica-surfactant hybrid material [20]. Fig. 5, a - g show Raman spectra for seven powder samples, a for the PTA powder exhibits five bands. The first three bands at 585, 594.3 and 619.2 cm"1 correspond to v(O-W-O) and the other two bands at 917 and 978 cm"1 are ascribed to v(W=0) [21]. b for the as-synthesized PTA/CTAC compound indicates that the v(W=O) bands shift to 968.3 and 999 cm"1 and the v(O-W-O) band locates at 558.3 cm"1. The other bands in b result from the CTAC surfactant (i. e., the broad band centered at 1455 cm'and the other two bands at 1309.5 and 766 cm"1 are due to the deformation, twisting and rock vibrations of CH2 groups, respectively [22].). It is worth noting that no new Raman bands were observed with the PTA/CTAC compound as compared with the Raman spectra of PTA and CTAC (spectrum for CTAC not shown). This is so because the PTA/CTAC compound was formed via the strong electrostatic attraction between PTA polyanions and CTAC cations not via the chemical binding between them. Four Raman spectra, c - f, were obtained with the samples calcined in air at 200, 250, 300 and 400°C, respectively, c for the sample calcined at 200°C does not present the v(W=O) band, implying that the PTA polyanionic structure was destroyed at 200°C. This is in agreement with the XRD results that calcination in air at 200°C caused the reaction of PTA with N(CH3)3 to produce a new compound [(CH3)4N]2WO4-1.5H2O. Comparisons among the Raman spectra c - f suggest that with increasing the calcination temperature the band at 804.5 cm"1 and its shoulder at shorter wave number, both arising from v(O-W-O) [21], gradually become strong. Two broad bands at ~ 1360 and ~ 1590 cm"1, extremely similar to the D and G bands of carbon [23], are present in the spectra c - e but disappear from f, giving an indication that it is difficult to completely remove the CTAC surfactant from the powder samples when the calcination temperature is below 400°C. This is due to the strong interaction between tungsten oxide and CTAC. Pure CTAC was found to be completely decomposed in air at temperatures > 300°C. Spectrum g for the sample calcined in two steps also include the v(O-W-O) bands, evidencing that after the treatment in nitrogen the powder sample still keeps the oxide state of tungsten. Both very weak bands at ~ 1360 and ~ 1590 cm"1 in g indicate that the carbon residue remains in the sample due to the incomplete combustion of CTAC in nitrogen. Combination of the XRD, TEM and Raman spectroscopy analyses makes it clear that calcination of the lamellar mesostructured PTA/CTAC compound first in air at 200°C and then in nitrogen at 400°C can result in the carbon-modified, cubic-phase crystalline WO3 powder with a preferred orientation being normal to the (100) plane of the cubic structure. On the basis of TEM results, the step-by-step calcined powder also contains a wormhole mesoporous structure with a small pore diameter ( < 1 nm). The TGDTA curves recorded during thermal treatments of the as-synthesized PTA/CTAC compound powder in air and in pure nitrogen were shown in Fig.

298

6(a). Calcination in air leads to two exothermic peaks, attributable to

20

100

260 340 420 Temperature (C)

CIO

1

1.5

2

2.5

Potenital (V vs Li/Li*)

Fig. 6. (a) TG-DTA curves obtained during thermal treatment of the as-synthesized PTA/CTAC compound powder in air (solid lines) and in nitrogen (dash lines); (b) Cyclic voltammograms of the carbon-modified, cubic-phase WO3 powder immobilized on a nickel mesh with Teflon glue. The scanning rate is 0.1 mV/s.

combustion of carbon chain of the CTAC surfactant. Owing to the lack of oxygen, these peaks were not observed during the thermal treatment in nitrogen. On the other hand, the weight loss induced during thermal treatment in nitrogen is smaller than that induced during calcination in air, giving a support of the presence of carbon in the sample after treatment in nitrogen. As an example of application, the electrochemical lithium-intercalation property of the carbonmodified, cubic-phase WO3 powder was investigated by cyclic voltammetry. The WO3 electrode was prepared by immobilizing the powder sampled mixed with Teflon glue (5 wt%) onto a nickel mesh. Both reference and counter electrodes were lithium metal. The electrolyte is 1M LJCIO4 in a mixed solution of ethylene carbonate (EC) and diethylene carbonate (DC) (V E C/VDC = 1)- Fig. 6(b) shows the first 3 cycles. No characteristic redox peaks were clearly observed. The cathodic charges for the second and third cycles are -286 C/g and -251 C/g, and the corresponding anodic charges are 180 C/g and 173 C/g. 4. Conclusion The present study has demonstrated significant and complicated influence of calcination on both the mesostructure and crystal structure of the tungsten oxide-based compounds. By calcination at 400°C in nitrogen of the PTA/CTAC compound, we successfully obtained the cubic-phase crystalline WO3 powder with a highly preferred orientation being normal to the (100) plane of the cubic structure. Such preferred orientation is attributed to the dimensional limitation by the lamellar mesostructure of the precursor material. Transformation of the amorphous inorganic layers into the crystalline ones through reaction of tungsten oxide with trimethylamine gas released from the CTAC surfactant was observed, for the first time, for the lamellar mesostructured PTA/CTAC

299

compound. It was confirmed that the lamellar mesostructure of the PTA/CTAC compound was stable at 200°C and collapsed at > 250°C. Creation of mesoporous WO3 via calcination in air of the mesostructured PTA/CTAC compound is not successful due to a lack of a rigid three-dimensional inorganic network. However, the TEM analyses indicate that the carbon-modified, wormhole-like mesoporous WO3 powder with small pore diameters (< 1 nm) could be prepared from the mesostructured PTA/CTAC compound by the twostep calcination, first in air at 200°C and then in nitrogen at 400°C. 5. References [1] I. Shiyanovskaya and M. Hepel, J. Electrochem. Soc. 146 (1999) 243. [2] M. Misono, Chem. Commun. (2001) 1141. [3] L. G. Teoh, Y. M. Hon, J. Shieh, W. H. Lai and M. H. Hon, Sens. Actuators. B 96 (2003) 219. [4] E. O. Zayim, P. Liu, S. Lee, C. E. Tracy, J. A. Turner, J. R. Pitts and S. K. Deb, Solid State Ioncs 165 (2003) 65. [5] S.-H. Baeck, K.-S. Choi, T. F. Jaramillo, G. D. Stucky and E. W. McFarland, Adv. Mater. 15(2003)269. [6] W. Cheng, E. Baudrin, B. Dunn and J. I. Zink, J. Mater. Chem. 11 (2001) 92. [7] Z. Qi, H. Zhou, T. Watanabe and I. Honma, J. Mater. Chem. 14 (2004) 3540. [8] P. Yang, D. Zhao, D. I. Margolese, B. F. Chmelka and G. D. Stucky, Nature 396 (1998) 152. [9] M. S. Whittingham, J. Guo, R. Chem, T. Chirayil, G. Janauer and P. Zavalij, Solid State Ionics 75 (1995) 257. [10] A. Stein, M. Fendorf, T. P. Jarvie, K. T. Muller, A. J. Benesi and T. E. Mallouk, Chem. Mater. 7 (1995) 304. [11] G. G. Janauer, A. Dobley, J. Guo, P. Zavalij and M. S. Whittingham, Chem. Mater. 8 (1996) 2096. [12] J. OI, A. Kishimoto and T. Kudo, J. Solid State Chem. 96 (1992) 13. [13] B. Orel, N. Groselj, U. O. Krasovec, M. Gabrscek, P. Bukovec and R. Reisfeld, Sens. Actuators. B 50 (1998) 234. [14] K. Itoh, K. Yamagishi, M. Nagasono and M. Murabayashi, Ber. Bunsen-Ges. Phys. Chem. 98 (1994) 1250. [15] H. Okamoto, T. Iwayanagi, K. Mochiji, H. Menace and T. Kudo, Appl. Phys. Lett. 49 (1986)298. [16] J. S. Beck, J. C. Vartuli, W. J. Roth, M. E. Leonowicz, C. T. Kresge, K. D. Schmirt, C. T-W. Chu, D. H. Olson, E. W. Sheppard, S. B. McCullen, J. B. Higgins and J. L. Schlenker, J. Am. Chem. Soc. 114(1992)10834. [17] Z. Chen, B. H. Loo, Y. Ma, Y. Cao, A. Ibrahim and J. Yao, ChemphysChem 5 (2004) 1020. [18] J. B. Mcmonagle and J. B. Moffat, J. Colloid Interface Sci. 101 (1984) 479. [19] A. R. Siedle, T. E. Wood, M. L. Brostrom, D. C. Koskenmaki, B. Montez and E. Oldfield, J. Am. Chem. Soc. 111 (1989) 1665.



301 301

Hydrothermal synthesis and characterization of mesoporous zirconia templated by triethanolamine Fu Ma a ' b ' c , Jihong Suna*, Hongjian Zhao a b ' c , Yun Lia>b and Shijie Luoa

"Department of Chemistry and Chemical Engineering, College of Environmental & Energy Engineering, Beijing University of Technology, Beijing, 100022, P. R. China b Key Laboratory of Energy and Chemical Engineering, NingXia University, Yinchuan, 750021, P. R. China c Department of Chemical Engineering, Ningxia Normal University, Guyuan, 756000, P. R. China

1. Introduction Since the discovery of M41S in 1992 [1], there has been great interest in the synthesis of mesoporous transition metal oxides with well-ordered and controllable structural features because of their potential applications in the fields of catalysis, optics, electronics, and magnetism [2, 3]. One special characteristic of zirconium oxide is that it contains both weakly acidic and basic surface sites, and promises a high activity in reactions with acid-base bifunctional catalysts. In the past, many great efforts have been performed to extend the surfactant templating strategy to the synthesis of mesoporous zirconia including cationic quaternary ammonium surfactants [4], anionic surfactants [2, 5], primary amines [6] and block copolymers [7] as the structure directing agents. However, relatively expensive surfactants usually cause substantially high cost and make the product poisonous [8]. Additionally, some of them were reported to have poor thermal stability [9]. These facts actually limit many practical applications. Here, by using small, non-surfactant templates to direct the formation of mesosized structural features during the hydrolysis and condensation procedure of zirconium n-propoxide, we report a new templating method to synthesis successfully mesoporous zirconia via the hydrothermal route, which is expected to extend the templating strategy for preparing non-siliceous mesostrutured materials.

302 302

2. Experimental Section Zirconium n-propoxide, triethanolamine (TEA) and water were combined at room temperature in a ratio of 1:0.2-1.0:10-150 to obtain a homogeneous mixture. After heated at 100°C for 24 h in air, a solidified gel was formed, which was then transferred into an autoclave and heated at 80-150°C for 1272h. Finally, the prepared sample was calcined at 600°C for lOh with a ramp rate of 1°C /min in air to obtain the final mesoporous materials. X-ray diffraction (XRD) of the samples was recorded using a Brucker-AXS D8 Advance X-ray diffractometer using Cu K a radiation. Transmission electron microscope (TEM) images were recorded on a JEOL JME-2010. Nitrogen adsorption-desorption isotherms were measured using a Micromeritics ASAP 2010 system, and pore size distributions were obtained from the N2 desorption branch isotherm using BJH method. 3. Results and Discussion XRD patterns for calcined samples are shown in Fig. 1. All of solids show diffraction patterns with only one strong 0 10 20 30 40 50 60 70 80 reflection during the low angle scale, and relative 2 6 value shifted around from 1.0 to 1.5 c CD depending on Zr/TEA/water molar ratio and aging condition during the sol-gel synthesis process. Similar single peak diffraction 10 4 patterns have been previously 26 (° ) observed in mesoporous AI2O3 [10], TUD-1 [11] and TiO2 Fig. 1. XRD patterns of the mesoporous ZrO2 sample, [12], indicating that such a the synthisis condition were as following: prepared sample possesses a (a)1.0Zr:0.6TEA:25H2O, aged at 150°C for 2 h, mesoporous structure. The (b)1.0Zr:0.6TEA:150H2O, aged at 150°C for 48 h, (c)1.0Zr:0.6TEA:25H2O, aged at 150°C for 48 h, shift of the single peak position in the XRD patterns (d)1.0Zr:1.0TEA:25H2O, aged at 150°C for 48 h, Inset: sample (c). All of samples were calcined at 600°C for reflects the change of dlOh. spacing value. After calcinations at 600°C, tetragonal zirconia has been formed (Fig. 1 insert). Meantime, a small amount of monoclinic zirconia may be present as indicated by the small shoulder peaks at 2 0=24.4,28.2,31.5°.

303

TEM image (Fig. 2) shows wormhole-like or possibly sponge-like pore channel for the typical mesoporus ZrC>2 sample, which is in good agreement with the only one diffraction peak in the XRD patterns. Similar pore channels have been observed for disordered mesoporous alumia [13] and Ti-TUD-1 [14] when TEA were also used as a template. 100 300

250

80

d V/ d ( l o g D) ( c m3 / g )

3

Ads or bed( c m / g)

90

70 60 50

200

150

100

50

0

40

1

30

10

Pore diameter(nm)

100

20 10 0

10nm

Fig.2. TEM image of the typical mesoporus ZrO2 s a m p l e

0

0. 0. 55

1

R e l a t i v e ppressure(p/p0) r e s s u r e ( p / p 0) Relative

Fig. 3. The typical N2 adsorption-desorption isotherm and corresponding pore size distribution of mesoporous zirconia (insert)

A typical nitrogen adsorption-desorption isotherm of the sample is shown in Fig. 3. The obvious hysteresis loops can be found at the relative pressure of 0.68-0.97, which is corresponding to the narrow pore size distribution (Fig.3 inset) with the mean pore size at 8.7nm and the surface area of 45 m2/g. On the other hand, it is evident that the mesoporous ZrO2 prepared calcined at 600°C for lOh in this work shows better thermal stability than any other mesoporous ZrC>2 previously synthesized by the surfactant-assisted methods [2, 4, 7], in which mesoporous struture was disappeared after calcined at 600° C. The further studies for the effects of other parameters are in progress. To explain our findings with combination of pioneering work [2, 12, 14-16] the following mechanism is postulated. It is well known that zirconia alkoxides are highly reactive with water to form precipitate. But when the zirconium sources were mixed with TEA firstly, the three OH groups of TEA can easily replace alcohol groups of alkoxides. After chelation with TEA, zirconium transforms into a complex, which oligomerizes by hydrolysis-polycondensation [15, 16]. Upon subjection to the thermal treatment, the oligomers condense further, releasing TEA and aggregating by self-assembly. Moreover, the TEA could template the formation of zirconia, and then, the particles directly condense into well-arranged pore walls. Combined with above results, TEA act not only as a hydrolysis retarding agent but also as a mesopore forming agent.

304

4. Conclusion Consequently, with zirconium n-propoxide as Zr source and TEA as template, a new hydrothermal synthesis route has been developed for the preparation of mesoporous zirconia, with a wormhole-like pore channel. The use of TEA as template is believed to be responsible for the improved thermal stability of mesoporus zirconia. 5. Acknowledgement This research was supported by Project Sponsored by the Scientific Research Fundation for the Returned Overseas Chinese Scholars, State Education Ministry, and the Natural Science Fundation of Ningxia Hui Autonomous Region (ZD02). 6. References [1] C. T. Kresge, M. E. Leonowice, W. J. Roth, J. C. Vartuli and J. S. Beck, Nature, 359 (1992) 710. [2] M. S. Wong and J. Y. Ying, Chem. Mater., 10 (1998) 2067. [3] X. Song and A. Sayari, Catal. Rev., 38 (1996) 329. [4] J. A. Knowles and M. J. Hudson, Chem. Commun., (1995) 2083. [5] G. Pacheco, E. Zhao, A. Carcia, A. Sklyarov and J. J. Fripiat, J. Mater. Chem., 8 (1998) 219, T. J. McCarthy and W. M. H. Sachtler, Appl. Catal .A, 148 (1996) 135 [6] P. Yang, D, Y.-Y. Huang, D. Zhao, I. Margolese, B. F.Chmelka and G. D.Stucky, Nature, 396 (1998) 152. [7] S. A. Bagshaw, E. Prouzet and T. J. Pinnavaia, Science, 269 (1995) 1242. [8] X. S. Zhao, G .Q. Lu and G. J. Millar, Ind. Eng. Chem. Res., 35 (1996) 2075 [9] S. A. Bagshaw and T. J. Pinnavaia, Angew. Chem. Int. Ed. Engl, 35 (1996) 1102. [10] J. C. Jansen, Z. S han, L. Marchese, W. Zhou, N.v.d. Puil and Th. Maschmeyer, Chem. Commun., (2001) 713. [11] C . F . M a , J . H. Sun and F. Wang, Chinese Invent Patent, No: CN2005100708798. [12] S. Cabrea, J. E. Haskouri, J. Alamo and P. Amoros, Adv. Mater., 11 (1999) 379. [13] Z. Shan, J. C. Jansen, L. Marchese and Th. Maschmeyer, Micropor. Mesopor. Mater., 48 (2001) 181. [14] S. Cabrea, J. E. Haskouri, M. D. Marcos and P. Amoros, Solid State Sci., 2 (2000) 405. [15] Y.-W. Suh, J.-W. Lee and H.-K. Rhee, Solid State Sci., 5 (2003) 995. [16] Y.-W. Suh, J.-W. Lee and H.-K. Rhee, Catal. Lett., 90 (2003) 103.


305 305

The role of triethanolamine in the synthesis of mesostructured TiO2 by sol-gel method Feng Wanga, Jihong Sunb* and Chongfang Maa "Key Laboratory of Enhanced Heat Transfer and Energy Conservation, Ministry of Education and Key Laboratory of Heat Transfer and Energy Conversion, Beijing Education Commission, College of Environmental and Energy Engineering, h Department of Chemistry and Chemical Engineering, College of Environmental and Energy Engineering, Beijing University of Technology, Beijing 100022, China.

1. Introduction With its unique characteristics in band position and surface performances, the mesostructured TiO2 material plays a prominent role in fundamental studies and has widely promising applications in many areas, such as solar energy conversion, and photocatalysis [1, 2]. Since the discovery M41S in 1992 [3], Mesoporous titania, with controllable structure and tailoring texture properties simultaneously, has been extensively synthesized for increasing its specific surface area and therefore realizing above high-performance. Among the various synthetic routes developed in the last decades, the most general and versatile hydrothermal synthetic strategy is based on the hydrolysis and condensation of titanium alkoxides via self-assembly mechanism. Meanwhile, progress has been made in using different types of amphiphiles as templates, including small charged surfactant molecules and large block copolymers [4-7]. However, due to the expensive and noxious surfactants, it deeply limits the wide industrialization and practice availability. Therefore, it is exciting useful to explore and design new templates to avoid those problems encountered in fundamental research and industrial demands. Recently, we reported that, by using triethanolamine (TEA) as template which is small, green and inexpensive non-surfactant chemicals, mesoporous TiO2 materials have been successfully synthesized with reproduceable and controllable structure [8, 9]. In this paper, the role of TEA in the synthesis of mesostructured TiO2 was investigated.

306 306

2. Experimental Section The typical synthesis procedure is as following: Tetrabutyltitanate (TBOT), TEA and water were mixed and stirred for 24 h at room temperature in ratio of 1: 0.5-5:20-30. After aging at room temperature for 24 h, this mixture was dried and aged at 373-453 K for 12-72 h in an autoclave. Finally, the sample was obtained as a white mesoporous solid by removal of the template either via Soxhlet extraction using ethanol or via calcinations at 723-873 K for 10 h in air. X-ray diffraction (XRD) data were recorded on a D8-ADVANCE with Cu Ka radiation. Transmission electro microscope (TEM) observations were obtained with JEOL-2010 apparatus. Nitrogen adsorption and desorption isotherms were measured using a Micrometeritics ASAP2020 system. The pore size distributions were calculated by the BJH method. UV-vis absorbance spectra were taken on a Shimadzu UV-2450 spectrophotometer. 3. Results and Discussion The N2 adsorption/desorption isotherms (not shown) of typical mesoporous titania via Soxhlet extraction using weak acid ethanol for 3 days. A clear hysteresis loop at high relative pressure is observed, which is related to the capillary condensation associated with large pores. The BET surface area is 525 m /g and its mean pore size is around 4.5 nm, but decreased to 300 m2/g when calcinated at 573 K. TEM image in Fig. 1 shows a wormhole-like structure with narrow pore distribution [8, 9]. Obviously, The large surface area of mesoporous TiO2 can be related with its special mesostructure. The XRD pattern of typical mesoporous TiO2 is shown in Fig. 2. It displayed that one diffractive peak with strong intensity at low angle of around 1.0 (2 theta), suggesting long-scale order in the arrangement of structure [10]. The analysis of the UV-vis spectrum indicated that absorption intensity of mesostructure TiO2 is higher than that of P25 (Degussa), especially in visible light area (shown in Fig. 3). In the synthesis of mesoporous TiO2, many parameters can be strongly influenced on the final internal structure, such as the sol composition , pH , hydrothermally treated time and Fig. 1 TEM image of the mesoporous TiO2 temperature. Presently, this work is doing under way.

307

v.

5000

60

4000 intensity

intensity

50

3000

40

30

20

10

2000

0 20

30

40

50

2θ/

60

70

80

o

1000

0 0

1

2

3

2θ /

4

5

6

o

Fig. 2 XRD patterns of the mesoporous TiO2 and with wide angle (insert)

2.0

1.5

Absorbtance

It is well known that TEA behaves as a tertiary amine in aqueous solution, and it easily forms weak cationic complexes by acting as a neutral nitrogen-donor ligand [11]. Therefore, it can be used as a inhibitor for the hydrolysis-polycondensation rate of Ti-alkoxide during the sol-gel processing, as can be shown in Fig. 4, leading to forming more stable aminetrialkoxo complexes, which is key to control meso structured TiO2 material by self-assembly route. On the basis of above results, the following mechanism is postulated. Initially, TEA as chelating ligand, the high reactivity of tetratitanium alkoxides Ti(OR)4 can be chemically modified, subsequently, hydrolysis and condensation processes became easily controlled [12]. Secondly, during aging and removal template processing, these complexes were decomposed and organic species were removed, leading to forming mesopore structure.

1.0

b

0.5

a

0.0 300

400

500

600

700

800

Wavelength/ Wavelength/ nm

Fig. 3 UV-DRS absorbtance spectrum for P25 (a) and the mesoporous TiO2 (b)

OBu. HOC2H4 BuOL + . N - C2H4OHBuO/ U Temperature

T

^f

N Ti Fig. 4 Schematic of interaction mechanism between TBOT and TEA

308 308

4. Conclusion This approach provides well defined mesostructured TiO2 with high surface area 525m2/g and wormhole-like pore structure. Meanwhile, the role of TEA is not only as a inhibitor to controll the hydrolyze and condense balance of ingorganic solutes, but also as a mesopore template via the amine-trialoxo ligand by self-assembly mechanism. 5. Acknowledgment This research was supported by the Major State Basic Research Development Program of China (973 Program No.203CB214500), the Natural Science Fundation of Ningxia Province (No. ZD02), and Project Sponsored by the Scientific Research Fundation for the Returned Overseas Chinese Scholars, State Education Ministry. 6. References [1] [2] [3] [4] [5] [6] [7] [8] [9]

P. E. Savage, Chem. Rev., 99(1999) 603. M. R. Hoffman, S. T. Martin and W. Choi, et al., Chem. Rev., 95 (1995) 69. C. T. Kresge, M. E. Leonowicz and W. J. Roth, et al.. Nature, 359 (1992) 710. D. M. Antonelli and J. Y. Ying, Angew. Chem. Int. Ed. Engl., 34 (1995) 2014. Y. D. Wang, C. L. Ma and X. D. Sun, et al., Appl. Catal. A: Gen., 246 (2003) 161. S. Cabrera, J. E. Haskouri and A. Porter, et al., Solid State Sci., 2 (2000) 513. P. D. Yang, D. Y. Zhao and D. Margolese, et al., Nature, 396 (1998) 152. C. F. Ma, J. H. Sun and F. Wang, et al., Chinese Invent Patent, CN2005100708798. F. Wang, L. X. Sang, L. X. Xu and J. H. Sun, et al., Journal of Shanghai Normal University, 11 (2005) 111. [10] T. Abe, A. Taguchi amd M. Jwamoto, Chem. Commum., 11(1994) 1387. [11] A. Naiini, V. Young and J. Verkade, Polyedron 14 (1995) 393. [12] J. C. Zhang and S. L. Marchese, et al., Chem. Commun., (2001) 713.


309 309

Nano-replication to mesoporous metal oxides using mesoporous silica as template Byung Guk So,a Jeong Kuk Shon,a Ji Ae Yu, Oh-Shim Joo b and Ji Man Kima'* " Department of Chemistry and SAINT, Sungkyunkwan University, Suwon, Suwon, 440746, Korea (Tel: 82-31-290-5930; Fax: 82-31-290-7075; E-mail: [email protected]) ' Eco-Nano Research Center, Korea Institute of Science & Technology, Seoul, 136-791, Korea

Mesoporous materials constructed with different framework compositions such as iron oxides and manganese oxides, etc. have been successfully obtained by the impregnation with desired metal precursors into the bicontinuous cubic Ia3d mesoporous silica, crystallization to metal oxides at desired temperature and subsequent silica removal using NaOH aqueous solution. 1. Introduction Since the discovery of mesoporous materials, ordered mesoporous silicas such as MCM-41, SBA-15 and KIT-6 have attracted much attention for various applications due to their tunable mesopore and the subsequent high surface area [1-3]. In addition, it is reported that mesoporous silicas can be used as a sacrificing template for the nano-replication to mesoporous materials constructed with different framework compositions [4]. Recently, preparation of ordered mesoporous materials metal oxides via nano-replication method using mesoporous silicas as a template has been reported [5-6]. These efforts enabled the preparation of mesoporous materials with various framework compositions, which are believed to have inherent properties as catalytic, optical and electronic materials. Moreover, these mesoporous metal oxides prepared by nano-replication method possess regular mesopore and high surface area. This can lead great advantages for applications such as catalysis or sensing due to its extremely high ratio of the number of surface atoms to the number of bulk atom. In this work, we have used large mesoporous silica, KIT-6 as a template for the fabrication of mesoporous materials constructed with various metal oxides such as iron oxide and manganese oxide.

310

2. Experimental Section The mesoporous silica KIT-6 has been prepared by the self-assembly method using the Pluronic PI23 triblock copolymer (EO20PO70EO20) and tetraethyl orthosilicate (TEOS). 30 g of P123 was dissolved in the mixture of 1085 g distilled water, 30 g of «-butanol and 59 g of HC1 (35%). After stirring the solution for 1 hr, 64.5 g of TEOS is added to the homogeneous clear solution. This mixture is left under constant stirring at 35°C for 24 hrs. The precipitate was filtered, dried at 80 °C and finally calcined at 550°C. For the synthesis of mesoporous metal oxides, 0.4 g of metal precursors (FeCl3-6H2O, 98%, Mn(NO3)3-xH2O, 98%, Aldrich) was dissolved in 1.0 g of distilled water. These solutions were incorporated into 1.0 g of mesoporous silica template using the impregnation method. The impregnated samples were dried in an oven at 80°C for 1 d and calcined at various temperature ranges, from 300 to 700°C. The silica template was removed from the composites of silica and metal oxide by treating three times using 1 - 2 M NaOH aqueous solution 3. Result and Discussion X-ray diffraction (XRD) patterns in Fig. 1 show typical diffraction patterns of bicontinuous cubic Ia3d mesophases of mesoporous silica KIT-6, and replicated mesoporous metal oxides that were heated at 500°C before the removal of silica template. XRD results of mesoporous metal oxides show relatively weak peaks at low angle, which have similar d-spacing values with the mesoporous silica

1 |L||kfjJ|L^|

Fig. 1. XRD patterns of KIT-6 and mesoporous metal oxides replicated from the KIT-6.

template. The XRD peaks in the 29 ranges of 0.7 - 3° can be indexed to 211, 220, and 332 which are typical characteristics of bicontinuous cubic Ia3d mesophase. Wide-angle XRD patterns on the right side of Fig. 1 clearly show crystalline framework structures for the replicated metal oxides. The line-widths

311 Table 1. Physical property of mesoporous silica and mesoporous metal oxides Materials K.IT-6 Fe2O3 MnO,

(mVg)

Pore Volume (cc/g)

Unit cell Parameter (rim)

700 99 109

0.91 0.22 0.39

22.5 22.5 22.5

Surface Area

Pore Size (nm) 2.5 2.5

of XRD patterns are relatively broad similar with those of nanoparticles. The crystallite size of mesoporous metal oxides that calculated by Scherrer equation is estimated to be around 10 nm. Table 1 show the physical properties such as surface area, pore size, unit cell parameter and pore volume of mesoporous silica, FeÔ^ and MnO2. The mesoporous silica, K.IT-6 with BET surface area of 700 m2/g, total pore volume of 0.91 cc/g and BJH pore size of 8 nm, is replicated to mesoporous Fe2C>3 and MnO2. The replicated mesoporous Fe2C>3 and MnO2 materials (in Fig. 1) exhibit quite high BET surface area of 99 and 109 m2/g, and total pore volume of 0.22 and 0.39 cc/g, respectively. BJH pore sizes of mesoporous Fe2O3 and MnO2 are around 2.5 nm in diameter. One more interesting thing is that the particle morphology of replicated mesoporous metal oxides is quite different with that of sacrificial silica template.

Fig. 2. FESEM images of iron oxide(left) and manganese oxide(right)

Fig. 3. HRTEM images of iron oxide(left) and manganese oxide(right)

312

Even though the particles of mesoporous silica template are very irregular and pretty big, the replicated mesoporous metal oxides have spherical morphology with very uniform particle size about 100 nm in diameter as shown in FESEM images in Fig. 2. HRTEM images of mesoporous metal oxides in Fig. 3 clearly reveal that the not only the mesoscopic order but also the atomic crystallinity of the replicated mesoporous metal oxides showing three dimensional network topology of metal oxide nano rods. 4. Conclusion Ordered mesoporous silica is successfully converted to mesoporous materials with various framework composition by means of nano-replication technique. The mesostructural properties are maintained after the template removal and framework crystallinity can be controlled by annealing process before the removal of rigid and thermally stable mesoporous silica template. This nanoreplication route would be able to used as a facile method for the preparation of mesoporous materials constructed with various crystalline frameworks, which would have intense potentials for the practical applications. 5. Acknowledgement The authors thank to the Korea Research Foundation Grant funded by the Korean Government (MOEHRD, KRF-2005-005-J11901). 6. References [1] F. Kleitz, S. H. Choi and R. Ryoo, Chem. Commun. (2003) 2137. [2] C. T. Kresge, M. E. Leonowicz, W. J. Roth, J. C. Vartuli and J. S. Beck, Nature 359 (1992) 710. [3] D. Zhao, J. Feng, Q. Huo, N. Melosh, G. H. Frendrickson,. F. Chmelka and G. D. Stucky, Science 279 (1998) 548. [4] M. Kang, S. H. Yi, H. I. Lee, J. E. Yie and J. M. Kim, Chem. Commun. (2002) 1944. [5] S. C. Laha and R. Ryoo, Chem., Commun. (2003) 2138. [6] B. Tian, X. Liu, H. Yang, S. Xie, C. Yu, B. Tu and D. Zhao, Adv. Mater. 15 (2003) 1370.


313 313

A novel synthesis of manganese oxide nanotubes Li Taoa, Cheng-Gao Suna, Mei-lian Fan3, Cai-Juan Huang3, He-Sheng Zhaib, Hai-Long Wu3 and Zi-Sheng Chao3* "College of Chemistry and Chemical Engineering, Key Laboratory of Chemometrics & Chemical Biological Sensing Technologies, Ministry of Education, Hunan University, Changsha 410082, P. R. China bCollege of Chemistry and Chemical Engineering, Xiamen University, Xiamen, 361005, P. R. China

This paper presents a novel redox-assisted supramolecular assembly of manganese oxide nanotubes, using KMnO4 and MnCl2 as inorganic precursors, polyoxyethylene fatty alcohol (AEO9) a template and acetaldehyde an additive, under hydrothermal condition. The nanotubes were characterized by XRD, TEM, BET, XPS and Raman spectroscopy. The results reveal that the nanotubes have an average inner diameter of ca. 14.7 nm, an average wall thickness of ca. 2 nm, and a length of over several hundreds nanometers, with the walls consisting of monoclinic manganite crystals. 1. Introduction Nanostructured manganese oxides are of considerable scientific interests, because of their versatile applications in the fields of adsorption, catalysis, batteries and functional materials [1-4]. Microporous manganese oxides have been prepared via soft-chemistry routes [5-7] and mesoporous manganese oxides by either a transformation of layered manganese oxides [8] or a supermolecular assembly process [9, 10]. It was also reported recently that nanofiberious Na-birnessite could be synthesized from an oxidation of MnCl2 by K.M11O4 [10] and manganese oxide nanotubes by cyclic voltammetric electrodeposition [2], In this work, we address the synthesis of manganese oxide nanotubes via a novel route of redox-assisted supramolecular assembly.

314

2. Experimental Section Polyoxyethylene fatty alcohol, namely AEO9, acetaldehyde and MnCl24H2O were dissolved into deionized water, forming a clear solution, into which a KMnO4 aqueous solution was then dropwise introduced under strong agitation. The gel obtained had a molar composition of 4.4 KMnO4: 4.4 MnCI2: 1.5 CH3CHO: 1.0 AEO9: 500 H2O. After treating hydrothermally the gel at 373 K for 24 h, precipitate was recovered by filtration and washed with deionized water. To remove the surfactant, the wet filter cake was dispersed into ethanol and refluxed for 6 h. The specimen was dried at 333 K for 10 h and then cooled to room temperature. The characterizations were performed via XRD (Bruker D8 Advance Diffractometer; Cu Kcd), XPS (Phi Quantum 2000 Scanning ESCA Microprobe; Al Ka), TEM and SAED (FEI Tecnai F30 Field Emitting HRTEM; accelerating voltage 300 kV), N2 adsorption-desorption at 77 K (Beckman Coulter SA3100) and Raman spectrcopy (LABRAM-010). 3. Results and Discussion 28=0J604

1.0

1.5 2.0 2.5 3.0

2-Thefci

20

30

40

50

2-Thefci

Fig. 1. XRD spectra of the manganese oxide nanotubes. (a) for low angle; (b) for high angle

The XRD patterns of manganese oxide nanotubes are shown in Fig. 1. An obvious diffraction peak occurs at 29 = 0.604° with a d-spacing of 14.6 nm in the low angle range (Fig. la), indicating the presence of a mesophase that may be constructed via the Fig. 2. SAED pattern and TEM micrographs of the orientated arrangement manganese oxide nanotubes. (a) SAED pattern (b) TEM of the manganese oxide nanotubes in axial direction. A group of diffraction peaks in the high angle range of 20-60° (Fig. lb) coincides with that of

315

monoclinic manganite (MnO(OH); cell parameter: a = 5.300, b = 5.278, c = 5.307, and p = 114.36) [11]. Fig. 2 shows the TEM micrographs and the selected area electron diffraction (SAED) pattern of the nanotubes. It reveals that the nanotubes have an average outer diameter of ca. 16.8 nm, the inner diameter of ca. 14.7 nm, and a length of above several hundred nanometers. The indexing of the SAED pattern suggests a rhombic tetrahedral crystalline structure of the nanotube wall. The N2 adsorption-desorption isotherm is shown in Fig.3, which indicates the presence of the mesostructure. The specific surface area of the specimen was determined to be 69.546 m2/g.

I' an

1 •3

•S

sea

-• sij

IOOO

uso

ism

ITSO

Wavenumber cm-1 Fig. 3. N2 adsorption-desorption isotherm curve of the manganese oxide nanotubes.

Fig. 4. Raman spectrum of the manganese oxide nanotubes

The Raman spectrum of the nanotubes is shown in Fig. 4. The peaks at ca. 660 and 320 cm'1 can be ascribed to the Mn-O vibrations in Mn(III) compounds [12-15]. This result provides further a proof to the conclusion, drawn by the XRD experiment, that the walls of the nanotubes consists of monoclinic manganite crystals. The Mn 2p XPS result indicates that the Mn 2pi/2 and Mn 2p3/2 peak has a binding energy (B.E.) of 652.5 and 641.28 eV, respectively. The B.E. of Mn 2p3/2 is often employed to estimate the oxidation state of manganese [16] It is found that the B.E. of Mn 2p3/2 in the manganese oxide nanotubes we synthesized is ca. 0.3-0.5 eV lower than those of Mn3+ for Mn2O3 [17] and MnO(OH) [17]and ca. 0.68 eV higher than that of Mn2+ for MnO [17], being different from those for the manganese oxides with a nanotubular2 or particulate [4,18] morphology reported in literatures. This results indicates that the nanotubes consist of the Mn(III) species and possess a high tendency to lose electrons. It is deduced that both the nano-tubular morphology and the crystalline phase of the monoclinic manganite in the nanotube walls, presented by our specimen, are responsible for the relatively "free" transportation of

316

electron and in turn the comparatively low energy necessitated for exciting electrons off the nanotube surface. 4. Conclusion we have synthesized the manganese oxide nanotubes using a redox-assisted supramolecular assembly route, using Mn7+ and Mn2+ compounds as inorganic procursors, AEO9 a surfactant, and acetaldehyde an additive. The walls of the nanotubes consist of the monoclinic manganite crystals, of which manganese is in a pure +3 valent state, being different from those reported in literatures. The photoelectron performance of the nanotubes, revealed by the XPS and Raman measurements, suggests their promising potential applications as functional materials relating with electron transportation. 5. Acknowledgment This work was supported by the Program for New Century Excellent Talents in University, the Ministry of Education of P.R. China, and the Program for FuRong Scholar in Hunan Province, P.R. China. 6. References [1] [2] [3] [4] [5] [6] [7] [8] [9] [10] [11] [12] [13] [14] [15] [16] [17] [18]

F. Caruso, Adv. Mater. 13 ( 2001) 11. M. S. Wu, J. T. Lee, Y. Y. Wang and C. C. Wan, J. Phys. Chem. B, 42 (2004) 16331. J. Chen, J. C. Lin, V. Purohit, M. B. Cutlip and S. L. Suib, Catal. Today, 33 (1997) 205. O. Giraldo, S. Brock, M. Marquez and L. S. Suib, J. Am. Chem. Soc, 122 (2000) 9330. S. L. Brock, N. Duan, Z. R. Tian, O. Giraldo, H. Zhou and S. L. Suib, J. Chem. Mater., 10 (1998)2619. J. K. Yuan, L. Kate, Q. H. Zhang and S. L. Suib, J. Am. Chem. Soc, 125 (2003) 4966. X. L. Hong, G. Y. Zhang, Y. I. Zhu and H. Q. Yang, J. Mater. Res. Bull., 38 (2003) 1695. J. Luo and S. L. Suib, Chem. Commun., (1997) 1031. X. Hong, G. Y. Zhang and H. Y. Zhu, in: Proceedings of the 7th International Conference on Surfactants & Detergents, Shenzhen, China, (2002). S. Ching, J. A. Landrigan, M. L. Jorgensen, N. Duan and S. L. Suib, Chem. Mater. 7 (1995) 1604. T. Rziha, H. Gies and J. Eur. Rius, J. Mineral., 8 (1996) 675. AIST Raman Spectra Database of Minerals and Inorganic Materials, http://www.aist.go.jp/RIODB/rasmin F. Buciuman, F. Patcas, R. Cracium and R. T. D. Zhan, J. Phys. Chem. Chem. Phys., 1 (1999)185. R. Radhakrishnan and S. T. Oyama, .1. Phys. Chem. B, 105 (2001) 4245. B. J. Aronson, C. F. Blanford and A. Stein, J. Phys. Chem. B, 104 (2000) 449. W. Li, G. V. Gibbs and S. T. Oyama, J. Am. Chem. Soc.,120 (1998) 9041. NIST X-ray Photoelectron Spectroscopy Database NIST Standard Reference Database 20, Version 3.4 (Web Version http://srdata.nist.gov/xps/). S. C. Pang and M. A. Anderson, J. Mater.Res., 15 (2000) 2096.


317 317

Synthesis of well ordered crystalline TiO2 photocatalyst with enhanced stability and photoactivity Zhenfeng Bian,a Jian Zhu b and Hexing Li*a "Department of Chemistry,Shanghai Normal University, Shanghai 200234 b Laboratory of Molecular Catalysis and Innovative Materials, Department of Chemistry, Fudan University, Shanghai 200433, P. R. China

Mesoporous TiO2 was successfully synthesized using a modified evaporation induced self-assembly (EISA) method. We find that doping proper La2O3, mesoporous TiO2 can enhance the thermal stability and also enhance its photocatalytic activity. Key words: Mesoporous TiO2, thermal stability, photocatalytic activity. 1. Introduction Photocatalysis has been widely used to mineralization organic compounds as environmental pollutants. Perhaps, TiO2 is the most frequently used photocatalysts owing to its cheapness, stability, and nontoxicity etc [1]. However, the low quantum efficiency seems a problem for its practical application. It has been proved that the photocatalytic performance of TiO2 is strongly correlated to the anatase/rutile ratio, crystallization degree of anatase, the surface area, the porous structure, lattice defects and oxygen vacancy etc [24], which obviously depend on the preparation methods and conditions as well as the modification of TiO2 [5-6]. One of the promising ways is to design the mesoporous TiO2 with large surface area and well ordered pore structure which might enhance light absorbance and also facilitate the transfer and adsorption of reactant molecules [7-9]. However, the mesoporous TiO2 usually exhibits very poor crystallization degree of anatase phase. Thus, calcination is essential to enhance the crystallization degree of anatase [10-12]. But, such heating treatment may inevitably induce the collapse of pore [13-15]. In this work, Ladoped mesoporous TiO2 was synthesized via a modified evaporation induced self-assembly (EISA) method which could undergo a heating treatment even at

318

550°C to obtain highly crystallized anatase without significant damage of the ordered porous structure and thus, exhibited much high activity than the corresponding undoped TiO2 during photocatalytic degradation of phenol. 2. Experimental Section 2.1. Sample preparation The La-doped TiO2 was prepared according to the following procedures. A mixture containing 1.0 g P123, 12 g ethanol, 1.7 g TiCl4, 3 g Ti(OBu)4, and certain amount of La(OAc)3 was stirred vigorously for at least 5 h at 0°C. The resulted transparent sol was transferred into a Petri dish to form a uniform thin layer. After being aged at 40°C for 24 h, the precursor was heated sequentially at 100, 150, 200, 250, 300°C, each for 12 h. The final sample was obtained by calcination at a desired temperature for 4 h and was denoted as TiO2-n-T, where n refers to La/Ti molar ratio(0~1.8%) in the initial mixture and T refers to the calcination temperature. 2.2. Characterization X-ray diffraction (XRD) patterns of all samples were collected on the Rigaku D/MAX-2550 ( CuKa 1 irradiation). Transmission electron microscopy (TEM) images were recorded on the JEOL JEM2011. Nitrogen adsorption-desorption isotherms were measured at 77 K on the Quantachrome NOVA 4000e from which surface area and porosity were calculated by BJH method. The light absorbance-emission ability were evaluated by using the photoluminescence spectra (PLS, Varian Cary-Eclipse 500). 2.3. Activity test The photodegradation of phenol in aqueous solution was chosen as a probe to evaluate the activity of the as-prepared TiO2-n-T samples. The reactions were carried out at 30°C using 50 ml 0.1 g/1 phenol and 0.05 g TiO2-n-T under vigorous stirring and irradiation with four 8 W UV lamps with characteristic wave length of 254 nm for 3 h. 3. Results and Discussion The low-angle powder XRD patterns revealed that both the undoped and Ladoped TiO2 samples displayed well ordered 2D-hexagonal mesostructure when they were calcinated at relatively low temperature. The N2 adsorptiondesorption measurements further confirmed that these samples show type-IV isotherms indicative of mesoporous structure [16]. The BJH pore-size analyses

319

performed on the desorption branch show that the average pore diameter calculated by BJH model matches well with the result measured from TEM image. The specific surface area of each sample is calculated by the multi-point Brunauer-Emmett-Teller (BET) method. The surface area reaches 120 m2g"! at 550°C. Treatment at 500°C of pure TiC>2 resulted in a complete destroy of the mesostructure. However, the La-doped TiO2(La/Ti = 0.36%) may still retained ordered mesoporous structure even after being treated at 550°C, showing the stabilizing effect of the La-dopant. This could be further confirmed by TEM characterizations.

Fig. 1 TEM images of different TiO2-n-T samples, (left two images) A

R

A R R

R AA

* f l J i ', AR R

AR

A

AA

R

650 A

Relative Intensity / a.u.

Relative Intensity / a.u.

TiO 2 R

A A 650 550

550 450

J

40

2Theta /

50 O

60

R

AA

A

AA

AA A

450 350

. A . . A . A 350 *° A 30

TiO2-0.36

10

20

30

40

50

2Theta/

60

70

80

o

Fig. 2 Wide angel XRD patterns of undoped and La-doped TiO2 treated at elevated temperatures, (right two images)

As shown in Fig. 1, the pure TiC>2 could remain its ordered structure only if the calcination temperature was below 500°C. While, well ordered mesoporous structure could still be observed even after calcination at 550°C. The stabilizing effect of the La-dopants could be attributed to its bigger size(0.1016 nm) than the Ti4+ (0.068 nm) [17]. Thus, the La-dopants could not replace Ti4+ inside the TiC>2 framework and were present mainly on the external surface of the TiC>2. These La2C>3 species could effectively prevent the collapse of mesoporous structure. The wide angle XRD patterns, as shown in Fig. 2, revealed that the crystallization degree of anatase increased with the increase of calcination temperature. The rutile phase appeared when the undoped TiC>2 was calcinated at the temperature above 350°C. While, no significant transformation from anatase to rutile phase appeared in the the La-doped TiC>2 sample (La/Ti = 0.36%) even when the sample was calcinated at 650°C. These results

320

demonstrated that the La-modification of TiO2 could effectively inhibit the formation of rutile phase when treated at high calcination temperature which was essential to obtain high crystallization degree of anatase. Fig. 3 shows the activities of both the undoped TiO2 and La-doped TiO2 samples during liquid phase phenol photocatalytic degradation. The activity of the La-doped TiO2 (La/Ti = 0.36%) first increased and then decreased with the increase of calcination temperature. The optimal calcination temperature was determined as 550°C. On one hand, the increase of calcination temperature could enhance the crystallization degree of anatase which was favorable for photocatalysis. On the other hand, the increase of calcination temperature may result in the decrease of surface area and even the damage of mesoporous structure. Meanwhile, rutile phase may appear at very high calcination temperature. These factors are unfavorable for the photocatalysis and thus, could account for the decrease of activity. Considering the effect of La-dopant, one could see that the photocatalytic activity first increased and then decreased with the increase of the amount of the La-dopant. The TiO2-0.36-550 exhibited the highest photocatalytic activity. The promoting effects of the La-dopant could be understood by considering the following factors. (1) The modification of the La-dopants may increase the crystallization degree of anatase, as shown in Fig. 2, which may facilitate the transfer of photo-generated holes and electrons and inhibit their recombination. (2) According to the PLS spectra, the La-modification may increase the emission peak of TiO2 around 382 nm corresponding to the increase of more oxygen vacancies and/or structural defects which could prevent the recombination between photo-generated holes and electrons. Meanwhile, the La-modification resulted in the decrease in the dual-frequency peak of TiO2 around 558 nm, indicating its absorbance ability for UV light increased after La-modification, which may induce more photogenerated holes acted as photocatalytc centers. (3) The a-modification could stabilize TiO2 from either the damage of mesoporous structure which may remain the surface and well ordered porous channels or the transfer to rutile phase. As well known, the high surface area may facilitate the adsorption of phenol molecules by the catalysts and the ordered pore channels would be favorable for the diffusion of both the reactants and products. Meanwhile, the anatase phase exhibit much higher activity than the rutile and thus, inhibition the transfer from anatase phase to rutile may inhibit the decline of photocatalytic activity. These results clearly demonstrated that modification of suitable amount of the La-dopants may enhance the quantum yield of TiO2 in photocatalysis [18]. However, too much La2O3 was harmful for the activity, possibly due to the coverage of too many active sites. Meanwhile, high amount of La2O3 may serve as the center for the recombination between photo-electrons and photo-holes, resulting in the decrease of quantum efficiency in photocatalysis. Detailed studies are still being underway.

321 100

100

B

90

Phenol degradation ratio %

Phenol degradation ratio %

A

80

70

60 300

400

500 500

600

Calcined Temperature /°C / oC

7700 0

0

90 80 70 60

1.8 0.0 0.2 0.4 0.6 0.8 1.0 1.2 1.4 1.6 1.8 La/Ti (%)

Fig. 3 Dependence of photocatalytic activity on (A) calcination temperature over the TiO2-0.36 and (B) The amount of the La-dopant after being treated at 550 °C for 3 h.

4. Conclusion The TiO2 sample prepared by EISA exhibited well ordered mesoporous structure and crystallized anatase phase. Doping TiO2 with La2O3 can increase both the structural and anatase phase stabilities against heating treatment at high temperature and in turn, could enhance its photocatalytic activity. The optimum calcination temperature was determined as 550°C and the optimum amount of the La-dopant was determined as 0.36%. The roles of both the calcinations temperature and the La-modification could be explained by considering the crystallization of anatase, the surface area, the porous structure, both the oxygen vacancies and surface defects, and the phase transformation between anatase and rutile, which were related with the quantum efficiency of photocatalysis. 5. Acknowledgment This work was supported by the National Natural Science Foundation of China (No. 20377031), the Shanghai Leading Academic Discipline Project (No. T0402), the Natural Science Foundation of Shanghai Science and Technology Committee (Nos. 02DJ14051, 0452nm070, 05QMX1442, 0552nm036), and the Shanghai Eduction Committee (No. 05DZ20). 6. References [1] J. G. Yu, J. C. Yu, M. K. P. Leung, W. K. Ho, B. Cheng, X. J. Zhao and J. C. Zhao, J. Catal. 69(2003)217. [2] J. C. Yu, J. G. Yu, W. K. Ho and L. Z. Zhang, Chem. Commun. (2001) 1942. [3] J. C. Yu, J. G. Yu, W. K. Ho and J. C. Zhao, J. Photochem. Photobiol. A 148 (2002) 263. [4] J. G. Yu, J. C. Yu, W. K. Ho and Z. T. Jiang, New J. Chem. 26 (2002) 607.

322 [5] H. X. Li, G. S. Li, J. Zhu and Y. Wan, J. Mol. Catal. A: Chemical 226 (2005) 97. [6] H. X. Li, J. Zhu, G. S. Li and Y. Wan, Chem. Letter. 33 (2004) 574. [7] J. C. Yu, X. C. Wang, L. Wu, W. K. Ho, L. Z. Zhang and G. T. Zhou, Adv. Funct. Mater. 14(2004)1178. [8] X. C. Wang, J. C. Yu, H. Y. Yip, L. Wu, P. K. Wong and S. Y. Lai, Chem. Eur. J. 11 (2005) 2997. [9] B. Smarsly, D. Grosso, T. Brezesinski, N. Pinna, C. Boissiere, M. Antonietti and C. Sanchez, Chem. Mater. 16 (2004) 2948. [10] E. Beyers, P. Cool and E. F. Vansant, J. Phys. Chem. B 109 (2005) 10081. [11] K. S. Liu, H. G. Fu, K. Y. Shi, F. S. Xiao, L. Q. Jing and B. F. Xin, J. Phys. Chem. B 109 (2005) 18719. [12] J. C. Yu, X. C. Wang and X. Z. Fu, Chem. Mater. 16 (2004) 1523. [13] P. C. A. Alberius, K. L. Frindell, R. C. Hay ward, E. J. Kramer, G. D. Stucky and B. F. Chemlka, Chem. Mater. 14 (2002) 3284. [14] H. Shibata, T. Ogura, T. Mukai, T. Ohkubo, H. Sakai and M. Abe, J. Am. Chem. Soc. 127 (2005) 16396. [15] E. Beyers, P. Cool and E. F. Vansant, J. Phys. Chem. B 109 (2005) 10081. [16] S. J. Gregg and K. S. W. Sing, Adsorption, Surface Area and Porosity, Academic Press, London, (1997)111. [17] C. P. Sibu, S. K. Kumar, P. Mukundan and K. G. K. Warner, Chem. Mater. 14 (2002) 2876. [18] W. Xu, Y. Gao and H. Q. Liu, J. Cata. 207 (2002) 151.


323 323

Crystallization of stable mesoporous zirconia and ceria-zirconia Anil K. Sinha and Kenichirou Suzuki Toyota Central R&D Labs Inc., Nagakute-4801192, Aichi, Japan

Crystallization of Mesoporous zirconia and ceria-zirconia structures were realized using a long-chain amine template. By controlled heating of the synthesis gel it was possible to prepare well-crystalline mesoporous strctures for these materials. The surface areas, mesopore ordering and thermal stabilities of the final product is dependent on the composition, ageing and heating condition for the precursor gel. 1. Introduction Ceria and zirconia based materials have received enormous attention due to their applications in various fields such as high temperature ceramics, catalysis and solid oxide fuel cells [1]. CeO2-ZrO2 is a well-known additive in the socalled three-way catalysts for automobile exhaust [2]. Pure ceria is known to be poorly thermostable and undergoes rapid sintering under high temperature conditions, thereby loosing oxygen buffer capacity [3, 4]. It has been more than ten years since our laboratory discovered that the addition of ZrO2 to CeO2 enhances oxygen storage capacity (OSC) as well as thermal stability [5, 6]. Following this discovery, CeO2-ZrO2 has been widely utilized for commercial catalysts. High surface area ceria and ceria-zirconia as well as their mesoporous structure have been prepared by different methods. Such materials by virtue of their large surface area exhibit greater catalytic activity. With the preparation in 1991 of mesoporous silica a new area of chemistry, allowing the exploitation of high surface area materials, was opened up [7]. This silica-based synthesis has been extended to a number of transition metal and main group oxides using various surfactants and inorganic precursors under different reaction conditions [8, 9]. Accordingly, several studies report the fabrication of mesoporous crystalline ceria [10-12]. However, the ceria, zirconia and ceria-zirconia

324

mesostructures often undergoes a severe breakdown throughout the final crystallization step, which leads to rather ill-defined porosity without controlled nanocrystallinity in the pore walls, in terms of the spatial distribution and the size of the oxide nanocrystals. Here in we report a method to prepare mesoporous zirconia and ceria-zirconia using a modified sol-gel route to obtain highly crystalline and stable mesoporous materials. 2. Experimental Section It was possible to prepare stable and crystalline mesoporous zirconia and ceria-zirconia by modified sol-gel method in mixed propanol-water medium, hexadecylamine template, triethanolamine additive and zirconium butoxide/zirconium isopropoxide, cerium acetate precursor. In a typical synthesis of mesoporous zirconia, 2 g of hexadecylamine (Wako) was dissolved in 6 g of propanol (Wako) followed by the addition of 2.1 g of zirconium isopropoxide (75% solution in 1-propanol, Wako). Finally 0.31 g of triethanol amine (Aldrich) was added. The resulting solution was vigorously stirred to obtain a homogeneous gel. The gel was aged at 50-70°C for 7 days followed by heat treatment at 120-200°C (l°C/min.) for 12 h. The sample was finally calcined by heating gradually (l°C/min.) to 400-500°C. Mesoporous ceriazirconia was also prepared in a similar way, adding cerium acetate, (CH3CO2)3Ce.H2O (Wako) prior to the addition of Zr orecursor to the synthesis mixture. The powder X-ray diffraction (XRD) patterns were obtained on a Rigaku Rint - 2400 instrument equipped with a rotating anode and using Cu Ka radiation (wavelength = 0.1542 nm). Nitrogen adsorption/desorption isotherms were obtained at -77 K on a Micromeritics ASAP 2010 apparatus to determine the total specific surface area (SBET), pore volume and pore size distribution of the samples. Transmission electron microscopy (TEM) observations were made using a JEOL JEM200CX instrument. Scanning electron microscopy (SEM) observations were made using a Hitachi S-55OO FE-SEM instrument. 3. Results and Discussion When the mesoporous zirconia precursor-gel was heated, upto 200°C the mesoporous structure was not crystallized completely yet as shown in fig. 1 and wide angle XRD shows that there is no crystalline phase present in the material. But when the sample was gradually heated (at 1°C /min.) to 450°C a well crystalline mesoporous material is obtained as indicated by XRD analysis. In higher 29 range 20-60° broad peaks are observed which could be assigned to the cubic zirconia phases (Fig. la). This implies that in the present synthesis, the evaporation induced self assembly of zirconia into a mesoporous structure assisted by the amine template is enhanced by increasing the crystallization temperature beyond 200°C.

325

In the case of mesoporous Ceria-Zirconia till 1-5 days of crystallization a low intensity broad peak at low angle was observed indicating gradual formation of mesostructure with increasing ageing time (Fig. 1 b). After 15 days 2.9 nm (b) d = 2.9 (b)

.2 nm d=7.2

(a) (a)

OC 450 450OC

/

Template-free

J.

/

V

t&c c

11

,

20 40 50 60 20 30 30 40 50 60

d=3.2 nm

\

15 Days Days v

22

33

44

Intensity (a.u.)

Intensity (a.u.)

10 10

55

20 20 25 25 30 30 35 35 40 40 45 45 50 50 55 55 60 60 65 65 70 70 75 75

22θ θ

10 10

20 60 20 30 30 40 40 50 50 60

Figure 1. XRD patterns of (a) mesoporous zirconia crystallization, (b) mesoporous ceria-zirconia crystallization.

1 5 Days Days

H\

o

Intensity (a.u.)

200 C

2

20

4

25

6

30

8

10

35

40

22θ θ

12

45

2

14

50

V

16

55

4

66

A

88

10

11 Day Day

H 2

44 2Q 66 2θ

88

10 10

3

Volume adsorbed (cm /g)

of crystallization a well crystalline mesoporous material was obtained as indicated by XRD analysis. In higher 20 range 20-60° broad peaks are observed which could be roughly assigned to semicrystalline tetragonal ceria-zirconia phases. After template removal by extraction with ethanol at 70°C followed by drying at 120°C and then calcination to 500°C there is considerable increase in XRD crystallinity along with decrease in d140 spacing (about 0.3 nm) due to appreciable lattice contraction after template removal. 120 Thus, unlike in case of mesoporous zirconia, mesoporous ceria-zirconia could luu -a 100 be formed at lower temperature (70°C) but -o f o "| .Q obtained only after prolonged ageing (about 80 o CA 15 days). CC The 500°C calcined mesoporous zirconia CD 60 E and ceria-zirconia materials showed surface _3 2 o 40 10 15 15 20 0 55 10 areas of 176 and 193 m /g respectively. The Pore size (nm) Pore (nm) materials showed N2 adsorption-desorption 1.0 0.0 0.2 0.4 0.6 0.8 1.0 isotherm of type IV, typical of mesoporous Relative Pressure Pressure P/Po Relative materials with step in the adsorption curve Figure 2. N sorption isotherm of mesoporous ceria-zirconia. between partial pressures P/Po of 0.3 to 0.8, 100

dv/drp

80 60 40 20 0

2

326 326

and a large hysteresis loop, due to capillary condensation in the mesoporous channels and/or cages and mean pore size of 2.0 nm (for mesoporous ceria-zirconia, Figure 2). TEM (fig. 3) and FE-SEM (Fig.4) analyses clearly showed the presence of disordered mesoporosity in these materials. High-resolution TEM (Fig. 3 inset) clearly shows that mesopore walls are made up of well-crystalline ceria-zirconia with less than 10 nm size average particle size.

2 nm 10 nm

Figure 3. TEM of mesoporous ceria-zirconia

4. Conclusion It was possible to prepare stable mesoporous zirconia and ceria-zirconia by a modified sol-gel procedure. Long crystallization time for the ceria-zirconia and higher crystallization temperature for zirconia was necessary to obtain such stable crystalline mesoporous structures.

10 nm

Figure 4. FE-SEM of mesoporous ceria-zirconia

5. Acknowledgement We thank N. Suzuki for TEM analysis, J. Seki for FE-SEM analysis and R. Asahi for helpful suggestions. 6. References [1] [2] [3] [4] [5] [6] [7] [8] [9]

[10] [11] [12]

A. Trovarelli, Catal. ReV. Sci. Eng. 38 (1996) 439 and references therein. J. G. Nunan, H. J. Robota, M. J. Cohn and S. A. Bradley, J. Catal. 133 (1992) 309. A. Laachir et al. J. Chem. Soc., Faraday Trans. 1 87 (1991) 1601. J. E.Kubsh, J. S. Rieck and N. D. Spencer, Stud. Surf. Sci. Catal. 71 (1994) 109. M. Ozawa, et al. : Japanese unexamined patent pub., 116741(1988), (in Japanese) M. Ozawa, et al. J. Alloys Comp., 193 (1993) 73. C. T. Kresge, M. E. Leonowicz, W. J. Roth, J. C. Vartuli and J. S. Beck, Nature, 359 (1992)710. A. Sayari, Microporous Mater., 12 (1997) 149. D. Yang, D. Y. Zhao, D. 1. Margolese, B. F. Chmelka, G. D. Stucky, Nature, 396 (1998) 152; .1. Y. Zheng, J. B. Pang, K. Y. Qiu and Y. Wei, Microporous Mesoporous Mater., 49 (2001) 189. M. Lundberg, B. Skarman, F. Cesar and L. R. Wallenberg, Microporous Mesoporous Mater. 54 (2002) 97. D. Terribile, A. Trovarelli, J. Llorca, C. Leitenburg, G. Dolcetti, J. Catal. 178 (1998) 299. D. M. Lyons, K. M. Ryan and M. A. Morris, J. Mater. Chem., 12 (2002) 1207.


327 327

Synthesis of mesoporous structures zinc sulfide by assembly of nanoparticles with block-copolymer as template Hongmei Ji,a Jieming Cao,* aJinsong Liu,a Mingbo Zheng,a Yongping Chen,a Yulin Cao a and Nongyue Heb " Nanomaterials Research Institute, College of Material Science and Technology, Nanjing University of Aeronautics and Astronautics, Nanjing 210016, PR China jmcao@nuaa. edu. en b Chien-Shiung Wu Laboratory, Southeast University, Nanjing 210096, China

1. Introduction Since the discovery of M41S family of silicas at Mobil in 1992 [1, 2], much research has been reported on the synthesis of mesoporous materials. The mesoporous materials with different compositions, new pore systems and novel properties have attracted considerable attentions because of their remarkably high surface area, narrow pore size distributions, which make them ideal candidates for catalysts, sorbents and drug delivery system [3]. In recent years, development of the mesoporous materials has been extended from oxide to chalcogenide mesostructured materials. Chalcogenide mesostructured materials were synthesized by using their nanoparticles as the building blocks and employing different surfactants as the structure-directing agents [4, 5]. As a kind of chalcogenide materials, nanosized ZnS materials have received increasing attention due to their unique electronic and optical properities, and their potential applications in light-emitting diode (LED), electrochemical devices, infrared window materials and phosphors for cathoderay tubes. To the best of our knowledge, only Henri Kessler's group synthesized nanosized zinc sulfide in the presence of cationic surfactants at room temperature [6] and a sonochemical technique was used to synthesize ZnS mesoporous network with dodecylamine as templating agent [7]. They both employed low molecular weight surfactants as structure-directing agents in order to obtain the ZnS mesoporous structure. Herein we describe the synthesis the mesoporous ZnS first by using amphiphilic poly (alkylene oxide) block-copolymer EO2Q

328

PO70EO20 as a structure-directing agent through novel alcohothermal method. The obtained products had a high BET (Brunauer-Emmett-Teller) surface area and narrow pore size distribution. And the specific surface area of the ZnS products remained high even after treated at 800°C. 2. Experimental Section In a typical synthesis process, 0.5 g of P123 was dissolved in 10 mL of ethanol and to this a solution of Zn(CH3COO)2-2H2O (0.0046 mol) in 5 mL ethanol was added dropwise. After stirring for 30 min, 8 mL of 0.58 M thioacetamide (TAA) was added into the above solution with further stirring to form a white emulsion. The resulting solution was transferred into a 30ml Telflon-lined stainless steel autoclave. The autoclave was sealed and maintained at 90°C for 10 h, then cooled into the room temperature naturally. The products removed from autoclave were collected by centrifugation and washed with thermal ethanol several times to remove the surfactant, and vacuum-dried at 50°C to obtain the white samples. The products were characterized by means of X-ray diffraction (XRD), Transmission electron microscopy (TEM), and nitrogen physisorption. 3. Results and Discussion

(a)

(111)

I

Jl

10

20

30

40

(220) A

(300)

50

2Theata(Degree)

60

70

80

4 6 2Theata (Degree)

Fig. 1. Powder X-Ray diffraction patterns of the template-extracted mesostructure ZnS sample (a) wide angle and (b) low angle.

Fig. 1 shows the X-ray diffraction (XRD) patterns of the ZnS products after extraction by the thermal ethanol. In the wide-angle of the X-Ray pattern (Fig.la), the observed three diffraction peaks correspond to (111), (220), and (311) planes, respectively, which could be indexed as the cubic sphalerite ZnS according to the JCPDS cards. The XRD pattern of Fig. l(b) shows a highintensity peak at low reflection angle near 20 = 1.1°, which indicates the lattice spacing d = 8.0 nm. However the single intense peak at high d-spacing in the

329

XRD was demonstrated that the products were short-range symmetry, which was in agreement with the results of other two reports about the meso-structure ZnS [6, 7], mesoporous alumina [8], hexagonal mesoporous silica HMS-type materials [9] and some other previous work [10]. We also performed TEM examination (Fig. 2). The as-prepared products are well-dispersed particles, and the TEM images of the sample show that the diameter of the particles produced is basically in the range of 4-10 nm and the particles have a mesoporous structure with a pore size of about 3-5 nm, and the mesophase is less of long-order.

Fig. 2. TEM images of the obtained ZnS products with (a) low and (b) high magnification.

Volume Adsorbed cm3 / g)

160 140

(a)

ZnS ZnS-500 ZnS-800

0.010

ZnS ZnS-500 ZnS-800

dV/dD

180

120

(b)

100 80

0.005

60 40 20 0 0.0

0.2

0.4

0.6

Relative Pressure (P/ P0)

0.8

1.0

2

4

6

Pore Diameter (nm) (nm)

8

10

Fig. 3. N2 adsorption-desorption results of samples treated at different temperature (a) N 2 adsorption desorption isotherms and (b) pore size distribution curves.(ZnS as the templateextracted sample, ZnS-500 as the products calcined at 500°C, ZnS-800 as the products calcined at 800°C)

Typical nitrogen adsorption-desorption isotherms and the corresponding pore size distribution for the products are shown in Fig. 3. The results could be

330

identified as a type IV isotherm. The BET (Braunauer-Emmett-Teller) surface area of the template-extracted ZnS sample was measured as 252 m2/g and this value was bigger than that of the mesostructured zinc sulfide reported previously. After calcined at 500 and 800°C, the BET surface area of the treated products ZnS-500 and ZnS-800 is decreased to 113 and 99 m2/g, respectively. It should be noted that our samples have the potential application at relatively high temperature. With the increasing of heating temperature the pore distribution of the products become broad and the peak of the pore size distribution curve in 3.8 nm decrease. The high temperature treatment lead to the formation of larger pore and reduce the fraction of smaller pore. These changes may be due to the agglomeration of nanoparticles during calcinations. 4. Conclusion In conclusion, we have demonstrated a solvothermal route for the formation of mesostructured ZnS. As a structure-directing agent, the block-copolymer PI23 played an important role in the reaction process. It induced the ZnS nanoparticles to assemble into mesoporous structure and the remaining surfactant after extracting process could prevent the nanoparticles aggregating in the framework. Although in our experiment the obtained products are not long-range symmetry, they still have high specific surface area and narrow pore size distribution, which would provide us with many opportunities for some potential applications as advanced materials. 5. References [1] C. T. Kresge, M. E. Leonowicz, W. J. Roth, J. C. Vartuli and J. S. Beck, Nature, 359 (1992) 710. [2] J. S. Beck, J. C. Vartuli, W. J. Roth, M. E. Leonowicsz, C. T. Kresge, K. D. Schmitt, C. T. W. Chu, D. H. Olson, E. W. Shepard, S. B. McCullen and J. B. Higgin, J. Am. Chem. Soc, 114(1992)10834. [3] X. He and D. Antonelli, Angew. Chem., Int. Ed., 41 (2001) 214. [4] B. J. Scott, G. Wirnsberger and G. D. Stucky, Chem. Mater., 13 (2001) 3140. [5] S. B. Yoon, J. Y. Kim and F. Kooli, Chem. Commun., 14 (2003) 1740. [6] J. Q. Li, H. Kessler, M. Soulard, L. Khouchaf and M. H. Tuilier, Adv. Mater., 10 (1998) 946. [7] R. K. Rana, L. Z. Zhang, J. C. Yu, Y. Mastai and A. Gedanken, Langmuir, 19 (2003) 5904. [8] P. T. Tanev, T. J. Pinnavaia, S. A. Bagshaw and T. J. Pinnavaia, Angew. Chem. Int. Ed., 35(1996)1102. [9] P. T. Tanev and T. J. Pinnavaia, Science, 267 (1995) 865. [10] F. Vaudry, S. Khodabandeh and M. E. Davis, Chem. Mater., 8 (1996) 1451.


331 331

Surfactant-free synthesis of mesoporous tin oxide with a crystalline wall Jieming Cao*, Haitao Hou, Xianjia Ma, Mingbo Zheng and Jinsong Liu Nanomaterials Research Institute, College of Materials Science and Technology, Nanjing University of Aeronautics and Astronautics, Nanjing 210016, PR China.

1. Introduction Mesoporous materials have gathered considerable attention due to their outstanding application to catalyst and separation technology [1-6]. Since appearance of MCM-41, various surfactants, including anionic surfactants, cationic surfactants, nonionic surfactant, block copolymers, have been used to synthesize mesoporous materials with highly ordered porous structures. However, the wall of these materials is normally amorphous, and crystallization usually results in collapse of the uniform mesoporous structure by means of heat treatment. Some surfactants have been chosen to directly synthesize crystalline ZnS mesoporous network, which also usually results in partial collapse of porous structures after the extraction of surfactants [7]. Recently, some mesoporous materials with crystalline structure have been prepared by initial strengthening of the porous structure through depositing another material on the inside surface of the mesopore and then calcining the sample to cause its crystallization or using a low-temperature crystallization technique in the presence of surfactant [8-13]. It is widely acknowledged that surfactants are necessary to synthesize mesoporous materials. Surfactant-free method to synthesize these materials is a big challenge, and few reports about this have been made until now9. Tin oxide, one of important semiconductors [14], has been widely used in the fileds such as gas sensors [15], electrode materials [16], and solar cell [17]. Two of the most important factors affecting the performance in these fields are its specific surface area and crystallinity. It would be exciting to prepare mesoporous tin oxide with a crystalline porous wall. Here we report a novel surfactant-free synthesis of mesoporous tin oxide with a crystalline wall by an approach of combination of ethanol thermal process and subsequent calcinations.

332

2. Experimental Section In a typical synthesis of mesoporous tin oxide with a crystalline pore wall, 7.01 g SnCl4-5H2O and 2.40 g urea were dissolved in 30 mL ethanol, and stirred for lmin, and then transferred into a 50 mL autoclave. The autoclave was sealed and kept at 175°C for 7 h, and then cooled into the room temperature naturally. The solid product was filtrated and dried at 60°C for 12 h, and then the assynthesized sample was calcined at 300°C for 3 h (temperature-rising rate: 2°C/min). The products were characterized by means of x-ray diffraction (XRD), nitrogen physisorption, and Transmission electron microscopy (TEM). 3. Results and Discussion Δ (NH A (NH4)2SnCl6 4)2SnCl6

1

2

33

4

2 θ / degrees 2θ/ degrees

5

6

(b) (b)

(112)

(211)

3

A .A S

0

NH4Cl U NfttQ •• SnO SnO2

(101)

(110)

2

I nt ens i t y ( a. u. )

I nt ens i t y ( a. u. )

(a)

10 10

20

30

40

S

(1) (1)

D

50

60

(2) (2)

70

80

2 θθ//degrees degrees

Figure 1. (a) Low X-ray diffraction pattern of the as-synthesized sample; (b) wide-angle X-ray diffraction patterns of (1) the as-synthesized sample and (2) the sample after calcination.

Figure la shows the low-angle X-ray diffraction patterns of the assynthesized sample. The diffraction pattern has a broad peak at around 26M.45 0 , respectively, which indicats there is meso-structure in the assynthesized sample. But, there's no peak for the calcined sample, which indicates that the meso-structure has been destroyed after calcining. Figure lb shows the wide-angle diffraction patterns of as-synthesized and calcined tin oxide sample. The product before calcining is composed of NH4C1, (NH4)2SnCl6, and SnO2. After calcining, all observed peaks correspond to (110), (101), (211) and (112) planes, respectively, which can be indexed to cassiterite tin oxide. Based on the line width of the diffraction peak corresponding to (110) reflection, the average crystallite size was calculated about 5.5 nm by the Scherrer formula. The mesoporous nature of the calcined sample is confirmed by nitrogen physisorption. Figure 2a shows adsorption-desorption isotherm of the sample after calcinations, which is characteristic of mesoporous materials. The specific surface area of the sample is 205 m2-g"'. The BJH pore diameter distribution

333

-1

(a)

3

120 100 80 60 40 20 0.0

(b)

0.006

•g

140

)

160 160

Pore volume / (cm

3 -1 Volume adsorbed / (cm • g ) STP

from adsorption branch was shown in Figure 2b, which is mainly distributed in the range of 3 - 8 nm.

0.004

0.002

0.000

0.2 0.4 0.6 0.8 Relative o) Relative pressure (P/P (P/Po)

1.0 1.0

2

4

66

88 10 10 12 12 14 14 16 16 18 18 20 20 Pore Pore diameter / nm

Figure 2. Nitrogen adsorption-desorption isotherms and BJH pore diameter distribution from adsorption branch (inset) ofmesoporous tin oxide.

The calcined sample was also characterized by TEM (Figure 3). Figure 3a indicates that the calcined product has spongy structure. The ED pattern (inset) shows that the wall of porous structure is made of cassiterite, which is in agreement with XRD result. From its higher magnification image (Figure 3b), the spongy structure is composed of particles with the size in the range of 3 - 5 nm, and some pore structures with the size of about 4 nm. Figure 3c shows the HRTEM image of the particles, which indicates the high crystallinity of the pore wall. The width of 0.34 nm from neighboring fringes corresponds to (110) planes.

Figure 3. (a) Transmission electron microscopy (TEM) and electron diffraction (ED), and (b) its high magnification image, and (c) HRTEM image.

It was reported that urea can react with SnCl4 in methanol to form the compound [SnCl4(urea)2], [18] and urea molecules can construct a coordination sphere around the metal atom and form a stable structure [19]. We think, in our experiment, the same complex was formed through reaction of SnCl4-5H2O, urea and ethanol during the solvothermal process. On one hand, the complex

334 334

prevents the growth of SnO2 particles, and facilitates formation of nanocrystallites, which subsequently act as pore wall; on the other hand, the decomposition of the complex leads to ordered spongy porous structure with the loss of urea molecules, which are absorbed around the metal atom, during subsequent calcinations. 4. Conclusion Mesoporous SnO2 with a crystalline wall was successfully synthesized by a novel surfactant-free method. The complex precursor was synthesized through reaction of SnCl4-5H2O and urea in the ethanol thermal process, and then the precursor was calcined to form mesoporous SnO2. The obtained SnO2 has a high specific surface area and a narrow pore size distribution, and the pore wall is composed of nanocrystallites. This surfactant-free method can be extended to synthesis of other mesoporous metal oxides with a crystalline wall. 5. References [1] C. T. Kresge, M. E. Leonowicz, W. .1. Roth, J. C. Vartuli and J. S. Beck, Nature, 359 (1992)710. [2] G. S. Attard, J. C. Glyde and C. G. Goltner, Nature, 378 (1995) 366. [3] S. A. Davis, S. L. Burkett, N. H. Mendelson and S. Mann, Nature, 385 (1997) 420. [4] Q. Huo, R. Leon, P. M. Petroffand G. D. Stucky, Science, 268 (1995) 1324. [5] D. Li, H. Zhou and I. Honma, Nat. Mater., 3 (2004) 65. [6] H. Miyata, T. Suzuki, A. Fukuoka, T. Sawada, M. Watanabe, T. Noma, K. Takada, T. Mukaide and K. Kuroda, Nat. Mater., 3 (2004) 651. [7] P. K. Rana, L. Z. Zhang, J. C. Yu, Y. Mastai and A. Gedanken, Langmuir, 19 (2003) 5904. [8] H. Shibata, T. Ogura, T. Mukai, T. Ohkubo, H. Sakai and M. Abe, J. Am. Chem. Soc, 127 (2005) 16396. [9] M. Vettraino, M. L. Trudeau, D. M. Antonelli, Adv. Mater., 12 (2000) 337-341. [10] Z. R. Tian, W. Tong and J. Y. Wang, Science, 276 (1997) 926. [11] H. Shibata, H. Mihara, T. Mlikai, T. Ogura, H. Kohno, T. Ohkubo, H. Sakait and M. Abe, Chem. Mater., 18(2006)2256. [12] F. Jiao, A. Harrison, J. C. Jumas, A. V. Chadwick, W. Kochelmann and P. G. Bruce, J. Am. Chem. Soc, 128 (2006) 5468. [13] V. N. Urade and H. W. Hillhouse, J. Phys. Chem. B, 109 (2005) 10538. [14] Y. Liu and M. L. Liu, Adv. Funct. Mater., 15 (2005), 57. [15] G. Xu, Y. W. Zhang, X. Sun, C. L. Xu and C. H. Yan, J. Phys. Chem. B, 109 (2005) 3269. [16] A. C. Bose, D. Kalpana, P. Thangadurai and Ramasamy, J. Power Sources, 107 (2002) 138.

[17] S. Chappel and A. Zaban, Sol. Energ. Mater. Sol. C, 71 (2002)141. [18] P. O. Dunstan, Thermochimica ACTA, 345 (2000) 117-123. [19] L. Qiu and L. Gao, J. Am. Ceram. Soc, 87 (2004) 352-357.


335 335

Mesoporous crystals of metal oxides and their properties Calum Dickinson,a Andrew Harrison,b Jim A. Anderson0 and Wuzong Zhou8"* "EastChem, School of Chemistry,University of St Andrews, St Andrews, KY169ST, UK b EastChem, School of Chemistry, University of Edinburgh, Edinburgh, EH9 3JJ, UK c Department of Chemistry, Aberdeen University, Aberdeen, AB24 3UE, UK

Porous single crystals of Cr2O3 and Co3O4 were synthesised using mesoporous silica, such as SBA-15 and KIT-6, as a template. Their structures were examined by using XRD and HRTEM. The magnetic properties of Cr2O3 revealed behaviour like nanoparticles and the catalytic properties showed 100% conversion of cyclohexene with 34% selectivity to the epoxide. 1. Introduction Since 1992, advancements in surfactant synthesised mesoporous material have been considerable. One of the biggest achievements has been creating mesoporous silica using the triblock copolymer surfactant. At the end of the century, the reverse framework of mesoporous silica was first replicated using carbon [1] via the so-called hard templating or nanocasting route. Using a similar method, negative replicas of mesoporous silica can be made with metal oxides. These replicas can be porous single crystals (PSC) [2]. With SBA-15 and KIT-6 as templates, several PSCs of metal oxides have been reported [2-4]. There are several ways to synthesise the PSCs by the impregnation of the metal oxide precursor into a mesoporous silica template. We further developed the synthesis method and investigated the physico-chemical properties of these porous crystals. 2. Experimental Section The hard templates, SBA-15 and KIT-6, were synthesised according to the literature and calcined at 500°C for 5 h in air [5, 6]. 0.15 g of the silica was then dispersed in 6.5 ml ethanol containing 0.65 g of Cr(NO3)3-9H2O or Co

336

(NO3)2-6H2O and stirred for 2 h. The ethanol was then evaporated at 40°C and the resulting powder was heated at 500°C. The silica template was dissolved by an aqueous 10% HF solution and centrifuged before decanting and washing with distilled water thrice. The sample was dried and characterised using XRD and high-resolution transmission electron microscopy (HRTEM). For magnetic measurements, -50 mg of the Cr2O3 PSC, templated by KIT-6, was weighed into a gelatine capsule of known, low magnetisation and loaded into a Quantum Design MPMS2 SQUID magnetometer. Magnetisation data were taken from 1.8 - 340 K in an applied field of 0.01 T. For catalytic tests, 0.05 g of Cr2O3 PSC was added to a stainless steel autoclave containing 0.74 mmol cyclohexene, 2.08 mmol dimethylpropanal and 25 ml of toluene as solvent. The reactor was purged with pure oxygen and pressurised to 10 bar. The contents were stirred at 85 °C for 16 h before the solution was analysed using a gas chromatography-mass spectrometer. 3. Results and Discussion 3.1. Characterisation of PSC With HRTEM, it can clearly be seen how the crystallinity of the material within the PSC crosses bridges between nanorods (negative replica of SBA-15) or across a cubic framework (negative replica of KIT-6) (Fig. la, b). It was revealed that the PSC of Cr2O3 filled only one of the bicontinuous channels of KIT-6, whereas the Co3O4 PSC filled both channels. This was believed to have resulted from the collapse of the complimentary pores in the Cr-containing KIT6, disallowing the communication between the two porous frameworks. This is possibly due to the effects of higher temperature for crystal growth and the expansion of the metal oxide crystal destabilising the silica framework. For understanding the formation mechanisms of these materials, XRD studies of the early stages of the decomposition of the nitrate within the silica reveals how it differs from the decomposition of the nitrate without the presence of silica [7]. Not only is the temperature of the decomposition of the material to the final metal oxide vastly reduced, but the intermediate products also differ. Intermediate products can be compounds rarely seen in the decomposition of the bulk, such as cobalt hydroxide nitrate. Fig 1. (c) displays XRD patterns, showing an example of the effect of the mesoporous host in the reduction of the crystallisation temperature of cobalt oxide. 3.2. Magnetic properties of PSC Cr2O3, in the fully dense form, shows antiferromagnetic order below approximately 308 K, whereas the dc susceptibility measurements for the PSC

337

show no sign of such a transition at so high a temperature, and indicate behaviour much more like of nanoparticulate Cr2C>3. Fig. Id displays the

Fig. 1. (a) TEM image of the KIT-6 templated PSC Cr2O3 viewed down the [111] zone axis of the mesostructural unit cell, and (b) the corresponding HRTEM image showing the single crystal property, (c) XRD patterns of Co3O4 grown inside the mesopores (bottom) and from bulk specimen (top), (d) Graph of magnetic behaviour against temperature of Cr2O3 PSC measured after cooling in zero magnetic field (zfc), or a field of 0.01 T (fc)

susceptibility taken after first cooling in zero magnetic field (zfc) and then after cooling in 0.0IT (fc): there is a divergence of the fc and zfc data below approximately 100 K, and a cusp in the zfc response at approximately 40 K that is similar to that attributed to the blocking of the magnetisation in 15 nm particles, as reported by Mahklouf [8]. The PSC sample also appears to have a weakly ferromagnetic response at low temperature, like the nanoparticulate sample. For the latter form of the material, the ferromagnetism has been attributed to an uncompensated excess of surface spins. This ferromagnetic effect increases as particles get smaller, as reported for cobalt oxide [9]. Recently, work carried out by Jiao et al, revealed the difference in magnetic properties between near single crystal mesoporous iron oxide and poly crystalline iron oxide [10]. The difference between these materials is rather significant and confirms the importance of the single crystallinity of the porous material.

338

3.3. Catalytic properties ofCr2O3PSC Results in the selective catalytic oxidation of cyclohexene to epoxide (oxabicycloheptane) showed 100% conversion of the cyclohexene along with 98.7% conversion of the sacrificial oxidant, 2,2-dimethylpropanal (pivaldehyde). The reaction was 34% selective to the epoxide with some formation of the non-selective cyclohex-1-one and the majority being the hydrolysis product of the epoxide leading to the diol. Traces of benzaldehyde were detected indicative of oxidation of the solvent. The complete conversion of pivaldehyde indicates that the PSC is capable of activation of molecular oxygen and its insertion into the aldehyde C-H bond. Furthermore, formation of the epoxide product indicates that the catalyst is able to activate the reagent and allow single oxygen atom transfer from the in-situ formed peracid. This is of significant interest given that this process is currently largely restricted to single site metal centered complex catalysts [11, 12]. 4. Conclusion The PSC form of Cr2O3 has been shown to have many different properties compared to the bulk material. The magnetic behaviour bears some similarity to nanoparticulate Cr2O3, with a mean blocking transition in the region of 40 K, and some evidence for weak ferromagnetism at low temperature. The PSC also reveals a possible catalytic application of the oxidation of cyclohexene, with 100% conversion and 34% selectivity to partial oxidation to the epoxide. 5. References [1] R. Ryoo, S. H. Joo and S. Jun, J. Phys. Chem., 103 (1999) 7743. [2] K. K. Zhu, B. Yue, W. Z. Zhou and H. Y. He, Chem. Commun., (2003) 98. [3] B. Yue, H. L. Tang, Z. P. Kong, K. K. Zhu, C. Dickinson, W. Z. Zhou and H. Y. He, Chem. Phys. Lett., 407 (2005) 83. [4] K. Jiao, B. Yue, Y. Ren, S. X. Liu, S.R. Yan, C. Dickinson, W. Z. Zhou and H. Y. He, Chem. Commun., (2005) 5618. [5] D. Y. Zhao, J. L. Feng, Q. S. Huo, N. Melosh, G. H. Fredrickson, B. F. Chmelka and G. D. Stucky, Science, 279 (1998) 546; [6] F. Kleitz, S. H. Choi and R. Ryoo, Chem. Commun., (2003) 2136. [7] C. Dickinson, W. Z. Zhou, R. P. Hodgkins,Y. F. Shi, D. Y. Zhao and H. Y. He, Chem. Mater. 18(2006)3088. [8] S. A. Makhlouf, J. Magn. Magn. Mater., 272 (2004) 1530. [9] Y. Q. Wang, CM. Yang, W. Schmidt, B. Spliethoff, E. Bill and F. Schuth, Adv. Mater., 17 (2005) 53. [10] F. Jiao, A. Harrison, J. C. Jumas, A. V. Chadwick, W. Kockelmann and P. G. Bruce, J. Am. [11] Chem. Soc, 128 (2006) 5468. [12] Y. Yamada, K. Imagawa, T. Nagata and T. Mukaiyama, Chem. Lett., (1992) 2231. [13] S. Bhattacharjee and J. A. Anderson, J. Mol. Catal, A, 249 (2006) 103.


339 339

Synthesis and characterization of lanthanum oxide nanotubes using dendritic surfactant Li Taoa, Cheng-Gao Suna, Mei-Lian Fan3, Qi Liua, Cai-Juan Huang3, He-Sheng Zhaib, Hai-Long Wua and Zi-Sheng Chaoa* "* College of Chemistry and Chemical Engineering, Hunan University; Key Laboratory of Chemometrics & Chemical Biological Sensing Technologies, Ministry of Education, Hunan University, Changsha 410082, P. R. China. b College of Chemistry and Chemical Engineering, Xiamen University, Xiamen 361005, P. R. China

Lanthanum oxide nanotubes were synthesized via a surpramolecular assembly route, employing a dendritic surfactant, 3,3',3",3'"-(ethane-l,2-diylbis (azanetriyl))tetrakis(N-(2-aminoethyl)propanamide), and a co-surfactant, polyoxyethylene fatty alcohol, namely AEO9. The nanotubes were characterized by means of XRD, TEM, SAED, and N2-physisorption, and the results indicate that the nanotubes possess an average length of above 160 nm and a mesomicroporous hierarchical structure with an average micropore size of ca.1.32 nm and average mesopore sizes of 6-8 nm and 25 nm. The employing of cosurfact AEO9 promoted the formation of dendimer surfactant micells that template the mesophase of the specimen via a cooperation route. The characteristic strip-like shape of the surfactant might contribute the formation of the nanotublar morphology and the hydrothermal treatment result in the crystallization of the lanthanum oxides and in turn the appearance of the micropores within the walls of the nanotubes. 1. Introduction Rare earths have found versatile applications in the areas like functional materials and catalysis and so on [1, 2]. Among the rare earths, lanthanum appeared to be the most extensively studied ones, because of their relatively low price and well physical and chemical performances in applications. In the preparation of La-containing nanomaterials, a few works dealt with the microporous lanthanum oxide with morphologies of thin films, particulates,

340 340

nanowires or nanorods [3-7]. Hexagonal and lamellar mesostructured lanthanum oxide was also synthesized via a cooperative assembly route [8, 9]. To the best of our knowledge, however, no lanthanum oxide nanotubes has been reported in literatures. We shall present here a supramolecular assembly of lanthanum oxide nanotubes, using a novel dendritic surfactant and a cosurfactant AEO9. The novelty we'd like to address here is not only the nanotubular morphology of the lanthanum oxides but also the surfactant employed, the one we synthesized via the reaction between methyl acrylate and ethylenediamine. 2. Experimental section 2.1. Synthesis of dendritic surfactant 3,3',3",3'"-(ethane-l,2-diylbis(azanetriyl) tetrakis(N-(2-aminoethyl)propanamide) At first, excess amount of methyl acrylate was reacted with ethylenediamine at 333-353 K for 6 h under stirring and refluxing, after that the unreacted methylaerylate was removed via vacuum distillation. Then, the product obtained above was reacted with excess amount of ethylenediamine at 353 K for 4 h under stirring and refluxing, with the removal of the by-product methanol and the unreacted ethylenediamine via a rotary evaporator after the reaction. 2.2. Synthesis of lanthanum oxide nanotubes The dendritic surfactant (2.5 g), AEO9 (1.5 g) and La(NO3)3-6H2O (3.0 g) were dissolved into 50 ml deionized water under agitation at room temperature, respectively. The mixture formed was subjected to a hydrothermal treatment at 373 K for 6 d without stirring. Precipitates were finally formed and collected after filtration, washing with distilled water and drying in air at 333 K. 2.3. Characerization TEM and SEAD (JEOL-3100), N2physisorption (Beckman Coulter SA3100) and EDS (Oxford INCA Energy 300) were employed to characterize the specimen. 3. Results and discussion When only the dendimer or AEO9 surfactant was employed, microporous solid and amorphous one was obtained, respectively. The combination of the two surfactants resulted in

Fig. 1. TEM micrograph of lanthanium oxide nanotubes

341

the lanthanium oxide nanotubes. Fig. 1 shows the TEM micrograph of the assynthesized nanotubes. It can be seen that the nanotubes have an average inner V(nl) and outer diameter of ca. 0.5 6 to 9 nm and 15 nm and an average length of at least 160 nm, respectively. The SAED pattern (the inset in Fig. 1) manifests, to some extent, a crystalline nature within the walls of the nanotubes. 0.5 Relative Pressure Ps/Po Fig. 2 shows the N2physisorption isotherm of Fig. 2. N2-physisorption isotherm and pore size the specimen. It reveals distribution curves (the insets) of lanthanium the presence of slip-type oxide nanotubes. (a) micropores; (b) mesopores mesopores, as evidenced by a strong hysteresis loop. The specific surface area and the pore volume were determined to be 88.38 m2/g and 0.37 ml/g, respectively. The pore size distribution curves (the insets in Fig. 2) indicate that the specimen contains three groups of pores, i.e., micropores with an average size of ca. 1.32 nm (inset a), two groups of mesopores with an average size of 6-8 and 25 nm (inset b), respectively. These results suggest that the nanotubes may possess a hierarchical pore structure, i.e., the inner diameter of the nanotubes is in the mesopore range and the wall of the nanotubes contains micropores. The mesopores with an average size of 25 nm are probably caused by the interconnected network of the nanotubes. Fig. 3 indicates the EDS Spectrum spectrum of the asO C !•» synthesized specimen which shows the presence of C, O, and La at a surface atomic ratio of 56:35:9. Nitrogen was failed to be detected out, being probably due that N atom has a low content in the surface of the specimen and a small sensitivity in the EDS Fig .3. EDS spectrum of the specimen templated by measurement. the mixture of dendrimers and AEO9 Basing on the above results, a formation mechanism of the lanthanum nanotubes could be proposed. The combination of the dendimers and the AEO9 could reduce largely the repulsive interaction between the polar groups in the former molecules, due to the dispersion interaction .

•

'•

.

.

I

342

between these two kinds of surfactants [10, 11], favoring the formation of micelles. Under the regulation of the micelles, the La species polymerized, following possibly a cooperation route, and finally the mesophase was formed. The characteristic strip-like shape of the surfactant is probably responsible to the nanotube morphology of the as-synthesized specimen. The hydrothermal treatment favored the crystallization of the lanthanum oxides within the nanotube walls, and in turn, resulted in the formation of the micropores among the crystals of the lanthanum oxides. 4. Conclusion The dendrimers was synthesized and employed together with the AEO9 to template the nanotubes of lanthanum oxides. The synthesized nanotubes were identified to possess a mesoporous-microporous hierarchical structure. The assembly of the nanotubes is proposed to be controlled by the micelles, consisting of the above mixed surfactants, via a cooperation route. The characteristic strip-like shape of the surfactant is responsible to the nanotube morphology and the hydrothermal treatment to the formation of the micropores within the nanotube walls. 5. Ackonwledgment This work was supported by the Program for New Century Excellent Talents in University, the Ministry of Education of P.R. China, and the Program for FuRong Scholar in Hunan Province, P.R. China. 6. References [1] S. J. Kim, J. R .Ireland and C. Kannewurf, et al., J. Solid State Chem., 155 (2000) 55. [2] D. Andriamasinoro, R. Kieffer, A. Kiennemann and P. Poix, J. Appl. Catal., 106 (1993) 201. [3] M. Nieminen, M. Putkonen and L. Niinisto, J. Appl. Surf. Sci., 174 (2001) 155. [4] X. Y. Ma, H. Zhang, Y. J. Ji, J. Xu and D. R.Yang, J. Materi. Lett., 58 (2004) 1180. [5] A. H. Mekhemer, et al., Colloids Surf. A Physicochem. Eng. Asp., 181 (2001) 19. [6] D. Zhu, H. Zhu and Y. Zhang., J. Phys. Condens. Matter., 14 (2002) 519. [7] Y. J. Zhang and H. M. Guan, J. Mater. Res. Bull., 40 (2005) 1536. [8] .1. M. Cao, H. M. Ji, J. S. Liu, et al. and J. Ma, et al., J. Mater. Lett., 59 (2005) 408. [9] Q. Huo, D. I. Margolese, U. Ciesla, P. Feng, T. E. Gier, P. Sieger, R. Leon, P. M. Petroff, F. Schuth and G. D. Stucky, Nature, 368 (1994) 317. [10] M. J. Rosen, Second Edtion, John Wiley & Sons.Tnc. Surfactants and interfacial Phenomena., (1989). [11] K. M. Prabal, C. Tahir, G. F. Wang and A. G. William, Macromolecules 37 ( 2004) 6236.


343 343

Nanostructured SiC from preceramic polymer via replication of hard templates Jia Yana, Hao Wangb, In-Kyung Sung0, Kyung-Hoon Park0, Anjie Wanga, Xiaodong Lib and Dong-Pyo Kirn0* " State Key Laboratory of Fine Chemicals, Dalian University of Technology, 158 Zhongshan Road, Dalian, P. R. China, 116012. b Key Lab of Ceramic Fiber and Composites, National University of Defense Technology, Changsha, P. R. China, 410073. c Department of Fine Chemical Engineering and Chemistry, Chungnam National University, Daejeon, Korea 305-764.

1. Introduction Nanocasting process, which is a method for replicating nanoscale structures using hard templates, has been widely used for the preparation of various nanoporous structures such as nanoporous carbon CMK-z, oxides, sulfides and metal [1]. Recently, this approach gradually extended to prepare the ordered nanoporous non-oxide ceramics, including macroporous (> 50 nm) and mesoporous (1.5 ~ 50 nm) materials [2], which possess high chemical and mechanical stabilities. Many nanostructured ceramics can not be fabricated by conventional methods such as powder processing and CVD. Some methods have been used successfully to prepare various nanostructured SiC. According to the Quin et al., a SiC-based disordered macropore structure 'wood ceramic' was prepared from carbonized wood powder and phenol resin via a direct reaction with Si powder [3]. In the field of mesoporous SiC, some disordered SiC structures have been prepared by a solid-gas reaction in active carbon [4] and a chemical vapor infiltration (CVI) into SBA-15 silica [5]. On the other hand, different types of tubular SiC nanostructures have been synthesized since Dai et al. first reported the preparation of SiC nanotubes using a shape memory synthesis method [6]. Most preparation methods are based on a carbothermal reduction and/or chemical vapor deposition, resulting in randomly disordered nanostructures. Liquid preceramic polymers such as polymethylsilane, polycarbonsilane and

344

polysilazene provide ideal precursors for the preparation of ordered nanostructured ceramics by nanocasting method, because they can be processed easily at temperatures lower than those required in conventional methods. Therefore, various ordered macroporous [7] and mesoporous [8] SiC ceramics have been prepared by this method. At this paper, we summarize our recent achievements in the field of various SiC porous products prepared by nanocasting of preceramic polymers into different sacrificial hard templates. The main concern is on macroporous SiC with pores larger than 50 nm, mesoporous SiC with pores ranging from 2 to 50 nm, and SiC nanotubes. 2. Experimental Section The various templates (silica or polystyrene spheres ordered assemblies, alumina membrane, macroporous carbon and mesoporous silica) were immersed in the precursor solution for SiC ceramic under nitrogen. After curing at 200°C, the polymer/template composites were pyrolyzed under argon at 1000~1400°C. SiC nanostructures such as macroporous or mesoporous materials, hollow spheres and nanotubes, were obtained upon fully etching the silica hosts with aqueous HF, or upon burning the carbon in air at 650°C. 3. Results and Discussion Fig. 1 summarizingly shows the macroporous and nanotublar SiC products and the used various hard templates. In particular, the macroporous SiC (Fig. IB) with a highly ordered pore array and high surface area (-170 m2/g) was prepared by nanocasting of preceramic polymer into colloidal silica crystalline template (Fig. 1 A). The pore size of 80 ~ 650 nm and the BET surface of 580 ~ 300 m2g"! of the obtained macroporous SiC can be controlled by using different size of the sacrificial templates. It is believed that the high Fig. 1 SEM and TEM images of (A) silica sphere, (B) surface area was due to macroporous SiC, (C) ordered macroporous carbon, (D) hollow the interfacial area beSiC sphere, (E) alumina membrane and (F) SiC nanotube. tween the sphere and the infiltrated polymer as well as to the formation of micropores at the ceramic wall during pyrolysis. In addition, 3-dimensional long range ordered hollow SiC

mm

345

sphere assemblies (Fig. ID) were prepared by embedding preceramic polymer into sacrificial 3D ordered macroporous carbon templates (Fig. 1C). After removing of the carbon template, the obtained SiC hollow spheres possessed high thermal stability. The obtained SiC sphere nanostructures with outer diameters ranging from 135 to 890 nm were proportional to the initial pore size of the sacrificial carbon templates. Fig. IF shows SEM and TEM images of well-aligned array of SiC tubes with a uniform wall thickness of 45 nm, which were prepared by nanocasting of polymethylsilane into sacrificial alumina membrane as a template (Fig. IE). After the pyrolysis at 1250°C and the etching off the template, the obtained SiC nanotubes with less crystalline wall displayed an electrical resistance of 6.9 x 10J to 4.85 x 101 Om at temperatures ranging from 20 to 300 °C with a negative temperature dependence, which is similar to a semiconductor-like behavior. In addition, Pt/Ru alloy nanoparticles could be selectively deposited on the inner wall of the nanotube. This material might be useful in the fields of heat-resistant nanodevices, fuel cells and nanofluidic devices. Furthermore, macroporous SiC pattern on Si wafer (Fig. 2B and D) with a high surface area and high thermal stability (>800°C in air) was prepared by a series of processes combined with soft lithography. The preceramic polymer was infiltrated into the polystyrene sphere template (Fig. 2A and C) patterned on a Si wafer, which was prepared from polydimethylsiloxane (PDMS) mold by soft lithography, and transformed to macroporous SiC monoliths after curing and pyrolysis. The pore size could be tailored independently according to the bead size, allowing for the easy integration of porous monoliths into a microreactor. The SiC ceramic monoliths obtained were used in the decomposition of ammonia after depositing a ruthenium catalyst via wet impregnation and calcinations. The efficient conversion of NHU to H2 with Fig. 2 SEM images of polystyrene spheres increasing reaction temperature demonspattern via soft lithgraphy (A, C) and trated its successful performance as a macroporous SiC pattern (B, D). hydrogen reformer for fuel cells [9]. These novel porous materials show great promises for use in high temperature micro-reactors possibly for the on-demand reforming of higher hydrocarbons into hydrogen for portable power sources. Highly ordered mesoporous SiC with a n- ? TCH • r-eo A I« < A^ A sur face area in the range of 495 m2/g and a Fig. 3 TEM images of SB A-15 (A) and

c-r-T/nx mesoporous SiC (B).

•

c

^ ,

.

.?

•

,

pore size or 3.4 nm was also synthesized r

J

346

by nanocasting of allylhydridopolycarbo-silane into trimethylsilyated SBA15 silica as sacrificial hard templates. The void channels of SBA-15 template (Fig. 3A) were converted into the SiC ceramic walls (Fig. 3B), whereas the silica walls of SBA-15 were removed to form hollow channels of mesoporous SiC, which indicated that the structures of the mesoporous SiC samples were exact inverse replicas of their silica templates with highly ordered microstructures. The small-angle XRD patterns of he obtained SiC products also indicated that the ordered mesoporous structures similar to that of their silica templates had been replicated. Alternatively, the similar work was reported by Zhao et al., which formed the ordered mesoporous SiC ceramics via a nanocasting process infiltrating commercial polycarbosilane into mesoporous silica materials, SBA-15 and KIT-6, as hard templates [10]. It is expected that these novel techniques will be suitable for synthesizing many other types of ordered mesoporous non-oxide ceramic materials with interesting pore topologies. 4. Conclusion A variety of SiC nanostructures were prepared by infiltration of preceramic polymer into different types of sacrificial templates. The obtained nanoporous SiC ceramics are promising materials for variety of applications including filters, membranes, sensors, catalyst supports, as well as biomedical and construction materials, due to their unique chemical and physical stabilities. 5. Acknowledgement This work was funded by the 2004 National Research Lab (NRL) Project [M 10400000320-05J0000-32010] administered by the Korean Ministry of Science and Technology (MOST). 6. References [1] H. F. Yang and D. Y. Zhao, J. Mater. Chem., 15 (2005) 1217. [2] P. Dibandjo, L. Bois, F. Chassagneux, D. Comu, J. M. Letoffe, B. Toury, F. Babonneau and P. Miele, Adv. Mater., 17 (2005) 571. [3] J. Quin, J. Wang, J. Zhihao and G. Qiao, Mat. Sci. Eng. A, 358 (2003) 304. [4] M. J. Ledoux and C. Pham-Huu, Cattech, 5 (2001) 226. [5] P. Krawiec, C. Weidenthaler and S. Kaskel, Chem. Mater., 16 (2004) 2869. [6] N. Keller, C. Pham-Huu, G. Ehret, V. Keller and M. J. Ledoux, Carbon, 41 (2003) 2132. [7] I. K. Sung, S. B. Yoon, J. S. Yu and D. P. Kim, Chem. Commun. (2002) 1480. [8] K. H. Park, I. K. Sung and D. P. Kim, J. Mater. Chem., 14 (2004) 3436. [9] I. K. Sung, Christian, M. Mitchell, D. P. Kim and P. J. A. Kenis, Adv. Funct. Mater., 15 (2005) 1336. [10] Y. F. Shi, Y. Meng, D. H. Chen, S. J. Cheng, P. Chen, H. F. Yang, Y. Wan and D. Y. Zhao, Adv. Funct. Mater., 16 (2006) 561.


347 347

Gas-sensing properties of ordered mesoporous C03O4 synthesized by replication of SBA-15 silica Thorsten Wagner,ab Jan Roggenbuck,a Claus-Dieter Kohl,b Michael Froba a and Michael Tiemann a "Institute of Inorganic and Analytical Chemistry, Justus Liebig University, HeinrichBuff-Ring 58, D-35392 Giessen, Germany b Institute of Applied Physics, Justus Liebig University, Heinrich-Buff-Ring 16, D-35392 Giessen, Germany

1. Introduction The concept of utilizing mesoporous silica or carbon phases as rigid structure matrices has recently become a widely-used procedure for the synthesis of periodically ordered mesoporous metal oxides [1-6]. Contrary to conventional supramolecular structure-directors, such "hard templates" can be applied to the synthesis of a much larger variety of materials. Furthermore, they tolerate high temperatures, allowing for the synthesis of crystalline products. This approach has brought forward the opportunity to prepare new porous metal oxides with interesting properties owing to finite crystal domain sizes, high specific surface areas, and regular mesopore arrangements. For example, mesoporous Co3O4 has been shown to exhibit ferromagnetic behavior scaling with the high surface-tovolume ratio [4]. Various monolithic metal oxides with multimodal porosity are promising candidates for HPLC applications [6]. We have prepared mesoporous MgO with basic surface properties [5]. Another important field for the application of new mesoporous metal oxides is their utilization as gas sensors. We have recently shown that mesoporous SnO2 materials exhibit high sensitivities and fast responses at low and technically relevant concentration ranges of various gas analytes (e.g. CO detection or CH4 explosion prevention according to German/European norms DIN/EN50194); the sensors turned out be largely insensitive towards changes in the relative humidity [7]. Here we report on the gas-sensing properties of mesoporous Co3O4 synthesized by utilization of SBA-15 silica as the structure matrix. As pointed out above, this synthesis concept allows high temperatures,

348

facilitating the preparation of crystalline materials; these will have reduced defect densities at the surfaces, which is essential for sensitivity, selectivity and stability of gas sensors. The suitability of Co3O4 as a gas sensor is based on its non-stoichiometric composition which results in p-type semiconducting properties owing to an excess of oxygen. The interaction of the particle surface with oxidizing/reducing gas molecules will lead to a change in electrical resistance. 2. Experimental Section SBA-15 silica was prepared according to a literature procedure [8]. For the synthesis of mesoporous Co3O4 by the incipient wetness technique 4 g SBA-15 were dispersed in 8 mL of an aqueous solution of Co(NO3)2 (4.5 mol L"1) at room temperature and stirred for ten minutes to impregnate the silica mesopores with Co(NO3)2. After filtration the non-dried sample was immediately transferred to a pre-heated oven (220°C, air atmosphere) to convert Co(NO3)2 to CO3O4. This procedure was repeated twice, with 4 mL Co(NO3)2 solution in the second and third cycle. Finally the sample was heated under air atmosphere to 550°C at a constant rate of 2.5°C min"1. The silica matrix was removed by repeatedly dispersing the sample in an aqueous solution of NaOH (2 mol L") and stirring for three hours at room temperature. For the preparation of the sensors 50 mg of the mesoporous or bulk Co3O4 powders were ground and dispersed in 4 ml water. After ultrasonication the dispersion was deposited onto substrates (Umweltsensortechnik, UST) with integrated heating and interdigitally structured platinum electrodes, dried at room temperature, and tempered for 24 hours at 500°C. The gas sensing properties were measured by means of a gas mixing equipment using standard mass flow controllers to provide a well-defined gas flow and a computer to control the experiment and record the resulting data. 3. Results and Discussion Figure 1 shows the X-ray diffraction diagram, TEM image, and selected area electron diffraction (SAED) pattern of mesoporous Co3O4. The material is the negative replica of the SBA-15 silica structure matrix, consisting of linear rods arranged in a two-dimensional hexagonal symmetry; the low-angle X-ray diffraction peaks are reminiscent to those of the parent SBA-15. The wide-angle X-ray pattern corresponds to the spinel structure of Co3O4; SEAD confirms that the porous material exhibits a relatively high degree of crystallinity. A largepore SBA-15 (9 nm pore diameter) was chosen in order to obtain a Co3O4 product with preferably thick pore walls, since the long-term application of the material as a gas sensor at elevated temperatures requires high stability. This results in a rather moderate specific BET surface area of 40 m2 g"1, lower than that reported for a similar synthesis by Tian et al. (82 m2 g"1) [2]. Nitrogen

349

physisorption (not shown) reveals a mean pore diameter of 3.9 nm (BJH method). 500

4 6 291 degrees

Figure 1. Left: Powder X-ray diffraction pattern of mesoporous Co3O4. The low-angle peaks (indexes in parenthesis) correspond to the p6mm hexagonal mesostructure; the wide-angle pattern shows the crystalline Co3O4 spinel structure. Right: TEM image and selected area electron diffraction (SAED) pattern of the same sample.

We have tested the gas-sensing properties of mesoporous CO3O4 for carbon monoxide in technically relevant concentrations between 1 and 5 ppm at a relative moisture of 50%. (In most countries the legal threshold for long-term exposure to CO gas without health damage is specified as ca. 30 ppm.) The performance of the sensor prepared from mesoporous CO3O4 was compared to that of a bulk (non-porous) CO3O4 sensor (specific BET surface area: 12 m2 g"1). The measurements were performed at various temperatures to determine the optimum operation conditions. The bulk sensor reaches its highest sensitivity at a temperature of 300 °C where it is more sensitive than the mesoporous sensor. However, the mesoporous sensor is most sensitive already at 220°C. At this rather low temperature its sensitivity is higher than the maximum sensitivity (i.e. 300°C) of the bulk sensor. In other words, the mesoporous sensor is (i) generally more sensitive and (ii) suitable for lower operating temperatures (lower power consumption for battery backed fail safe applications). Figure 2 (left) shows the sensitivity (which is the measured resistance normalized to the resistance in absence of CO gas) at 220°C. The mesoporous sensor delivers a prompt and steep response to the CO gas, even though saturation is not reached within the measuring interval of 30 min. The bulk sensor shows saturation after 5 min, but the signal is noisy and weak in relation to drift effects. The sensitivities at both temperatures, 220°C and 300°C, are compared in the right-hand plot in Figure 2; as described above, the porous sensor combines the more favorable operating conditions (lower temperature) with a higher sensitivity.

350 1,7

1,5

1,6

___o

1,4

1,5 1.4

S 1,3

1,3

5 1,2

o

-n _^

to

1,2

—-n—

1,1

1,1

8

1.0 120

180 240 f/me / minutes

300

360

—o

•

D -O I^Ô

1,0 2

3

4

CO concentration I ppm

Figure 2. Left: Gas sensor measurement at 220°C showing the CO gas concentration (dotted line) and sensitivities of the mesoporous Co3O4 sensor (black solid line) and of the bulk Co3O4 sensor (grey solid line). Right: Comparison of the sensitivities at the respective optimum operation temperatures, which lie at 220°C for the mesoporous and at 300°C for the bulk sensor. All measurements were performed with 50 % relative humidity.

4. References [1] A.-H. Lu, W. Schmidt, A. Taguchi, B. Spliethoff, B. Tesche and F. Schuth, Angew. Chem. Int. Ed., 41 (2002) 3489. [2] B. Tian, X. Liu, H. Yang, S. Xie, C. Yu, B. Tu and D. Zhao, Adv. Mater., 15 (2003)1370. [3] K. Zhu, B. Yue, W. Zhou, and H. He, Chem. Commun., (2003) 98. [4] Y.Wang, C.-M. Yang, W.Schmidt, B. Spliethoff, E. Bill and F. Schuth, Adv. Mater., 17(2005) 53. [5] J. Roggenbuck, and M.Tiemann, J. Am. Chem. Soc, 127 (2005) 1096. [6] J. -H. Smatt, C. Weidenthaler, J. B. Rosenholm and M. Linden, Chem. Mater., 18 (2006) 1443. [7] T. Wagner, C. -D. Kohl, M. FrOba and M. Tiemann, Sensors, 6 (2006) 318. [8] D. Zhao, Q. Huo, J. Feng, B. F. Chmelka and G. D.Stucky, J. Am. Chem. Soc, 120 (1998) 6024.


351 351

Direct synthesis of mesoporous spinel-type Zn-Al complex oxide with a crystalline framework Lu Zou, Feng Li *, Xu Xiang, David G. Evans and Xue Duan State Key Laboratory of Chemical Resource Engineering, P. O. Box 98, Beijing University of Chemical Technology, Beijing 100029, P.R. China.

Crystallized mesoporous solid solution of spinel-type Zn-Al complex oxide (Z11AI2O4) with roughly spherical morphology was directly synthesized via a solvothermal route in the presence of urea without using any templates. The assynthesized ZnAl2O4 possesses a disordered mesoporous structure with spineltype framework, and has a high BET surface area of 472 m2 g"1 and narrow pore-size distribution centered at ~3.4 nm. The amount of inversion of the mesoporous ZnAl2O4 is found to be small (4.8 %). 1. Introduction Since the discovery of mesoporous silica materials, increasing attention has been focused on the preparation and applications of non-siliceous mesoporous materials based on transition metal oxides [1-3]. Up to now, a large number of mesoporous metal oxides and complex metal oxides have been reported and they are expected to be useful for various applications particularly as heterogeneous catalysts [1-4]. However, the wall of these materials is normally amorphous, and under heat treatment, crystallization results in collapse of the uniform mesoporous structure [5]. Zinc aluminate (ZnAl2O4), also referred as spinel-type Zn-Al complex oxide, has a wide range of uses. It mainly serves as catalysts and catalyst supports in synthesis, dehydrogenation, dehydrocyclization, hydrogenation, dehydration, isomerization, and combustion processes [6-7]. Besides, it is a wide band-gap semiconductor (3.8ev) that can be used as transparent conductor, dielectric, or optical materials [8]. To prepare ZnAl2O4, high-temperature treatment of precursors such as solid ZnO and a-Al2O3 or Aland Zn-containing complexes are generally employed. In the present study, we report a novel method for preparing crystallized mesoporous ZnAl2O4 via a

352

solvothermal route based on controlled hydrolysis of urea in propanol-water system. 2. Experimental Section In a typical experiment, urea (0.8 mol), and stoichiometric zinc nitrate (0.04 mol) and aluminum nitrate (0.08 mol) were dissolved in 75 ml of deionized water or propanol-water (v/v =1:1) mixed solvent to form a transparent solution. Then the solution was transferred into a teflon-lined autoclave, and heated at 453 K for 12 h. After cooling to room temperature, the product was filtered, washed with deionized water and then ethanol to obtain a white gel. Finally the gel was dried at 363 K for 12 h. Urea is used here as a homogeneous precipitator. The as-synthesized samples in water and propanol-water system are denoted ZA-W and ZA-P, respectively. Powder X-ray diffraction (XRD) patterns were obtained using a Rigaku D/Max2500 with CuKa radiation (A=0.15418 nm). The scanning electron microscopy (SEM) image was obtained on a Hitachi S-3500N scanning electron microscope. Transmission electron microscopy (TEM) image was recorded with a Philips TECNAI-20 highresolution transmission electron microscope. The accelerating voltage was 200 kV. N2 sorption isotherm was measured using a Quantachrome Autosorb-lCVP system. 27A1 solid-state magic-angle spinning (MAS) NMR spectra were measured on a Bruker AV300 spectrometer operating at 78.20 MHz with a pulse width of 0.5 s, spinning rate of 8000 Hz and an acquisition delay of 0.5 s between successive pulses to avoid saturation effects. 3. Results and Discussion Fig. la shows the low-angle power X-ray diffraction (XRD) patterns of samples. Sample ZA-P prepared in propanol-water system shows one broad peak at 10.9 A, meaning that the sample has a disordered mesostructure with no discernible long-range order in the mesopore range. The wide-angle XRD pattern (Fig. lb) of sample ZA-P shows broad characteristic diffraction peaks of cubic ZnAl2O4 spinel phase following JCPDS No.05-0669, signifying that the mesoporous walls of sample ZA-P is composed of nanocrystalline ZnAl2O4. However, if reaction happens in water system, the obtained material is composed of boehmitic AIO(OH) and Zn(OH)2 with a disrupted framework (no low-angle diffraction peak). Therefore it is worth noting that the hydrolysis of urea could be effectively controlled by using propanol/water as the solvent in a closed vessel to obtain a porous ZnAl2O4 network. The morphology of mesoporous ZnAl2O4 (sample ZA-P) was determined by SEM and TEM experiments. As shown in the typical SEM image (Fig. 2a), the ZnAl2O4 product exhibited a roughly spherical morphology. From the TEM image (Fig. 2b), we can see that a disordered mesoporous structure existed in the product, which is consistent with the low-angle XRD result. The selected

353 353

area electron diffraction pattern, shown as inset to Fig. 2b, verifies the presence of crystalline ZnAl2O4 in the mesostructured framework. i x

311

(a)

.-JJ

0 1 2 3 4 5 6 7 8 20 (degrees)

10

20

30

40

50

60

70

80

20 (degrees)

Fig. 1. (a) Low and (b) wide-angle X-ray diffraction patterns of sample (i) ZA-W and (ii) ZA-P. (O) Zn OH)2; ( • ) boehmitic AIO(OH).

Fig. 2. (a) Typical SEM image and (b) TEM image of sample ZA-P. The electron diffraction pattern is shown in the inset of TEM image.

The low temperature nitrogen adsorption-desorption isotherm and the corresponding BJH pore size distribution curve of mesoporous ZnAl2O4 are shown in Fig.3. The nitrogen adsorption isotherm shows an adsorption jump at P/Po of 0.5-0.8, characteristic of capillary condensation in mesopore. The poresize distribution is highly narrow and centered at ~ 3.4 nm. The BET surface area and total pore volume are as high as 472 m2 g"1 and 0.45 cm3 g"1, respectively. The 27A1 MAS NMR spectra of the samples ZA-W and ZA-P are shown in Fig. 4. The presence of both tetrahedral A1O4 sites (chemical shift at ~ 63 ppm) and octahedral A1O6 sites (chemical shift at ~ 6 ppm) is unequivocally demonstrated. The proportion of tetrahedrally coordinated Al for samples ZAW and ZA-P, which is calculated from the octahedral to tetrahedral peak area

354

ratio, is approximately 1.7 % and 4.8 %, respectively. It indicates that the amount of inversion is small in mesoporous Z11AI2O4 sample. In addition, investigation of tuning the structural and textural properties of mesoporous ZnAl2O4 through varying reaction parameters is currently underway. 4. Conclusion In summary, we have successfully synthesized mesoporous ZnAl2O4 spineltype oxide via a facile solvothermal route. Such mesoporous ZnAl 2 O 4 spinels should be desirable for various applications, such as for supports in heterogeneous catalysis, as they have very interesting textural and structural properties. Moreover, the one-pot synthesis approach described might open a new route to fabricate many different ceramic, spinel materials concerned with pore systems. ~° 6.30

Pore Volume (cm3g-1nm-1)

0.016

0.012

0.000

0

5

10

15

20

25

Pore Diameter (nm)

30

b

6.34

250

0.004

64.01

300

0.008

200 150 100 50 0.0

a 0.2

0.4

0.6

0.8

1.0

P/ P0 P/P Fig. 3. N2 sorption isotherms and BJH pore size distribution (inset) of sample ZA-P.

200 150 100 200 15010050 100

62.48

Volume (cm3 g-1, STP)

350

50

0

-50

-100 -100

5 (ppm) (ppm) Fig. 4. Al solid-state MAS NMR spectra of sample (a) ZA-W and (b) ZA-P.

5. References [1] F. Schuth, Chem. Mater., 13 (2001) 3184. [2] M. A. Carreon and V. V. Guliants, Eur. J. Inorg. Chem., (2005) 27. [3] P. Yang, D. Zhao, D. I. Margolese, B. F. Chmelka and G. D. Stucky, Nature, 396 (1998) 152. [4] X. He and D. Antonelli, Angew. Chem. Int. Ed., 41 (2002) 214. [5] H. Shibata, T. Ogura, T. Mukai, T. Ohkubo, H. Sakai and M. Abe, J. Am. Chem. Soc, 127 (2005) 16396. [6] H. Grabowska, M. Zawadzki and L. Syper, Appl. Catal. A: Gen., 265 (2004) 221. [7] L. Chen, X. Sun, Y. Liu, K. Zhou and Y. Li, J. Alloys Compd., 376 (2004) 257. [8] S. Mathur, M. Veith, M. Haas, H. Shen, N. Lecerf, V. Huch, S. Hiifher, R. Haberkorn, H. P. Beck, M. Jilavi, J. Am. Ceram. Soc, 84 (2001) 1921.


355 355

Visible light activated mesoporous TiO2.xNx nanocrystalline photocatalyst Zheng Jiang, Farhan Al-Shahrani, Tsung-Wu Lin, Yingying Cui and Tiancun Xiao* Inorganic Chemistry Laboratory, University of Oxford, South Parks Road, OX1 3QR, U.K.

Mesoporous TiO2.xNx has been prepared using template-free solvothermal synthesis with post-ammonolysis at 500°C. The characterizations using XRD, Raman, XPS, N2 ad-desorption and TEM showed that the TiO2.xNx is typical mesopores anatase nanocrystaline. The nitrogen dopant causes the absorption edge of TiO2 shift to a lower energy region which enhances its visible light absorption. Under visible light irradiation, the TiO2.xNx exhibits higher activity than commercial P25 but similar activity in decoloration of methylene blue under UV irradiation. 1. Introduction There have been great interests in porous titania for its potential application in photocatalysis, sensor, and photovoltaics [1]. Different synthesis strategies to produce mesoporous titania have been developed using a variety of surfactant templates [1, 2]. However, post-synthetic removal of the template requires additional processes that can be costly, wasteful and of environmental concern, as well as damages the mesoporous texture of titania for thermal nucleation [2]. Despite of its high surface area and accessibility, mesoporous TiO2 absorbs only the UV part (2-3 %) in solar light, which seriously affects its efficient utilization of sunlight [3]. Various methods have also been employed to enhance the adsorption of visible light for TiO2 material through bandgap engineering routes, such as loading or doping with transition metals or noble metals. However, such methods are either inefficient or unstable [4]. The preparation of visible light activated stable titania still remain a challenge. Therefore, visible-light activated titania with mesporous texture has been the aim for development, but not completely available yet.

356

Recent investigations showed that N-doped titania, TiO2.xNx is one of the most active and stable candidates among the visible light active titania [3,4]. It possesses the advantages of duration and activity over transition metal doped TiO2. However, no work has been reported so far in preparing mesoporous TiO2.xNx using template-free methods. Herein, we report the mesoporous TiO2 synthesized by solvothermal route, followed by ammonolysis to get TiO2.xNx for the first time. The process is more convenient than template method as it need not directing reagent. 2. Experimental Section Typically, 2 mL distilled water was added dropwise to 20 ml 0.5M Ti(BuO)4 ethanol solution under vigorously stirring. The obtained gel was transferred to autoclave heated at 100°C for 18 h. The resultant gel was dried at 110°C and calcined at 500°C in air for 2 hours, the obtained material was denoted as TiO2ST. The yellowish N-doped TiO2.xNx-ST sample was prepared by ammonolysis of TiO2-ST in NH3/Ar (NH3/Ar=l/4 mol ratio) flow for another 2 h. The asprepared white TiO2-ST and yellowish TiO2.xNx-ST was characterized using various physical techniques. The XRD patterns of the catalysts were obtained with a Philips PW1710 diffractometer using Cu-Ka radiation X-ray at 40 eV and 30 mA. All samples were mounted on a quartz plate with a groove cut into it and measured at room temperature. Nitrogen adsorption-desorption properties were measured at 77 K on a ASAP 2000 sorptionmeter. TEM and HRTEM were conducted on JEOL 2000FX and JEOL 4000 EX respectively. X-ray photoelectron spectroscopy (XPS) measurements were performed with a KROTOS XSAM 800 system, equipped with a dual Mg/Al anode. The spectra were excited with Al Ka. radiation operated at 12 kV and 10 mA. The analysis was carried out in an FRR mode. The Raman spectra of the resultant materials were recorded in a Yion Jobin Labram 300 spectrometer with a resolution of 2 cm"1. It is equipped with a CCD camera enabling microanalysis on a sample point. A 514.5 nm Ar+ laser source was used and the spectra were acquired in a back-scattered confocal arrangement. The visible light photo-catalytic activity on destruction of methylene blue (MB) was compared with commercial P25 (Degussa, SSA ~ 50 m2/g). 3. Results and Discussion Fig.l shows the XRD patterns and Raman spectra of the TiO2-ST and TiO2. N X X-ST photocatalysts calcined at 500°C. It can been seen that the undoped TiO2-ST and the N-doped TiO2.xNx-ST have the similar anatase structure (JCPDS21-1272), but the characteristic diffraction peaks of TiO2.xNx-ST are much sharper and narrower than those of TiO2-ST, suggesting that the particle size of TiO2.xNx-ST anatase is a bit larger than that of TiO2-ST. In addition, the

357

two titania are not well-ordered mesoporous oxides because there is no small angle diffraction peaks detected for both of them. Because Raman spectra are much more sensitive than XRD in identifying the coordination and local domain of the surfaces and small crystalline species, it was used to determine the phase

4000

(101)

140.5(E g)

JCPDS 21-1272

8000

3500

3000 6000

2000

634 (Eg)

514.3 (A1g+B1g)

391.2 (B1g)

4000

191.4 (Eg)

1000

Intensity

(204)

(220)

(a)

(105) (211)

2000

1500

(200)

(103) (004) (112)

Intensity

2500

(a)

500

(b)

(b) 0 20 20

0

30 30

40 40

50 50

60

70

100 100

200 200

300 300

400 400

o

500 500

600 600

700 700

800 800

900 900

-1

Raman Shift (cm (cm -1) Raman

2Thela (f)) 2Theta

Fig. 1 XRD patterns and Raman spectra of (a) TiO2-xNx-ST and (b) TiO2-ST calcined at 500°C composition of the two catalysts. As shown in the laser Raman spectra, the observation of Raman shifts at 399, 519 and 638 cm"1 further proves that both Ti(XxNx-ST and TiO2-ST only possesses anatase phase without any rutile phase [5]-" Fig.2 shows the N2 adsorptiondesportion isotherm and BJH pore size distribution (inset) of TiO2-ST and TiO2. 1 / !/1 r XNX-ST. As shown in Fig. 2, the two catalysts are all of obvious IV hysteresis loops, indicating there exists mesopores in the two catalysts. The inset pore size distribution profile shows the mesoporous structures of such materials. In fact, the average pore diameter of TiO2-ST and Fig.2 N2 ad-desportion isotherm and BJH TiO2.xNx-ST are both around 10 nm. pore size distribution (inset) of TiO2-ST Furthermore, the specific surface area of and TiO2.xNx-ST TiO2_xNx-ST is about 85 m2/g which is much smaller than that of TiO2-ST (148 m7g)), but much higher than the SSA of P25 (~ 50 m2/g). This suggests that significant sintering of such mesoporous titania occurred in the ammonolysis process. The isotherm plots also imply there is no ordered mesopores existing in such materials. All the XRD and N2 adsorption-desorption results imply the mesopores of TiO2.xNx-ST resulting from the stacks of TiO2.xNx-ST nano-crystal particles. The images of TEM and 200 180

-m- TiO TiO 2-ST -ST ^.-'-w 2 -m- TiO TiO^N^-ST/" / N -ST 2-x x

I

160 140

Y Axis Title

120 100 80 60

0

J\ 10

20

30

40

50

Pore Diameter (nm)

40 20

0 0.0

0.2

0.4

0.6

P/P0

0.8

1.0

358

HRTEM as shown in Fig. 3 suggested the presence of the irregular mesopores. The TEM image shows that the size of TiO2.xNx-ST particles is about 15 nm. The clear lattice fringe shown in HRTEM image further supports that TiO2_xNxST is crystalline material, which is well consistent with the results of XRD.

Fig. 3 TEM(Left) and HRTEM(Right) images of TiO2.xNx-ST

As shown in Fig. 4, the UV-Vis-DRS indicates the mesoporous TiO2-xNx-ST can adsorb visible light with wavelength up to 550 nm (-2.26 eV), in comparison, TiO2-ST is much similar to the P25(~ 3.20 eV) [3]. This suggests that N-dopant is of visible light activation and the potential activity in visible light photocatalysis reactions. XPS results (inset of Fig.4) indicate that the element N is doped into anatase crystal matrix according to the N bonding energy changing from 395 to 402 eV [3]. As expected, the TiO2.xNx-ST sample shows higher activity under TiO -ST visible light for decolorizing of N1s XPS of TiO N methylene blue, but TiO2-ST and P25 are roughly inactive under the | similar conditions. It is noteworthy f a the absorbance of TiO2.xNx-ST is much lower that that of TiO2-ST in TiO N ultraviolet range. However, the TiO2XNX sample shows the similar UV reactivity in comparison with P25 Wavelength(nm) Wavelength(nm) (results not shown here). The detailed photocatalysis reaction Fig.4 UV-Vis-DRS of TiO2-ST and NIs kinetics and mechanism is under XPS spectra of TiO2.xNx-ST (the inset) study. 2200

1.6

2

1.5

2100

1.3 1.2

2-x

CPS

1.1

Absorbence

N1s

Experiment Fitting

1.4

1.0

x

2000

0.9 0.8

1900

0.7 0.6

1800

0.5

410

0.4

405

400

395

390

Binding Energy (eV)

0.3 0.2

2-x

x

0.1

0.0 200

300

400

500

600

700

800

900

4. Conclusion The combination of the template-free solvothermal synthesis of TiO2-ST and post-ammonolysized TiO2.xNx-ST is an effective method for preparing

359

mesoporous N-doped TiO2. The mesopores of TiO2-xNx-ST result from the aggregation of their nano-crystalline particles. The crystal anatase phase of TiO2.xNx-ST is an important feature for photocatalysis. The TiO2.xNx-ST can adsorb the visible light up to 550 nm, therefore exhibits higher visible light activity. 5. References [1] [2] [3] [4] [5]

Y. Yue and Z. Gao, Chem. Commun. (2000) 1755. A. Collins, D. Carriazo, S. A. Davis and S. Mann, Chem. Commun., (2004) 568. S. Sakthivel, M. Janczarek and H. Kisch, J. Phys. Chem. B, 108 (2005) 19384. R. Asahi, T. Morikawa, T. Ohwaki, A. Aoki and Y. Taga, Science, 293 (2001) 269. K. Cassiers, T. Linssen, V. Meynen, P. V. D. Voort, P. Cool and E. F. Vansant, Chem. Commun., (2003) 1178.



361 361

Mesoporous metal oxides and mixed oxides nanocasted from mesoporous vinylsilica and their applications in catalysis Y. G. Wang, Y. Q. Wang*, Y. Guo, Y. L. Guo, X. H. Liu and G. Z. Lu Lab for Advanced Materials, Research Institute of Industrial Catalysis, East China University of Science and Technology, Shanghai 200237, P. R. China

Mesoporous metal oxides and mixed oxides, such as CeO2, Cr2O3, CoCr 2 0 4 and CexZri.xO2 (x = 0.8 and 0.6) have been synthesized by nanocasting from mesoporous cubic {laid) vinylsilica. Their structural properties were characterized by XRD, TEM and N2 sorption. The redox properties of CexZri_ XO2 were characterized by H2-TPR and the catalytic properties of Cr2O3 and CoCr2O4 were tested in the oxidation of toluene. 1. Introduction: Mesostructured metal oxides/composites with framework compositions other than silica are attractive research targets because of their special properties, such as their magnetic and catalytic properties. Recent research showed that mesoporous Cr2O3 have excellent properties in VOCs removal [1]. There have been several reports concerning the synthesis of mesoporous metal oxides via surfactant-templated, ligand-assisted and triblock copolymer templated pathways. However, the direct synthesis of this kind of mesoporous materials with surfactants is quite difficult compared with that of silica materials. One difficulty may the crystallization induced structural collapse, during the mesostructure formations and the removal of the organic templates. The nanocasting pathway for carbon, pioneered by the group of Ryoo [2], is an attractive alternative to the cooperative assembly routes and has been extended to the nanocasting of metals [3], metal oxides [4-7], and metal sulfides [8]. This is a good method to synthesize mesoporous non-silicious materials, especially metal oxide composites, such as spinal-type ferromagnetic ferrites, cerium-zirconium oxide solid solutions (CexZri_xO2) and perovskites, which are hard to be successfully synthesized with the assembly of surfactant-inorganic

362

precursors [9]. While cerium-zirconium oxide solid solution is the most important three way catalysts [9, 10] due to its high oxygen storage capacity, and CoCr2O4 and perovskites are good catalysts for VOCs removal [11, 12] and methane combustion [13]. So in this work, the nanocasting procedure to transition metal oxides, rare earth oxide (CeO2) and composites were investigated. 2. Experimental Section The synthesis of mesoporous cubic vinyl-funcationalized silica [TEVS/(TEVS+TEOS)* 100=20%] is according to the processor of reference [ 14] and the nanocasting of mesoporous metal oxides and mixed metal oxides is similar to that in reference [7]. The redox properties of mesoporous CexZr].xO2was determined by means of H2-TPR method in a quartz reactor coupled with a thermal conductivity detector. Catalytic activity of Cr2O3 and CoCr2O4 were performed in a continuous-flow fixed-bed microreactor (10 mm i.d.) for toluene combustion (space velocity: 30000 h"'; toluene: 486 ppm; air: 470 ml/min). 3. Results and Discussion Mesoporous metal oxides and mixed oxides were synthesized by nanocasting from mesoporous vinylsilica [14]. Their meso-structures were characterized by small-angle XRD , TEM and N2 sorption, their phase composition were confirmed by wide-angle XRD. The small-angle XRD patterns (Fig. 1) confirm the mesostructure, although it is not well-resolved. The wide-angle XRD patterns of the mesoporous Cr2O3 and CoCr2O4 (Fig. la, inset)

2

3

2e/degree

4

2

3 28/degree

4

Fig. 1. XRD patterns of mesoporous metal oxides and mixed oxides: a) Cr2O3 and CoCr2O4, b) CeO2, Ce0 8Zr0 2O2 and Ce0 8Zr02O2.

clearly show that the materials have well-crystalline rhombohedral phase and spinel phase, respectively. The wide-angle XRD pattern of the CeO2 and CexZri_

363

CeZrO. —2 (JCPDS card no.4-0593), whereas for Ceo.8Zro.2O2 and Ceo.6Zro.4O2, the cZ-values are shifted towards higher angle with the increase of zirconium. N2 sorption shows that thus-prepared mesoporous materials possess a high BET surface area (110-190 m2g"'). The H2-TPR of CeO2 and CexZri.xO2 are shown in Figure 2, which is different from that of CeO2 and CexZr].xO2 prepared by reverse emulsion or coprecipitation method[15], it maybe due to the incorporation of silicon in the framework. The catalytic activity of mesoporous Cr2O3 and CoCr2O4 in toluene oxidation is shown in Fig. 3. Mesoporous Cr2O3 shows good activity than commercial Cr2O3, which is in accordance with Sinha's work [1]. In summary, mesoporous metal oxides and mixed oxides were successfully synthesized by nanocasting from mesoporous vinylsilica. Thus-prepared mesoporous materials possess a high BET surface area, pore volume and uniform mesopores. XRD patterns show that some of this materials have a relative ordered structure; H2-TPR shows the mesoporous CeO2 have plentiful of surface oxygen due to it's mesoporous structure and the introduction of zirconium changes the oxygen storage property of the mesostructured CexZri_ XO2 , which is different from previous report. The catalytic activity of mesoporous Cr2O3 and CoCr2O4 in toluene oxidation shows that mesoporous Cr2O3 have good activity than commercial Cr2O3. 4. Acknowledgment

This project was supported financially by the National Basic Research Program of China (No. 2004CB719500) and Commission of Science and Technology of Shanghai Municipality (O552nmO3O), China.

364 364

5. References [1] A. K. Sinha and K. Suzuki, Angew. Chem. Int. Ed. 44 (2005) 271. [2] R. Ryoo, S. H. Joo and S. Jun, J. Phys. Chem. B 103 (1999) 7743. [3] D. H. Wang, H. M. Luo, R. Kou, M. P. Gil, S. G. Xiao, V. O. Golub, Z. Z. Yang, C. J. Brinker and Y. F. Lu, Angew. Chem. Int. Ed. 43 (2004) 6169. [4] K. Jiao, B. Zhang, B. Yue, Y. Ren, S. X. Liu, S. R. Yan, C. Dickinson, W. Z. Zhou and H. Y. He, Chem. Commun. 45 (2005) 5618. [5] B. Z. Tian, X. Y. Liu, H. F. Yang, S. H. Xie, C. Z. Yu, B. Tu and D. Y. Zhao, Adv. Mater. 15(2003) 1370. [6] B. Z. Tian, X. Y. Liu, L. A. Solovyov, Z. Liu, H. F. Yang, Z. D. Zhang, S. H. Xie, F. Q. Zhang, B. Tu, C. Z. Yu, O. Terasaki and D. Y. Zhao, J. Am. Chem. Soc. 126 (2004) 865. [7] Y. Q. Wang, C. M. Yang, W. Schmidt, B. Spliethoff, E. Bill and F. Schuth, Adv. Mater. 17 (2005) 53. [8] X. Y. Liu, B. Z. Tian, C. Z. Yu, B. Tu, Z. Liu, O. Terasaki and D. Y. Zhao, Chem. Lett. 32 (2003) 824. [9] E. L. Crepaldi, Soler-Illia, A. Bouchara, D. Grosso, D. Durand and C. Sanchez, Angew. Chem. Int. Ed. 42 (2003) 347. [10] J. R. Gonzalez-Velasco, M. A. Gutierrez-Ortiz, J. L. Marc, J. A. Botas, M. P. GonzalezMarcos and G. Blanchard, Appl. Catal. B-Environ. 22 (3) (1999) 167. [11] D. C. Kim and S. K. Ihm, Environ. Sci. Technol. 35 (2001) 222. [12] R. Spinicci, M. Faticanti, P. Marini, S. De Rossi and P. Porta, J. Mol. Catal. A-Chem. 197 (2003)147. [13] S. Cimino, L. Lisi, S. De Rossi, M. Fanticanti and P. porta, Appl. Catal. B-Environ. 43 (2003) 397 [14] Y. Q. Wang, C. M. Yang, B. Zibrowius, B. Spliethoff, M. Linden and F. Schuth, Chem. Mater. 15(26) (2003) 5029. [15] M. Daturi, E. Finocchio, C. Binet, J. C. Lavalley, F. Fally, V. Perrichon, H. Vidal and N. Hickey, J. Kaspar, J. Phys. Chem. B 104 (2000) 9186.


365 365

Surface functionalization of templated porous carbon materials Dan Yu, Zhiyong Wang, Nicholas S. Ergang and Andreas Stein* University of Minnesota, Department of Chemistry, 207 Pleasant St. SE, Minneapolis, MN 55455, U.S.A.

1. Introduction Recently, several important advances have been made to synthesize carbon materials with controlled porosity in both the mesopore and macropore size ranges [1-3]. These include carbonization of porous polymers prepared by block-copolymer templating or colloidal crystal templating, as well as carbonization of precursors infiltrated into hard templates, such as porous silica. Just as surface functionalization of porous silica materials has benefited potential applications, controlled functionalization of porous carbon materials will be useful to modify surface and bulk properties and to adapt the materials to applications as sorbents, catalysts, sensors, electrodes, etc. Here we present methods of attaching molecular surface modifiers and nanoparticles to threedimensionally ordered macroporous (3DOM) carbon materials prepared by colloidal crystal templating. The methods for molecular surface groups should also be adaptable to mesoporous carbons. 2. Experimental Section 3D0M carbon was synthesized by infiltration of resorcinol-formaldehyde precursors into PMMA colloidal crystals and carbonization at elevated temperatures in a nitrogen atmosphere [3]. The surface of 3 DOM C was oxidized by boiling the solid in concentrated HNO3 for 1 h and washing with water by Soxhlet extraction for 1 d. The resulting surface carboxylic acid groups were reduced to hydroxyl groups by refluxing 1 g of dried, oxidized 3D0M C in 50 mLl.OM BH 3 THF solution in THF for 1 d, then washing with water by Soxhlet extraction for 1 d. The 3D0M C-OH surface was then brominated by reacting 1 g material in 10 mL JV,./V-dimethyl formamide (DMF) solution containing 1.65 g CBr4 and 1.31 g PPh3 at 80°C for 1 d. The product

366

was washed by Soxhlet extraction for 1 d using THF as the solvent. For substitution of bromide to thiol groups [4], 1 g 3D0M C-Br was dried under vacuum for 2 h, then 5 mL anhydrous DMF was added, followed by 0.28 g CH3COSK. The mixture was heated at 120 °C for 2 d. The product was washed with DMF and water several times and then stirred in 20 mL of 1 M NaOH solution for 1 d to hydrolyze the thioester group. The final 3D0M C-SH product was washed by Soxhlet extraction in water for 1 d. This procedure is summarized in Figure 1. Heavy metal adsorption on thiol-functionalized carbon was evaluated using 1.5 mM lead nitrate solution at pH 5. Functionalization of 3D0M C with nanoparticles (e.g., titania) by hydrothermal reaction involved prior deposition of polyelectrolyte layers following reported procedures [5]. Materials were characterized by XRD, SEM, TEM, nitrogen sorption analysis, XPS, EDS, FTIR and elemental analysis.

( 3DOM Carbon

Br

Figure 1. Scheme of the surface modification process for 3D0M C.

3. Results and Discussion 3D0M carbon samples with pore diameters between 250-350 nm were used as starting materials for functionalization. The glassy-carbon wall skeleton was mostly microporous with some mesoporosity (140-300 m2/g). Based on analysis by FTIR and titration, oxidation with nitric acid introduced lactone and carboxylic acid groups and enhanced the content of phenol and ketone groups [5]. The IR spectrum showed a carbonyl absorption at 1728 cm"1 after 15 min boiling in HNO3. The absorption intensity increased with time. However, treatments longer than 90 min degraded the mechanical strength of 3DOM C, by oxidizing not only the macropore surface but also bulk components of the carbon skeleton. An appropriate oxidation time was determined to be 60 min. Oxidation increased the surface area of the sample by introducing additional micropores [5]. Two broad (002) and (100) XRD reflections associated with disordered graphene layers became only slightly broader after this treatment [5]. Carboxylic acid groups provided negative charge for electrostatic attachment of

367

nanoparticles or could be reduced to hydroxyl groups under mild conditions for subsequent conversion to other molecular surface groups. Modification with molecular surface groups. In porous silicates, thiol groups are known to provide good anchoring sites for toxic heavy metals. Decoration of porous carbon with thiol groups was possible by first brominating hydroxyls and then substituting bromine by a thiolation agent. The transformation of surface carboxylic acid groups to hydroxyl groups was performed using a BH3-THF solution as a mild reducing agent which could readily infiltrate the macropores. Elemental analysis, FTIR and XPS spectra confirmed the transformation of surface functional groups. The CHON mole ratios varied from CH0.072O0.030N0.005 in the original 3 D 0 M C to CH0.i88O0.234N0.010 in the oxidized carbon to CH0.28iO0.140N0.012 in the reduced product ( 3 D 0 M C-OH). The

intensity of the carbonyl peak in the IR decreased significantly after reduction, while the relatively broad hydroxyl absorption around 3430 cm"1 grew in intensity. In the XPS spectra, Figure 2, the major peak at 285.0 eV was present in all three samples and was assigned to skeletal carbon. The original 3D0M carbon showed a weaker shoulder near 287 eV, assigned to carbonyl or quinone groups [6] that had also been identified by titration methods [5]. After oxidation, a distinct peak appeared at 288.8 eV in the spectral region for carboxylic acid groups. Following reduction, a resolved peak was no longer seen in this region, but a broad peak at 287 eV appeared, consistent with a lower oxidation state of carbon. Phenolic peaks may be present in the envelope between 285-287 eV.

B

C

Original 3DOM C

HNO3 treated 3DOM C

BH3 treated 3DOM C-OH

2

71 70 B.E.(eV)

Figure 2. XPS spectra showing (A) the C Is region of the original 3D0M C, HNO3-treated 3D0M C and BH3 treated 3D0M C-OH; (B) the Br 3d region of 3D0M C-Br; (C) the S 2p region of 3DOMC-SH.

A variety of reagents were screened for the bromination reaction, including PBr3, SOBr2 and CBr4/PPh3. Substitution without significant side reactions was only achieved with CBr4/PPh3. In the XPS spectrum of the product, a Br 3d5/2 peak was observed at 71 eV due to Br covalently bonded to C. The transformation of bromine to thiol on the surface of 3D0M C was realized by two steps: the substitution of bromine to thioacetate and the hydrolysis of thioacetate to thiol under basic conditions [4]. The XPS spectrum of the final product showed a major S 2p peak at 164.6 eV, which originated from thiol groups [7]. Elemental analysis of the product revealed 1.6 wt% sulfur,

368

corresponding to 0.5 mmol g"1. Based on absorption from 1.5 mM lead nitrate solution the thiol-functionalized 3D0M carbon had a 0.2 mmol/g capacity for lead, compared to 0.06 mmol/g for the unmodified carbon. The periodic macropore structure was maintained throughout the whole conversion process (Fig. 3 left), which is an alternative to functionalization with diazonium compounds [8].

Figure 3. Left: SEM image of 3D0M C functionalized with thiol surface groups. Right: SEM image of 3D0M C coated with polyelectrolytes and titania nanoparticles.

Surface modification with nanoparticles [5]. Macropores in 3D0M C are large enough to accommodate nanoparticles. These can be attached to the carbon surface electrostatically, using layer-by-layer (LbL) growth of positively and negatively charged polyelectrolytes. With multiple layers of poly(diallyldimethylammonium chloride) (PDDA) and poly(4-styrene sulfonate) (PSS), terminating with a PDDA layer, it was possible to synthesize nanocrystalline titania hydrothermally on the surface of 3D0M C, using an aqueous solution of titanium(IV) bis(ammonium lactato) dihydroxide (TAL) at concentrations varying from 0.01 M to 0.2 M and temperatures from 140-200°C (24 h). An example of the uniform titania coating obtained with 0.1 M TAL at 200°C is shown in Figure 3, right. Higher concentrations resulted in thicker walls. At a reaction temperature of 240°C, PDDA decomposed and nanoparticles formed within the macropores, detached from the walls. The LbL coating had the additional effect of blocking micropores and reducing the BET surface area of the porous carbon by an order of magnitude. Thus it can be used to modify the texture (microporosity and mesoporosity) of porous carbon materials. 4. References [1] H. Yang and D. Zhao, J. Mater. Chem., 15 (2005) 1217. [2] R. Ryoo, S. H. Joo and S. Jun, J. Phys. Chem. B, 103 (1999) 7743. [3] K. T. Lee, J. C. Lytle, N. S. Ergang, S. M. Oh and A. Stein, Adv. Funct. Mater., 15 (2005) 547. [4] T. C. Zheng, M. Burkart and D. E. Richardson, Tetrahedron Letters, 40 (1999) 603. [5] Z. Wang, N. S. Ergang, M. A. Al-Daous and A. Stein, Chem. Mater., 17 (2005) 6805. [6] K. Laszlo, E. Tombacz and K. Josepovits, Carbon, 39 (2001) 1217. [7] M. Volmer, M. Sratmann and H. Viefhaus, Surf. Interface Anal, 16 (1990) 278. [8] Z. Li and S. Dai, Chem. Mater., 17 (2005) 1717.


369 369

Rational control of the micro/mesoporosity of multimodally porous carbon monoliths synthesized by nanocasting Jan-Henrik Smart8, An-Hui Lub, Stefan Backlund3 and Mika Lindena "Dept. Physical Chemistry, Abo Akademi University, Porthansgatan 3-5, FIN-20500 Turku, Finland. b Dept. Heterogeneous Catalysis, Max-Planck-Institutfur Kohlenforschung,D-45470 Miilheim an der Ruhr, Germany

Hierarchically porous carbon monoliths have been synthesized by the nanocasting technique. The macroscopic shape and the macropore structure of the carbon monoliths are direct replicas of the silica mold, while the mesopore size is related to the thickness of the silica mesopore walls. It is shown that the carbon mesopore size decreases with increasing amount of a surfactant, CTAB, used in the synthesis of the monolithic silica mold. Simultaneously, the carbon monoliths become less microporous. 1. Introduction Recently, our group succeeded in preparing hierarchically porous carbon monoliths by using the nanocasting technique [l].The method is similar to the technique for preparing mesoporous carbon material introduced by Ryoo et al. [1]. However, in our case we used macro/mesoporous silica monoliths as molds [1, 2] instead of silica powders with ordered mesopores. A similar approach to prepare carbon monoliths have also been described by Shi et a/.[l]. Later, we investigated the effects of diluting the carbon precursor in order to create carbon monoliths with a bimodal mesopore structure [1, 2]. In this paper, we will demonstrate the possibility to rationally alter the mesopore size and to induce micropores in the nanocast carbon monoliths by variation of amount of surfactant introduced to the sol during the synthesis of the monolithic silica used as the mold for the carbon monoliths.

370 370

2. Experimental Section The monolithic silica molds were prepared according to an earlier described synthesis [4]. TEOS was used as silica precursor, while PEG (Mw ~ 35,000) was used to induce the phase separation and CTAB to form surfactant templated mesopores. In this series of samples the CTAB amount has been set as a variable. The final H2O/HNO3/TEOS/PEG/CTAB molar ratio in the sol was 14.69:0.25:1:0.54:0-0.24. After gelation and further aging in the mother liquid, solvent exchange in 1 M NH4OH is performed and subsequently the monoliths are dried and calcined at 55O°C. Subsequently, the carbon precursor (furfuryl alcohol, FA) was introduced together with a catalyst (oxalic acid, OxA) in the pore system of the different SiO2 monoliths by impregnation (nFA/nOxA = 200-300). Alternatively, the furfuryl alcohol was dissolved in 1,3,5-trimethylbenzene, TMB, in order to dilute the carbon precursor (in this case 60 vol % TMB). The polymerization of FA was carried out at 60 and 80°C for one day each and subsequently the polymer was carbonized at 850°C under an Ar atmosphere. Finally, to obtain the carbon replica, the silica portion of the composite was removed by etching in aqueous hydrofluoric acid solution. The carbon samples are denoted C-x, where x indicates the wt % CTAB in the starting silica molds. The structure of the silica and carbon monoliths was characterized by SEM (S-3500N, Hitachi) and TEM (HF2000, Hitachi). The micropores and the mesopores in the samples were studied by nitrogen sorption (ASAP 2010, Micromeritics). FT-Raman (FRA 106, Bruker) and XRD (X'pert, Phillips) was performed to determine the degree of graphitization of the carbon monoliths. 3. Results and Discussion As can be seen in Figure 1, by using hierarchically porous silica monoliths as molds it has been possible to prepare carbon monoliths with similar hierarchically porous structures by nanocasting techniques [1, 6, 7]. Depending on the studied length scale the carbon replica is either a positive (+) or a negative (-) of the original silica monolith. On the micrometer length scale the carbon monoliths are positive replicas, indicating that the macroscopic shape and the macropores of the carbons can directly be controlled by altering the silica mold. On the nanometer length scale it is possible to alter the carbon structure either by changing the silica mold or by diluting the carbon precursor. The effects of altering the silica mold structure by solvent exchange in different ammonia solutions together with dilution of the carbon precursor in TMB has been described earlier [6, 7]. In this work we have focused on the effects of adding CTAB to the starting sols when preparing the silica molds. When no CTAB is added the silica monoliths only contain textural porosity between the silica particles that build up the monolithic structure. By increasing the CTAB

371

concentration the silica particles will obtain an increasing amount of surfactant templated mesopores with pore diameters of ~ 4 nm [4]. Figure 1. Comparison of the starting silica monolith and the carbon replica on different length scales, a) and b) photographs of the macroscopic morphology, c) and d) SEM images of the silica the carbon macropores, e) and f) TEM images of the silica the carbon mesopores.

Table 1. Nitrogen sorption properties for the carbon replica monoliths.

Sample C-0 C-3 C-5 C-7 C-9 C-12

BET area [m2/g]

Micropore area

Mesopore volume

Micropore volume

1493 1015 766 831 1297 1123

460 205 195 122 43 0

2.17 1.41 0.82 0.82 1.19 0.74

0.208 0.088 0.086 0.049 0.007 0.000

rm2/gi

rcm3/gl

rcm3/gl

Pore Size (BJHads) [nml 14.3 7.6 6.0 4.2 2.9 2.4

Based on the results presented Table 1 it is clear that the mesopore size and volume of the carbon monoliths decrease with increasing CTAB amount used in the synthesis of the silica mold. Since the carbon monoliths are negative replicas of the original silica structure on this particular length scale, the silica mesopore walls become carbon mesopores and vice versa. The increase of porosity in the silica particles is reflected as a decrease in both pore size and volume in the replica. Thus, the results imply that the addition of CTAB can be used for a direct control of the pore wall thickness of the silica mesopores.

372

Furthermore, by increasing the CTAB amount the micropore portion in the carbon replicas is remarkably reduced, as determined from the nitrogen sorption t-plots (see Table 1). Our hypothesis is that the textural pores are large enough that the carbon structure formed inside these mesopores and also in the macropores is of an amorphous character, which normally is microporous [1]. However, when silica monoliths having a bimodal mesoporosity are used in the nanocasting process, less microporosity can be detected. The carbon structure inside these pores will also have a more dense structure due to the confinement, leading to almost nonexistent internal microporosity. Raman can be used to determine the degree of graphitization by comparing the ratio between the D band (disordered graphene sheets) and the G band (ideal graphene sheets) observed at ~1300 cm"1 and ~1595 cm"1, respectively. The Raman spectra of samples C-0 and C-9 (not shown) were compared and C-0 gave a lower G/D value than C-9 (0.83 vs. 0.89). Moreover, XRD indicated that the carbon was mainly amorphous for both samples. Nonetheless, sample C-9 had a slightly sharper and more intense (101)/(100) reflection at ~44° 29. Both results indicate that the carbon prepared from silica monoliths synthesized with a high CTAB amount have a more organized structure. It has been shown, that by altering the CTAB amount in the starting silica monoliths, the size of the mesopores and the portion of microporosity in the carbon replicas can be varied. 4. Acknowledgement The Academy of Finland, the European Integrated Project: AIMs, and the Alexander von Humbolt foundation (M.L) are gratefully acknowledged for financial support. 5. References [1] [2] [3] [4] [5] [6] [7]

A. Taguchi, J.-H. Smart and M. Linden, Adv. Mater., 15 (2003) 1209. R. Ryoo, S.H. Joo and S. Jun, J. Phys. Chem. B, 103 (1999) 7743. K. Nakanishi, J. Porous Mater. 4 (1997) 67, and references therein. J.-H. Smatt, S. Schunk and M. Linden, Chem. Mater., 15 (2003) 2354. Z. G. Shi, Y. Q. Feng, L. Xu, S. L. Da, M. Zhang, Carbon 41 (2003) 2677. A. H. Lu, J.-H. Smatt and M. Linden, Adv. Funct. Mater., 15 (2005) 865. A. H. Lu, J.-H. Smatt, S. Backlund and M. Linden, Microporous and Mesoporous Mater., 72 (2004) 59. [8] N. R. Khalili, M. Pan, G. Sandi, Carbon, 38 (2000) 573.


373 373

Synthesis of mesoporous carbon frameworks with graphitic walls by secondary hard template method Renyuan Zhang, Bo Tu, Dongyuan Zhao* Department of Chemistry and Shanghai Key Laboratory of Molecular Catalysis and Innovative Materials, Fudan University, Shanghai 200433, P. R. China.

1. Introduction Ordered mesoporous carbons have been intensively studied because of their remarkable properties since reported by Ryoo and co-workers1. The nanocasting strategy is used to prepare the mesoporous carbon replicates from the parent mesoporous silica1'5. The carbon replicates are constructed into nanorod arrays reversed from silica mesostructures. Among them, mesoporous carbon with graphitic walls attracts even more attention for the applications in electrochemistry such as fuel cells and lithium ion batteries4. Recently, selfassembly of surfactant and resol (phenol/formaldehyde) was reported to obtain mesoporous carbon with open framework structures6. However, that carbon frameworks can hardly been graphitized. Here, we report a secondary hard template method to synthesize mesoporous carbon frameworks (MCF) with graphitic walls by using highly ordered mesoporous Co3O4 nanorod replicas as a template mesophase pitch as a carbon source. 2. Experimental Section Mesoporous CO3O4 template was prepared according to the literature method7. MCF-1 preparation: in a typical synthesis, 0.3 g mesophase pitches5 was heated at 140°C in a ceramic crucible with stirring until a highly flexible fluidic black melt was formed. 1.0 g of mesoporous CO3O4 template was added to the melt step by step during stirring, finally yielding powders. The composites were carbonized at 900°C for 6 h under N2. The CO3O4 hard template was dissolved by 2 M HC1 solution. After filtration, washed with water and dried, the solid product was obtained. MCF-2 was obtained by a similar method except that the

374

carbonization was carried out after headed at 400°C and removing the CO3O4 hard template as the first step. Powder XRD patterns were recorded with a Bruker D4 powder X-ray diffractometer, using Cu Ka radiation. Raman spectra were obtained with a Dilor LabRam-lB microscopic Raman spectrum, using the He-Ne laser with the excitation wavelength of 632.8 nm. TEM images were taken with a JEOL JEM2011 electron microscope operating at 200 kV. Nitrogen adsorption/ desorption isotherms were measured at 77 K with a Micromeritcs Tristar 3000 analyzer (USA). 3. Results and discussion Well-ordered hexagonal mesoporous CO3O4 nanorods can be replicated from mesoporous silica SBA-15, which is evinced by its XRD pattern (Fig. 1). The

Intensity

\

>

•

•

\

•

r 002 002

MCF-1 MCF-2 Intensity

— SBA-15 Co3O4 — Co3O4 - MCF-1 — MCF-2

10 004

110

V.

• A — 1.0

1.5 2.5

2.0 3.0

2.5

3.0

20

2 theta theta

30

40

50

60

70

80

2 theta

Figure 1 XRD patterns of mesoporous silica SBA-15, mesoporous CO3O4 replica template and MCF products from the secondary hard template of Co3O4 replica.

Intten ensity

CO3O4 nanorods replicates can be used as the secondary hard template to prepare MCFs. XRD patterns show that MCF-2 has a hexagonal mesostructure in small domain similar to SBA-15 (Fig. 1). The regularity of MCF-1 is much — MCF-1 lower than that of MCF-2, suggesting . —MCF-2 MCF-2 p. ordered hexagonal mesostructure is ~\ lossed, possibly due to the reaction of the C and CO3O4 at high temperature. —"^ A The wide-angle XRD patterns for // \\ / \ MCF products show two intense diffraction peaks which can be A A indexed to 002 and 10 diffractions for typical graphitic structure (Fig. 1). soo 800 1000 1200 1400 1600 1800 -1 It shows that MCF-1 is better Wave number(cm number(cm-1) ) crystallized, probably due to the Figure 2. Raman spectra of MCFs

A / \

375

catalysis of cobalt oxide template at high temperature. And for MCF-1, the 10 diffraction peak splits to two peaks which can be indexed to 100 and 110 reflections of graphitic carbon.

Figure 3 TEM images of MCF-1 (a & b) and MCF-2 (c & d).

Volumn Adsorbed (cm3/g STP)

Raman spectra show a vibration at 1580 cm"1 (G-band) assigned to the interplane sp2 C-C stretching, which is the characteristic feature of graphitic carbon. A strong bond near 1580 cm'1 can be observed for the MCFs (Fig. 2), revealing a well-defined graphitized structure. The bands of MCF-1 are sharper than those of MCF-2, sug-gesting it is better graphitized. TEM image of MCF-1 (Fig. 600 MCF-1 3) shows a piece domain of Q. 500 MCF-2 hexagonal mesostructure, though XRD diffractions is 400 not observed. It is interesting O 300 that in the previous reports of mesoporous carbon with 200 graphitic walls, the orientation 100 of the graphite lattices was all perpendicular to the (001) o 0 0.0 0.2 0.4 0.6 0.8 1.0 direction of hexagonal mesoRelative Pressure(P/P Pressure(P/P0) structures. Here, the graphite 0) lattice orientation of MCF-1 is Figure 4 N2 adsorption-desorption isotherm parallel to the (001) direction plots of MCFs

376

of the mesostructure. Type IV N2 sorption isotherms with Hi hysteresis loop are also obtained for the MCF products. As shown in Fig. 4, MCF-1 has a wide pore size distribution, suggesting a disordered mesostructure. However, MCF-2 shows typical isotherms of ordered mesoporous materials. MCF-1 has a BET surface area of 289 m2/g, a pore volume of 0.55 cm3/g and MCF-2 has a surface area of 612 m2/g, a pore volume of 0.9 cm3/g. The surface areas and pore volumes are much lower than the normal amorphous meso-porous carbons templated by mesoporous silica, such as CMK-3 with the same pore structures (1500 m2/g and 1.3 cm3/g, respectively1). The reason may be attributed to the graphitized crystalline nature of the carbon frameworks. 4. Conclusion We primarily show a secondary hard template method to synthesize mesoporous carbon frameworks with graphitic walls. Small domain of hexagonal mesostructure with graphitized frameworks is observed. Since the growth direction of the graphitic layer of MCF products is parallelized to the (001) direction of the mesostructure, which show a possibility to fabricate highly ordered carbon nanotube arrays. 5. References [1] [2] [3] [4] [5]

R. Ryoo, S.-H. Joo and S. Jun. J. Phys. Chem. B, 103 (1999), 7743. J. -W. Lee, S.-H. Yoon, T. Hyeon, S. M. Oh and K. B. Kim. Chem. Commun., (1999) 2177. R. Ryoo, S. H. Joo, M. Kruk, and M. Jaroniec. Adv. Mater., 13 (2001) 677. T.-W. Kim, I.-S. Park and R. Ryoo, Angew. Chem. Int. Ed., 42 (2003) 4375. H. F. Yang, Y. Yan, Y. Liu, F. Q. Zhang, R. Y. Zhang, Y. Meng, M. Li, S. H. Xie, B. Tu and D. Y. Zhao, J. Phys. Chem. B, 108 (2004) 17320. [6] Y. Meng, D. Gu, F. Q. Zhang, Y. F. Shi, H. F. Yang, Z. Li, C. Z. Yu, B. Tu and D. Y. Zhao, Angew. Chem. Int. Ed. 44 (2005), 7053; F. Q. Zhang, Y. Meng, D. Gu, Y. Yan, C. Z. Yu, B. Tu and D. Zhao. J. Am. Chem. Soc, 127 (2005) 13508. [7] B. Tian, X. Liu, H. Yang, S. Xie, C. Yu, B. Tu and D. Y. Zhao, Adv. Mater., 15 (2003) 1370.


377 377

Porous carbons cast from meso- or nonporous silica nanoparticles Camila Ramos da Silvaa, Martin Wallauab, Eduardo Prado Baston, Rita Karolinny Chaves de Lima and Ernesto A. Urquieta-Gonzaleza* "Universidade Federal de Sao Carlos, Departamento de Engenharia Qulmica, C. Postal 676, CEP 13565-905, Sao Carlos -SP, Brazil; *e-mail: [email protected] Present adress: Universidade Federal de Pelotas, Instituto de Quimica e Geociencias, C. Postal 354, CEP 96010-900 Pelotas - RS, Brazil

Porous carbons prepared from MCM-41 or MCM-48 silica spheres as nanocast possess uniform pore diameter similar to that of the mesoporous silica wall thickness, while carbons from non-porous silica spheres or from Aerosil show wide pore size distributions. Using MCM-41 or MCM-48 spheres as cast, the parcial preservation of the silica structure in the obtained carbons indicates interconnected mesopores, which is supported by the occurrence of the tensile strength effect. 1. Introduction Mesoporous carbons are of great interest in catalysis and adsorption [1] or as hard template for the synthesis of mesoporous zeolites [2]. Recently, we described carbons cast by silica spheres analogous to MCM-41 and MCM-48 [3]. The results suggested that the MCM-41 spheres possess an interconnected pore system. To support that, we present here the analysis of the pore radius distribution of the carbon replica, obtained from the adsorption and from the desorption branch of the N2 isotherms, which showed the occurrence of the tensile strength effect [[4]], this supporting the pore connection in the used MCM-41 spherical particles, as reported previously by Tan et al. [5]. 2. Experimental Section Mesoporous silica spheres analogous to MCM-41 (S41) and MCM-48 (S48) [3], nonporous silica spheres with diameters of 160 (S16o) and 260 nm (S260) [6]

378

and pyrogenic silica (Aerosil 200 Degussa AG) were used in the form of powders or as agglomerates [3]. The porous carbons were prepared by mixing a sucrose/H2SC>4 solution with the silica powder or soaking it into agglomerates, carbonisation under inert atmosphere and dissolution of the silica cast [3]. The denomination of the carbons is given in Table 1, where Cuncast means sucrose carbonised without a silica cast. The silica casts and the carbons were characterised by physisorption of nitrogen, SEM and SAXRD. 3. Results and Discussion The specific surface area (SBET), the external specific surface area (Sext)> the total specfic pore volume (Vlol) and specific micropore volume (Vmic) of the used silica casts and carbons are given in Table 1 and their pore radius distributions (PRD) calculated by the BJH method are shown in Fig. 1 a - d. Table 1. Used silica cast and textural properties of the obtained carbons.

Aerosil

Powder S48* S41*

Sample

C-Aerosil

C48 n c

C41 n c

SBET[m2/g] S e «[m 2 /g]

369 148

534 429 0.459 0.047

Cast

0.376 V,o, [cm 3 /g] Vmic [crnVg] 0.147

Agglomerate S41+

S48*

S,60?

S 2 60 t

Without

C41 706 652

C48 a c

Cl60

C26O

c

589 262

856 851

0.410 0.135

0.547 0.049

0.714 0.040

1124 852 1.524 0.121

487 387 0.424 0.045

ûncast

61 61 0.056 0.000

*uncalcined; +calcined at 800 °C; Wintered at 700 °C.

5

45 10 (KVt H d l U l [11(11]

1{

S 10 pott f-idlu* [nm]

11

pof* ndiiix |nm

Fig. 1. PRD: a) C41 n c ; C48 n c and C48 a g ; b) S41 and C41; c) C 160 and C 260 ; d) C Aerosi | and C uncast .

Table 1 reveals that sucrose carbonised in the absence of a silica cast yields a carbon with low surface area and pore volume (Cuncast). The formation of such

379 379

carbon explains the lower surface areas of the carbons cast by powders. In the silica powders, the distance between the particles is larger than in the agglomerates and for that reason, the nonporous carbon formed in the large interstices reduces the specific surface area and the pore volume. Another factor influencing the textural properties is the particle size, as it is observed comparing the casts (Fig. 2) for carbons Ci60 and C260- Thus, one expects that CAerosii, which is prepared using primary silica particles with diameters around 12 nm, should show a higher specific surface area. However, in this case, the low Sext and V,n, is probably due to the use of Aerosil powder that favours formation of nonporous carbon or to the small pores between the primary particles, Fig. 2. SEM images of the silica casts: a) S41; b) which do not allow the S48;c)S 160 andd)S 260 . penetration of the sucrose. The PRD obtained from the desorption branch of the nitrogen isotherms of the C41nc, C48nc and C48ag (Fig. la) and of the C41 (Fig. lb) show a peak around 1.8 nm, which is absent in the PRD obtained using the adsorption branch (not shown). This fact indicates the presence of interconnected pores with radii higher than 2.0 nm, which empty through smaller pores, causing a tensile strength effect [4]. Furthermore, the PRD given in Fig. la and lb reveal for C48nc, C48ag and C41 a peak around 1.0 nm, which is also observed as a shoulder for C41nc. This peak is attributed to pores with diameters around 2.0 nm corresponding to the wall thickness of the mesoporous silica S41 (« 1.7 nm) and S48 (« 2.0 nm). On the other hand, for carbons cast with nonporous particles (C]6o, C26o and CAerosji) a wide PRD is observed (Fig. lc and Id). The presence of regular mesopores corresponding to the walls of the silica cast is expected for C48nc (Fig. 3) and C48ag, where the silica S48 possesses a three-dimensional pore system [7] but not for mesoporous materials analogous to MCM-41. Nevertheless, mesoporous spheres prepared by the used method [3] possess in addition to their periodic arrays the pores oriented radially toward the edges of the particles [5]. To explain the formation of radially oriented pores in silica spheres analogous to MCM-41 Tan et al. [5] studied the formation of such silica spheres by different techniques, including transmission electron microscopy, using the same synthesis conditions as applied here. From their results they concluded that mesoporous silica spheres are formed by aggregation of disordered silica/surfactant micelles into spherical aggregates

380

with interconnected pores [5]. During their growing, the micelles are aligned into a hexagonal pore arrangement perpendicular to the sphere surface. The partially preservation of the symmetry of the S41 pore array in its C41 replica (Fig. 4) as well as the presence of uniform mesopores in C41 indicate that the parent mould S41 possesses interconnected pores [7], so that our observations can be taken as an indirect confirmation of the formation mechanism proposed by Tan et. al. [5].

S4M44V 2

Fig. 3. SAXRD of C41nc and C48nc.

4'!l)

S

S

ID

Fig. 4. SAXRD of S41, S41/C41 and C41.

4. Conclusion Mesoporous carbons with uniform pores were obtained using mesoporous silica spheres as cast. This confirms for silica spheres analogous to MCM-41 the presence of interconnected mesopores as it was already proposed by other authors [5]. Carbons with high surface area but a wide pore size distribution are obtained using non-porous silica spheres as cast. 5. Acknowledgement Acknowledgements are given to CNPq, Brazil (grant 477759/2003-3 and 505157/2004-7) and to PVE program/Capes, Brazil (M.W.). 6. References [1] J. S. Lee, S. H. Joo and R. Ryoo, J. Am. Chem. Soc. 124 (2002) 1156. [2] Z. Yang, Y. Xia and R. Mokaya, Adv. Mater. 16 (2004) 727. [3] M. Wallau, L. Dimitrov and E. A. Urquieta-Gonzalez, Stud. Surf. Sci. Catal. 156 (2005) 535. [4] J. C. Groen and J. Perez-Ramirez, Appl. Catal. A 268 (2004) 121. [5] B. Tan and S.E. Rankin, J. Phys. Chem B 108 (2004) 20122. [6] Y. K. Ferreira, M. Wallau and E. A. Urquieta-Gonzalez, Stud. Surf. Sci. Catal. 146 (2003) 197. [7] M. Kruk, M. Jaroniec, R. Ryoo and S. H. Joo, J. Phys. Chem. B 104 (2000) 7960.


381 381

Carbon fiber-templated growth of hierarchical analcime hollow fibers Xueying Chen, Zhiying Lou, Minghua Qiao*, Kangnian Fan and Heyong He* Department of Chemistry and Shanghai Key Laboratory of Molecular Catalysis and Innovative Materials, Fudan University, Shanghai 200433, P. R. China

1. Introduction Zeolites are crystalline materials that have been widely used in catalysis, separation, and adsorption [1, 2]. However, the diffusion of guest species in practical applications is usually limited by the narrow pore size of zeolites (0.32.0 nm), especially in reactions involving large molecules. To overcome such shortcomings, intensive research has been undertaken to construct hierarchical zeolite architectures containing tailored meso- or macro-pores [3-5]. Such hierarchical zeolite architectures are expected to be of great technological importance, since they combine advantages of each pore-size regime [6-8]. Compared with other shapes (such as spherical or corpuscular), fibrous zeolite materials such as zeolite-coated fibers and hollow fibers consisting solely of zeolites have attracted considerable attention, since they can offer faster diffusion and lower pressure drop in practical applications and enhance the efficiency of catalytic and adsorptive reactions [ 9-13]. Here, we report the fabrication of hierarchical ANA hollow fibers with nanozeolite walls by using CF as the template. 2. Experimental Section 2.1. Sample preparation In a typical synthesis, the starting CF template is first treated with a HNO3 aqueous solution (10 wt%) for 2 h at 100°C to facilitate the adhesion of colloidal seed crystals. Then, CF was added into a Na 2 Si0 3 aqueous solution in batches under vigorous stirring at 90°C. After the addition of the Ni5oAl50 alloy

382

in batches, the mixture was stirred under the same condition for 2 h for further dealumination. Then ethylamine was added, followed by sulphuric acid. The nominal molar composition of the mixture was 1 SiO2: 1 Na2O : 0.22 Ni : 0.48 Al : 1.26 C2H5NH2: 0.63 H2SO4: 0.36 CF : 19 H2O. The mixture was stirred to homogeneity and then sealed in a teflon autoclave for crystallization at 180°C for 6 days. The product was washed with distilled water 6 times, ultrasonicated, and separated from the residual Raney Ni by magnetic interaction, then washed with ethanol 6 times, dried at ambient temperature, and finally calcined at 550°C in air for 6 h to remove the CF template. 2.2. Characterization The X-ray diffraction (XRD) patterns were collected on a Bruker AXS D8 Advance X-ray diffractometer using Cu Koc radiation. The morphology and element distribution were measured by scanning electron microscopy (SEM, Philips XL30). The microstructures were characterized by transmission electron microscopy (TEM, JEOL JEM2011). 3. Results and Discussion Fig. 1 shows the SEM and TEM images of the initial CF template. As shown in the figures, the CF template is curving fibers with diameter ranging from 600 nm to 1.2 p.m and aspect ratio (fiber length to fiber diameter) varying in the range of 5-50.

Fig. 1 (a) SEM and (b) TEM images of the initial CF template.

Fig. 2 shows the SEM and TEM images of the as-prepared products. The products are composed of fiber-like materials with uniform diameter of ca. 4 H.m. They are hollow in the interior and the thickness of the walls is relatively homogeneous both along and around the fibers (~ 1 urn). The surface of the hollow fibers is rough, which is composed of aggregates of nanocrystals. From

383 383

Figs. 2c and 2d, we can see that the diameter of the nanocrystals on the surface of the hollow fiber is ranging from 60-150 nm.

Fig. 2 SEM (a, b, c) and TEM (d) images of the as-prepared products.

_WUU IL*_A_J|A~_JWLJA

Fig. 3 XRD patterns of the as-prepared products.

J\~JLJL^yuv_A

384

The XRD patterns of the as-prepared products are shown in Fig. 3. The diffraction peaks are characteristic of ANA which belongs to the laid space group. Neither other crystalline phases nor any indication of amorphous material was found in the XRD patterns. 4. Conclusion Hollow fibers consisting solely of zeolite analcime (ANA) were prepared by in situ deposition of ANA nanoseeds over carbon fiber (CF) template which was removed during a subsequent calcination. Colloidal ANA seeds were produced by reacting Ni5oAl5o alloy with the aqueous solution of Na 2 Si0 3 at 90°C. CF template was surface-modified to facilitate the adsorption and crystallization of the ANA nanoseeds. The ANA hollow fibers produced showed a rough surface constituted of nanocrystals about 60-150 nm and a relatively uniform fiber wall thickness of 1.0 (im both along and around the fibers. This work was supported by Shanghai Science and Technology Committee (03 QB14004, 06JC14009), and the Fok Ying Tong Education Foundation (104022). 5. References [1] [2] [3] [4] [5] [6] [7] [8] [9] [10] [11] [12] [13]

M. E. Davis, Ind. Eng. Chem. Res., 30 (1991) 1675. D. W. Breck, Zeolite Molecular Sieves, Wiley, New York, 1974. L. Toshevaand V. Valtchev, Chem. Mater., 17 (2005) 2494. V. Valtchev and S. Mintova, Micropor. Mesopor. Mater., 43 (2001) 41. V. Valtchev, Chem. Mater. 14 (2002) 4371. B. T. Holland, L. Abrams and A. Stein, J. Am. Chem. Soc, 121 (1999) 4308. L. Huang, X. D. Wang, J. Sun, L. Miao, Q. Li, Y. Yan and D. Y. Zhao, J. Am. Chem. Soc, 122 (2000) 3530. Y. J. Wang, Y. Tang, Z. Ni, W. M. Hua, W. L. Yang, X. D. Wang, W. C. Tao and Z. Gao, Chem. Lett., (2000)510. K. Okada, H. Shinkawa, T. Takei, S. Hayashi and A. Yasumori, J. Porous Mater., 5 (1998) 163. K. Okada, K. Kuboyama, T. Takei, Y. Kameshima, A. Yasumori and M. Yoshimura, Micropor. Mesopor. Mater., 37 (2000) 99. S. Mintova and V. Valtchev, Zeolites, 16 (1996) 31. V. Valtchev, B. J. Schoeman, J. Hedlund, L. S. Mintova and J. Sterte, Zeolites, 17 (1996) 408. Y. L. Wang, Y. Tang, X. D. Wang, W. L. Yang and Z. Gao, Chem. Lett., (2000) 1344.


385 385

Synthesis of mesoporous silica and mesoporous carbon using gelatin as organic template Chun-Han Hsua, Hong-Ping Lina*, Chih-Yuan Tangb and Ching-Yen Linb "Department of Chemistry, National Cheng Kung University, Tainan, Taiwan, 701. b Department of Zoology, National Taiwan University, Taipei, Taiwan 106

Mesoporous silica of high surface area, large pore size were readily prepared by using the bio-degradable gelatin as template and sodium silicate solution as silica source. Pore size of the mesoporous silica is dependent on the pH value of the hydrothermal solution. In addition, the gelatin-phenol formaldehyde polymer blend can also be used as the template to synthesize the mesoporous silica or mesoporous carbon via proper preparation processes. 1. Introduction Since the discovery of the quaternary ammonium surfactant-templated mesoporous silicas by Yanagisawa et al. and Mobile researcher [1], the surfactant-templating method has been extensively performed to prepare various mesoporous silicas with high surface area, tunable pore dimension, and desired morphology for the applications in catalysts, adsorbents, and nanotemplates [2-4]. In the typical synthetic composition, the cationic and neutral block-copolymer surfactants of amphiphilic property have widely used as the mesostructural template [1-4]. The pore size is, thus, mainly determined by the hydrophobic chain length of the surfactants. However, the hydrophobic parts of the surfactants decompose slowly in the environment under ambient condition [5]. With recently increasing concern on the aquatic toxicity from the surfactants, using natural-friendly reagents to prepare the mesoporous silica is much desirable. According to the silica chemistry [6], the gelatin of watersoluble natural protein, which possess lots of amino (-NH2) functional groups can have a high affinity to strongly interact with silanol groups (Si-OH) on the silicate species via multiple hydrogen bonds. Therefore, the gelatin could be regarded as an alternative template to synthesize the porous silicas.

386 386

2. Experimental Section Typical synthetic procedure for the porous silicas using gelatin is as following: 1.0 g of gelatin was dissolved in 25.0 g of water to form a clear solution. To prepare a silicate stock solution, a mixture of 4.0 g of sodium silicate (SiO2: 27 wt.%, NaOH: 14 wt.%, Aldrich) and a 25.0 g of water was added into a 25.0 ml 0.1 M H2SO4, and then the pH value was adjusted to about 5.0 at 40°C. Then, the gelatin solution was poured directly into the silicate stock solution under stirring and light-yellow precipitate was generated within seconds. After stirring for 30 min, the pH value of the gel solution was adjusted to 6.0-3.0. Fin ally, the gel solution was transferred into an autoclave, and hydrothermally treated at 100°C for 1 d. Filtration, washing, drying and calcination at 550°C gave the mesoporous silica. Silica recovery is about 95%. To synthesize the mesoporous carbon, 1.0 g of gelatin and 1.0 g of phenol formaldehyde (denoted as PF) polymer was dissolved in 5.0 g ethanol, then that solution was added into 25.0 g of water. Combining with the silicate stock solution, a PF-gelatin-silica composite was generated. After drying at 100°C, pyrolysis at 1000°C and silica removal by 6.0 wt.% HF, the mesoporous carbon was obtained. To prepare the mesoporous silica, the gelatin-PF-silica composite was hydrothermally treated at 100°C for 1 d and calcined at 550°C [7]. 3. Results and Discussion Figure 1A shows the TGA curves of the gelatin-silica composite before and after hydrothermal reaction. The high gelatin content (~ 40 wt.%) in the composite is due to that the gelatin with lots of amine groups (-NH2) can bind strongly with the silicate species through multiple hydrogen-bonds at pH « 5.0. After hydrothermal treatment, the gelatin content decrease to ~20 wt.%. This decrease indicates that some gelatins leave form the gelatin-silica composite during hydrothermal reaction. Analyzing the N2 adsorption-desorption isotherms of the calcined silicas before and after hydrothermal treatment (Figure IB), one can clearly see that the microporous silica with a type I isotherm was obtained before hydrothermal treatment, and a mesoporous silica with a type IV isotherm was prepared after hydrothermal treatment. The mesoporous silica has an apparent capillary condensation at P/Po around 0.85, and the average pore size calculated by BJH method is about 12.5 nm. It is reasonable to suppose that the pore size expansion results from further silica condensation and gelatin's leaving during hydrothermal reaction. To identify the mesostructure, the TEM image of the mesoporous silica reveals the disordered mesostructure and the pore size is about 10.0 nm (Figure 1C). When pH value of the hydrothermal solution was decreased, the pore size of the mesoporous silica decreases (Figure ID). Combining with a simple hydrothermal treatment, the mesoporous silica of tunable pore size and large

387

105

Weight loss / %

95

After hydrothermal treatment Before hydrothermal treatment

A

3 -1

100

Volume adsorbed/cm g , STP

surface area (>300 m2g"') can be synthesized with the nature-friendly gelatin and cheap sodium silicate.

90 85 80 75 70 65 60 55

700

After hydrotheraml treatment before hydrothermal treatment

hydrotheraml treatment B —— t• —— After before hydrothermal treatment

600 500 400 300 200 100 0

100

200

300

400 0

500

600

0.0

0.2

0.4

Temperature /C Temperature/°C

P/P0

0.6

0.8

D

800

— . — ppH=6.0 H=6.0 —»— pH=5.0 pH=3.0 — • —pH=3.0

700

1.0

.

dV/dD

3 -1

C


900

1

600 500 400

5

10 20 25 30 10 15 I&tffi-Hs 30

Pore Diameter(nm)

300

/

/

/

/

200 100 0 0.0

0.2

0.4 4 O

0.6

- P/P P / P0 0 - 6

0.8

1.0

Figure 1. A. The TGA curves of the gelatin-silica before and after hydrothermal treatment at 100°C. B. N2 adsorption-desorption isotherms of the calcined porous silicas. C. TEM image of the calcined mesoporous silica after hydrothermal treatment. D. N2 adsorption-desorption isotherms of the calcined mesoporous silicas hydrothermally treated in solutions of different pH values. The inset is the pore size distributions calculated by BJH method.

Owing to the gelatin is one kind of natural polymers, it thus can blend with other polymers through proper intermolecular interactions. It is well known that the thermal-setting PF polymer, a carbon source widely used in industry, has many -CH2OH and phenol groups. Therefore, the gelatin and PF polymer can form a homogenous blend through multiple hydrogen-bonding interaction. When combinding the gelatin-PF polymer blend with the silicate solution at pH « 5.0, a PF-gelatin-silica composite was readily synthesized. Because the PFgelatin-silica composite contains the carbonizable PF polymer, the mesoporous carbon was obtained from pyrolysis under N2 atmosphere and silica removal. The TEM image of the resulting mesoporous carbon reveals the disordered mesostructure and the meso-voids («few nanometers, Figure 2A). In parallel, the mesoporous carbon exhibits a type-IV N2 adsorption-desorption isotherm (Figure 2B). Analyzing the adsorption isotherm, the BET surface area is about 1200 m2g"] and pore size is around 2.5 nm. The mesoporous carbon shows the apparent vibrational band around 1580 cm"1 (G-band, interplane sp2 C-C stretching) in the Raman spectrum that reflects a high graphitized degree.

388

Alternatively, the mesoporous silica can be obtained from hydrothermal treatment and calcination of the PF-gelatin-silica composite (Figure 2C). 800

A


700

B

C

3 -1

600 500

dP/dD

400 D-band

200 100

2

3

4

5

6

7

G-band

Intensity (a.u.)

300

8

Pore Diameter/nm

0 0.00

0.2

0.4

0.6

P/P 0

0.8

1.0 1.0

50 50 nm nm

1200

1300

1400

1500

1600 -1

Wavelength/cm

1700

1800

100 nm

Figure 2. (A). N2 adsorption-desorption isotherms of the mesoporous carbon prepared with a template of the PF—gelatin blend. The inset exhibits the pore size distribution analyzed by BJH method. (B). TEM image of the mesoporous carbon. The inset shows the Raman spectrum. (C). TEM image of the mesoporous silica templated by the PF-gelatin blend.

4. Conclusion In conclusion, we performed the environment-friendly gelatin and gelatin-PF polymer blend as new templates to prepare the mesoporous silicas and mesoporous carbons with high surface areas and tunable pore size. With the textural properties of the porous silica and carbons can be feasibly controlled, potential applications in catalyst, absorption for large molecules, solar absorber, hard-template for metal oxides and electrode materials can be further explored. 5. References [1] (a). T. Yanagisawa, T. Shimizu, K. Kuroda and C. Kato, Bull. Chem. Soc. Jpn., 63, (1990) 988. (b). C. T. Kresge, M. E. Leonowicz, W. J. Roth, J. C. Vartuli, and J. S. Beck, Nature, 359,(1992)710. [2] D. Zhao, J. Feng, Q. Huo, N. Melosh, G. H. Fredrickson, B. F. Chmelka and G. D. Stucky, Science, 279(1998)548. [3] J. Y. Ying, C. P. Mehnert and M. S. Wong, Angew. Chem. Int. Ed., 38 (1999) 57. [4] L. Pei, K. Kurumada, M. Tanigaki,; M. Hiro and K. Susa, J. Coll. Int. Sci., 284 (2005) 222. [5] K. Holmberg, B. Jonsson, B. Kronberg and B. Lindman, "Surfactant and Polymers in Aqueous Solution" 2nd ed, England, John Wiley & Sons (2003). [6] R. K. Her, "The Chemistry of Silica: Solubility, Polymerization, Colloid and Surface Properties, and Biochemistry," Wiley, New York (1979). [7] D. W. Chen, C. Y. Chang-Chien, H. P. Lin, and C. Y. Tang, Chem. Lett., 33 (2004) 1574. (b) H. P. Lin, C. Y. Chang-Chien, C. Y. Tang and C. Y. Lin, Microporous and Mesoporous Mater., 93 (2006) 344.


389 389

A study on the synthesis of mesoporous silica and carbon platelets with perpendicular nanochannels Yi-Qi Yeh a , Gui-Min Teoa, Bi-Chang Chenb, Hong-Ping Lina*, Chih-Yuan Tang0 and Chin-Yen Lin°

"Department of Chemistry, National Cheng Kung University, Tainan 701, Taiwan. b Department of Chemistry, National Taiwan University, Taipei 106, Taiwan. 'Department of Zoology, National Taiwan University, Taipei 106, Taiwan.

Free-standing mesoporous silica platelets in micron-scale consisting of perpendicular nanochannels were prepared with a ternary-surfactant composition of cationic, anionic and neutral block copolymer surfactants. The mesostructure of the mesoporous silica platelet(J_) is templated by Pluronic 123 surfactant, and the platelet morphology is determined by the catanionic surfactant. The mesoporous silica platelet(_L) was utilized as the nano-template to synthesize the mesoporous carbon platelet(-L). 1. Introduction Since the discovery of surfactant-templating technology for the synthesis of mesoporous materials with high surface area, tunable pore size and large pore volume in the early 1990s [1], an increasing interest has been shown in the design of novel porous materials tailored with various pore organizations and dimensions for potential applications in separation, catalysis, chemical sensing, nanotemplate and low-dielectric coating [2, 3]. The macroscopic alignment of nanochannels in the form of thin films is quite important for producing advanced materials with desired functions [3-5]. Although mesoporous silica films can be produced by dip coating or spin coating via evaporation-induce self-assembly on proper substrates [3, 4], the channels direction in the mesoporous silica film is almost parallel to the substrate surface. In order to provide a simple sol-gel synthetic method for aligning the direction of the nanochannels [5,6], we reported a convenient method for the preparation of free-standing mesoporous silica platelets with vertical channels (denoted as platelets(-L)) by using a ternary-surfactant mixture as the template.

390 390

2. Experimental Section The mesoporous silica platelet(-L) in micrometer size was synthesized by a ternary-surfactant mixture with the alkyltrimethylammonium halide (CnTMAX, n > 12, X = Br or Cl, Acros) , dodecyl sulfate sodium salt (SDS, Acros) and triblock copolymer poly(ethylene glycol)-blockpoly(propylene glycol)-blockpoly(ethylene glycol) (EO20PO70EO20, PI23, Aldrich). The ternary surfactant system was prepared by dissolving 0.72 g of C]8TMAB, (0.8-1.2) g of SDS, and 0.7 g of P123 in 150 ml water under stirring for 3 hours at 40-45°C to form a solution. After that, a 150 ml sodium silicate (SiO2*NaOH) solution as the silica source with [SiCy** 80.0 mM at pH « 4.0-5.0 was poured into above solution. A white precipitate was formed in minutes and then that gel-solution was hydrothermally treated at 100°C for 1 d. The mesoporous silica platelets(_L) were obtained from filtration, washing, drying, and calcined at 600°C [6]. The synthetic procedures of carbon film were as followed: 1.5 g of phenol formaldehyde (PF) resin was dissolved in 10.0 g of ethanol to form a lowviscosity solution, and then l.Og calcined mesoporous silica platelet(J_) was added. The mixture was opened to allow a slow evaporation of ethanol under stirring and then dried at 100°C. After that, the dried PF resin containing mesoporous silica platelet(J-) was carbonized at 1000°C for 2 h under nitrogen atmosphere. Finally, the silica template was removed by HF (6 wt.%) etching. Filtering, washing, and drying gave the mesoporous carbon platelet(l) [7]. 3. Results and Discussion Figure 1A shows the well-ordered hexagonal mesostructure of the micronsized platelet obtained from silicification of the CigTMACl/SDS/P123 template at SDS/Ci8TMACl molar ratio of 1.66. From the microtome TEM image, we found the mesoporous silica platelet(-L) is consisted of the vertical nanochannels, and the length of nanochannel's were estimated about tens nanometers. In parallel to the TEM observation, the mesoporous silica platelet(l) exhibits four XRD peaks at low angle range of 20«0.7-3.0°, which can be indexed as (100), (110), (200) and (210) reflection of a well-ordered p6mm hexagonal mesostructure with a unit cell ao « 10.0 nm (Figure IB). The N2 adsorptiondesorption isotherms of the calcined mesoporous silica platelet(X) demonstrates a type-IV adsorption-desorption isotherm (Figure 1C). Analyzing the adsorption isotherm, the BET surface area of mesoporous silica platelet(l) is 512 m2g*', and the pore size distribution calculated by BJH method centers around 9.0 nm. According to these analyzing results, the porosity mesoporous silica platelet(-L) is templated with the P123 copolymer rather than the CisTMAB and SDS surfactant. As our previously proposed formation model [6], in the ternary surfactant system, the catanionic (i.e. cationic+anionic) surfactant bilayer acts as the template of the platelet morphology, and the PI23 copolymers intercalated within the negatively-charged platelets of the Ci8TMACl/SDS

391 391 600

B

r. C

550 500

A

450 dV/dD

3 -1


100

i

400 350

j j 300 300|

110 200

250 250

2

4

6

8

10

12

14

16

18

20

Pore Diameter/nm

200 150 100 100

210

50 50 0

0.5

1.0

1.5

2.0

2 θ /degree

2.5

3.0

0.0

0.2

0.4

0.6

0.8

1.0

P/P0

Figure 1. (A). The TEM image of the mesoporous silica platelet(-L) synthesized with C|8TMABSDS-P123 template. The inset exhibit the microtome TEM of the mesoporous silica platelet(J-). (B). XRD pattern of the mesoporous silica platelet(-L). (C). N2 adsorption-desorption isotherms of the calcined mesoporous silica platelet(±). The inset shows the pore size distribution analyzed by BJH method.

catanionic surfactant. After silicification at pH « 4.0-5.0, the vertical silicaPi 23 nanochannels were formed to avoid the energy-unfavorable contact of negatively charged bilayer and negatively charged silica species [6]. In addition to the Ci8TMACl-SDS catanionic surfactant, other CnTMAX-SDS bilayer-template could be used to synthesize the mesoporous silica platelet(-L). Table 1 lists the textural properties of the mesoporous silica platelet(-L) prepared with different CnTMAX-SDS-P123 composites. Obviously, the pore size is not dependent on the CnTMAX, but similar to that of the P123-template SBA-15 mesoporous silica. This result is in agreement with the formation model we proposed [6]. In practice, the mesoporous silica platelet(l) could be used as the solid nanotemplate to synthesize the mesoporous carbon platelet(_L). The TEM micrograph of the resulting mesoporous carbon platelet shows the well-ordered hexagonal-arrayed nanorods vertical to the platelet (Figure 2A). The XRD pattern of the mesoporous carbon platelet(l) shows three peaks indexed as Table 1. The textural properties of the mesoporous silica platelets prepared with different CnTMAX-SDS-Pluronic 123 ternary surfactant composites.

CnTMAX-SDS-Pluronic 123 V, A-'pore dioo '-'BET cmV /nm /nm surfactant template /nm /my C,2TMAB-SDS-P123 693 8.5 0.77 10.6 12.26 C14TMAB-SDS-P123 560 8.5 0.80 10.3 12.13 Ci6TMAB-SDS-P123 520 9.0 0.83 11.0 12.92 (100), (110), and (200) reflections of a well-ordered hexagonal mesostructure with a unit cell (a 0 «10.5 nm). Moreover, the carbon platelet(J_) exhibits two intensive diffraction peaks at high-angle, which are indexed to (002) and (100) diffraction for the graphite carbon [7]. The surface area calculated by BET method is about 865 m g"1. The pore size distribution of the mesoporous carbon platelet(-L), analyzed by BJH method, centers at 3.7 nm.

392 600

(002

/I // /

i

500

(100

3 -1

450

/

400 350

S1 300 300-

20

30

40

50

60

2 θ /degree

«

A

250 100 200

150 I ,M-

110 200 0.5

1.0

1.5

r

dV/dD

i

C c

550

Volume adsorbed(cm g ), STP

X-ray intensity

100

XRD intensity

B

100 50

2

3

4

5

6

7

8

9

10

Pore Diameter/nm

2.0

2 θ /degree

2.5

3.0

0 0.0

0.2

0.4

0.6

0.8

1.0

P/P 0

Figure 2. (A). TEM image of the mesoporous carbon platelet(X) film prepared by using the mesoporous silica platelet(l) as template. (B). XRD patterns of the mesoporous carbon platelet(_L). The inset show the high-angle XRD. (C) N2 adsorption-desorption isotherms of the mesoporous carbon platelet(_L).The inset exhibits the pore size distribution analyzed by BJH method.

4. Conclusion In this work, we provided the novel ternary-surfactant system as template to synthesize the mesoporous silica platelets(i-) of nanometered channel length. Furthermore, the mesoporous carbon platelets(_L) were also be generated using the mesoporous silica platelets(l) as solid template. Although, the nanochannels direction and length was readily controlled by using terna rysurfactant system, extending the dimension of the mesoporous platelets to millimeter scale is also important for many possible applications in catalysts, absorbents, nanotemplates, sensors, electrode materials and nanotechnology [5].Preparing a well-order 2D mesoporous materials film on substrate will be further studied. 5. References [1] C. T. Kresge, M. E.Leonowicz, W. J.Roth, J. C.Vartuli and J. S. Beck, Nature 359 (1992) 710. [2] D. Zhao, J. Feng, Q. Huo, N. Melosh, G. H. Fredrickson, B. F. Chmelka and G. D. Stucky, Science, 279, 548 (1998). [3] D. Zhao, P. Yang, N. Melosh, J. Feng, B. F. Chmelka and G. D. Stucky, Adv. Mater., 10 (1998) 1380. [4] S. Tanaka, N. Nishiyama, Y. Oku, Y. Egashira and K. Ueyama, J. Am. Chem. Soc, 126 (2004) 4854. [5] Y. Yamauchi, M. Sawada, T. Noma, H. Ito, S. Furumi, Y. Sakka and K. Kuroda, J. Mater. Chem., 15(2005)1137. [6] B. C. Chen, H. P. Lin, M. C. Chao, C. Y. Mou and C. Y. Tang, Adv. Mater., 16 (2004) 1657. [7] D. W. Chen, C. Y. Chang-Chien, H. P. Lin and C. Y. Tang, Chem. Lett., 33 (2004) 1574.


393 393

Preparation of versatile silica/carbon nanocom positcs via carbonization of ethyl-bridged periodic mesoporous organosilica Zhuxian Yang, Yongde Xia and Robert Mokaya School of Chemistry, University of Nottingham, University Park, Nottingham NG7 2RD, UK

Mesoporous silica/carbon composites may be obtained from periodic mesoporous organosilica (PMO) mesophases via pyrolysis under argon flow at 800 - 950°C. The composite materials are mesostructurally well ordered with surface area of ca. 820 m2/g and pore volume of 0.4 cm3/g. Calcination of the composites, at 550°C for 8 h in air, generates well ordered mesoporous silicas with surface area > 700 m2/g, while nanoporous carbons with surface area > 500 m2/g and which exhibit graphitic characteristics are generated via silica etching of the composites. The silica/carbon composites, mesoporous silicas and nanostructured carbons retained the morphology of the PMO mesophases. 1. Introduction Silica-based composites such as metal/silica, metal oxide/silica, polymer/silica and silica/carbon materials are attractive because of their optical, magnetic, thermal, mechanical, and electric properties. Silica/carbon nanocomposites may be synthesized by carbonization or pyrolysis of various carbon precursors [1-4]. In addition to their interesting properties, nanostructured silica/carbon composites are potentially useful as starting points for the simple and direct preparation of nanoporous silica and carbon materials. This is particularly attractive for mesoporous carbons given that the conventional hard templating process for their formation involves several steps [5]. Recently there have been efforts to prepare mesoporous carbon via more direct routes by carbonization of silica organic-inorganic hybrid composites, [6] or organosilica/surfactant mesophases, [4] followed by removal of silica. Mesoporous carbons have also been fabricated via direct carbonization of

394

organic-organic nanocomposites comprising of a thermosetting polymer and thermally decomposable surfactant [7]. Here we report on the formation of versatile silica/carbon composites via carbonization of ethyl-bridged periodic mesoporous organosilica (PMO) mesophases and show that they are suitable precursors for the preparation of mesoporous silica and nanostructured carbon. 2. Experimental, Results and Discussion Ethyl bridged PMO mesophases were prepared using established procedures, [8] from a synthesis gel of molar ratio BTME : 0.8 CTAB : 2.3 NaOH : 340 H2O, (BTME is 1,2-bis(trimethoxysilyl) ethane and CTAB is cetyltrimethylammonium bromide. The gel was stirred for 20 h at room temperature, and then aged at 90°C for 24 h. The product was obtained by filtration and washed with a large amount of distilled water and dried at room temperature to yield the as-synthesised PMO mesophase. To prepare silica/carbon composites, the PMO mesophase was thermally treated under a flow of argon at 800 or 950°C for 20 h and the resulting silica/carbon composites were denoted as COM800 or COM950 respectively. The silica/carbon composites were then calcined, at 550 °C for 8 h in static air, to yield silica products or treated in 25% hydrofluoric (HF) acid to generate carbons. The silica products were denoted as Silica800 and Silica950, while carbon materials were denoted as Carbon800 and Carbon950. As shown in Fig. 1, the silica/carbon composites are well ordered mesoporous materials. The XRD patterns of the composites exhibit a basal diffraction peak consistent with the presence of mesostructural ordering. The basal spacing of the composites (4.1 and 3.97 nm for COM800 and COM950 respectively) is lower than that of the PMO mesophase (4.37 nm) due to thermally induced contraction. The nitrogen sorption isotherms of COM800 and COM950 (Fig. 1) are typical for mesoporous materials. The isotherms exhibit a relatively sharp adsorption step in the PlPo range up to 0.4, indicative of the presence of uniform mesopores. The mesostructural ordering of the composites is confirmed by the TEM images in Fig. 2, which indicate the presence of relatively well-ordered pore channels. The surface area of the silica/carbon composites is relatively high (841 and 818 m2/g for COM800 and COM950 respectively) and they have a pore volume of ca. 0.4 cm3/g. The pore size of composites, estimated using BJH analysis of adsorption data, is ca. 2.3 nm. TGA analysis indicated that the silica/carbon frameworks are made up of 16 wt% carbon and 84 wt% silica. The carbon/silicon molar ratio is therefore 0.95, which is very close to the expected 1/1 ratio based on the C/Si mole ratio in the building units (Oi 5 Si-CH 2 -CH2-Si0i 5) of the BTME organosilica precursor.

395 400

A A

Intensity (a. u.)

J

Volume adsorbed (cm3g-1 STP)

B B

£ 300

c

E

J 200

I 00

X

22

r • if c

b

!

V

> 100 100

bb a 44 66 (degree) 22 θθ(degree)

88

10 10

0 0.0 0.0

0.2 0.4 0.6 0.8 0.2 0.4 0.6 0.8 (P/Po) o) Partial pressure (P/P

1.0 1.0

Fig. 1. XRD patterns (A) and nitrogen sorption isotherms (B) of (a) ethyl-bridged PMO mesophase and silica/carbon composites derived from carbonisation at; (b) 800 °C, (c) 950 °C.

Fig. 2. TEM images of mesoporous (a,b) silica/carbon composite COM800 and (c) Silica800.

The XRD patterns of silicas obtained via calcination of the silica/carbon composites are shown in Fig. 3A. The XRD patterns exhibit a basal peak indicating that the silica materials posses mesostructural ordering retained from the silica/carbon composites. The basal spacing of the silicas (3.91 and 3.8 nm for Silica800 and Silica950 respectively) was lower than that of the PMO mesophase and the composites from which they were derived. The composites underwent a lattice contraction of ca. 4.5% during removal of carbon and conversion to silica. Thermogravimetric analysis confirmed that the silicas were virtually carbon-free. The presence of mesostructural ordering in the silicas was also observed via TEM as shown by the image of sample Silica800 in Fig. 2c. The XRD patterns of carbons derived from the silica/carbon composites after silica etching in HF acid are shown in Fig. 3C; no low angle (basal peak) was observed due to a lower level of mesostructural ordering and therefore only the wide angle region of the patterns is presented. The XRD patterns exhibit peaks at 20= 26° and 43.5°, due to (002) and (101) diffractions from graphitic carbon [9]. These peaks suggest that the carbons possess a significant level of graphitisation. The nitrogen sorption isotherms of the carbons (Fig. 3D) indicate the presence of micropores or small mesopores. The surface area (835 and 536 m2/g) and pore volume (0.3 and 0.43 cnrVg) for Carbon800 and Carbon950

396 396

respectively, are comparable to those of the silica/carbon composites and nanostructured silica described above. The pore size of the nanostructured carbons is in the range 1.8 - 2.2 nm. 300

A

B

b

C

350

(002)

D

a

250

d

300 Volume adsorbed (cm3g-1 STP)

b

d

Intensity (a. u.)

Volume adsorbed (cm3g-1 STP)

Intensity (a. u.)

c (101)

200

150

100

50

250

200

150

100

c

a 0

2

4 6 2 θ(degree)

8

10

0 0.0

0.2 0.4 0.6 0.8 Partial pressure (P/Po)

1.0

10

20

30 40 2 θ(degree)

50

60

50 0.0

0.2 0.4 0.6 0.8 Partial pressure (P/Po)

1.0

Fig. 3. XRD patterns (A,C) and nitrogen sorption isotherms (B,D) of mesoporous silica (a) Silica800 and (b) Silica950, and nanostructured carbon (c) Carbon800 and (d) Carbon950.

Fig. 4. SEM images of (a) PMO mesophase, and (b) silica/carbon composite (c) mesoporous silica and (d) porous carbon, derived from the PMO mesophase.

As shown in Fig. 4, the silica/carbon composites, silica and carbon materials retain the particle morphology of the PMO from which they are derived. 3. References [1] J. Aguado-Serrano, M. L. Rojas-Cervantes, A. J. Lopez-Peinado and V. Gomez-Serrano, Microporous and Mesoporous Mater., 74 (2004) 111. [2] P. R. Giunta, L. J. van de Burgt and A. E. Stiegman, Chem. Mater., 17 (2005) 1234. [3] J. Pang, V. T. John, D. A. Loy, Z. Yang and Y. Lu, Adv. Mater., 17 (2005) 704. [4] Z. Yang, Y. Xia and R. Mokaya, J. Mater. Chem., 16 (2006) 3417. [5] S. Jun, S. H. Joo, R. Ryoo, M. Kruk, M. Jaroniec, Z. Liu, T. Ohsuna and O. Terasaki, J. Am. Chem. Soc, 122 (2000) 10712. [6] B.-H. Han, W. Zhou and A. Sayari, J. Am. Chem. Soc, 125 (2003) 3444. [7] S. Tanaka, N. Nishiyama, Y. Egashira and K. Ueyama, Chem. Commun., (2005) 2125. [8] S. Inagaki, S. Guan, Y. Fukushima, T. Ohsuna and O. Terasaki, J. Am. Chem. Soc, 121 (1999)9611. [9] (a) T.-W Kim, I.-S. Park and R. Ryoo, Angew. Chem. Int. Ed., 42 (2003) 4375. (b) Y. Xia and R. Mokaya, Adv. Mater., 16 (2004) 1553. (c) Y. Xia and R. Mokaya, J. Phys. Chem. B, 108 (2004) 19293. (d) Y. Xia and R. Mokaya, Chem. Mater., 17 (2005) 1553. (e) Y. Xia, Z. Yang and R. Mokaya, Chem. Mater., 18 (2006) 140.


397 397

Ordered mesoporous carbon as new support for direct methanol fuel cell: controlling of microporosity and graphitic character Chanho Paka'*, Sang Hoon Jooa, Dae Jong Youa, Hyung Ik Leeb, Ji Man Kimb*, Hyuk Changa and Doyoung Seunga " Samsung Advanced Institute of Technology, P.O. Box, 111, Suwon, 440-600, Korea Department of Chemistry and SKKU Advanced Institute ofNanoTechnology, Sungkyunkwan University, Suwon, 440-749, Korea ([email protected])

As a new carbon support for the fuel cell, ordered mesoporous carbon (OMC) was prepared by the nano template method using ordered mesoporous silica. The structural properties of OMC such as microporosity and graphitic character were controlled by addition of nano silica powder during synthesis of OMC or the uses of different carbon precursors. The performance of direct methanol fuel cell in the single cell was affected significantly by the graphitic character of OMC support. 1. Introduction Direct methanol fuel cell (DMFC) is considered as a promising power source for the next-generation portable electronics, owing to its characteristics such as a high energy density, green emission, convenient refueling of liquid fuel, and ambient operation conditions [1]. However, there still remain several critical problems to be overcome in order to commercialize the DMFC system as a real power source. Among the technical issues, increasing the catalytic activities of electrode catalysts is one of the most important issues. In this regard, recently, nanostructured carbons, including carbon nanotubes, carbon nanofibers and ordered mesoporous carbons (OMC), were exploited as new carbon supports for DMFC catalysts, to enhance the catalytic activities in electrode reactions. Among a variety of nanostructured carbons, in particular, the OMCs are highly intriguing as support materials for DMFC, due to their high surface area, uniform mesopore, and high thermal and chemical stabilities. Consequently, recent reports demonstrated that the promising catalytic activities were obtained using OMC-supported catalysts [2-6]. In this presentation, as a part of our

398

ongoing efforts toward rational design of OMC materials for DMFC application, the effects of structural properties of OMC supports such as microporosity and graphitic character on the performance of OMC supported catalysts were investigated. 2. Experimental Section A hexagonally ordered SBA-15-type mesoporous silica was prepared using sodium silicate solution as a silica source by modifying the methods reported in the literature [7], and used as template for the preparation of OMCs. The synthesis of OMC with controlled microporosity was performed by combination of nano-replication and nano-imprinting techniques using dual silica templates: mesoporous silica and silica nanoparticles (SNP) [7]. Detail synthesis procedure was described in the previous report [7]. Graphitic character of OMC materials was controlled by the uses of different carbon precursors: sucrose and phenanthrene without SNP [8]. Two OMC samples were designated as SuOMC and Ph-OMC, respectively, depending on the carbon precursors. To evaluate the OMCs as supports for the DMFC catalysts, Pt catalysts with nominal loading of 60 wt% were prepared onto OMC supports by impregnation and H2 reduction [6], and used in the cathode of single cell of DMFC. The preparation of membrane electrode assembly and measurement of performance for DMFC single cell was reported in detail elsewhere [8]. 3. Results and Discussion The synthesis of OMC using dual silica templates was resulted bimodal pore system: mesopore from framework of ordered mesoporous silica template and micropore embedded in carbon rods from SNP prepared sol-gel process, respectively [7]. The additional SNP developed a micropore around -1.5 nm within the carbon rods in the OMC. The micropore volume estimated from the Horvath-Kawazoe equation at 0.16 p/p0 was increased from 0.53 to 0.69 cm3/g with the amount of SNP from 0 to 30%. In addition, the surface area of OMC was increased from 1279 to 1635 m2/g with the amount of SNP from 0 % to 30 % SNP-added sample in the synthesis mixture. Preparation of Pt catalysts on the OMC support having increased microporosity and the fabrication of membrane electrode assembly for the DMFC are under investigation. Two OMC samples with different graphitic characters prepared from phenanthrene (Ph-OMC) and sucrose (Su-OMC) exhibited large BET surface area of 884 and 1147 m2/g, respectively, and uniform mesopores around 4 nm in diameter. The XRD (not shown) of two OMC supports showed the good mesoporous structure. The Ph-OMC exhibited lower sheet resistance (54 mQ/cm2 at 75.4 kgf/cm2) than that (202 mQ/cm2) of the Su-OMC sample. The Ph-OMC showed lower surface area and sheet resistance than the Su-OMC

399

.'

:

Fig.l. TEM images of Pt supported on (a) Su-OMC and (b) Ph-OMC. Scale bars are 20 nm.

because the aromatic precursor is known to be easily graphitized than the nongraphitizing precursor, sucrose [9]. The XRD patterns (not shown) for 60 wt% Pt loaded on Ph-OMC and Su-OMC showed four peaks at 2 6= 39.8°, 46.3°, 67.5° and 81.3°, corresponding to the face-centered cubic structure of Pt crystal. The particle sizes of Pt particles, as shown in Fig. 1, in the catalysts using two OMC supports were controlled to be similar around 2-3 nm. Fig. 1 displays the Pt particles were uniformly dispersed along the carbon nanorods of OMCs without agglomeration of particles. It is worthy to be noted that internal, open mesopore structure of OMS was maintained after the Pt/Ph-OMC loading of Pt particles [6]. Pt/Su-OMC The single cell performances of DMFC were evaluated at 323 K using Pt-supported carbons as cathode catalysts and PtRu black as anode catalysts. The performance curves in Fig. 2 indicate that the Pt/Ph-OMC catalyst the 0.1 higher performance than 0.0 that of Pt/Su-OMC. The 50 100 150 200 250 300 350 400 current densities at 0.4 V 2 Current Density (mA cm' ) and 323 K were found to be Fig. 2 Potentiodynamic polarization curve plots of 119 and 87 m A / W for DMFC single cell at 323 K using Pt/Ph-OMC and, Pt/Ph-OMC and Pt/SuPt/Su-OMC as cathode catalysts. OMC, respectively.

400

Considering that the particle sizes of Pt in two catalysts are very similar, it is suggested that the enhanced performance of Pt/Ph-OMC, compared with Pt/SuOMC, may be originated from the lower sheet resistance (i.e. higher electrical conductivity) of Ph-OMC. Previously, the effect of graphitic character on the DMFC performances was reported using PtRu nanoparticles supported on several types of carbon nanofibers and carbon nanotubes by Steigerwalt et al. [10]. They suggested that activities of DMFC single cells parallel the trend of electrical conductivity of MEA. The results obtained in the present work further support their conclusion, in that the electrical conductivity of carbon support makes a significant effect on the single cell performance. 4. Conclusion The microporosity and graphitic character of OMC were controlled by addition of nano silica powder or the uses of different carbon precursors during the synthesis of OMC. Ph-OMC and Su-OMC were prepared using phenanthrene and sucrose as carbon precursors. Ph-OMC exhibited 4-fold decreased sheet resistance, compared with Su-OMC, indicative of the higher electrical conductivity. Two OMC were used as supports for highly dispersed Pt nanoparticles with less than 3nm in size and 60wt%. It was suggested that the graphitic character of OMC is of significant importance in enhancing the DMFC cell efficiency, as Pt catalyst supported on more graphitic Ph-OMC exhibited better cell performance than Pt catalyst used Su-OMC as a support. 5. References [1] L. Carrette, K. A. Friedrich and U. Stimming, Fuel Cells 1 (2001) 5. [2] S. H. Joo, S. J. Choi, I. Oh, J. Kwak, Z. Liu, O. Terasaki and R. Ryoo, Nature, 412 (2001) 169. [3] J. Ding, K.-Y. Chan, J. Ren and F.-S. Xiao, Electrochim. Acta 50 (2005) 3131. [4] F. Su, J. Zeng, X. Bao, Y. Yu, J. Y. Lee and X. S. Zhao, Chem. Mater. 17 (2005) 3960. [5] J.-H. Nam, Y.-Y. Jang, Y.-U. Kwon and J.-D. Nam, Electrochem. Commun. 6 (2004) 737. [6] C. Pak, D. J. Yoo, S.-A. Lee, J. M. Kim and H. Chang, Samsung J. Innovative Tech. 1 (2005) 239. [7] H. I. Lee, C. Pak, C.-H. Shin, H. Chang, D. Seung, J. E. Yie and J. M. Kim, Chem. Commun., (2005) 6035. [8] S. H. Joo, C. Pak, D. J. You, S.-A. Lee, H. I. Lee, J. M. Kim, H. Chang and D. Seung, Electrochim. Acta, in press (2006). [9] C. H. Kim, D.-K. Lee and T. J. Pinnavaia, Langmuir 20 (2004) 5157. [10] E. S. Steigerwalt, G. A. Deluga and C. M. Lukehart, J. Phys. Chem. B 106 (2002) 760.


401 401

Direct sulfonation of ordered mesoporous carbon for catalyst support of direct methanol fuel cell Chanho Paka*, Sang Hoon Jooa, Dae Jong You3, Ji Man Kimb, Hyuk Chang3 and Doyoung Seunga " Samsung Advanced Institute of Technology, P.O. Box, 111, Suwon, 440-600, Korea h Department of Chemistry andSKKUAdvanced Institute of NanoTechnology, Sungkyunkwan University, Suwon, 440-749, Korea

Ordered mesoporous carbon (OMC) prepared by nano-replication method was directly functionalized with sulfonic acid group by using the ammonium sulfate salts. PtRu nanoparticles below 3 nm was supported on the sulfonatedOMC support with 70 wt% loading, and the resulting catalysts exhibited promising catalytic activity for methanol oxidation reactions. 1. Introduction Recently, new types of mesostructured carbon materials have been synthesized using mesoporous silica templates [1], and their prospective applications as adsorbent, electrochemical double-layer capacitor and catalyst support for fuel cell have been explored. In particular, the structural characteristics of ordered mesoporous carbon (OMC) including high surface area, uniform mesopore, and high thermal and chemical stabilities are highly intriguing for fuel cell applications. Since Joo et al. [2] reported that the mass activity for oxygen reduction of Pt catalyst supported on CMK-5 increased more than ten times compared to the catalyst using conventional carbon black support, several reports have demonstrated that the promising catalytic activities were obtained using OMC-supported catalysts [3-7]. For example, we reported the enhancement of single cell performance for DMFC by using the 60 wt% Pt supported catalyst on OMC support [6]. To enhance activity of DMFC electrode reactions, the number of triple-phase boundary, where catalyst, ionomer and reactant simultaneously exists, should be increased [8]. In this regard, the sulfonation of carbon support was recently

402

reported to increase proton conductivity and consequently catalyst utilization [9]. In this study, the pore surface of OMC was directly functionalized with sulfonic acid group. The physicochemical properties of OMC and sulfonatedOMC samples were investigated nitrogen adsorption, X-ray diffraction (XRD), thermogravimetric analysis (TGA) and X-ray photoelectron spectroscopy (XPS). Further, to explore the possibility of sulfonated-OMC samples as support for DMFC catalyst, PtRu nanoparticles were supported onto sulfonated-OMC and their activity toward methanol oxidation reaction was measured 2. Experimental Section

Volume Adsorbed (cm3 g-1, STP)

A template SBA-15-type hexagonally ordered mesoporous silica particle was prepared with sodium silicate solution by modifying the method reported in the literature [10]. The pristine OMC sample was prepared via nano-replication method using new aromatic precursor, phenanthrene [7]. Direct sulfonation of OMC was conducted by using ammonium sulfate salts, (NH^SO^ with different amount as reported earlier [8]. In brief, the ammonium sulfate was dissolved in the mixture solution of acetone and deionized water and mixed with the OMC sample in the plastic bag. After drying the sample at the ambient condition and further in an oven at 60 °C, the mixture was heated to 250 °C and kept for 5 h in static air. Two samples were prepared with different amount of salts for 10 wt% and 20 wt% sulfonic acid group and designated as SulOMCl and SulOMC2. The pore structure and chemical state of OMC and sulfonated OMC samples were characterized 800 by nitrogen adsorption, TGA and XPS. pax D. The 70 wt% PtRu (1:1 atomic to ; ratio) supported catalysts were 600 a) a) prepared using the modified polyol £ process from the reported method [11] with SulOMCl and SulOMC2 i-rT 400 as supports. The methanol r oxidation activity of the catalyst 8 was measured in the 0.5 M H2SO4 b) b < 200 200 JT ' ^h-+ —\ and 2 M CH3OH solution by linear c) c) sweep method from 0.2 to 0.8 vs. o normal hydrogen electrode (NHE).

/ r

f

f *>* Lr

&

0 o.o 0.0

we

0 m 0.2

0.4

0.6

0.8

1.0 1.0

Relative Relative Pressure Pressure (P/P00)

Fig. 1. Nitrogen adsorption-desorption isotherms for (a) pristine OMC ( • ) , (b) SulOMCl ( • ) and (c) SulOMC2 ( • )


As shown Fig. 1, the typical type IV nitrogen adsorption and desorption isotherms were obtained from

403

Intenity (a.u.)

the pristine OMC, SulOMC 1 and SulOMC2 samples [1,2,6]. The mesopore size of sulfonated-OMCs obtained from the desorption branch of isotherms was 4.3 nm, which is the same as the OMC sample. The surface areas of SulOMC 1 and SulOMC2 decreased from 883 m2/g of pristine OMC to 392 and 319 m2/g, respectively. For the SulOMC 1 and SulOMC2 sample, the pore volume from the micropore (< 2 nm) decreased from the 16.8x10" cm3/g of OMC sample to 6.5xlO'3cm3/g for SulOMCl and 5.1xl0"3cm3/g for SulOMC2, respectively. The XRD patterns for OMC and sulfonated-OMC (not shown) exhibited similar diffraction lines corresponding to the hexagonal mesostructure, indicating that the structural regularity of the pristine OMC was maintained after the functionalization with sulfonic acid groups. The thermal properties and loading amounts of sulfonic acid group in SulOMC samples were analyzed by TGA. The TGA of SulOMC samples showed significant weight loss in temperature range of 250°C and 350°C, which can be attributed to thermal decomposition of sulfonic acid group. The amounts of sulfonic acid group in the SulOMCl and SulOMC2 were determined as 8.6 wt% and 17.5 wt%, respectively, which is similar to the nominal value from the initial amount of salts used in the impregnation step. The chemical nature of attached functional group in SulOMC samples was probed by XPS. The X-ray photoelectron spectra of S 2p core level revealed that the peak position corresponded to the -SO3H, and its intensity linearly increased with the amount of initial sulfate salts. The sulfur to carbon ratios of two samples increased to 0.014 for SulOMCl and 0.027 for SulOMC2 from 0.004 for OMC, respectively. Fig. 2 shows the power XRD patterns for the 70 wt% PtRu supported on SulOMCl and SulOMC2. The peaks corresponding to (111), (200), (220) and (311) of Pt face-centered cubic (fee) crystal structure were observed from all supported catalysts, which suggests that the Ru atoms were homogeneously substituted into the lattice cites of Pt fee crystal [12]. The crystalline size of PtRu particles in the catalysts estimated from the half width of a peak around 68° by Scherrer equation was 2.9 nm for all samples. It is noteworthy that the particle size of PtRu particles was controlled below 3 nm despite the loading of PtRu was as high as 70 wt%. Furthermore, it should be n o t e d tnat 10 20 30 40 50 60 70 80 90 although the 2 θ (degree) 2θ BET surface areas of sulfonated-OMC supports Fig. 2. XRD patterns of 70 wt% PtRu supported on decreased to below the half a) SulOMCl and (b) SulOMC2

404

of that of the pristine OMC, the choice of suitable preparation method (polyol route) could yield the highly dispersed catalysts. The mass activities for the methanol oxidation of PtRu catalysts supported on SulOMCl and SulOMC2 were 14.3 and 16.7 A/gptRU, respectively, which is slightly higher than that (12.2 A/gptRu) of commercial 60% PtRu supported catalyst from Johnson Matthey (HiSpec 10100) and is comparable to that (16.2A/gp(Ru) of PtRu catalyst supported on OMC itself. The preparation of highly dispersed catalyst particles in combination with their promising catalytic activities toward methanol oxidation suggest that the sulfonated OMC support can be applied as catalyst support for the direct methanol fuel cells. The fabrication of membrane electrode assembly employing sulfonated-OMC supported catalysts and optimization of their single cell performances for DMFC are under way. 4. Conclusion The sulfonic acid group was successfully introduced into OMC sample without collapsing the mesostructure and changing the mesopore size. The introduction of sulfonic acid group resulted in the decreasing the surface area of OMC samples. The amount of sulfonic acid group can be controlled by adjusting the amount of ammonium sulfate salts used in the impregnation step PtRu nanoparticle with 2.9 nm in size was supported on the sulfonated OMC supports with 70 wt% loading and showed improved mass activity for the methanol oxidation reaction compared to the commercial PtRu catalysts, which suggest the sulfonated OMC sample can be used as a new catalyst support for DMFC. 5. References [1] R. Ryoo, S. H. Joo, M. Kruk and M. Jaroniec, Adv. Mater. 13 (2001) 677. [2] S. H. Joo, S. J. Choi, I. Oh, J. Kwak, Z. Liu, O. Terasaki and R. Ryoo, Nature 412 (2001) 169. [3] J. Ding, K.-Y. Chan, J. Ren and F.-S. Xiao, Electrochim. Acta 50 (2005) 3131. [4] F. Su, J. Zeng, X. Bao, Y. Yu, J. Y. Lee and X. S. Zhao, Chem. Mater. 17 (2005) 3960. [5] J.-H. Nam, Y.-Y. Jang, Y.-U. Kwon and J.-D. Nam, Electrochem. Commun. 6 (2004) 737. [6] C. Pak, D. J. Yoo, S.-A. Lee, J. M. Kim and H. Chang, Samsung J. Innovative Tech. 1 (2005) 239. [7] Y. S. Choi, S. H. Joo, S.-A. Lee, D. J. You, H. Kim, C. Pak, H. Chang, and D. Seung, Macromolecules 39 (2006) 3275. [8] K. A. Mauritz and R. B. Moore, Chem. Rev. 104 (2004) 4535. [9] Z. Zu, Z. Qi and A. Kaufman, Electrochem. Solid-State Lett. 8 (2005) A313. [10] S.-S. Kim, T. R. Pauly and T. J. Pinnavaia, Chem. Commun. (2000) 1661. [11] Z. Liu, X. Y. Ling, X. Su and J. Y. Lee, J. Phys. Chem. B 108 (2004), 8234. [12] E. Antolini, L. Giorgi, F. Cardellini and E. Passaacqua, J. Solid State Electrochem. 5 (2001) 131.


405 405

Effect of chemically surface modified MWNTs on the mechanical and electrical properties of epoxy nanocomposites Joohyuk Park* and Abu Bakar Bin Sulong Department of Mechanical Engineering, Sejong University, 98 Kunja-dong, Kwanjin-gu, Seoul 143-747, Korea

1. Introduction The primary benefit of polymer matrix composites is the potential for enhancement in strength-to-weight ratios. Many researches have been conducted on carbon nanotubes (CNT) reinforced nanocomposites due to their exceptional mechanical, electrical and functional properties [1]. Dispersion of CNT in polymer matrix by ultra sonic wave achieved greater nano dispersion than with a mechanical stirrer [2]. Dispersion quality and interfacial bonding strength CNT with polymer matrix can be increased by chemical surface modification of CNT [3]. In this study, epoxy is chosen as a polymer matrix. Recently, many researchers have been interested in the chemical surface modification of CNT (oxidized CNT, amine treated CNT and plasma treated CNT) to achieve a better dispersion and to increase the interfacial bonding strength between CNT and epoxy matrix for enhanced mechanical properties [4, 5]. The effect of Asproduced CNT on both mechanical and electrical properties of CNT reinforced epoxy nanocomposites has been reported [6]. However, few studies reported the effect of different types of the chemically surface modified CNT on both properties of CNT reinforced epoxy nanocomposites. Therefore, the effect of two types of chemically surface modified CNT and surfactant additive CNT on mechanical strength and electrical conductivity are investigated as a function of CNT loading concentrations.

406

2. Experimental Section The epoxy resin is Bisphenol-A-based epoxy resin (KER215), which contains mono-epoxidized alcohol as reactive diluents, is supplied by Kumho P&B Chemicals. Multi-walled carbon nanotubes (MWNT) which synthesized by thermo-chemical vapor decomposition of hydrocarbon gases is supplied by Iljin. Nanocomposites are fabricated by an injection molding process, and their properties in mechanical strength and electrical conductivity are compared to different MWNT functional groups (as-produced MWNT, chemically surface modified MWNT and surfactant additive MWNT-TRITON X-100) and MWNT loading concentrations. Characterization of chemically surface modified MWNT and the optimized dispersion method are reported elsewhere [7]. The characteristics of mechanical strength are measured by the universal test machine based on ASTM D 3039. Change in fracture surfaces have been observed by a scanning electron microscopic to study the effect of chemically surface modified MWNT on the fracture mechanism and interfacial bonding strength. Moreover, the electrical conductivity is measured by an applied controllable DC voltage wherein resistance is obtained from current intensity versus voltage curve.

1.75

(a)

Young's Modulus (GPa)

1.70

(3

Ultimate Tensile Strength (MPa)


1.65 1.60 1.55 1.50

Pure Epoxy As-produced MWNTs 45As-produced - A - Surfactant Surfactant add. add. MWNTs - » - Carboxylated MWNTs Octadecylated MWNTs -«—Octadecylated

1.45 1.40 1.35 1.30 0.0

0.5

1.0

1.5

2.0

48

( bb ))

46 44 42 40 38 36 34 32

Pure Epoxy Pure As-produced MWNTs - Surfactant Surfactant add. add. MWNTs MWNTs Carboxylated MWNTs MWNTs Carboxylated Octadecylated MWNTs MWNTs Octadecylated

30 28 26 24 22 20 0.0

15

3.0

(( c )

14

2.7 2.6

\

2.5 2.4

J

2.3

I

2.2

-—

2.1 2.0 1.9 1.8 1.7 1.6

i

. — - " • " " • "

—.0 Pure Pure Epoxy 1.9As-produced As-produced MWNTs - » - Surfactant add. add. MWNTs -T-Carboxylated MWNTs Carboxylated MWNTs 1.6Octadecylated MWNTs Octadecylated MWNTs

1

0.5

1.0

1.5

(wt%) MWNTs concentration (wt%)

2.0

12 11 10

30 25

(d)

20 15 10 5

(e)

0 0.0

0.5

1.0

1.5

2.0

2.5

3.0

Strain (%)

9 8 7

Pure epoxy As-produced MWNTs Surfactant add. MWNTs Carboxylated MWNTs Octadecylated MWNTs

6 5 4 3

1.5 0.0

1.5

Pure epoxy As-produced MWNTs Surfactant add. MWNTs Carboxylated MWNTs Octadecylated MWNTs

35

Stress (MPa)

13

Stress (MPa)

Fracture Strain (%)

2.8

1.0

45 40

2.9

0.5

MWNTs concentration (wt%) (wt%) MWNTs

MWNTs MWNTs concentration (wt% (wt%))

2.0

0.3

0.4

0.5

0.6

0.7

0.8

0.9

1.0

Strain (%) (%) Strain

Figure 1. Variation of mechanical properties of epoxy nanocomposites (a) Young's modulus, (b) ultimate tensile strength, (c) fracture strain, (d) representative stress-strain behavior of 2.0 wt% MWNT nanocomposites, and (e) magnification of stress-strain behavior of (d).

407

Figure 1 shows the variation of mechanical properties of epoxy nanocomposites as a function of MWNT functional types and loading concentrations. Incorporating MWNT into epoxy matrix greater enhanced the mechanical properties than pure epoxy. It is clear that the mechanical properties are increased with increase in MWNT loading concentration. Moreover, chemically surface modified MWNT (carboxylated and octadecylated MWNT) gave higher Young's modulus and ultimate strength than non-chemically surface modified MWNT reinforced nanocomposites. It can be assumed that chemically surface modified MWNT gave a higher interfacial bonding strength than epoxy matrix. Figure 2 shows the fracture surfaces of the various MWNT functional types. The fracture surfaces of pure epoxy and as-produced MWNT reinforced nanocomposites show less rough surface area than chemically surface modified MWNT nanocomposites, which indicates more easily fractured during the uniaxial tensile loading.

Figure 2. Initiation of the fracture for (a) Pure epoxy, (b) As-produced MWNTs, (c) Carboxylated MWNTs and (d) Octadecylated MWNTs reinforced epoxy nanocomposites.

In figure 3, non-chemically surface modified MWNTs are pulled out from epoxy matrix, so longer CNTs can be observed. This indicates the lower interfacial bonding strength of MWNTs with epoxy matrix. However, chemically surface modified MWNTs were shown to be firmly embedded in the epoxy matrix, which indicated stronger interfacial bonding strength with epoxy matrix than non-chemically surface modified MWNTs nanocomposites.

Figure 3. Interfacial bonding strength of (a) As-produced MWNTs, (b) Carboxylated MWNTs, and (c) Octadecylated MWNTs with epoxy polymer matrix.

Moreover, non-conductive epoxy polymer becomes conductive by adding MWNTs, as in figure 4(a). The electrical conductivity is increased with increases in MWNTs loading concentrations. By introducing chemical functional groups on the surface of MWNT, the electrical conductivity of nanocomposites is significantly decreases compared to as-produced MWNT and

408

(a)

1E-4

(b)

0.05

1E-5 1E-6 1E-7 1E-8

electrostatic dissipation line

1E-9 1E-10 1E-11

As-produced MWNTs Surfactant add. MWNTs Carboxylated MWNTs Octadecylated MWNTs

1E-12 1E-13 0.0

0.5

1.0

1.5

MWNTs concentration (wt%)

2.0

Current Intensity (A)

Electrical Conductivity (S/cm) - DC Voltage

Surfactant additive MWNT nanocomposites. It can be assumed that chemical functional groups produce repulsive force due to unbalance polarity for separate CNT agglomeration into individual CNT. Thus, it could disturb the electrical conductivity CNT pathway network which was occurred at as-produced CNT in epoxy matrix. Moreover, severe defects on the CNT walls through chemical surface modification also may damage tube chirality of graphite sheet at CNT which react as medium for selectivity either metallic or semi-conducting property of CNT. However, surfactant (TRITON X-100) only increased dispersion of As-produced MWNT agglomeration, instead of allowing electric current flow through it due to its non-ionic property.

0.04

0.03

0.02

2wt% Surfactant add. add. MWNTs-a 2wt% 2wt% Surfactant add. add. MWNTs-b 2wt% 2wt% Surfactant add. add. MWNTs-c 2wt% Linear fit curve (a) Linear fit cutve (b) Linear fit curve (c)

0.01

0.00 0

25

50

75

100

125

150

175

200

225

250

DC Voltage (V)

Figure 4. (a) Variation of electrical conductivity of MWNT reinforced epoxy composites, and (b) representative of variation of current intensity versus voltage results and its linear fit lines.

4. Conclusion This study's results indicate the chemical surface modification increases the interfacial bonding strength of CNTs with polymer matrix. Furthermore, it can be concluded that chemical surface modification is necessary to enhance the mechanical properties for structural application. However, non-chemically surface modified CNTs are more suitable for electrical applications. 5. Acknowledgement This work was supported by grant No. R01-2003-000-10-72-0 from the Basic Research Program of the Korea Science & Engineering Foundation 6. References [1] [2] [3] [4] [5] [6] [7]

E. T. Thostenson, Z. Ren and T. W. Chou, Comp. Sci. & Tech., 61 (2001) 1899. Y. Wang, J. Wu and F. Wei, Carbon, 41 (2003) 2939. A. Hirsh, Angrew Chem. Int. Ed., 41 (2002) 1853. J. A. Kim, D. G. Seong, T. J. Kang and J. Youn, Carbon, 44 (2006) 1898. F. H. Gojny and K. Schulte, Comp. Sci. & Tech., 64 (2004) 2303. A. Allaoui, S. Bai, H. M. Cheng and J. B. Bai, Comp. Sci. & Tech., 62 (2002) 1993. A. B. Sulong, J. H. Park, N. S. Lee and J. H. Goak, J. of Comp. Mat., (2006) to be appeared.


409 409

Synthesis of uniform carbon nanotubes by chemical vapor infiltration method using SBA-15 mesoporous silica as template An-Ya Loa, Shou-Heng Liub, Shing-Jong Huangb, Huang-Kai Shena, Cheng-Tzu Kuoa and Shang-Bin Liub * "Department of Material Science and Engineering, National Chiao Tung University, Hsingchu 300, Taiwan Institute of Atomic and Molecular Sciences, Academia Sinica, Taipei 10617, Taiwan

1. Introduction Carbon nanotubes (CNTs) have been widely studied for the past decade owing to their practical applications in a variety of different areas [1-5]. Various attempts have been made to manipulate the physical properties of CNTs using different strategies and synthesis conditions [6-10]. For example, by using anodic aluminum oxides (AAOs) as template, Yuan et al. [11] have demonstrated that CNTs with tunable diameters can be synthesized with modest yield using chemical vapor deposition (CVD) method. In view of the recent advances in routine synthesis of mesoporous silica materials that possess welldefined pore structure with uniform and tunable pore size (5-50 nm), this study aims to employ mesoporous silica SBA-15 [12] as support to incorporate metal (Fe) catalyst with controlled particle size to fabricate CNTs with uniform diameter and improved production yield by chemical vapor infiltration (CVI) method [13]. In addition, the morphologies, structural and physical properties, and product yields of CNTs fabricated by two supported Fe/SBA-15 catalysts respectively prepared by using co-precipitation and impregnation methods, were compared and discussed. 2. Experimental Section Mesoporous SBA-15 silica with an averaged pore size of 7.7 nm was prepared following the recipe reported earlier by Mou et al. [14]. Subsequently, two different methods, namely co-precipitation and impregnation, were adopted

410

to incorporate the iron (Fe) catalyst particles into the pore channels of the silica support. The supported Fe/SBA-15 catalyst prepared by co-precipitation method (denotes as Fe(co)/SBA-15) was carried out by stirring ca. 0.4 g of Fe(NO3)3(S) in suspended solution of SBA-15 (ca. 1 g) for 0.5 h, followed by filtering and drying (at 373 K). The resultant product was then subjected to reduction treatment under flowing H2 (50 seem; ca. 2 kPa pressure) from room temperature to 1073 K and kept at the same temperature for ca. 10 min. On the other hand, samples prepared by impregnation method (denotes as Fe(im)/SBA15) was obtained by the following procedures: first, ca. 0.4 g Fe(NO3)3(s) and ca. 1 g of SBA-15 powder were stirred, and dried by a vapor evaporator. Subsequently, the CH2C12(1) was added to facilitate the migration of residual Fe(NO3)3(aq) into the pore channels of SBA-15 [15]. This procedure was repeated once, and then the sample was also subjected to the same reduction treatment mentioned above. Fabrication of CNTs was carried out by introducing either Fe(co)/SBA-15 or Fe(im)/SBA-15 catalyst in a home-made quartz reactor, followed by CVI procedure carried out at 1073 K. This was done by injecting C2H2/H2 gas mixture under a flow rate of 50/50 seem and ca. 2 kPa pressure. The resultant product was then digested with aqueous HF solution (1M) to remove the silica support, followed by filtering and drying. X-ray diffraction (XRD) patterns were obtained with a Philips X'Pert PRO diffractometer using CuKa radiation. Transmission electron microscopy experiments were performed on a JEOL JEM-2100 instrument operated at 200 keV. 3. Results and Discussion The TEM image (Fig. la) and XRD profile (Fig. 2a) of the parent SBA-15 sample reveal the expected well-ordered hexagonal structure with uniform pore diameter. While the XRD pattern of Fe(co)/SBA-15 (Fig. 2b) shows characteristic diffraction peaks analogous to that of the parent SBA-15, its TEM micrograph (not shown) revealed that majority of the Fe catalyst particles are deposited on the external surfaces of the support. On the other hand, while the XRD pattern of the Fe(im)/SBA-15 exhibits only a weak (100) diffraction peak

Fig. 1. TEM images recorded alone the [110] direction of (a) parent SBA-15 and (b) Fe(im)/SBA-15. Insert: along the [100] direction.

411

compared to the parent SBA-15, indicating that incorporation of Fe catalyst does have substantial influence to the hexagonal mesostructure, they are most likely presented in the pore channels of the mesoporous silica support. This is further verified by the TEM image shown in Fig. lb, which reveals welldispersed, nano-sized Fe particles within the pore channels of the SBA-15. Further CVI process using the supported Fe(co)/SBA-15 and Fe(im)/SBA-15 catalysts both lead to formation of CNTs. However, owing to the uncontrollable catalyst particle size in Fe(co)/SBA-15, the CNTs so produced tend to have a wide distribution of diameter (10-30 nm). In contrast, the CNTs produced using Fe(im)/SBA-15 appears to have uniform s diameter of ca. 8 nm, which is comparable to the pore diameter of it parent SBA-15 support, as shown by the TEM image in Fig. 3a. A closer examination of the TEM image observed no Fe catalyst particle in the tips of these close-end type CNTs (Fig. 3b), suggesting that their formation follow the base growth mechanism. The reasons for such preferred mechanism in the powdered substrate system is rather intriguing and deserves further investigation. Finally, it is worth mentioning that the 1 2 3 4 5 6 7 8 methodology and CVI procedure 26 /degree reported herein for fabricating CNTs Fig. 2. Low angle XRD patterns of (a) with controllable sizes were also found parent SBA-15, (b) Fe(co)/SBA-15, and to be unique in promoting the production (c)Fe(im)/SBA-15. yield. More specifically, a maximum

Fig. 3. TEM images of CNTs growth from Fe(im)/SBA-15 revealing that they are CNTs with (a) an averaged diameter of ca. 7.7 nm and (b) closed ends.

412

CNTs yield of ca. 2.5 g/h was achieved for the supported Fe/SBA-15 catalysts in the present system design with a reactor chamber volume of ca. 30 mL. Taking the weight ratio of CNTs/carbon in C2H2 into account, it is estimated that ca. 78% of the C2H2 carbon source were effectively transferred into CNTs. Thus, the methodology reported herein should be useful for industrial applications, particularly in quality control and mass production of CNTs. 4. Conclusion By using mesoporous silica as template and catalyst support, we have demonstrated that high quality CNTs can be fabricated not only with superior yield but also with uniform diameter tailored by the pore size of their template. 5. References [1] Y. Saito and S. Uemura, Carbon, 38 (2000) 169. [2] C. Liu, Y. Y. Fan, M. Liu, H. T. Cong, H. M. Cheng and M. S. Dresselhaus, Science, 286 (1999)1127. [3] E. T. Thostenson, Z. Ren and T. W. Chou, Compos. Sci. Technol., 61 (2001) 1899. [4] R. K. Roy, M. P. Chowdhury and A.K. Pal, Vacuum, 77 (2005) 223. [5] C. T. Kuo, C. H. Lin and A. Y. Lo, Diamond Relat. Mater., 12 (2003) 799. [6] C. J. Lee, S. C. Lyu, Y. R. Cho, J. H. Lee and K. I. Cho, Chem. Phys. Lett., 341 (2001) 245. [7] Y. C. Choi, Y. M. Ghin, Y. H. Lee, B. S. Lee, G. S. Park, W. B. Choi, N. S. Lee and J. M. Kim, Appl. Phys. Lett., 76 (2000) 2367. [8] Z. F. Ren, Z. P. Huang, J. W. Xu, J. H. Wang, P. Bush, M. P. Siegal and P. N. Provencio, Science, 282(1998)1105. [9] W. Z. Li, D. Z. Wang, S. X. Yang, J. G. Wen and Z. F. Ren, Chem. Phys. Lett., 335 (2001) 141. [10] C. H. Kuo, A. Bai, C. H. Huang, Y. Y. Li, C. C. Hu and C. C. Chen, Carbon, 43 (2005) 2760. [11] Z. H. Yuan, H. Huang, L. Liu and S. S. Fan, Chem. Phys. Lett., 345 (2001) 39. [12] D. Zhao, J. Feng, Q. Huo, N. Melosh, G. H. Fredrickson, B. F. Chmelka and G. D. Stucky, Science, 279 (1998) 548. [13] A. Y. Lo , S. J. Huang, W. H. Chen, Y. R. Peng , C. T. Kuo and S. B. Liu, Thin Solid Films, 498(2006)193. [14] C. Y. Mou and H. P. Lin, Pure Appl. Chem., 72 (2000) 137. [15] Y. J. Han, J. M. Kim and G. D. Stucky, Chem. Mater., 12 (2000) 2068.


413 413

Synthesis of large pore mesoporous carbon using colloidal silica template Huachun Li and Shunai Che* School of Chemistry and Chemical Technology, State Key Laboratory of Composite Materials, Shanghai Jiao Tong University, 800 Dongchuan Road, Shanghai 200240, China.

1. Introduction Recently, Ryoo et al. reported the synthesis of mesoporous carbon by employing mesoporous silicas as templates [1]. The carbons exhibited varieties of pore structures and pore diameters, depending on silica templates that are synthesized with various structures and wall thickness. Usually, these wellordered mesoporous carbons exhibited the pore size smaller than 4 nm arising from the dissolved silica wall. Compared to mesoporous silica, the use of the colloidal silica as template provides another way to fabricate macroporous carbons [2-7]. In this report, we present the synthesis of large pore mesoporous carbon with high surface area and large mesopore volume affected by particle size and pH value of colloidal silica sol. In comparison to small pore mesoporous carbons, these latter carbons should be much more suitable templating media for the "nanocasting" of various materials. 2. Experimental Section The synthesis of large pore meosporous carbon using colloidal silica as template and sucrose as carbon source was performed according the method of Ryoo et al [1]. Snowtex (ST) colloidal silica solutions (Table 1) with different silica particle sizes and pH values were used as sources of porous silica accumulations, provided by Nissan Chemical Ltd. The silica sols with higher pH were stabilized by Na+; Na+ was removed in the silica sol with lower pH; and silica sol ST-AK was stabilized by Al3+. The silica templates and carbon replicas were denoted as S-X and C-X, respectively, where X indicates the colloidal silica sol used.

414

The colloidal sols were evaporated under 373 K for overnight to get the mesoporous silica templates. In a typical synthesis of the mesoporous carbon, the solution of 0.8 g sucrose and 0.08 g H2SO4 dissolved in 6.0 g H2O was added to 2.0 g S-ST-OS silica template. After dried at 373 K for 6 h, raised to 433 K. and kept for 6 h, the silica containing partial carbonizing sucrose was mixed with a clear aqueous solution consisting of 0.48 g sucrose, 0.046 g H2SO4 and 6.0 g H2O. The resultant mixture was dried again at 373 K for 6 h, raised to 433 K and kept for 6 h. The carbon/silica composite sample was then heated to 1173 K for 6 h under N2 flow. The carbon replicas were obtained after the silica removal by using HF solution. 3. Results and Discussion The particle sizes and pH values of colloidal silica sols, pore sizes of the mesoporous silica templates obtained from the corresponding colloidal silica sols, and pore sizes and BET (Brunauer-Emmett-Teller) surface areas of the corresponding large mesoporous carbon replicas are summarized in Table 1. Table 1. Properties of colloidal silica sols, mesoporous silica templates and the corresponding carbon replicas. pH value of silica sol 2.0-4.0

Silica template

Ds (nm)

Carbon replica

Dc (nm)

(m*g-')

ST-OS

Particle size (nm) 8-11

S-ST-OS

1.8

C-ST-OS

6.7

1361.1

ST-S

8-11

9.5-10.5

S-ST-S

2.4

C-ST-S

14.4

1038

ST-O

10-20

2.0-4.0

S-ST-0

3.6

C-ST-O

7.3

1161.7

ST-AK

10-20

4.0-6.0

5.8

C-ST-AK

9.1

1585.8

ST-20

10-20

9.5-10.0

S-STAK S-ST-20

4.3

C-ST-20

14.4

758.7

ST-O40

20-30

2.0-4.0

5.3

13.6

1327.8

ST-50

20-30

8.5-9.5

C-STO40 C-ST-50

20.3

1090.1

Colloid al silica

S-STO40 S-ST-50

6.8

Ds and Dc are the pore size of silica template and carbon replica calculated using BJH method from desorption branch, respectively. S is the BET surface area.

Figure la, b and c show N2 adsorption-desorption isotherms and the corresponding pore size distributions of the different colloidal silica accumulation that obtained from the colloidal silica sols with particle size of 811, 10-20 and 20-30 nm with different pH, respectively. All the samples show type IV isotherms with capillary condensation at relative pressure PlPo = 0.40.8, indicating the presence of mesopores caused by the voids space of silica particles. As expectation, the pore size of silica templates was increased with increasing silica particle size when the silica sols have the same pH value.

415

However, interestingly, the larger pore size of the silica template obtained from higher pH value of silica sol with the same particle size, which caused by the repulsion between the same charged silica particles covered by Na+ in base medium. Among the silica sols with the same particle of 10-20 nm (Fig. lb), SST-AK with middle pH value shows the largest pore size, which would caused by strong repulsion of the silica particles highly charged by Al3+.

80 60 40 1

2 3 4 5 Pore siz e(nm)

6

160

b

3 -1

3 -1

120

100

20

S-ST-O S-ST-AK S-ST-20

Adsorbed amount (cm g , STP)

S-ST-S

120

140

a

S-ST-OS


3 -1


140

100 80 60 40 20

c

140 120 100 2

80

4 6 8 10 Pore Size(nm)

12

60 40 20

S-ST-O40 S-ST-50

0

0 0

0.2

0.4

0.6

0.8 0.8

Relative pressure pressure P/Po P/Po Relative

1

0

0.4 0.2

0.6 0.4

2

0.81 0.6

4 6 Pore Pore size (nm) (nm) 0.8 size 1

Relative pressure pressure P/Po P/Po Relative

8

0 0

0.2 0.2

0.4 0.4

0.6 0.6

0.8 0.8

11

Relative Relative pressure pressure P/Po P/Po

Fig. 1 N2 adsorption-desorption isotherms and the corresponding pore size distributions of silica templates.

Figure 2 and 3 shows the N2 adsorption-desorption isotherms, the corresponding pore size distributions and scanning electron microscope (SEM) images of the mesoporous carbons synthesized with different colloidal silica templates shown in Figure 1. All the isotherms of the mesoporous carbons show the hysteresis loops at high relative pressures corresponding to type IV behavior, indicating the presence of larger mesopores. The sharpness of the isotherm indicates the narrow pore size distribution. The pore size uniformity was also confirmed by SEM images. Mesoporous carbons with large pore size of 6-20 nm, large surface area of 700-1600 m g"1, and large pore volume of 1.24.4 cm g" have been formed through the carbon replication of mesostructured silicas. As shown in Figure 2 and 3, the pore size of the carbon replicas was increased with increasing silica particle size, when the silica sols with similar pH have been used. On the other hand, interestingly, the larger pore size of carbons has been obtained with higher pH value of silica sol with the same particle size, which is not in agreement with the particle size of the colloidal silicas. The carbon replicas seem quite different based on the nature of the colloidal silica. The pore size larger than particle size of silica has been replicated with colloidal silicas with higher pH value. In the mesoporous carbon synthesized with silica sol having particle size of 10-20 nm in different pH value, C-ST-AK shows the thickest carbon walls than the others, which is consistent with the largest pore size in the silica templates.

416

1000

15 25 35 Pore size(nm)

800 600 400 C-ST-OS

200

1200

3 -1

1200

b

1400

5

1000

15 25 Pore siz e (nm)

35

800 600 400 C-ST-O C-ST-AK C-ST-20

200

C-ST-S

0

0 0

0.2

0.4

0.6

0.8

Relative pressure P/Po P/Po

1

Ad so rb ed amo u n t (cm g , ST P)

3 -1

1400 5

3000

1600

a

1600


3 -1


1800

0

0.2

0.4

0.6

0.8

Relative pressure P/Po

c

2500 2000 1500 5

1000

15 25 35 Pore size(nm)

500 C-ST-O40 C-ST-50

0

1

0

0.2

0.4

0.6

0.8

1

P/Po Relative pressure P/Po

Fig.2. N 2 adsorption-desorption isotherms and the corresponding pore size distributions of carbon replicas.

Fig.3. SEM images of mesoporous carbons: (a) C-ST-O, (b) C-ST-AK, (c) C-ST-20, (d) C-STO40 and (e) C-ST-50.

4. Conclusion The colloidal silica template presented here was a simple and viable route for the production of large mesoporous carbons with high surface areas and large pore volumes, whose pore sizes can be easily controlled by monitoring the sizes of the silica spheres and the pH value of silica sols. 5. References [1] (a) R. Ryoo, S. H. Joo and S. Jun, J. Phys. Chem. B 103 (1999) 7743. (b) J. S. Lee, S. H. Joo and R. Ryoo, J. Am. Chem. Soc. 124 (2002) 1156. [2] A. A. Zakhidov, R. H. Baughman, Z. Iqbal, C. Cui, I. Khayrullin, S. O. Dantas, J. Marti and V. G. Ralchenko, Science 282(1998) 897. [3] J. Jang and B. Lim, Adv. Mater., 14 (2002) 1390. [4] F. Schuth, Angew.Chem., Int. Ed., 42 (2003) 3604. [5] S. A. Johnson, P. J. Ollivier and T. E. Mallouk, Science, 283 (1999) 963. [6] Z. Li and M. Jaroniec, J. Am. Chem. Soc, 123 (2001) 9208. [7] J. S. Jang, B. K. Lim and M. J. Choi, Chem. Commun. (2005) 4214.


417 417

Study of mercury(II) binding to thiol-modified ordered mesoporous silicas by analytical and electrochemical analyses: influence of the pore structure and the functionalization process Fabrice Gaslain,a Cyril Delacote,b Benedicte Lebeau,a Claire Marichal,a Joel Patarina and Alain Walcarius b " Laboratoire de Materiaux a Porosite Controlee - UMR 7016 - CNRS - ENSCMu Universite de Haute Alsace, 3 rue Alfred Werner, 68093 Mulhouse, France b Laboratoire de Chimie Physique et Microbiologie pour VEnvironnement - UMR 756 CNRS - Universite H. Poincare Nancy I, 405 rue de Vandoeuvre, 54600 Villers-lesNancy, France

1. Introduction During the last decade, an increasing interest has been devoted to the organic pore surface modification of ordered mesoporous siliceous materials [1]. In particular, the high potential of these mesoporous hybrid materials for heavy metal sorption has been demonstrated [2]. Among the ligands available, the widely studied thiol ligand has been chosen as a model Hg(II) sorbent ligand. However, two critical parameters affecting the performance of such hybrid materials in remediation and sensing that are the sorption capacity and the rate of access to the active center have received low attention [2, 3]. MCM-41- and MCM-48-type silicas functionalized with thiol groups by postsynthesis grafting or by direct synthesis have been prepared following a very similar procedure to obtain comparable materials in terms of particle size, morphology and framework. Indeed the aim of this work was to study the influence of the porous network geometry and the functionalization process on the accessibility to the thiol sites and diffusion rates of the Hg(II) species in the mesoporous solids. Their ability to bind Hg(II) species was evaluated from batch experiments and the reaction rate of the uptake process was characterized by applying an electrochemical methodology developed in our group [3].

418

2. Experimental section All the materials were prepared by adapting procedures previously reported [4, 5]. The amount of water was doubled for the preparation of MCM-48 siliceous materials. Direct synthesis was made from a mixture of TEOS and 3mercapto-propyltrimethoxysilane (MPTMS) in the molar ratio 9.1 TEOS: 0.9MPTMS. For post-synthesis grafting, pure siliceous materials [5] were suspended in dry toluene containing MPTMS (1.8 mmol g"1) under reflux for 24 h. Removal of the surfactant was performed by calcination (pure silica materials) or under reflux with a mixture of HC1 and ethanol (direct synthesis of functionalized materials). All hybrid materials were characterized by X-ray diffraction (XRD), nitrogen adsorption-desorption measurements, 29Si and 13C solid state nuclear magnetic resonance (NMR), scanning electron microscopy (SEM), and elemental chemical analysis. The electrochemical method applied to study the rate of access of Hg(II) species to the binding sites was reported earlier [3]. 3. Results and discussions 3.1. Physico-chemical characterization X-ray diffraction patterns (Fig. 1) were characteristic of well ordered hexagonal or cubic pore arrangements (of MCM-41 and MCM-48 types, respectively). Nearly spherical particles with an average diameter of 0.5 um were observed for all samples by SEM (Fig. 2). For all surfactant extracted solids, the nitrogen adsorption-desorption isotherms were of type IV characteristic of mesoporous materials. In all cases a sharp pore size distribution was observed with an average BJH pore size of 2.5-3 nm (Table 1). Whatever the type of material and the functionalization process, distinct resonances characteristic of the silica network [Qn = Si(OSi)n(OH)4.n, n = 2-4] and of the Table 1. Some physico-chemical date for thiol-functionalized materials. Material

Surf, area

Pore vol.

Pore0

SH groups

Hg" binding (mmol g"1)

type

/mV

/mL g 1

/mmol g"1

pH2

pH4

0.9

0.7

0.9

MCM41-SHgr

839

0.60

MCM41-SHM

1550

0.76

/nm 2.8 2.6

1.4

1.3

1.5

MCM48-SHgr

938

0.68

2.9

0.9

0.8

1.0

MCM48-SHC

941

0.58

2.9

1.4

1.2

1.4

m

organosiloxane network [T = RSi(OSi)m(OH)3.m, m=l-3] after functionalization were observed by 29Si MAS NMR. The presence of the T units (ca. 10%) confirms that the functionalization was successful. Post-synthesis grafted sample showed a more condensed silica network but a lower condensed

419

Intensity (a.u.)

organosiloxane network (due to extraction and functionalization processes, respectively). 13C CP-MAS NMR confirms that 3-mercaptopropyl groups are present as intact organic moieties.

40000

(a) (b) (c) (d) 2

3

44

5

2 θθ (degree)

6

7

Fig. 1. XRD patterns of MCM-41 (a,b) and MCM-48 (c,d) materials obtained by direct synthesis: pure silica (a,c) and mercaptopropyl-functionalized solids (b,d).

Fig.2. SEM pictures of MCM-41 (a,b) and MCM-48 (c,d) materials obtained by direct synthesis: pure silica (a,c) and mercaptopropyl-functionalized solids (b,d).

3.2. Mercury(II) accumulation The uptake of mercury(II) by these thiol-functionalized materials was studied at two pH values (i.e., 2 & 4). A complete accessibility was observed at pH 4 where Hg(II) species are in the form of Hg(OH)2. A less complete filling (Table 1) was obtained when performing the uptake experiments at pH 2 where Hg(II) species are in the form of Hg2+. Because Hg2+ binding to thiol groups involves the formation of a positive charge, this results in significant repulsive electrostatic interactions in the mesopore channels [2d], which could contribute to explain the restricted access of Hg2+ to the binding sites. The speed of this binding reaction was not very much affected by the structure of the materials, yet displaying slightly faster processes in materials with a hexagonal mesostructure (Fig. 3). For materials having approximately the same structure (hexagonal or cubic), the hybrids obtained by post-synthesis grafting were characterized by uptake reaction rates higher than their homologues obtained by the one-step co-condensation route, especially at the early beginning (50-70%) filling levels. This is probably due to the fact that the grafting would preferentially occur at the mesopore entrance, resulting in a greater density of binding sites at the boundaries of the particles, while a somewhat more homogeneous distribution of the organo-functional groups is thought to occur in mesoporous hybrids obtained by co-condensation. In this last case, a higher amount of Hg2+ species

420

must diffuse deeply in the bulk of the particle and 100% filling occurs in several hours, while this binding capacity was observed in less than 10 min for grafted adsorbents (Fig. 3).

100

Time (s)

200

300

100

500

Time (s)

Fig.3. Evolution of reaction rates for Hg2+ binding to thiol functionalized MCM-41 (A) and MCM-48 (B) materials (Q/Qo represents the extent of uptake which is equal to 1 at 100% binding): (a) post-synthesis grafted solids, (b) in situ functionalized adsorbents. Insets represent the variations of apparent diffusion coefficients (Dapp) with Q/Qo-

4. Conclusion MCM-41 and MCM-48 organized mesoporous silicas were functionalized by mercaptopropyl groups using two routes: post synthesis treatment of pure silica and direct functionalization by a co-condensation procedure. 29Si NMR showed that the functionalization process lead to different T and Q condensed units. The reaction rates of Hg2+ binding are faster for the post-synthesis grafted samples, especially at high uptake levels. Such a result suggests that grafting would preferentially occur at the mesopore entrance, resulting in a greater density of binding sites at the boundaries of the particles. 5. References [1] A. Stein et al. Adv. Mater. 12 (2000) 1403; b) A. Vinu et al. J. Nano. Nanotechnol. 5 (2005) 347. [2] X. Feng et al. Science 276 (1997) 923; b) L. Mercier, T. Pinnavaia, Adv. Mater. 9 (1997) 500; c) J. Brown et al. Microporous Mesoporous Mater. 37 (2000) 41; d) A. Walcarius et al. Anal. Chim. Acta 547 (2005) 3. [3] A. Walcarius et al. Chem. Mater. 14 (2002) 2757; b) A. Walcarius et al. Chem. Mater. 15 (2003) 2161; c) A. Walcarius et al. Chem. Mater. 15 (2003) 4181. [4] M. Etienne et al. New J. Chem. 26 (2002) 384. [5] M. Grun et al. Microporous Mesoporous Mater. 27 (1999) 207.

Mesostructured Materials Recent Progress in Mesostructured D. Zhao, S. Qiu, Y. Tang and C. Yu (Editors) © 2007 Elsevier B.V. All rights reserved.

421 421

The effect of inorganic salt on the synthesis of large-pore PMO with aromatic moieties in the framework Sung Soo Park, Booyoun An, Yunji Kang, Mina Park, II Kim and Chang-Sik Ha* Department of Polymer Science and Engineering, Pusan National University, Busan 609-735, Korea

We report on the effect of inorganic salt on the synthesis of large-pore PMO materials with aromatic groups inside the channel wall. The triblock copolymer template with the aid of inorganic salt could provide a new method to prepare large-pore mesoporous organosilica material with hollow sphere morphology. By adding inorganic salt in reaction mixture, we have successfully controlled ordered structure, morphology, wall thickness, and pore size of PMO with aromatic moieties in the framework. 1. Introduction Periodic mesoporous organosilica (PMO) materials with organic groups inside the channel walls [1] provide new opportunities for controlling the chemical, physical, mechanical properties of the materials. Inorganic salts have been used to improve the hydrothermal stability, control the morphology, extend the synthesis domain, and tailor the framework porosity during the formation of mesoporous materials, via self-assembly interaction between surfactant head groups and inorganic species. Previous studies have shown that the reaction conditions, inorganic salts and solvent-assistance play important roles in controlling the morphology of mesoporous silicas [2, 3]. Guo et al. [4] and Qiao et al. [5] reported synthesis of PMOs with highly ordered mesostructure, rod- and plate-like morphologies using ethane-bridged organosilica precursor with the assistance of inorganic salts. In this work, we report on the effect of inorganic salt for the synthesis of large-pore PMO with hollow sphere morphology, controllable pore size and wall thickness, ordered structure, and aromatic moiety in the framework.

422

2. Experimental Section The PMO materials were synthesized using the following reactant molar ratios [2]: 0.6 for (EtO)3SiC6H4Si(OEt)3 (BTES-benzene) and (EtO)3Si(C6H4)2(OEt)3 (BTES-biphenyl)} : 0.017 P123 : 0-6.08 NaCl : 5.07 HCl : 178 H2O. The reactant solution was stirred at 40 °C for 24 h and heated at 80 °C for 24 h. Template in PMO material was removed by solvent-extraction with HC1EtOH solution. Small angle X-ray scattering (SAXS) was performed at Pohang Accelerator Laboratory (PAL), Korea with Co-Ka (A, = 1.608 A) radiation. Nitrogen adsorption and desorption isotherms were measured at -196°C using a NOVA 4000e instrument. Scanning electron microscopy (SEM) images were obtained using a Hitachi E-1010 sputter coater prior to imaging. Transmission electron microscopy (TEM) images were obtained using a JEOL JEM-2010 microscope operating at 200 kV. 3. Results and Discussion

0.2 0.4 0.6 0.8 Relative pmssure(P/J'o)

Fig. 1. TEM images of BTES-benzene (a and b) and BTES-biphenyl (c and d) synthesized without (a and c)and with (b and d) NaCl in reaction mixture.

Fig. 2. N2 adsorption-desorption isotherms of (A) BTES-benzene and (B) BTES - biphenyl synthesized using different content of NaCl in the range from 0 to 6.08 in reaction mixture.

Fig. 1 shows TEM images of PMO materials synthesized with bridged organic groups such as benzene and biphenyl in the framework using the nonionic triblock copolymer Pluronic PI23 as template with and without inorganic salt in reaction mixture. PMO materials synthesized with the aid of inorganic salt have huge hollow spherical morphologies with the smaller mesopores in shell, as shown in TEM images of Fig. l(b) and (d). Inorganic

423

salts can reduce the solubility (salting-out effect), critical micellar concentration, critical micellar temperature, and the cloud point of the block copolymers, and can also decrease the thermodynamic radius of the micelles [6]. In this work, formation of huge hollow spherical morphologies can be attributed to the lower solubility of micelles' solution by the addition of inorganic salt in reaction mixture. Table 1. Textural properties ofPMO materials with aromatic moieties in framework synthesized using reactant composition with different content of inorganic salt. Sample BTES -benzene

BTES -biphenyl

NaCl ratios in reaction mixture 0 2.54 4.06 6.08 0 2.54 4.06 6.08

dioo

(A) 113.0 117.4 138.4 139.9 125.7 128.2

Wall thickness* (A)

(m2g')

29.8 49.2 48.9 45.9 46.1

1964 1277 1332 1385 1497 1245 1557 1320

SBET

Primary pore (A)

Secondary pore (A)

30-800 57.8 40.0 42.2

188 169 152 15-800

33.6 33.9 36.0

148 147 142

Total pore volume 1.07 1.85 1.51 0.75 1.10 0.92 1.26 1.05

Wall thickness = ao-primary pore size, ao=2dioo/V3.

Table 1 shows textural properties of PMO materials with aromatic moieties in framework synthesized using reactant composition with different content of inorganic salt. The formation of secondary pores can be attributed to the aggregated particles based on nanosized particles and hollow spheres. The analysis of N2 adsorption-desorption isotherms clearly exhibited the strong adsorption at relative pressure (P/Po) close to 1.0, as shown in Fig. 2. BTESbenzene and BTES-biphenyl samples synthesized without NaC 1 have broad pore size distribution in the range of 30-800 A and 15-800 A, respectively. On the other hand, BTES-benzene and BTES-biphenyl samples synthesized with NaCl containing reactants have hollow sphere morphologies with narrow pore size distribution. The result is explainable based on the fact that inorganic salt plays an important role in the increased interaction between organosilane species and dehydrated PEO end blocks and the decreased solubility of triblock copolymer solution in water [4, 6]. The addition of inorganic salt causes dehydration of ethylene oxide units from the hydrated PEO shell remaining adjacent to the PPO core, leading to an increase in the hydrophobicity of the PPO moieties and a reduction in the hydrophilicity of the PEO moieties [4, 6]. For both the BTES-benzene and BTES-biphenyl samples, the secondary pore size was decreased from 188.0 to 151.5 A and from 148.3 to 142.0 A with increasing NaCl contents. It is due to the decrease in the micelles' size on adding salt, leading to the decrease of aggregated nanoparticle size[7]. In case

424

of the BTES-benzene samples, with the different content of NaCl in reactant, primary pore size changed from 57.8 A to 40.0 A. It is also due to the increase of interaction between hydrophobic benzene-group containing organosilane and dehydrated PEO shell. BTES-benzene sample synthesized with 6.08 NaCl ratio have slightly higher primary pore size than that of 4.06 NaCl ratio. It may be attributed to the increase of micelle diameter by the existence of surplus salt layer around triblock copolymer micelles. Increment of primary pore size for BTES-biphenyl sample synthesized with 6.08 NaCl ratio can be explained with the same reason. With the different NaCl content, surface area and total pore volume of BTES-benzene and BTES-biphenyl samples were 1964.0 m g' 1 1277.0 m2g"\ 1245 - 1557.0 m2g"' and 1.85 - 0.746 cm3g"\ 0.919 - 1.260 cm3g" ', respectively. 4. Conclusion The triblock copolymer template with the aid inorganic salt could provide a new method to prepare bridged aromatic moieties containing PMO hollow spheres. Hollow sphere, permeable shell, large pore size, high adsorption capacity of the samples may be useful as the solid nanocapsules for drug delivery, DNA therapy application, immobilization of hydrophobic enzymes, and bio-catalyst. 5. Acknowledgment This study was supported by the National Reserch Laboratory Program, the SRC/ERC program of MOST/KOSEF (Rl 1-2000-070-080020) and the BK21 Project. Thanks to the Pohang Accelerator Laboratory for SAXS measurements. 6. References [1] [2] [3] [4]

T. Asefa, M. J. MacLachian, N. Coombs and G. A. Ozin, Nature, 402 (1999) 867. C. Z. Yu, J. Fan, B. Z. Tian and D. Y. Zhao, Chem. Mater., 16 (2004) 889. C. Z. Yu, J. Fan, B. Z. Tian, D. Y. Zhao and G. D. Stucky, Adv. Mater., 14 (2002) 1742. (a) W. Guo, I. Kim and C.-S. Ha, Chem. Commun., (2003) 2692. (b) W. Guo, J.-Y. Park, M.-O. Oh, H.-W. Jeong, W.-J. Cho, I. Kim and C.-S. Ha, Chem. Mater., 15 (2003) 2295. [5] S. Z. Qiao, C. Z. Yu, Q. H. Hu, Y. G. Jin, X. F. Zhou, X. S. Zhao and G. Q. Lu, Micropor. Mesopor. Mater., 91 (2006) 59. [6] W.-H. Zhang, L. Zhang, J. Xiu, Z. Shen, Y. Li, P. Ying and C. Li, Micropor. Mesopor. Mater., 89 (2006) 179. [7] C. Booth and D. Attwood, Macromol. Rapid Commun., 21 (2000) 501.


425 425

Bovine serum albumin adsorption in large pore amine functionalized mesoporous silica S. Z. Qiao,a* Haiying Zhang,a Xufeng Zhou,ab Sandy Budihartonoa and G. Q. Lua* "ARC Centre for Functional Nanomaterials, The University of Queensland, St Lucia, QLD 4072, Australia h Department of Chemistry, Fudan University, Shanghai 200433, P.R.China

1. Introduction Ordered mesoporous materials with functionalized groups are promising for many emerging applications in adsorption separation, enzyme immobilization, bio-catalysis, drug delivery and sensors [1-3]. Some studies reported that the adsorption of proteins on mesoporous solids was size selective and the small entrance sizes of mesoporous materials may limit their applications in the processes involving large protein molecules [4, 5]. Meanwhile the loading amount of proteins was strongly influenced by the functional surface of materials and the adsorption conditions such as pH and ionic strength of solution [2, 3, 6]. Recently, the mesoporous silica FDU-12 with very large pore size (>20 nm) was successfully synthesized by a low temperature strategy using nonionic block copolymer as template [7]. The large entrance size of the material provided great advantages in the adsorption and diffusion of protein [8]. However, to the best of our knowledge, there have been no reports on the synthesis of hybrid mesoporous silica with very large pore by the low temperature strategy and their protein adsorption so far. Here we report a low temperature synthesis of highly ordered amine functionalized mesoporous silica with very large pore size. BSA was selected as model protein to study the effect of functional surface, entrance size and pH on the adsorption capacities. 2. Experimental Section In a typical synthesis, 0.5 g of triblock copolymers EOi06PO70EOi06 (Pluronic F127), 2.5 g of KC1 and 0.6 g of trimethylbenzene (TMB) were dissolved in 30

426

g of 2 M HC1 at 15 oC for 6 hours. The mixture of 1.97 g tetramethyl orthosilicate (TEOS, 99%, Fluka) and 0.14 g of 3-aminopropyl-triethoxysilane (APTES, 99%, Aldrich) was then added to the solution under stirring. The final reactant molar composition Si/F127/TMB/KCl/HCl/H2O was 1.00/0.0037/0.50/ 3.36/6.00/155. After being stirred for 24 hours at 15°C, the solution was transferred into an autoclave and heated at 100°C for 24 h. The as-made sample was collected by filtration. The sample was washed by 100 ml of ethanol and 5 ml of 2M HC1 at 60°C for two times to remove the templates and denoted as N100. For the 140°C hydrothermal treatment, as-made sample was added to a solution of 30 ml 2 M HC1 in an autoclave and heated at 140°C for another 48 h. The resulting product was obtained by filtration and washed by the mixture of ethanol and HC1 as mentioned above. The sample was denoted as N-140. Adsorption isotherm of BSA (Sigma Aldrich) was measured by batch experiments performed in a water bath at 25 °C. 50 mg of solid degassed under vacuum at 120°C was put in 5ml of BSA solution with different concentrations (from 0.5 to 15.0 g/L, acetic buffer of pH 3.4 or 4.7). The mixture was left in a shaker operating at 180 rpm for 24h, which was confirmed to reach equilibrium. The samples were centrifuged and filtered through cellulose nitrate membrane filters, and the equilibrium concentration of protein in the supernatant liquid was diluted and analyzed using UV-Vis spectrophotometer at 280 nm. The amount adsorbed on solids was determined by the mass balance of the protein.

331 3 31

N-140 33 3 44 2

31 1

0.5

(a)

1.0 , -11) q (nm

N-100 1.5

2.0

Amount Adsorbed (cm3 STP g-1)

0.0

31 1

111

111


|

1200

(b) 800 N-140 400 N-100 0 0.0

0.2 0.4 0.6 0.8 Relative Pressure Pressure (p/p (p/poo) Relative

1.0 1.0

Fig. 1 SAXS traces (a) and nitrogen adsorption isotherms (b) of samples synthesized using different hydrothermal temperatures

Figure la shows the small angle X-ray scattering (SAXS) patterns of surfactantextracted amine functionalized mesoporous silicas. Five well-resolved peaks of sample N-l 00, which can be exactly indexed to the 111,311,331, 333 and 442 reflections, indicate that it is a highly ordered Fm3m fee structure. The SAXS pattern of sample N-140 shows three well-resolved peaks at least. High peak intensity and resolution of peaks can be attributed to the regularity of porous materials. The cell parameters of N-100 and N-140 are 31.2 and 36.4 nm respectively. The transmission electron microscopy (TEM) images of samples N-100 and N-140 are shown in Figure 2, which confirms their highly ordered

427

mesostructure. The nitrogen adsorption and desorption isotherms are shown in Figure lb. The cavity size and entrance size can be determined from the adsorption and desorption branches of the isotherms respectively by BdB model. Our study revealed that the entrance sizes of materials were enlarged from 5.8 nm to 10.4 nm by increasing the hydrothermal treatment temperature from 100 to 140°C. Meanwhile the cavity sizes also increased from 19.0 to 27.9 nm. The cavity size, entrance size, BET surface area (calculated using adsorption data in a relative pressure range p/p°=0.05-0.25) and pore volume (estimated from the adsorbed amount at a relative pressure of about 0.99) are summarized in Table 1. For comparison, the structural parameters of large pore mesoporous pure silica (b)

Fig. 2 TEM images of samples synthesized using different hydrothermal temperature (a) 100 °C (b) 140 °C.

(denoted as S-140), synthesized according to the reference 7 with 140°C hydrothermal treatment, are also listed in Table 1. Table 1. Physicochemical properties of samples Unit cell

Cavity size

Surface area

(nm)

Entrance size (nm)

Pore volume

(nm)

(cmV1)

(mV)

N-100

31.2

19.0

5.8

0.826

441.2

N-140

36.4

27.9

10.4

1.146

482.4

S-140

40.2

36.3

13.0

0.917

239.3

Sample

Figure 3 shows the adsorption isotherm of BSA on different samples. All isotherms show a sharp initial rise and then reach maximum adsorption amounts, suggesting that isotherms are of Langmuir type. It can be seen that the adsorbed amount of BSA on N-140 (entrance size 10.4 nm) reaches to 222.0 mg/g, much higher than the adsorbed amount (60.4 mg/g) on sample N-100 (entrance size 5.8 nm). BSA is a large protein (the size is 4*4*14 nm) and can not enter the pore smaller than 4 nm. However it may undergo orientation adjustment and adapt its long axis to be parallel to the pore axis to enter into the pore larger than 4 nm [5]. Moreover, BSA molecules can be adsorbed on the external

428

Amount Adsorbed (mg/g)

surface of the material. Our study reveals 300 that the entrance size of sample affects "5) N-140,pH 4.7 N-140,pH4.7 the adsorbed amount significantly. 200 Comparing with BSA adsorption on the amine functionalized surface (N-140), the S-140,pH S-140,pH 4.7 adsorbed amount on pure silica FDU-12 < 100 (S-140) is significantly decreased (79.0 N-100,pH 4.7 N-100,pH4.7 N-140,pH3.4 N-140,pH 3.4 mg/g) although it has larger entrance 0 sizes. It indicates that amine functional 0 3 6 9 12 15 12 15 groups improve BSA adsorption. The Equilibrium Concentration (mg/ml) reason is probably the hydrophobic surface of amine functional silica which Fig. 3 Adsorption isotherm curves of BSA. The solid lines are fitting results of is beneficial to the adsorption of BSA. The adsorbed amount of BSA on the the Langmuir equation. sample N-140 at pH 3.4 (15.9 mg/g) is much lower than the adsorbed amount of 222.0 mg/g at pH 4.7 (isoelectric point of BSA, 4.7-4.9). It is believed to be largely due to the strong electrostatic repulsion between positively charged BSA and amine groups as well as among BSA molecules at pH 3.4. 4. Conclusion In this study we investigated the adsorption of BSA on the large pore amine functionalized mesoporous silica synthesized by a low temperature strategy. The BSA adsorption capacity was found to be highly dependent on the entrance size of materials and surface properties. The modification of the inner surface with amine group can enhance its interaction with BSA and improve the protein adsorption. The adsorbed amount of BSA is higher at its isoelectric point and the electrostatic and hydrophobic interactions are dominative forces in the BSA adsorption on amine functionalized silica surface. 5. References [1] [2] [3] [4] [5] [6] [7] [8]

J. Y. Han, G. D. Stucky and A. Butler, J. Am. Chem. Soc, 121 (1999) 9897. H. H. P. Yiu and P.A. Weight, J. Mater. Chem., 15 (2005) 3690. M. Hartmann, Chem. Mater., 17(2005) 4577. H. H. P. Yiu, C. H. Botting, N. P. Botting and P. A. Weight, Phys. Chem. Chem. Phys., 3 (2001)2983. S. W. Song and K. Hidajat, Langmuir, 21 (2005) 9568. S. Z. Qiao, C. Yu, W. Xing, Q. H. Hu, H. Djojoputro and G. Q. Lu, Chem. Mater., 17 (2005)6172. J. Fan, C. Yu, J. Lei, Q. Zhang, T. C. Li, B. To, W. Zhou and D. Y. Zhao, J. Am. Chem. Soc, 127 (2005) 10794. J. Fan, C. Yu, F. Gao, J. Lei, B. Tain, L. Wang, Q. Luo, B. Tu, W. Zhou and D. Y. Zhao, Angew. Chem. Int. Ed., 42 (2003) 3146.


429 429

Effect of various templates on the formation of mesoporous benzene-silica hybrid material K.-F. Zhou a , Q.-H. Xia a '*, H.-B. Zhu a , D. Hu a and Z.-M. Liu b * a

Ministry-of-Education Key Laboratory for the Synthesis and Application of Organic Functional Molecules, Hubei University, Wuhan 430062, China b Dalian Institute of Chemical Physics, Academia Sinica, Dalian 116023, China.

The chain length of the template seriously affected the formation of mesoporous benzene-silica hybrid material from a basic medium under our experimental conditions. Only Ci6 surfactant could template a PMO solid with XRD peaks at low angles of 26 = 2.0, 3.6, 4.2°, similar to those of ordered MCM-41. PMO materials could not be formed by [CnH2n+i(CH3)3N+, n=8, 12, 22] and [(CnH2n+i)4NOH, n = 2, 4], but the recovered organosilica solids possessed similar infrared framework vibrations and XRD peaks at high angles of ca. 20=11.5, 23.4, 35.4°. In an acidic medium mesoporous benzene-silica hybrid materials could be mediated by [CnH2n+i(CH3)3N+, n=12, 16], in which C ]6 templated a 3D-cage like mesopore structure, similar to SBA-1. Keywords: mesoporous benzene-silica, PMO, MCM-41, SBA-1 1. Introduction Inagaki et al. reported the surfactant-mediated synthesis of a benzene-silica hybrid PMO material in 2002 [1]. Since then, much effort has been focused on the research of various organic-inorganic hybrid periodic mesoporous organosilicas (PMO) using some organic silicate esters as starting materials [2]. Those PMO materials are thought to consist of crystal-like wall structures, as evidenced mainly by XRD patterns, where additional four sharp peaks emerge at d=1.6, 3.8, 2.5 and 1.9 A (29 = 10-70°), different from those of MCM-41. The literature proposed that the self-assembly of organosilane BTEB molecules formed the periodic structure in the walls of the mesoporous benzene-silica, probably because hydrophobic and hydrophilic interactions directed the selfassembly of BTEB molecules [1]. Our present results show that the formation

430

of mesoporous benzene-silica hybrid solid in a basic medium could be similar to that of MCM-41, while in an acidic medium similar to that of SB A-1. 2. Experimental Section The used alkyl ammoniums included [CnH2n+i(CH3)3NBr, n=8,12,16,22] and [(CnH2n+i)4NOH, n=2,4) ], and organosilica source was 1,4-bis(triethoxysilyl) benzene (BTEB, 98 wt%, self-made [3]). The synthesis of PMO in a basic medium was carried out in the following procedure. Appropriate amount of surfactant was first dissolved in the solution consisting of 120 g of distilled water and 7 ml of 3 M aqueous NaOH at 25°C. While stirring vigorously, 3.24 g of BTEB was well dispersed into the basic solution. The molar composition was 0.806BTEB: 0.63surf.: 2.1NaOH : 667H2O. The stirring was continued for another 24 h, then the suspension was statically refluxed at 90°C for a period of 72-240 h. Thereafter, the white solid was recovered by filtration, washed repeatedly with distilled water, and dried at 100°C overnight. The surfactant molecules were removed by extraction through stirring the as-prepared solids in the solution of 200 ml ethanol and 6 ml concentrated HC1 (36%) at60°C for 6 h, followed by filtration and drying at 80 °C for 5 h. This extraction was repeated twice. In an acidic medium mesoporous benzene-silica materials were synthesized in the presence of [CnH2n+i(CH3)3N+, n=12,16]. Under stirring the surfactant was dissolved in the solution consisting of 10 ml concentrated HC1 and 36 ml water at 0, 23, 30 and 60°C, respectively. While stirring vigorously, 2.25 g of BTEB was dispersed into the acidic solution. The molar composition was 5.6BTEB: 3.3surf.: 323.6HC1: 2000H2O. The stirring was continued for another 24 h, and then the suspension was statically aged for 72 h at 0, 23, 30 and 90 °C, respectively. Finally, the recovered solid underwent identical treatments as described above. All the solid samples were well characterized by XRD, IR, BET, TEM and 13C CP MAS NMR techniques. 3. Results and Discussion In a basic medium the addition of Ci6H33(CH3)3N+ achieved benzene-silica PMO material, while the use of both [CnH2n+,(CH3)3N+, n=8,12,22] and [(CnH2n+i)4NOH, n=2,4] did not yield any mesoporous solid. Figure 1 compares XRD patterns and IR spectra of six solids templated by [CnH2n+i(CH3)3N+, n=8,12,16,22] and [(CnH2n+i)4NOH, n=2,4] in the basic medium, in which six samples show similar IR framework vibrations. The sample synthesized with Ci6 exhibits an XRD pattern of highly ordered PMO solid, but others mediated by Cg, C12, C22 and [(CnH2n+04NOH, n=2,4] do not show any mesoporous characteristic. These samples show similar diffraction peaks at high angles of ca 20=11.5, 23.4 and 35.4°, while the PMO induced by Q 6 contains diffraction peaks at low angles of 26= 2.0, 3.6 and 4.2°, similar to ordered MCM-41.

431 C-22 5000 5000 -

C-16

Intensity /cps

SB 4000 -

C-12 C-8

' 3000 3000 -

C-4 C-2

C-16 C-22 C-12 C-8

2000 1000 1000 -

4000 400 4000 3600 3600 3200 3200 2800 2800 2400 2400 2000 2000 1600 1600 1200 1200 800 800 400

0 0

-1 WAVENUMBER / / cm-1

C-4

C-2 5

10

15 15

20 25 20 25 2θ 2θ/°/°

30

35

40

Figure 1. Effect of basic medium on IR spectra and XRD patterns of samples. -Ph-Ph* band * Side band

*

ULU *

*

300 300

250 250

200 200

150 150

100 100 ppm ppm

50

0

-50 -50

Figure 2. 1 3 C CP MAS NMR spectrum. 13/-

Figure 3. TEM image of 3D-cage pore.

C CP MAS NMR spectrum of thus-synthesized PMO solid contains only one signal at 133.2 ppm, with some side bands, due to the phenylene carbon (Fig. 2). The formation of benzene-silica PMO solid from a basic medium was affected by the chain length of the template. The PMO solid induced by C 1 6 had well-defined mesopores averaging 31 A, a pore volume of 0.46 cm3/g, and a surface area of 858 m2/g. Surface area (m2/g) and pore volume (crnVg) of other organosilica solids were (342.8, 0.18)for C 22 , (595.6, 0.62)for C 12 , (233.2, 0.35) for C8, (541.2, 1.17) for (C4H9)4NOH, (504.4, 0.93) for (C 2 H 9 ) 4 NOH without detectable mesopore. This seems to indicate a possible mechanism, i.e. BTEB molecules were first hydrolyzed by aqueous base to form negatively-charged benzene-silica hybrid colloidal particles with a certain degree of polymerization, which then surrounded positively-charged rod-like micelles in the solution to array hexagonally into integrated mesoporous framework.

432 C-16 (60°C, (60°C, 90°C)

^f

5000

Intensity/cps

^T\

C-16 (30°C, 30°C) C-16 (0°C, 30°C)

4000 . 4000

C-16 (0°C, 0°C) C-12 (23°C, 23°C)

3000

°C) C-16 (30°C, 30 C-16(30°C, 30°C) C-16(0°C, C-16 (0°C, 00°C) °C) C-16(0°C, 30°C) C-16 (0°C, 30 °C) C-16 (60 (60°C, 90°C) C-16 °C, 90 °C) C-12 °C, 23 °C) C-12 (23 (23°C, 23°C)

2000 • 1000 1000 •

4000 3600 400 4000 3600 3200 3200 2800 2800 2400 2400 2000 2000 1600 1600 1200 1200 800 800 400 -1 WAVENUMBER/cm WAVENUMBER /cm-1

0 0 0

2

4

6

8

10

2θ /° 2θ/°

Figure 4. Effect of acidic medium on IR spectra and XRD patterns of samples.

In an acidic medium mesoporous benzene-silica hybrid materials could be formed in the presence of d e ^ C F t ^ N * and Ci2H25(CH3)3N+. After the removal of tern plate molecules by extraction, the sample templated by Ci6 exhibits three diffraction peaks at low angles of ca. 20 = 2.02, 2.24, 2.44°, similar to those of a 3D-cage SBA-1, obviously different from that induced by Cn with only a broad XRD peak at ca. 2.92° 20 (Fig. 4). IR spectra in Fig. 4 show the similarity of their infrared framework vibrations, and the difference from those in Fig. 1. The use of C]6 was beneficial to the formation of benzenesilica solid from an acidic medium, which was evidenced by TEM image in Fig. 3. This material possessed a 3D-cage like pore structure [4], with a pore size of ca. 28 A, a pore volume of 0.31 cm /g, and a surface area of 529.3 m /g. 4. Conclusion The formation of mesoporous benzene-silica solid from a basic medium was affected by the chain length of organic templates, in which only Ci 6 effectively templated a PMO solid with XRD peaks at low angles of 20 = 2.0, 3.6, 4.2°, similar to those of ordered MCM-41. Six samples displayed similar diffraction peaks at high angles of ca. 2#=11.5, 23.4, 35.4°, which seems to propose the similarity of formation processes of PMO and ordered MCM-41 in the basic solution. In an acidic medium mesoporous benzene-silica materials could be mediated by [CnH2n+i(CH3)3N+, n=12,16], in which only Ci6 templated a 3Dcage like mesopore structure similar to SBA-1. 5. References [1] [2] [3] [4]

S. Inagaki, S. Guan, T. Ohsuna and O. Terasaki, Nature, 416 (2002) 304. F. Fajula and F. Di Renzo, Microporous Mesoporous Mater., 82 (2005) 227. K. J. Shea, D. A. Loy and O. Webster, J. Am. Chem. Soc, 114 (1992) 6700. Y. Goto and S. Inagaki, Microporous Mesoporous Mater., 89 (2006) 103.


433 433

Synthesis of layered organosilica binding with selfassembled LB film Takayuki Chujo,a Yu Gonda," Yasunori Oumi,* Tsuneji Sano * and Hideaki Yoshitakea " Division of Materials Science and Chemical Engineering, Graduate School of Engineering, Yokohama National University, 79-5 Tokiwadai,Hodogaya-ku Yokohama 240-8501, Japan b Department of Applied Chemistry, Graduate School of Engineering, Hiroshima University, 1-3-2 Kagamiyama, Higashi-Hiroshima 739-8511, Japan.

We synthesized a layered organosilica whose interlayer is a micelle of alkanoic acid. The bond between carboxylate and 3-aminopropylsiloxane is critical for the formation of the layered structure. The micelles can be exchanged with carboxylic acids with a different chain length to form a lamellar structure with the corresponding basal spacing. 1. Introduction Mesostructured organosilicas have extensively been studied since the discovery of synthetic routes of ordered mesoporous silica with the aid of selfassembly of surfactant molecules [1, 2]. This has been a success due to the utilization rod-like micelles. On the other hand, one of the most widely studied self-assembled structures of amphiphilic molecules is Langmuir or LangmuirBlodgett film, which has been recognized as a versatile and stable layered structure. If a cationic organosilane can be polymerized with the ionic interaction with film-like carboxylate micelles, the resulting "solid" will have an extremely high density of anionic and cationic sites. Such mesostructured silicate will theoretically provide the densest functional groups, all of which could work without mutual interference. In this study, we report how to synthesize a layered organosilica binding with self-assembled LB film and how to control the layer distance by interlayer exchanges.

434

2. Experimental Section The surfactant used in this study were in the form of CnH2n+iCOONa: laurate (LAS, n=l 1), myristate (MAS, n=13), palmitate (PAS, n=15) and stearate (SAS, n=17). The surfactant was dissolved in ethanol-water at 333 K by continuously stirring. 3-aminopropyltriethoxysilane (APTES) was added dropwise into the solution. The molar ratio of the reactants were 1 surfactant: 1 APTES: 180H2O: 20 EtOH (40EtOH for SAS). This mixture was kept in stirring at room temperature (for LAS) or at 333 K (for the other surfactants) for lh before the addition of 0.1 M HC1 to adjust pH (= 10) of the solution where the initial pH = 11. The mixture was then heated at 373 K for 2 d. The product was dried in air at 373 K. This organosilica composite is hereafter denoted as SiOi 5-X (X: carboxylate), because the formula of these products was determined to be CnH2n+iCOOHNH2C3H6SiOi.5. With caprylate and decanoate (n=7 and n=9, respectively), no precipitate was formed. To exchange the surfactant interlayer, the reactant mixture without APTES was added to a SiOi 5-X and was stirred under reflux condition for a certain time. The solid was filtrated, dried at 373 K and the lattice constant was measured by XRD. 3. Results and Discussion Figure 1 shows the time evolutional XRD patterns of SiOi 5-PAS in the course of drying. The pattern with peaks at 2.4, 3.0, 3.5, 4,6, 6.8, 9.1 and 11.2'o for the solid after 6 h-drying suggests the formation of a phase mixture. Although the number of peaks decreased, new peaks emerged until 2 d. Finally, the pattern conversed into a lamellar structure with 29 = 2.5, 5.0 and 6.9°. This complicated change implies that several stable phases exist near the most stable one, which shows a typical lamellar pattern. The degree of condensation in the final product is nearly 100 %, revealed by 29Si-MAS NMR, and it is likely that the formation of siloxane network is closely related to these phase changes. This mode of growing was more or less observed in all SiOi 5-X. With the Bragg's formula, the basal spacings were calculated for the XRD pattern of each product. The result was plotted against (h2+/^+l2)'05 in Figure 1, where h=\, 2, 3, 4 and 5 and &=/=0. (For LAS and MAS, h=\,2 and 3 due to the absence of higher diffractions.) The af-value decreased linearly for all XRD patterns, showing the formation of a series of lamellar structures. In fact, when dm is determined in Figure 1 and plotted against n, all dm is well explained with the equationrfioo(/nm)=1.082 + 0.166«. This linearity demonstrates that the layer distance increases at the same ratio with the number of carbons in alkanoate. If all carbons in the alkyl chain are in the anti- conformation and the chain is normal to the layer plane, the increase ratio par carbon atom would be 0.25 that is clearly larger than the slope observed for a series of SiOi 5-X. This disagreement suggests that, unlike lamellar alkylsiloxanes [3-5], the alkyl chain is inclined to the plane of siloxane layer.

435 3.57 nm nm

4.5

(300) (500)

(100)(200)

4

(g) (g)

×5

3.5

(f)

×5

j O

(e)

×5

(d)

×5

(c) (c)

×5

(b)

×5

(a)

d / nm

Intensity/a.u

3

×5

2.5 2 1.5 1 0.5

3.74 nm 0

5

10 10

15 15 2θ/degree

20 20

25 25

30

0 0

0.2

0.4 0.4

0.6 0.6 2

0.8 0.8 2

11

1.2

2 -0.5

(h +k +l )

Figure 1 (Left) XRD of SiO, 5-PAS dried for (a)6 h (b) 12 h (c)l d (d)2 d (e)3 d (f)4 d and (g)10 d at 373 K. (Right) d-value vs (h2+l^+l2y0$ of SiO, 5-X. X= LAS(»), M A S ( B ) , PAS(^), SAS(A).

The elemental analysis of these SiOi 5-LAS revealed that the contents of carbon and nitrogen were 56.5 and 4.3 wt %, respectively. We propose the chemical formula of SiO,.5-LAS from this result (CnH 23 COOH) (NH2C3H6SiOi 5). The condensation of silane was confirmed by the absence of 2 T and lT peaks in 29Si-NMR spectrum of SiO,.5-LAS. The f3C-NMR of the same solid showed the peaks at 174.5, 30.7, 23.5 and 14.6 ppm. They can be assigned to carboxyl, 2 and 4-9 carbons, 3 and 11 carbons, and methyl carbon, respectively, where the carbons were numbered from carboxyl (1) to methyl (12) in LAS. An additional shoulder peak appeared around 32.0 ppm. The pattern for the alkyl carbons is similar to the spectra of alkane (main peak at 31 ppm) in a liquid phase. In a liquid phase, the configuration is considered to be in the antigauche equilibrium. In contrast, a position of resonance 6.5 ppm higher than the liquid alkane has been observed in high density crystalline polyethylenes. This NMR result implies that the alkyl chains in SiOi 5-LAS include the anti- and gauche- configurations. The lack of lateral "crystallization" in these SiOi5-X layered material suggests an easy accessibility of guest molecule into the interlayer surfactant assembly, which can facilitate intercalation, ion exchange, substitution of surfactant, etc. We show here an example of such reactions. The interlayer alkanoate micelles can be substituted by another carboxylate with a different chain length as shown in Figure 2. When SiOi 5-LAS was treated with ethanol-water solution of PAS, the peaks observed in XRD were

436

gradually shifted and the positions finally became almost identical to those measured for SiOi 5-PAS (see Fig. l(g)). The d2oo and J3Oo peaks were clearly observed, though their relative intensities were not the same as those in the fresh SiOi 5-PAS, suggesting the degradation of the periodic structure. The result implies the possibility of controlling the layer distance by an ionic exchange reaction of interlayer micelle. This exchange has not been carried out successfully in the previous studies on lamellar organosilicates [3-5], simply because the alkyl chain was covalently bound to silicone atom in their materials.

3.59 nm

(c) 3.62

in

I

(b) 2.94 nm

-5

0

5

10

15

20

25

30

26/degree

Figure 2 Exchange of surfactant molecules in SiO, 5-LAS by PAS. (a) SiO, 5-LAS, (b) after the reaction for 3 d and (c) after the reaction for 1 w.

4. References [1] C. T. Kresge, M. E. Leonovicz, W. J. Roth, J. C. Vartuli and J. S. Beck, Nature 710 (1992) 359. [2] T. Yanagisawa, T. Shimizu, K. Kuroda, and C. Kato, Bull. Chem. Soc. Jpn., 63 (1990) 988. [3] N. Parikh, M. A. Schivley, E. Koo, K. Seshadri, D. Aurentz, K. Mueller and D. L. Allara, J. Am. Chem. Soc. 119 (1997) 3135. [4] R. Maoz, S. Matlis, E. DiMasi, B. M. Ocko and J. Sagiv, Nature 384 (1996) 150. [5] Shimojima, Y. Sugaharaand K. Kuroda, Bull. Chem. Soc. Jpn. 70 (1997) 2847.


437 437

Synthesis of highly ordered mesoporous benzenesilicas using PEO-PLGA-PEO triblock copolymers Eun-Bum Choa*, Hyojung Kimb and Dukjoon Kima " Polymer Technology Institute, Sungkyunkwan University, 300 Chunchun-dong, Jangan-gu, Suwon, Gyeonggi-do 440-746, Korea. b Central R&D Center, Samsung Electro-Mechanics, 314 Maetan-dong, Youngtong-gu, Suwon, Gyeonggi-do 443-803, Korea.

1. Introduction The synthesis of mesoporous materials using organic templates has been investigated using high molecular weight block copolymers as well as low molecular weight surfactants to expand pore size, increasing of stability, modifying of inorganic network, and constructing of extraordinary mesophases and so on [1]. In preparing periodic mesoporous organosilica (PMO) materials using high molecular weight block copolymer, interactive interfaces originated from each block of the block copolymer and the organo-bridged inorganic specie have to be considered in hybridizing them in solution. The independent control of hydrophobicity in one specific block, which leaves other interactive forces intact, has an important meaning in academic concern as well as in property of end products [2]. Herein, we have used poly(ethylene oxide)-poly(DL-lactic acid-coglycolic acid)-poly(ethylene oxide) (PEO-PLGA-PEO) block copolymers with a different hydrophobic interactive force from that of typical PEO-PPO-PEO triblock copolymers in aqueous solution and report more facile synthesis and characterization of highly ordered mesoporous benzene-silica powder and film including the structural property of framework wall. PLGA chain is about quadruple as hydrophobic as PPO chain [3] and the adequate solubility of PEOPLGA-PEO block copolymer in aqueous solution makes it feasible to build the homogeneous co-assembly, which is believed to be a main factor to obtain highly ordered mesoporous functionalized materials with high surface area in water based sol-gel process.

438 438

2. Experimental Section We have synthesized the PEO-PLGA-PEO triblock copolymer in laboratory through ring opening metathesis polymerization. Number averaged molecular weight of EO16(L29G7)EOi6 (LGE538) was obtained to be 5,310 and polydispersity index 1.28 by using a GPC-RI (Waters HPLC) system. The volume fraction of PEO block (O P E O) was calculated to be 0.38 from the group contribution method. l,4-bis(triethoxysilyl)benzene (BTEB) (Aldrich) used as the benzene-silica precursor. The molar composition of the final mixture was LGE538:BTEB:HCl:ethanol:H2O = 1.0:19.0-21.9:23.7-30.1:0-115.4:12,8192,850. Precipitates were obtained after the mixture was stirred for about 1 h at 313 K and the white solids were aged for 24 h at 368 K. Mesoporous benzenesilica films with 0.5-2 mm thickness were obtained through slow solvent evaporation method at the aging step of 368 K. Extraction of the block copolymer template was carried out by successive treatment with distilled water, ethanol, and acetone using a suction flask and then dried at 353 K. In the case of film, residual block copolymer was removed by stirring mesoporous benzenesilica film (0.5 g) in HCl/ethanol (4 g of 37 wt%/120 ml) solution for 10 h. 3. Results and Discussion We have synthesized LGE538 PEO-PLGA-PEO triblock copolymer with an adequate molecular weight soluble in water and reasonable volume ratio of the PEO block to get the hexagonal mesophase. Synchrotron SAXS (A. = 1.246 A) and WAXD results of mesoporous benzene-silica powder and film are shown in Figure 1. We found that block copolymer-free benzene-silica powder has highly ordered 2D-hexagonal (p6mm) mesophase with four well- ( a ) ' resolved peaks indexed as (100), (110), (200), and (210) reflections as shown in Figure l(a). The intense (100) peak represents the large lattice spacing of hkl d(A) d = 8.78 nm corresponding to 110 50.63 the 2D-hexagonal unit cell 200 43.79 210 33.16 parameter a = 10.13 nm. Wideangle diffraction pattern of the inset in Figure l(a) displays two Fig. 1 Synchrotron SAXS and WAXD patterns of reflection peaks at d = 7.7 and 3.8 A indicating molecular scale mesoporous benzene-silicas prepared in this study. Trace (a) is SAXS pattern of the block copolymerperiodicity of bridged-benzene free powder and (b) is of the film with 0.5 mm moiety inside benzene-silica thick-ness. Diffraction patterns in the high-angle framework wall. However, the region (0.88 < qz < 5.78; 10 < 29 < 70) are shown degree of periodicity is not in the insets, respectively.

439

significant and framework wall of benzene-silica is just crystal-like pattern. Benzene-silica films are obtained by slow evaporation induced self-assembly (EISA) at the final condensation step, and their thickness are obtained as 0.5-2 mm, and SAXS patterns represent the p6mm hexagonal mesostructure as shown in Figure l(b). Wide-angle diffraction pattern also displays two weak reflection peaks at d = 7.7 and 3.8 A (the inset of Figure l(b)) indicating molecular scale periodicity. Figure 2 demonstrates TEM images and corresponding Fourier transform images of mesoporous benzene-silicas synthesized with a LGE538 template. Figure 2(a) and (b) images, which are parallel and perpendicular to the channel, also represent uniform 2D hexagonal patterned mesopores. Fig. 2 TEM images and corresponding Fourier Nitrogen sorption isotherms transform images of mesoporous benzene-silicas synthesized with a EO16(L29G7)EOi6 template. of polymer-free mesoporous benzene-silica powder and film show the typical type-IV adsorption isotherms with a steep increase at P/Po = 0.65-0.70 due to capillary condensation of nitrogen in the mesopores. The BET surface area, pore volume, and micropore volume of a benzene-silica powder are determined to be 1,415 m2/g, 1.417 cm3/g, and 0.194 cm3/g, respectively, as shown in Table 1. Uniform pore size distribution with a maximum pore diameter of 6.5 nm is obtained from the BJH method and wall thickness is as 3.6 nm. In the case of the benzene-silica film, BET surface area, pore volume, and micropore volume are obtained to be 1,543 m2/g, 1.824 cm3/g, and 0.082 cm3/g, respectively. Pore size with a maximum pore diameter of 6.4 nm is obtained and wall thickness is as 3.7 nm. High porosity is a characteristic of mesoporous benzene-silica synthesized in this study.

440 Table 1. Physicochemical properties of mesoporous benzene-silica prepared in this study Sample

(m2/g)

V (cm3/g)

(nm)

W (nm)

BSP42

1,415

1.417

6.5

BSF26

1,543

1.824

6.4

SBET

Dp

V v

^micro

(cmVg)

Vv • micro

(cmVg)

(%)

3.6

1.223

0.194

13.7

3.7

1.742

0.082

4.5

meso

BSP42: mesoporous benzene-silica powder, BSF26: mesoporous benzene-silica film, SBET: BET surface area, V: pore volume, Dp: pore diameter, W: wall thickness (= 2afioc/V3 - Dp), Vmeso: mesopore volume, Vmicro: micropore volume, Omicro: fraction of micropore volume to total pore volume.

The 13C CP-MAS NMR spectrum represents a resonance peak at 133 ppm assigned to carbons on the benzene ring and 29Si CP-MAS NMR spectrum shows the characteristic signals assigned to GS7(OSi)3 (T3, 8 -78), CSi(OSi)2(OH) (T2, 8 -69), and GS7(OSi)(OH)2 (T1, 8 -61) confirming the homogeneous distribution of benzene moieties inside the benzene-silica framework. The absence of Q peaks between -90 and -120 ppm confirms that carbon-silicon bond cleavage of BTEB precursors is not occurred through sol-gel synthesis. The T3/T2 peak intensity ratio is lower than that of mesoporous benzene-silica prepared with a surfactant under basic condition [4]. The low T3/T2 peak intensity ratio and low molecular-scale periodicity suggests the interactive forces of BTEB precursors and between PEO chain and BTEB precursors works weakly under acidic condition. However, the framework wall of benzene-silica prepared in this study represents extremely high thermal stability up to 863 K in N2 atmosphere by thermogravimetric analysis. 4. Conclusion We have synthesized highly ordered 2D hexagonal (p6mm) mesoporous benzene-silica hybrid materials using new EOi6(L29G7)EOi6 triblock copolymer templates in wide experimental conditions. Mesoporous benzene-silica materials prepared with PEO-PLGA-PEO triblock copolymer templates display spherical external morphology and molecular scale periodicity different from the benzene-silica prepared with PI23 (PEO-PPO-PEO) template, which is believed to be originated from the end-capping property of a PEOPLGA-PEO template. Moreover, mesoporous benzene-silica can be formed easily as the film pattern of 0.5-2 mm thickness by tuning of solvent evaporation rates at the final condensation step of silanol group and has high thermal stability up to 863 K in N2 atmosphere. From these results, PEOPLGA-PEO triblock copolymers are successfully proved to be the useful structure-directing agent to prepare periodic mesoporous benzene-silica.

441

5. Acknowledgement This work was supported by the Korea Research Foundation Grant (KRF 2004-005-D00064). Small angle X-ray scattering experiment performed at 5C2 beam line of the Pohang Light Source was supported in part by GIST. We special thank Dr. Y. Lim at LG Chem Research Park for TEM evaluation and thank Mr. Y. Kim for assistance in synthesis. 6. References [1] [2] [3] [4]

Y. Goto and S. Inagaki, Chem. Commun., (2002) 2410. E.-B. Cho and K. Char, Chem. Mater., 16 (2004) 270. C. Booth and D. Attwood, Macromol. Rapid. Commun., 21 (2000) 501. S. Inagaki, S. Guan, T. Ohsuna, and O. Terasaki, Nature, 416 (2002) 304.



443 443

Tailoring cage-like organosilicas with multifunctional bridging and surface groups Rafal M. Grudzien, Bogna E. Grabicka, Donald J. Knoblocha and Mietek Jaroniec* Department of Chemistry, Kent State University, Kent, Ohio 44242, USA

Monofunctional and bifunctional cubic silicas with cage-like structure (FDU1) containing surface and bridging groups were prepared by one-pot synthesis route using various organosilanes such as tetraethyl orthosilicate (TEOS) along with ureidopropyltrimethoxysilane (UP), 3-mercaptopropylsilane (MP) and bis(triethoxysilylpropyl)disulfide (DS). The aforementioned mesostructures were characterized by X-ray diffraction, N2 adsorption and elemental analysis. 1. Introduction Ordered mesoporous organosilicas (OMOs) of FDU-1-type structure [1] feature spherical cages of uniform dimensions connected with twelve identical cages via small apertures creating a three-dimensional arrangement of pores. Cage-like OMOs are very attractive because of great opportunities in tailoring their surface and structural properties as well as their potential applications in many fields such as selective adsorption of toxic compounds from air and water, catalysis, host-guest chemistry, and separations. The aim of the current work is to synthesize cage-like OMOs with multifunctional surface and bridging groups and to monitor the changes in their adsorption, surface and structural properties upon introduction of various concentrations of functional groups. The present study is focused on the FDU-1 materials [1], which are face-centered (Fm3m) cubic mesostructures [2].

Corresponding author: Email. iaroniec(a),kent.edu Tel. 1-330-672 3790, Fax. 1-330-672 3816 " This work was partially supported by NSF Grants CHE-0093707 and CTS-0553014. " NSF-REU 2005 (CHE-0353737) undergraduate student from Saint Vincent College, Latrobe, PA 15650, USA.

444

2. Experimental Section Synthesis of functionalized FDU-1 mesoporous silicas [1] was carried out by co-condensation of TEOS and proper organosilanes (see Scheme 1) in the presence of poly(ethylene oxide)-poly(butylene oxide)-poly(ethylene oxide) triblock copolymer B50-6600 [(EO)39(BO)47(EO)39]. The synthesis recipe was analogous to that reported elsewhere [3]. In a typical synthesis, TEOS was added slowly to the polymer solution at 25°C under vigorous stirring followed by addition of organic silane (see Table 1). After being further stirred for 6 h at room temperature, the slurry was sealed in a polypropylene bottle and kept at 100°C for 6 h. The samples were collected by filtration, washed with deionized water and dried at 70°C. Extracted with 1) ethanol and HC1 solution the resulting Si SH samples are denoted as UPx, UP-MPx and DSx, where UP, UP-MP and DS denote A 2) O ureidopropylsilyl ligand, bifunctional Si NH2 NH ureidopropylsilyl-mercapto-propylsilyl surface ligands and bis(silylpropyl)3) S Si disulfide bridging group, respectively, Si S whereas x refers to the concentration of ligands (see Table 1). Scheme 1. Mesopore cage (A) together with Nitrogen adsorption isotherms were chem i ca i structures of ligands: 3measured at -196°C using 2010 and 2020 mercaptopropylsilyl (1), ureidopropylsilyl volumetric analyzers, Micromeritics, Inc. (2) and bis(silylpropyl) disulfide (3) Powder X-diffraction (XRD) data were incorporated to FDU-1. recorded using a PANanalytical, Inc. X'Pert Pro (MPD) Multi Purpose Diffractometer with Cu Ka radiation. Elemental analysis was conducted using a LECO Model CHNS-932 instrument from St. Joseph, MI. 3. Results and Discussion Quantitative characterization of incorporated organic groups into cage-like mesoporous silicas was performed by CHNS elemental analysis of nitrogen and sulfur (Table 1). As can be seen from this table the percentages of nitrogen and sulfur increase progressively with increasing concentration of functional organosilanes. These data confirm the presence of surface and bridging groups in the resulting materials. The structural ordering of extracted materials was examined by powder X-ray diffraction, which provided the XRD profiles characteristic for a cubic structure of Fm3m symmetry. The calculated unit cell parameters (see Table 1) tended to insignificantly decrease with increasing concentration of surface groups for UP FDU-1 and more meaningfully decrease for UP-MP and DS FDU-1 silicas.

445

Amount Adsorbed (cm3 STP g-1)

Shown in Figures 1A, IB and 1C are nitrogen adsorption isotherms measured at -196°C for template-free cage-like FDU-1 silicas with the following ligands: ureidopropylsilyl, bifunctional ureidopropylsilyl-mercaptopropylsilyl and bis(silylpropyl)disulfide, respectively. The corresponding pore size distributions (PSDs) for these OMOs are presented in Figures ID, IE and IF. The adsorption parameters such as the BET surface area, pore volumes and pore diameters are given in Table 1. These isotherms are of type IV with apparent hysteresis loops A

to

00

600

400

700

500 B

o UP 1 UP • UP 2 2. CH3-O-CH3

CHj-OH + C6H5-OH

acid

O-alkylation

H2O

catalyst C-alkylation

CH 3 -C 6 H 4 -OH

Scheme 1 Etherification reactions of phenol and methanol over acid catalyst

Figure 4 shows an illustration of in situ FT-IR 3D spectra recorded for 24 h. The evolution of the peaks in IR spectra during the reaction is clearly visible by decreasing the intensity of the methanol peaks and appearing of new peaks. The trend of methanol and phenol conversion to dimethylether, anisole and cresol is shown in the figure 5. A negligible amount of polyaromatics was also observed. It is evident that the major product is dimethylether and little anisole and cresol were formed. In etherification reaction of phenol on acid catalyst, at least three

Fig. 4:3D in situ FTIR spectra of the etherification reactions of methanol and phenol on ASMES material at 180°C

454 20

3,5

0,25

(b

16

(a)

14

2,5

12

2

10 1,5

8 6

1

4

C o n c e n t r a t i o n ( m o l/ L )

3

C o n c e n t r a t io n ( m o l/L )

C o n c e n t r a t io n ( m o l/L )

18

0,2

0,15

0,1

0,05

0,5

2 0

0

0

2

4

6

8

10

12

14

Reaction Time (hr) F»-Methanol Methanol

Dimethylether

Phenol

Anisole & Cresol

0 0

2

4

6

8

10

12

14

Reaction Time (hr) experimental

Fig. 5 Evolution of concentrations of (a) methanol & phenol (b) anisole & cresol at 180°C on ASMES

parallel reactions are competing. These reactions as shown in scheme 1 are alcohol condensation, O-alkylation and C-alkylation [5,6]. The very preliminary results reported in Figure 5 indicate that the arene sulfonic mesostructured ethane silica synthesized in this work can be used as an etherification catalyst. Obviously the etherification of methanol to dimethylether is much faster than both O- and C-alkylation of phenol in the conditions of the limited experimental tests reported here. Actually we reported recently the high activity of ASMES materials in the formation of dibutylether from 1-butanol [7]. The present results indicate that the etherification of methanol over these catalysts is at least two times faster than the one of butanol. 4. Conclusion Arene sulfonic mesostructured ethane silica with exchange capacity of 0.80 mmol H+/g SiO2 was prepared and its thermal stability was studied. Some limited data indicated that this catalyst having acid sites in hydrophobic surface environment is potentially useful as catalyst for etherification of alcohols and phenolic compounds. 5. References [1] F. Hoffman, M. Cornelius, J. Morell and M. Froba, Angew. Chem. Int. Ed., 45 (2006) 3216. [2] S. Inagaki, S. Guan, T. Ohsuna and O. Terasaki, Nature, 416 (2002) 304. [3] S. Mikhailenko, D. Desplantier-Giscard, C. Danumah and S. Kaliaguine, Micropor. Mespor. Mater., 52 (2002) 29. [4] S. Hamoudi and S. Kaliaguine, Micropor. Mespor. Mater., 59 (2003) 195. [5] K. G. Bhattacharyya, A. K. Talukdar, P. Das and S. Sivasanker, J. Mol.Catal., 195 (2002) 255. [6] M. C. Samolada, E. Grigoriadou, Z. Kiparissides and I. A.Vasalos, J.Catal., 152 (1994) 52 [7] B. Sow, S. Hamoudi, M. H. Zahedi-Niaki and S. Kaliaguine, Micropor. Mespor. Mater., 79 (2005) 129.

455 455


Highly efficient microwave-assisted asymmetric transfer hydrogenation with SBA-15-supported TsCHDA chiral ligands Myung-Jong Jin*, M. S. Sarkar and Ji-Young Jung School of Chemical Science and Engineering, Inha University, Incheon, 402-751, Korea

A fast and efficient procedure has been developed for microwave-assisted asymmetric transfer hydrogenation of ketones. The reactions were brought to full conversion in short time using SBA-15-supported TsCHDA chiral ligands. 1. Introduction Asymmetric transfer hydrogenation of ketones is an attractive method for the synthesis of optically active secondary alcohols [1]. The heterogeneous transfer reactions facilitated by supported catalysts have received much attention in recent years. Heterogeneous catalysis typically requires long reaction time to reach completion. It is well known that microwave-assisted reactions can occur much faster than reactions using conventional heating [2]. Efficient supported chiral ligands have been developed for the heterogeneous catalysis [3]. This strategy offers practical advantages such as simplified separation and potential reuse of the expensive chiral ligands. SBA-15-supported Ru-TsDPEN 3b has been previously used for asymmetric transfer hydrogenation of ketones [4].

i)

O (MeO) ( M e O3)Si3 S i ^

\ NH2

H2 N 1

/=\ i

II 4 ' , NH SS HN HN N H 22 0 O 22

ii)

O

*-

O

S i - OO- SSii - v Si S Oi O S

/—v II i S HN S H N O O

SBA-15

SBA-15-TsCHDA SBA-15-TsCHDA 33

i) 2-(4-chlorosulfonylphenyl)ethyltriraethoxysilane, Et3N, CH2C12, -10 "C, 2 h ii) toluene, reflux, 18 h

Scheme 1

.

NH

N H 22

456 Recently, we developed new mesoporous silica SBA-15-supported TsCHDA chiral ligand 3. Our interest in the catalysis using microwave irradiation led to investigate microwave (MW) assisted asymmetric transfer hydrogenation in the presence of the SBA-15-supported chiral ligands. In this paper, we describe the results of the microwave-assisted asymmetric transfer hydrogenation using the immobilized TsCHDA chiral ligand 3. 2. Experimental Section 2.1.

Preparation of SBA-15-supported TsCHDA 3

A solution of 2-(4-chlorosulfonylphenyl)ethyltrimethoxysilane (0.198 g, 0.61 mmol) in CH2C12 (5 mL) was slowly added to a stirred solution of (\R,2R)diaminocyclohexane (0.070 g, 0.61 mmol) and triethylamine (0.067 g, 0.67 mmol) in CH2C12 (10 ml) at -10 °C. The reaction mixture was allowed to warm to RT. After stirring for 2 h, the mixture was diluted with CH2C12, and washed with cold water. The organic layer was dried with MgSC>4, and concentrated under reduced pressure. The crude product was purified by flash chromatography to give (liJ^^-A^trimethoxysilylpropyl-Af-sulfonyO-l^-cyclohaxanediamine 2 in 80% yield. SBA-15 silica (0.7 g) was added to a solution of compound 2 (46 mg, 0.11 mmol) in hot toluene (15 ml) and the mixture was refluxed for 18 h. After filtering the reaction mixture, the solid was washed several times with methylene chloride and dried under vacuum at 70 °C to give SBA-15-supported TsCHDA 3. Weight gain showed that 0.15 mmol of TsCHDA was grafted in 1.0 g of the SBA15 silica 3. 2.2.

Asymmetric transfer hydrogenation under microwave-irradiation

SBA-15-supported TsCHDA 3 (0.090 g, 0.013 mmol) was suspended in water (1.5 ml) and heated with [Ru(p-cymene)Cl2]2 (3 mg, 0.005 mmol) for 3 min under MW (60 W). Ketone (0.45 mmol) and HCO2Na (0.153 g, 2.2 mmol) were added to the solution and heated under MW (40-60 W) for short time. The mixture was cooled to RT, and diluted with diethyl ether. After general work-up, crude product was purified by short-column chromatography. Conversion was measured by GC analysis. Chiral HPLC analysis using Daicel OD-H column was used for the determination of enantiomeric excess of the diol. 3. Results and Discussion The immobilization of the TsCHDA chiral ligands onto SBA-15 silica was

2S

Fig I. XRD pattern profiles

457

performed in two steps. Reaction of (li?,2/?)-diaminocyclohexane with 2-(4chlorosulfonylphenyl)ethyltrimethoxysilane afforded trimethoxysilylpropylated 2amino(sulfoamido)cyclohexane 2 in high yield. Subsequent treatment with SBA-15 silica in refluxing toluene gave SBA-15-supported TsCHDA 3 (0.15 mmol/g). Hexagonal mesoporous structure of the SBA-15 could be sustained after the modification steps. The XRD obtained from the supported SBA-15 material is shown in Fig 1. Apparently, no changeoccurred in the lattice upon the immobilizing process and pore arrays are conserved. Table 1. Asymmetric transfer hydrogenation under microwave irradiation3 O

OH Supported ligand 3

^Y^R HCO2Na - H2O, MW

I*

Ketoneb

Ligand

Power (W)

Time (min)

Conv. (%)c

E.e. (%)d

Acp

3b

60

40

60

51

Acpe

3a

0 W, 90 °C

600

72

73

Acp

3a

60

30

100

80

Acp

3a

50

30

99

79

Acp

3a

40

40

96

80

Pp

3a

60

40

90

61

a-tetralone

3a

60

40

90

92

3-Cl-Acp

3a

40

20

100

85

3-Cl-Acp

3a

40

30

95

83

3-CI-ACD

3b

40

40

57

55

"Molar ratio; ketone : Ru : ligand 3 (loading ratio = 0.15 mmol/g) = (100 : 1 : 3), HCO2Na (5 equiv.) and H2O 1 ml. bAcp = acetophenone, Pp = propiophenone. 'Determined by GC analysis. d

Determined by HPLC analysis using Chiralcel OD-H column (3% 2-propanol in hexane, 1 ml/min). 'Conventional themal condition.

With the supported TsCHDA 3, we performed microwave-assisted asymmetric transfer hydrogenation of ketones in aqueous HCO2Na. The SBA-supported chiral Ru(II) complexes were prepared in situ by MW-heating a mixture of [Ru(pcymene)Cl2]2 and the supported TsCHDA 3 in H2O for 3 min. As indicated in

458

Table 1, the MW-assisted reactions could reach completion with 20~40 min. Satisfactory enantioselectivities were obtained with excellent conversions. When the identical reaction was performed under thermal condition, the reaction required considerably longer reaction time of 600 min. 4. Conclusion It is noteworthy that our SBA-15-supported TsCHDA 3 a gave better enantioselectivity and higher reactivity than SBA-15-supported TsDPEN 3b. In conclusion, it has been shown that MW-assisted reaction can be an useful methodology for the heterogeneous transfer hydrogenation of ketones. 5. References [1] [2] [3] [4]

R.Noyori and S. Hashiguchi, Ace. Chem. Res. 30 (1997) 97. C. O. Kappe, Angew. Chem. Int. Ed. 43 (2004) 6250. C. E. Song and S.-g. Lee, Chem. Rev. 102 (2002) 3495. P. N. Liu, J. G. Deng, Y. Q. Tu and S. H. Wang, Chem. Commun. (2004) 2070.


459 459

Preparation of bimodal MCM-41 encapsulated Co(III)-porphyrin complex and its catalytic properties in cyclohexane oxidation Shijie Luo and Jihong Sun* Department of Chemistry and Chemical Engineering, College of Environmental & Energy Engineering, Beijing University of Technology, Beijing, 100022, P. R. China

1. Introduction Following the discovery of the M41S family of silicas [ 1], considerable research effort has recently been focused on the preparation of hybrid mesoporous materials with controllable hierarchical structure, and its potential application [2]. The heterogenization of metal complexes is an area of growing interest, particularly on zeolite and mesoporous silicate with its large pore, high surface area, and a large number of surface silanol groups. Recently, several metals have been immobilized on ZSM-5 [3] and M41S [4]. Moreira et al. [5] have grafted Iron porphyrins on the surface of MCM-41 through aminosilane linker by adduct formation, and such kind of the catalysts were found to be active for hydrocarbon oxidation. Here, we report that a new hybrid material by using bimodal mesoporous materials (BMMs) as support, whereas, Cobaltporphyrins have been immobilized on the pore surface of BMMs via grafted techniques. We hope this new hybrid material could give more promising catalytic activity for cyclohexane oxidation. 2. Experimental Section BMMs were hydrothermally synthesized according to the literature [6]. The preparation procedure of new hybird material is as followed: BMMs (0.5 g) was mixed with a chloroform solution contained 3-aminopropyltriethoxysilane (APTES) (50 ml, 0.1M) [7], and stirred at room temperature for 12 h, after filtered, washed with chloroform, and dired at room temperature in vacuum overnight. The product was named BMMs (m). Stirring a mixture of BMMs(m)(0.5 g) and Co-porphyrin in dichloromethane (10 ml, 0.2 mM) at

460

room temperature for lh gave the encapsulated product (Co-BMMs). The oxidation of Cyclohexane with oxygen by Co-BMMs were carried out in the reactor. X-ray diffraction (XRD) of the samples was recorded using a BruckerAXS D8 diffractometer using Cu Kal radiation. Scanning electron microscopy (SEM) images were obtained with a JEOL JSM-6500 microscope. Transmission electron microscope (TEM) images were recorded on a JEOL JME-2010. Nitrogen adsorption-desorption isotherms were measured using a Micromeritics ASAP 2010 system. Pore size distributions were obtained from the N2 desorption branch isotherm using BJH method. The content of phenanthrene in filtrate (solution) was analyzed using GC-17A with a capillary column. 3. Results and Discussion 1400

0

Figure 1 XRD patterns of BMMs (a) and CoBMMs (b)

0.2 0.4 0.6 0.8 1 Relative Pressure (p/p )

Figure 2 N2 adsorption-desorption isotherms of (b) and corresponding t 0 t n e p O r e s j z e distribution (inset)

B M M s ( a ) a n d Co -BMMs

The XRD pattern of the calcined BMMs (in Figure l a ) shows two reflections in the 2 theta range 2 - 10 °, indexed for a hexagonal cell as (100) and (110) respectively. However, the peak (110) is not obvious, the most reason is that the peak (100) was very broad with high intensity in the XRD pattern. The d value of the (100) reflection was 35.4 A leading to a lattice constant of a = 40.9 A. Upon functionalization of BMMs and subsequent inclusion of the Cobalt porphyrin complex (Co-BMMs), the two characteristic diffraction peaks in XRD pattern, as can be seen in Figure lb, were still observed at about the same positions as that of BMMs, demonstrating that the long range hexagonal

461

symmetry of the mesoporous host was preserved after modification by APTES and immbization by Cobalt-porphyrin complex. The isotherms of both BMMs and Co-BMMs on the basis of N2 adsorptiondesorption data exhibit two inflections: a first increase occurs at relative pressures 0.4n-I-a/NCM41 Cata 01

(R=n-ft)

RaoECH

Cl TBMEsolvent

„ ^

cycle > 73%ee 2CyClC>

3 cycle > 73°/oee

4. Conclusion

In summary, we have synthesized heterogeneous chiral dinuclear complexes and demonstrated their catalytic activity in ARO of terminal epoxides with carboxylic acid as a nucleophile. The resolved ring opened product combined with ring closing in the presence of base and catalyst afforded optically pure terminal epoxides such as (R)-GB in morderate ee% and quantitaive yield by using immobilized chiral salen catalyst on H-MCM-41 and chiral ECH as a reactant. The heterogeneous catalyst can be easily synthesized and the catalytic activity was retained for several times reuse without any regeneration step. Further studies concerning the application in the chiral catalysis are currently under investigation for a broad applicability as a general catalyst. 5. References [1] M. Tokunaga, J.F. Larrow, F. Kakiuchi and E.N. Jacobsen, Science, 277 (1997) 936; M. E. Furrow, S. E. Schaus and E. N. Jacobsen, J. Org. Chem. 63 (1998) 6776. [2] M. Moghadam, S. Tangestaninejad, V. Mirkhani and R. Shaibani, Tetrahedron, 60 (2004) 6105. [3] E. N. Jacobsen, F. Kakiuchi, R. G. Konsler, J. F. Larrow and M. Tokunaga, Tetrahedron Lett., 38(1997)773. [4] S. S. Thakur, W. Li, S. J. Kim and G.-J. Kim, Tetrahedron Lett., 46 (2005) 2263. [5] R. Ryoo, C.H. Ko and R.F. Howe, Chem. Mater., 19 (1997) 1607. [6] W. Li, S. S.Thakur, S.-W. Chen, C.-K.Shin, R. B.Kawthekar and G.-J. Kim, Tetrahedron Lett., 47 (2006) 3453.


467 467

Chiral (salen) cobalt complexes encapsulated in mesoporous mordenite as an enantioselective catalyst for phenolic ring opening of terminal epoxides Kwang-Yeon Lee, Young-Hee Lee, Chang-Kyo Shin and Geon-Joong Kim* Department of Chemical engineering, Inha University Incheon 402-751, Korea

Phenolic ring opening of epoxides was performed successfully by using chiral (salen) Co(III) caralysts encapsuled in mesoporous mordenite. 1. Introduction The chiral (salen) Co (III) catalysts is the great interest for the synthesis of chiral intermediates [1]. Many types of heterogeneous catalysts have been developed by grafting on the inorganic material [2] or copolymerization on the polymer [3] and by encapsulation in the pores [4] or attachment on the membrane [5] due to simple separation. Microporous crystalline zeolites have unique properties, but their pore sizes are not efficient at processing large molecules. The mesoporous cage structures can be the attractive hosts for the design of hybrid systems. Herein we report the synthesis of chiral (salen) Co (III) complex in the pores of mosoporous mordenite by ship-in-bottle method and enhanced catalytic activity in the phenolic ring opening of terminal epoxides. 2. Experimental Section 2.1. Mesoporosity formation in mordenite by desilication-dealumination Mordenite (JRC-Z-M-15(1), TOSOH Corporation) was treated in 0.3-0.9 N NaOH solution at 338K for 5 hr to form mesoporisity by desilication [6]. After treatement of alkaline solution, dealumination was carried out [7] by refluxing

468

the sample in 3-N HCl solution for 3h. This support was ion-exchanged in hot CoCl2-6H2O aqueous solution for 5 h. The obtained sample was characterized by XRD, SEM and BET analyses. The formation of mesoporosity was confirmed by N2-adsorption by BET method. 2.2. Preparation of the chiral (salen) Co (III) complex encapsulated in mesoporous mordenite ooooooo I ooooooo ooooooo ooooooo 1 .Alkarine ooooooo ooooooo 2-Acld I ooooooo ooooooo ooooooo

i

AOBOOOO

1 .CO(II)O*

c

4H 2 O

THF

A

1. coated by water 2. end-capped by Ti[OCH(CH3)2l4

Scheme 1

Scheme 1 shows the sequence to incorporate the chiral (salen) Co (III) catalysts into the mesopores of mordenite by ship-in-bottle method. First, (lR,2R)-l,2-cyclohexandiamine solution in MC was introduced into the drying mordenite and the sample was dried by evaporation under vacuum. Additionally 3,5-di-tert-butyl-2-hydroxybenzaldehyde was added by the same procedure. This treatment step was adopted repeatedly for 3 times. The mixture of additional components for salen construction, pre-treated mordenite and MeOH soution were stirred together for 12h. The powder was collected after washing with different solvents and incorporation of Co(II) ion and the treatment of MX3 and 4-nitrobenzenesulfonic acid(NBSA) was done to obtain the corresponding Co(III)-NBSA type catalyst. After removal of solvent, the surfaces of mordenite were coated with water and then Ti[OCH(CH3)2]4 in MC/THF was treated to reduce the opened large aperture by hydrolysis. The repeated treatment for three times was performed for encapsulation of salen molecules. 3. Results and Discussion Fig. 1 shows the SEM images of starting mordenite sample and desilicated and dealuminated one. Mordenite was so stable to maintain the crystal structure

469

under the severe condition of 0.9-N NaOH and 3-N HCl treatment as shown in Fig. 1. The strong XRD peak was found after alkaline and acid solution. However, mesopore formation could be confirmed by BET analysis. The mesopores of 15-20 nm was formed inside of mordenite crystals. This mesopore channel was used to Hfti.SEMilI1H8esof

Fig 2. XRD patterns of mordenites (A) and pore distribution of mordenites (B). Adsorptiondesorption isotherms for original mordenite(C), desilicated powder by 0.3N NaOH (D) and 0.9N NaOH (E) solution, treated by 0.9N NaOH solution and 3N HCl solution (F). Table 1. The Phenolic Kinetic Resolution using Heterogeneous Co(III) Catalysts. OH

Cat. Cl

t-BME

Salen

Conversion

Enantiomeric

(MX,)

(%)

Excess(%)

H

AlCb

44

88

H

InCI3

46

3-CHj

AlCb

40

Ri

Salen

Conversion

Enantiomeric

(MX3)

(%)

Excess(%)

3-CH3

InCl3

38

68

91

3-CI

AlCb

43

86

75

3-C1

GaCl3

45

86

Ri

470 Table 2. Recycle Ability of Co(III)-NBSA type Salen Catalyst Encapsulated in Mesoporous Mordenite.

The enantioselective catalytic activity of encapsulated chiral (salen) catalyst was examined for the phenolic ring opening Salen Conversion Enantiomeric Recycle reaction of epichlorohydrin Excess(%) (MXs) (ECH). The obtained result is 42 91 H summarized in Table 1. The salen catalysts showed 87 Cycle 2 38 remarkable enhanced reactivity Cycle 3 90 43 with substantially low loadings. The reaction using encapsulated 74 Cycle 1 36 3-CH3 AICI3 Co-salen catalysts exhibited 33 Cycle 2 70 slightly lower enantioselectivity than homogeneous ones (conv.; 40 73 Cycle 3 >45%, ee%; >99%). Cobaltexchanged zeolite itself shows no 86 43 3-CI GaCl3 Cycle 1 activity in this reaction, As a 80 42 Cycle 2 result, the formation of large mesopores in mordenite can be 86 44 Cycle 3 supported by the activity of salens encapsulated in pores. The For cycle 1 and cycle 2, heterogeneous salens were used immobilized catalyst was without regeneration by 4-NBSA. Cycle 3 shows the recoverable by simple filtration result of PHK after regeneration of catalyst with 4-NBSA. and solvent rinse. It is so easy to isolate the immobilized salen catalysts from the product solution containing epoxide and diols. This heterogenized salen catalysts retained the catalytic activity and enantioselectivity after repeated use without regeneration. The ship-in-bottle encapsulation of chiral salen showed not only the formation of mesopores in microporous mordenite crystal but also the way to expand the application of salen catalysts as a heterogenized form. 4. References [1] H. J. Federsel and J. Crosby, Chirality in industry II, J.Wiley & Sons, 1997, p. 295. [2] G. J. Kim and J. H. Shin, Tetrahedron Letters, 40 (1999) 6827. [3] K. B. M. Janssen, I. Laquiere, W. Dehaen, R.F. Parton, I. F. J. Vankelecom and P. A. Jacobs, Tetrahedron: Asymmetry, 8 (1997) 3481. [4] L. Drozdova, J. Novakova, G. Schulz-Ekloff and N. I. Jaeger, Microporous and Mesoporous Materials, 28 (1999) 395. [5] S. D. Choi and G. J. Kim, Catalysis Letters, 92 (2004) 35. [6] J. S. Jung, J. W. Park and G. Seo, Appled Catalysis A:General, 288 (2005) 149. [7] C. Schuster and W. F. Holderich, Catalysis Today, 60 (2000) 193. [8] C. K. Shin, S. J. Kim and G. J. Kim, Tetrahedron Letters, 45 (2004) 7429.


471 471

Effect of surface functional groups on adsorption and release of bovine serum albumin on SBA-15 S.-W. Song, S.-P. Zhong, K. Hidajat and S. Kawi* Department of Chemical and Biomolecular Engineering, National University of Singapore, 4 Engineering Drive 4, Singapore 119260

1. Introduction The rapid progress of peptide and protein synthesis technology has boosted the development of controlled protein or peptide delivery systems. The most widely investigated protein delivery systems are polymer or liposome-based system [1-2]. With an emerging and increasing interest in the application of mesoporous silica as a drug delivery system, we propose to employ SBA-15, a member of mesoporous silica as an alternative candidate for protein drug matrix as it has tunable large pores to host protein molecules [3] and the potential to overcome the limitations associated with polymers or liposomes, such as detrimental protein integrity during processing, small protein loading or low mechanical stability. As surface chemical composition is one of the important factors determining the availability of certain functional species to interact with proteins, we introduce three different functional groups, -NH2, -SH, or -COOH onto SBA-15 to study their effects on the adsorption and release of model protein drug bovine serum albumin (BSA). 2. Experimental Section Functionalized SBA-15 materials were prepared by one-pot synthesis according to the procedure reported by our previous study [4]. The molar composition of the mixture was 1 TEOS: 0.05 X-TES: 0.017 P123: 2.9 HC1: 202.6 H2O. (X-TES refers to 3-aminopropyltriethoxysilane, mercaptopropyltriethoxysilane, or 4-triethoxysilylbutyronitril). The adsorption isotherms of BSA on SBA-15 were obtained at 22°C in citrate-phosphate buffer solution of pH 4.69. The BSA release studies were conducted in phosphate buffered saline solutions (PBS, pH 7.4) at 37±0.1°C. Surface areas, pore size distributions and

472

total pore volumes were determined from N2 adsorption/desorption data using Quantachrome Autosorb-1. FT-IR spectra were collected using Shimadzu FTIR-8700. XPS was performed on Kratos Axis His instrument. The cytotoxicity of SBA-15 materials was evaluated using 3-[4,5-dimethylthiazol-2-yl]2,5-diphenyltetrazolium bromide thiazolyl blue (MTT) assay, and the cell viability was expressed as % of the corresponding control values. Circular Dichroism (CD) spectra were collected on a Jasco-810 spectropolarimeter over 200-250 nm at 22°C. 3. Results and Discussion 3.1. Characterization of SBA-15 materials Table 1 shows that the hydrothermal treatment temperature has a more significant effect on enlarging the pore sizes of NH2-SB A-15 than on other functionalized SBA-15. In addition, it should be noted that the advantage of one-pot synthesis of COOH-SBA-15 is that no further hydrolysis step is required during the synthesis as the intermediate -CN group could be directly converted to -COOH group in the highly acidic hydrothermal treatment condition [5]. Table 1. Physicochemical characteristics of pure and functionalized SBA-15 samples Sample ID

Reaction temperature* (°C)

BET surface area

(A)

Pore volume (cm}/g)

Nitrogen content (wt%)

Sulphur content (wt%)

Pore size

2

(m /g) S-0

40, 100

602.3

86.2

1.12

0

0

NH2-S-1

40, 100

424.7

86.8

1.10

0.56

0

NH2-S-2

40, 140

421.8

106.1

1.03

0.58

0

COOH-S-1

40, 100

475.2

84.2

1.02

0

0

COOH-S-2

40, 130

437.3

86.1

0.99

0

0

SH-S-1

40, 100

559.4

71.5

1.04

0

1.31

SH-S-2

40, 130

512.8

86.7

0.94

0

1.13

* Reaction at 40 °C for 24 hours, then hydrothermal treatment at higher temperature for 48 hours.

The incorporation of functional groups can be confirmed from elemental analysis results, FTIR or XPS spectra. The FTIR spectra (not shown) show that there is a peak appearing at 1602 cm'1 for NH2-S-1 (corresponding to -NH2 bending mode) or 1718 cm"1 for COOH-S-2 (corresponding to -C=O stretching vibration for -COOH group). The XPS spectra of Cls, Nls and S2p (not shown)

473

respectively show that there are peaks at 286 eV for COOH-S-2, 399 and 401 eV for NH2-S-1, and 164 eV for SH-S-2, showing the presence of-COOH [6], NH2 [7] or -SH groups [8] on functionalized SBA-15.

3.3. Cytotoxicity of SBA-15 and conformational change of released BSA

BSA loading amount (mg/g solid)

Figure 1 shows the adsorption isotherms of BSA (in phosphate-citrate buffer solutions having an ionic strength of 0.16 M at pH 4.69) on S-0, COOH-S-2, SH-S-2 and NH 2 -S-1, all of which have similar pore sizes. A higher loading amount of BSA is obtained on SH-S-2 and NH2-S-1 than on S-0 and COOH-S-2. The initial slope of the adsorption isotherm of BSA on NH2-S-I is steeper than that on SH-S-2, suggesting - based on pseudo-Langmuir model - that there is a stronger binding affinity between BSA and NH2-S-1 [9]. Figure 2 shows the release profiles of BSA from SH-S-2 and NH2-S-1. BSA is immediately released from SH-S-2 (within 30 min) but sustainedly released from NH2S-l (within 480 min) due to the stronger interaction between BSA and NH2-S-1.

200

d c

150

b 100

a 50

0 0.0

0.5

1.0

1.5

2.0

2.5

3.0

Solution concentration (mg/ml)

Figure 1. Adsorption isotherms of BSA on: a- COOH-S-2; b- S-0; c- SH-S-2 andd-NH,-S-l. 100

Cumulative released BSA (%)

3.2. Adsorption and release of BSA on SBA-15

90

80

70 SH-S-2 NH2-S-1

60

50

0

100

200

300

400

500

Figure 2. Release profiles of BSA fromNH2-S-l and SH-S-2.

Since a higher BSA loading amount and a slower release rate could be obtained on NH2-S-1, subsequent studies of cytotoxity and conformation of the released BSA were conducted on NH2-SBA-15. Figure 3 shows the cell viability of pure and NH2-SBA-15 at two different concentrations of SBA-15, i.e. 0.1 and 0.5 mg/ml. The results indicate that the cytotoxicity effect of NH2SBA-15 is very low as compared with pure SBA-15; the cell viability is more than 80% even at a high concentration of 0.5 mg/ml, suggesting that introduction of amine groups could attenuate the cytotoxicity induced by pure SBA-15. Figure 4 shows that CD spectrum of the released BSA from NH2-SBA-15 is similar to that of the native BSA. In addition, the calculated percentage of ahelix in the native and released BSA are 66.8% and 64.3%, respectively, indicating that BSA conformation has not been severely or irreversibly altered by its adsorption on hydrophilic NH2-SBA-15 prepared by one-pot synthesis.

474

H Amine-Functionalized Amine-Functionalized SBA-15 SBA-15

• Control Control

Cell Viability (%)

100

.2 >

80

60

3 «40 20 0

0.1

0.5

Concentration (mg/ml)

20

2

• Pure Pure SBA-15 SBA-15

10

-3

120

Molar Ellipticity (10 deg•cm /dmol)

This result is in good agreement with that reported by Norde and Giacomelli [10], who found that BSA adsorption is reversible on hydrophilic surfaces.

0

-10

Released BSA

-20

Native BSA

-30 200

210

220 220

230

240

250

Wavelength (nm) Wavelength

Figure 3. Cytotoxicity of pure and fitnctionalized SBA-15 materials.

Figure 4. CD spectra of native BSA and released BSA.

4. Conclusion Three different functional groups, -NH2, -SH, or -COOH, were directly incorporated into mesoporous silica SBA-15 materials by one-pot synthesis. Adsorption isotherms of BSA on the resulting SBA-15 materials show that higher adsorption capacities were obtained on NH2- and SH-functionalized SBA-15. However the release profiles show that BSA could be sustainedly released only from NH2-functionalized SBA-15. CD spectra show that BSA conformation could be well-maintained even after adsorption and subsequent release from NH2-functionalized SBA-15. Furthermore, the cytotoxicity results indicate that surface NH2 groups can inhibit cytotoxicity of pure mesoporous silica materials. 5. References [1] E. Mathiowitz (ed), Encyclopedia of controlled drug delivery, Vol.2, Wiley-Interscience, New York, 1999. pp. 816 [2] D. Simberg, S. Weisman, Y. Talmon and Y. Barenholz, Crit Rev. Ther. Drug, 21 (2004) 257. [3] D. Zhao, J. Feng, Q. Huo, N. Melosh, G. H. Fredrickson, B. F. Chmelka and G. D. Stucky, Science, 279 (1998) 548. [4] S. W. Song, K. Hidajat and S. Kawi, Langmuir, 21 (2005) 9568. [5] H. H. P. Yiu, P. A. Wright and N. P. Botting, J. Mol. Catal. B, 15 (2001) 81. [6] C. D. Bain, E. B. Troughton, Y.-T. Tao, J. Evall, G. M. Whitesides and R. G. Nuzzo, J. Am. Chem. Soc, 111(1989)321. [7] K. M. R. Kallury, P. M. Macdonald and M. Thompson, Langmuir, 10 (1994) 492. [8] Q. Zhang, H. Z. Huang, H. X. He, H. F. Chen, H. B. Shao and Z. F. Liu, Surf. Sci., 440 (1999) 142. [9] C. A. Haynes and W. Norde, Colloids Surf. B, 2 (1994) 517. [10] W. Norde and C. E. Giacomelli, J. Biotechnol, 79 (2000) 259


475 475

Microstructure understanding of organic-inorganic hybrid mesoporous silica by SAXS Yan-jun Gonga*, Zhi-hong Lib and Tao Doua "Catalysis Key Laboratory, CNPC, University of Petroleum, Beijing 102249, China. Lab of Synchrotron Radiation, Institute of High Energy Physics, Beijing 100039, China.

1. Introduction Incorporation of organic moieties into mesoporous silica framework is of considerable interest due to its scientific and industrial applications [1]. For organically modified mesoporous silica (OMMS), their pore structure and composition properties have been examined clearly by HRTEM, N2 adsorption, FT-IR, NMR and SAXS [1,2], but the microstructure concerning its interfacial and skeleton is less reported, mainly due to the higher difficulty in achieving well-established analysis procedures used for OMMS. We previously synthesized the OMMS by one-pot template-directed synthesis strategies and employed SAXS technique to characterize the microscopic structure [3-5]. The results showed that the organically modified groups covalently linked with the matrix of mesoporous silica and formed an interfacial layer, which led to the scattering of the pore distortion and gave a negative deviation from Porod's law. The average wall thickness of the interfacial layer could be obtained by analyzing this deviation [3-5]. The present report focuses on a detailed study of a negative deviation behavior of organically modified MSU-X mesoporous silica by SAXS. In order to evaluate the textural characteristics of organicinorganic MSU-X, the porod's deviation resulted from some different synthesis parameters, such as template, the organic groups and their fractal dimensions were also discussed. 2. Experimental Section As shown in Scheme 1, the organically modified silica (R-MSU-1) were prepared by one-pot synthesis strategy using tetraethoxysilane (TEOS) and organotriethoxysilane (RTES, R=methyl or Phenyl) as precursor and non-ionic

476

surfactant Cn-isI^-^tCI-kCHO^H as template [3]. The bi-functionalized mesoporous silicates were prepared by using TEOS and other two organosiloxanes as silicon sources to form binary organically modified-MSU-1. The template was extracted over ethanol for 48 hrs.

RSi(OEt)3 + Si(OEt)4

Tem late Template p

R R

R R

R R

R R R R

R R

R R

Template Extraction •

R R

R R

R R

R R R R

R R

R R R R R R

Scheme. 1 Synthesis of organically modified MSU-1

SAXS experiments were performed using synchrot ron radiation as X-ray source with a long-slit collimation system at Beijing Synchrotron Radiation Facility. Incident X-ray wavelength A. was 0.154 nm, and the scattering angle 29 was approximately 0-3°, the scattering vector was denoted as q, 300 3ootemplating method involving 48 hr 250 ^ 250 preparation of mesoporous o 200 > 150 200 carbon. Note that SBA-15 is 150 100 chosen as an example of a 100 50 50 mesoporous material to 0.8 0.0 0.2 0.4 0.6 0.8 1.0 examine our method. To Relative Pressure, P/Po P/Po Relative retain an ordered mesoFigure 1. N2 adsorption/desorption isotherms structure is not our present 1000

Pore Diameter [Å]

of the final samples. The insert shows the adsorption pore size distributions.

aim.

Table 1. N2 sorption data of selected samples Crystallization time

Surface area (m2/g)

Micropore volume (cc/g)

Pore diameter (adsorption, nm)

Total pore volume (cc/g)

7h

333

-

5.2

0.477

24 h

382

-

5.4

0.456

48 h

327

0.07

2.5; 6.0

0.263

N2 adsorption and desorption isotherms, shown in Fig. 1, indicate that there is a gradual decrease of the mesoporous volume as a function of crystallization time. However, after 48 h crystallization a significant amount of mesopores remains (Table 1). In comparison with experiments without carbon (also carried out in our lab), the mesopores are more stable because of a well-developed carbon structure. Though the force exerted by the growing zeolite crystals is

505

Intensity / au

very strong the carbon in the SBA-15 mesopores is not crushed. The decrease in mesopore size is associated with the growth of zeolite crystals. Bigger crystals may be stripped from the mesopore walls or even move out of the mesostructure because the wall thickness (in between 3.1-6.4 nm) is too small to accommodate larger particles. XRD patterns (Fig. 2) indicate the formation of silicalite-1 (MFI type) crystals in samples after 24 h and 48 h. The steady increase of 4000 the diffraction peaks suggests 3500 the increasing amount of 7h 3000 crystalline material in the samples. N2 sorption data also 2500 \ 24 h reveals the appearance of fc. 2000 2000 micropores (Table 1), which is 1500 1500 in agreement with XRD results. 1000 1000 The small angle X-ray scattering results (Fig. 3) reveal 500 •Si JUJU UUL 48 h that samples 7h and 24 h have 0 0 10 20 30 40 50 the typical SBA-15 (100) peak. Figure 2. XRD patterns of the final samples. However, in sample 48 h the peak is very small, demonstrating the deterioration of the mesoporous order after a longer 7 hh crystallization time. The HRTEM image of sample 24h (Fig 4) shows ordered 'in 24 h mesopores. A longer treatment 48 48hh (48h), however, results in worm-like mesopores. While the mesopores are retained 0.5 1.01.52.0 1.0 1.5 2.0 2.5 3.03.54.0 3.0 3.5 4.0 during the crystallization / 2-Theta degree process, the order deteriorates with time. This is in a good Figure 3. X-ray scattering patterns of the samples. agreement with X-ray scattering results. A similar phenomenon was reported by Trong On and Kaliaguine [11, 13]. To explain why the carbon structure did not preserve the ordered structure,

i

600

I n t e n s i t y / a .u .

500

400

300

200

100

0

Fig. 4 HRTEM images of samples 24h (left) and 48h (right).

506

we suspect that the transformation to a worm-like structure happened during the final combustion of the carbon framework. In both samples zeolitic features can be recognized by EDX. It appears that crystalline material is imbedded in the mesoporous structure in most parts of the sample, while in some areas it is more like a composite of mesoporous and crystalline materials. 4. Conclusion By employing a method combining carbon templating and crystallization we have synthesized zeolite materials (silicalite-1) with a meso-structure. Our method shows promising results. The stability of the mesopores probably improves because of a well-developed carbon structure inside the mesopores of SBA-15. Further testing, including chemical reactions, should provide us with a better understanding of the samples. 5. References [1] M.-O. Coppens, Structured Catalysts and Reactors, 2nd Editon, edited by A.Cybulski and J. A. Moulijn, (2006) 779. [2] Y. S. Tao, H. Kanoh, L. Abrams and K. Kaneko, Chem. Rev., 106 (2006) 896. [3] S. van Donk, A. H. Janssen, J. H. Bitter and K. P. de Jong, Catal. Rev., 45 (2003) 297. [4] P. Kortunov, S. Vasenkov, J. Karger, R.Valiulin, P.Gottschalk, M.Fe" Elia, M.Perez, M. Stacker, B. Drescher, G. McElhiney, C. Berger, R. Glaser and J. Weitkamp, J. Am. Chem.Soc, 127 (2005) 13055. [5] C. T. Kresge, M. E. Leonowicz, W. J. Roth, J. C. Vartuli and J. S. Beck, Nature, 359 (1992)710. [6] D. Y. Zhao, J. L. Feng, Q. S. Huo, N. Melosh, G. H. Fredrickson, B. F. Chmelka and G. D. Stucky, Science, 279 (1998) 548. [7] T. Linssen, K. Cassiers, P. Cool and E. F. Vansant, Adv.Coll.Inter.Sci, 103 (2003) 121. [8] A. Taguchi and F.Schuth, Micro.Meso.Mater., 77(2005)1. [9] J. Wang and M. -O. Coppens, in Preparation, (2006) [10] A. -H. Lu, W. Schmidt, A. Taguchi, B. Spliethoff, B. Tesche and F. Schuth, Angew.Chem., 114(2002)3639. [11] D. Trong On and S. Kaliaguine, Angew.Chem.Int.Ed., 40(2001)3251. [12] A. -H. Lu, W. -C.Li, W. Schmidt, W. Kiefer and F. Schuth, Carbon, 42 (2004) 2939. [13] D. Trong On and S. Kaliaguine, Nanoporous Materials: Science and Engineering, edited by G. Q. Lu and X. S. Zhao, Imperial Colleage Press, (2004) 47.


507 507

Assembly of mesocellular silica foams from colloidal zeolite nanocrystals through template free process Yuxin Jiaa'b, Wei Han ab , Guoxing Xionga*and Weishen Yang"1* "State Key Laboratory of Catalysis, Dalian Institute of Chemical Physics, Chinese Acedemy Science, 457 Zhongshan Road, Dalian 116023, People's Republic of China h Graduate School of the Chinese Academy of Sciences, Beijing 100049, People's Republic of China

Mesocellular silica foams were successfully prepared by assembly of colloidal silicalite-1 nanocrystals without templates. The products were examined by scanning electron microscopy (SEM), transmission electron microscopy (TEM), N2 adsorption-desorption and FTIR, showing foam-like structure composed of spherical cells with pore size of about 10 nm and zeolitic walls. 1. Introduction The discoveries of MCM-41 [1] and other oxides were met with great excitement in the hope of their potential applications as host structures, adsorbents, and catalysts for reactions involving large molecules [2]. By using dilute Pluronic P123 solutions in the presence of 1,3,5-trimethylbenzene (TMB) as organic cosolvent, the mesocellular foams composed of uniformly sized, large spherical cells were synthesized in aqueous acid, which were promising candidates in separations involving large molecules and low-dielectric applications [3-5]. Unfortunately, limited success had been made in industrial applications of these materials owing to the weak acidity and hydrothermal stability originated from the amorphous nature of the mesoporous materials [6], Recently, efforts have been made to prepare mesoporous materials that exhibit the acidity and stability of zeolitic materials. Starting with the work of Kloetstra et al, in which mesoporous materials with surface-tectosilicate structures were prepared by partial recrystallization of the surface of MCM-41 and HMS [7],

508

the mesoporous materials with zeolitic characters were obtained by fabrication of mesoporous solids [ 8, 9] or template-directed assembly of zeolite nanocrystals [10]. However, the environmental and economic problems were brought by using templates in the methods mentioned above. As far as we know, no one has described the synthesis of mesoporous materials with zeolitic walls and foam-like structure other than by using templates. Here we report a novel and facile template free route to prepare mesocellular silica foams with zeolitic walls and large spherical cells by assembly of zeolite nanocrystals. 2. Experimental Section Mesocellular silica foams (denoted as MSF) were prepared by the following procedure: mixing tetraethyl orthosilicate (TEOS) and tetrapropylammonium hydroxide (TPAOH) under vigorous stirring, a clear silicalite-1 nanocrystal sol was achieved followed by drying in ambient temperature for several days without stirring till a transparent gel formed. Subsequently, the gel was heated in air up to 823 K with a constant heat rate of 5K/min and calcinated for 6 h at 823 K. Characterization was carried out using SEM, TEM, N2 adsorptiondesorption measurements and FTIR. 3. Results and Discussion

10

°

Figure 1 displays the particle size distribution as measured by dynamic light scattering (DLS) of the silicalite-1 nanocrystal sol. The average DLS colloid size was about 3 nm, which contributed to the formation of 2.8-nm-sized primary units known as zeoslabs [11]. Figure 2 is the typical SEM image of 10 100 1000 MSF. The morphologies of the materials Size (nm) show an array of pores with circular Figure 1. Particle size distribution as openings ranging from 0.5 to 3.0 urn (Figure 2a), which generated from the measured by dynamic light scattering (DLS) of colloidal zeolite nanocrystals. phase-separation of gaseous species [12], and an amorphous phase when observed at a high magnification (Figure 2b). TEM was conducted to show the details of the morphologies of MSF (figure 3a). The solid is clearly characterized by a spherical cellular structure. The cells deviated from the spherical shape originate from the interference by the neighboring cells. The HRTEM image (Figure 3a inset) illustrates in more details of the material lattice fringes, which is compatible with silicalite-1. FTIR band at ca. 550 cm"1 (Figure 3b) which is characteristic of five-membered ring units in the pentasils also indicates that silicalite-1 nanocrystals are present within the MSF materials [13].

509

Nitrogen adsorptiondesorption isotherm and pore size distribution of MSF were shown in figure 4. The isotherm (TEM was conducted to show the details of the morphologies of MSF (figure 3 a). The solid is clearly characterized by a spherical cellular structure. The cells deviated from the spherical shape originate from the interference by the neighboring cells. The HRTEM image (Figure 3a inset) illustrates in

1 |im

Figure 2. SEM images of MSF at low (a) and high (b) magnification

700

6.0

5.0

400

material lattice fringes, which is compatible with silicalite-1. FTIR band at ca. 550 cm-1 (Figure 3b) which is characteristic of five-membered ring units in the pentasils also indicates that silicalite-1 nanocrystals are present within the MSF materials [13]. 4a) located between type I and type IV was obtained, which attributes to the coexistence of micporosity and mesoporosity. Micropore size distribution (TEM was conducted to show the details of the morphologies of MSF (figure 3a). The solid is clearly characterized by a spherical cellular structure. The cells deviated from the spherical shape originate from the interference by the neighboring cells. The HRTEM image (Figure 3a inset) illustrates in more details of the material lattice fringes, which is compatible with silicalite-1. FTIR band at ca. 550 cm-1 (Figure 3b) which is characteristic of five-membered ring units in the pentasils also indicates that silicalite-1 nanocrystals are present within the MSF materials [13]. 4b) of MSF determined by HK method centralizes in 0.53 nm corresponding to the channel opening size of silicalite-1. Mesopore size distribution (TEM was conducted to show the details of the morphologies of MSF (figure 3a). The solid is clearly characterized by a spherical cellular structure. The cells deviated from the spherical shape originate from the interference by the neighboring cells. The HRTEM image (Figure 3a inset) illustrates in more details of the material lattice fringes, which is compatible with silicalite-1. FTIR band at ca. 550 cm-1 (Figure 3b) which is characteristic of five-membered ring units in the pentasils also indicates that silicalite-1 nanocrystals are present within the MSF materials [13]. 4c) calculated from BJH method using the adsorption branch of the isotherm shows the average Figure 3. TEM images of MSF (a) and FTIR for MSF (b)

510

pore size of MSF is 7 nm, which was less than the results observed by TEM because the BJH method underestimated the size of the mesopores [14]. 4. Conclusion Without using template, the mesocellular silica foam was successfully prepared by assembly of colloidal zeolite nanocrystals. The as-synthesized products are hierarchical pore structured composite. T he microporosity was introduced by silicalite-1 nanocrystals. Further studies of mesoporous foamed structure are now ongoing in our group to investigate the formation mechanism and various factors in controlling the porosity. 5. Acknowledgment This work was supported by SINOPEC (NO.X503008) and NSFC (NO. 20321303). 6. References [1] C. T. Kresge, M. E. Leonowicz, W. J. Roth, J. C. Vartuli and J. S. Beck. Nature 1992, 359, 710. [2] G. J. D. Soler-illia, C. Sanchez, B. Lebeau and J. Patarin. Chem. Rev 2002, 102, 4093. [3] P. Schmidt-Winkel, W. W. Lukens, D. Y. Zhao, P. D. Yang, B. F. Chmelka and G. D. Stucky. J. Am. Chem. Soc. 1999,121, 254. [4] P. Schmidt-Winkel, W. W. Lukens, P. D. Yang, D. I. Margolese, J. S. Lettow, J. Y. Ying and G. D. Stucky. Chem. Mater. 2000, 12, 686. [5] W. W. Lukens, P. D. Yang and G. D. Stucky. Chem. Mater. 2001, 13, 28. [6] A. Corma. Chem. Rev 1997, 97, 2373. [7] K. R. Kloetstra, H. vanBekkum and J. C. Jansen. Chem. Commun. 1997, 2281. [8] D. T. On and S. Kaliaguine. J. Am. Chem. Soc. 2003, 125, 618. [9] Y. Liu, W. Z. Zhang and T. J. Pinnavaia. J. Am. Chem. Soc. 2000, 122, 8791. [10] Z. T. Zhang, Y. Han, F. S. Xiao, S. L. Qiu, L. Zhu, R. W. Wang, Y. Yu, Z. Zhang, B. S. Zou, Y. Q. Wang, H. P. Sun, D. Y. Zhao and Y. Wei. J. Am. Chem. Soc. 2001, 123, 5014. [11] V. B. C. E. A. Kirschhock, S. Kremer, R. Ravishankar, C. J. Y. Houssin, B. L. Mojet, R. A. van Santen, P. J. Grobet, P. A. Jacobs and J. A. Martens. Angew. Chem. Int. Ed. 2001, 40, 2637. [12] K. Kurumada, N. Kitao, M. Tanigaki, K. Susaand M. Hiro. Langmuir 2004, 20, 4771. [13] E. G. D. a. J. W. P. A. Jacobs. J. Chem. Soc. Chem. Commun. 1981, 591. [14] P. S.-W. W.W. Lukens Jr., J. Feng and G.D. Stucky. Langmuir 1999, 15, 5403.


511 511

Microwave assisted-direct synthesis of highly ordered large pore functionalized mesoporous SBA Sujandi, Sang-Cheol Han, Dae-Soo Han and Sang-Eon Park* Lab. ofNano-Green Catalysis, Nano Center for Fine Chemicals Fusion Technology, Dep't of Chemistry, Inha University, Incheon 402-751, Korea

Microwave sysnthesis has been successfully applied for the direct synthesis of organo-functionalized SBA-15 and 16 mesoporous materials through the cocondensations of organosilanes with sodium metasilicate in the presence of triblock copolymers as structure directing agents. The obtained materials have large pores, long range order of cubic and hexagonal mesostructures, and the loading of organo groups up to 10% of the silica frameworks. 1. Introduction Recently, microwave sysnthesis has been applied to the rapid and economical synthesis route of various nanoporous materials which normally required several days to prepare under traditional hydrothermal conditions. The microwave synthesis also offers potential advantages over hydrothermal synthesis, such as rapid and homogeneous heating throughout the reaction vessel, homogeneous nucleation and rapid crystallization, phase selectivity, and facile particle size and morphological control, etc. This method has been successfully applied to the synthesis of various kind of nanoporous materials, namely zeolite A, Y, Beta, ZMS-5, MCM-41, SBA-15, and SBA-16 [1-5]. Recently, Kormaneni and co-worker have applied microwave synthesis method in the direct synthesis of transition metal substituted SBA-15 under acidic condition.6"7 It rapid heating and fast supersaturation were believed to facilitate the co-condensation processes during the synthesis [6]. However, to the best of our knowledge, there has been no report on the microwave synthesis of organofunctionalized SBA-15 and 16 through the co-condensation of organosilanes and silica source. The organo-functionalization has been known to play important role in expanding the applications of mesoporous silica in catalysis, separation, and sensor design [8]. Herein, we report the synthesis of large pore

512

organo-functionalized SBA-15 and 16 mesoporous silica through cocondensation reactions between organosilanes and sodium metalicate in the acidic condition under microwave irradiation. 2. Experimental Section The organo-functionalized SBA-15 and 16 mesoporous materials were synthesized according to the same procedure by co-condensations of organosilanes (chloropropyltriethoxysilane/CPTES, cyanopropyltriethoxysilane/ CNPTES, propylanilinetriethoxysilane/PATES, and aminopropyltriethoxysilane/APTES) with a sodium metasilicate in the presence of a triblock copolymer as a structure directing agent under microwave irradiation. Preparation of chloropropyl-functionalized SBA-15 is given as an example. In a typical synthesis, 16 g of 10% (w/w) aqueous solution of PI23 was poured into 26.6 g distilled water and then 0.016-(0.016 x x%) mole of sodium metasilicate was added to the solutions. To the vigorously stirred solutions, 13 g of concentrated hydrochloric acid (37.6%) was quickly added followed by 0.016 x x% mole ofCPTES (x = 5, 7.5, and 10). The final gel mixtures were stirred for 1 hour at 313 K before subjected to the microwave digestion system (CEM Corporation, MARS-5) of which condition was set at 373 K for 2 h at operated power of 300 W (100%). The crystallized products were filtered, washed with warm distilled water and finally dried at 333 K. The surfactant was then selectively removed by Soxhlet extraction over ethano} for 24 h. For the synthesis of the organo-functionalized SBA-16, a triblock copolymer F127 was used as the structure directing agent. 3. Results and Discussion Surfactant-free SBA-15 and SBA-16 functionalized with different organic functional groups prepared by the microwave assisted-direct synthesis showed XRD patterns (not shown) with a very intense diffraction peak in the range of 0.8-1.0° 20 and two or more additional peaks at higher degree within 1.2-2.0° 20. The XRD patterns indicated the long range ordered and excellent textural uniformity of the organo-functionalized SBA-15 and SBA-16 mesoporous materials with hexagonal and cubic mesostructures obtained from triblock copolymers as structure-directing agents [9]. The N2 adsorption and desorption isotherms (not shown) of all the surfactant-free samples showed the defined type IV behavior with hysteresis loops, which are characteristic for mesoporous materials with narrow distribution of pore size that facilitate the condensation of N2 [9]. Table 1. provides the textural properties of the organo-functionalized mesoporous materials synthesized from the microwave assisted-direct synthesis. These results show that well ordered mesoporous materials could be synthesized at organo functionalization levels corresponding to x values of at

513

(f) (f)

Intensity (a.u.)

(e)

(d)

(c) (b)

(a) 1

2

3

2 theta (degree) (degree)

Fig. 1. XRD patterns of Clpr-SBA-16: (a)x=10, (b)*=7.5, (c)*=5 andClprSBA-15: (d)x=10, (e)jt=7.5, (f)*=5

4

least 10% organic group to silica molar ratio regardless the nature of the organosilanes added into the synthesis gel. In all cases the mean pore sizes were large than 5 nm for SBA-15 and 3 nm for SBA-16, respectively. In general, the pore sizes were not affected by the amounts of organosilanes added to the synthesis gels. The successful functionalizations were proven by near infrared and mid infrared spectra which showed the vibration bands for the organic moieties. Addition of different amounts of CPTES into the initial gel mixtures during the synthesis seems to give effect to the mesostructure of the SBA15 materials. At CPTES to silica molar ratio = 5 and 7.5%, the XRD patterns (Fig. le and If) could be indexed as a hexagonal mesostructure of SBA-15 mesoporous materials, respectively.

However, at molar ratio = 10%, the XRD pattern showed the characteristic for mesoporous material with cubic structure of laid symmetry.10 The mesophase transformation due to the presence of CPTES during the synthesis were clearly shown by the TEM image (Fig. 3d). The XRD patterns of Clpr-SBA-16 synthesized from the co-condensation of CPTES and sodium metasilicate in the presence of F127 surfactant were characteristic for the expected SBA-16 mesoporous material with Im3m symmetry, with very intense main diffraction peaks of 110 plane and additional diffraction peaks at higher 20 of 200, 211, and 220 planes. Further evidences were provided scanning electron microscopic (SEM) and transmission electron microscopic (TEM) images (Fig. 3a and 3b). The SEM and TEM images showed the typical dodecahedron morphology and cage-type Im3m cubic structure of SBA-16, respectively.4 (a)

(b)

(c)

(d)

50 nm

Fig. 2. SEM and TEM images of Clpr-SBA-16 and Clpr-SBA-15. (a) and (b) SEM and TEM images of Clpr-SBA-16 (x = 10); (c) and (d) SEM and TEM images of Clpr-SBA-15 (* = 10).

514 Table 1. Textural properties of organo-functionalized SBA-15 and 16 Resulted material P123 5 Clpr-SBA-15 CPTES P123 7.5 Clpr-SBA-15 CPTES P123 10 CPTES Clpr-SBA-15 F127 5 CPTES Clpr-SBA-16 F127 7.5 CPTES Clpr-SBA-16 F127 10 CPTES Clpr-SBA-16 P123 5 CNpr-SBA-15 CNPTES P123 10 CNPTES CNpr-SBA-15 PATES P123 5 ANpr-SBA-15 PATES P123 10 ANpr-SBA-15 APTES P123 5 NH2pr-SBA-15 P123 7.5 APTES NH2pr-SBA-15 P123 10 NH2pr-SBA-15 APTES *Calculated from desorption branch of the full isotherm Organosilane

SDA

X

Framework d/nm structure Hexagonal/P6m/« 8.9 Hexagonal//'(5/n/n 9.7 Cvtb\dla3d 8.7 Cub\c/Im3m 10.4 Cubic/Im3m 10.0 Cubic/Im3m 9.7 HexsLgonai/P6mm 8.8 Hexagona\/P6mm 8.5 Hexagonal/P6mm 10.2 Hexagonal/.P 0.2) normally observed for mesoporous

521 (100)

500 LTHMS 450

LTAl-MMS50

Volume adsorbed (ml/g STP)

400

Intensity (a.u.)

LTHMS

LTAl-MMS50

LTAl-MMS20

LTAl-MMS20 350 300 250 LTAl-MMS10 200 LTAl-MMS5

150 150

LTAl-MMS10

100 100

LTAl-MMS5

50 50 0

22

44

66

88

(degrees) 22 θθ (degrees)

10 10

0.0

12 12

0.2

0.4

0.6 P/P0

0.8

1.0 1.0

Fig. 1. Powder XRD patterns (left) and nitrogen sorption isotherms (right) of primary amine templated silica (LTHMS) and aluminosilicate (LTAl-MMS) materials prepared at ca. 5 °C.

materials [1, 2]. The pore size of the materials (obtained via BJH analysis of adsorption data), given in Table 1, ranges from 14 - 19 A and confirms the super-microporous nature of the materials. It is interesting that even the pure silica sample, LTHMS, is super-microporous. The surface area (450 and 1230 m2/g) and pore volume (0.24 - 0.57 cm3/g) are similar to those of comparable mesoporous materials [1,2,8,10]. In particular samples prepared at Si/Al of 20 and 50 exhibit high surface area. The proportion of micropore surface area (47 86%) and pore volume (40 - 75%), given in Table 1, is the highest we have ever observed for primary amine-templated materials [8,10]. This further emphasizes the super-microporous nature of the LTHMS/LTAl-MMS materials. Table 1. Textural properties, elemental composition and acidity of primary amine templated materials prepared at ca. 5°C. Values in parenthesis are micropore surface area and pore volume. Sample

LTHMS LTA1-MMS50 LTA1-MMS20 LTAl-MMS 10 LTA1-MMS5

Si/Al ratio

51.7 26.2 13.7 7.3

Pore

(A)

Surface area (m2/g)

Pore volume (cm3/g)

29.4 28.9 28.1 27.3 26.6

1036 1190 1230 482 444

0.50 (0.24) 19.3 0.56 18.8 0.57 (0.23) 18.5 0.28 (0.19) 14.0 0.24 (0.18) 14.0

Basal spacing

(561) (581) (406) (384)

size (A)

Acidity (mmol/g)

0.19 0.45 0.62 0.73

522

LTAl-MMS5

LTAl-MMS10

LTAl-MMS20

LTAl-MMS50 150

100

50

0

-50

-100

-150

ppm

Fig. 2.27A1 MAS NMR of calcined primary amine-templated super-microporous aluminosilicate materials prepared at ca. 5°C.

The Al content of the materials (Table 1) is similar to that of comparable mesoporous analogues [10]. Super-microporosity cannot therefore be ascribed to a high Al content [8], but rather appears to be a consequence of the low synthesis temperature. Al MAS NMR of the super-microporous materials is shown in Fig. 2. The spectra of all samples exhibit resonances at 55 and 0 ppm arising from tetrahedral (framework) and octahedrally coordinated (nonframework) Al respectively. Most of the Al is in tetrahedral framework positions, and the proportion of non-framework Al is greatest at high Al content (sample LTA1-MMS5). As expected, the samples exhibit significant acidity (Table 1), which increases with the Al content. In summary, we have shown that low temperature synthesis offers a facile route for the preparation of primary amine-templated super-microporous silica and aluminosilica materials, with structural ordering, textural parameters, and acidity similar to those of comparable mesoporous materials. 4. References [1] A. Corma, Chem. Rev., 97 (1997) 2373. [2] D. T. On, D. Desplantier-Giscard, C. Danumah, S. Kaliaguine, Appl. Catal. A: Gen., 222 (2001) 299. (b) J. Y. Ying, C. P. Mehnert and M. S. Wong, Angew. Chem. Int. Ed., 38 (1999) 56. [3] S. A. Bagshaw and A. R. Hayman, Chem. Commun., (2000) 533. [4] D. P. Serrano, J. Aguado, J. M. Escola and E. Garagorri, Chem. Commun., (2000) 2041. [5] K. Yano and Y. Fukushima, J. Mater. Chem., 13 (2003) 2577. [6] Y. S. Lin, H. P. Lin and H. Y. Mou, Microporous Mesoporous Mater., 76 (2004) 203. [7] T. Sun, M. S. Wong and J. Y. Ying, Chem. Commun., (2000) 2057. [8] (a) E. Bastardo-Gonzalez, R. Mokaya and W. Jones, Chem. Commun., (2001) 1016. (b) E. Bastardo-Gonzalez, R. Mokaya and W. Jones, Stud. Surf, Sci. Catal., 141 (2002) 141. [9] Y. Di, X. Z. Meng, L. F. Wang, S. G. Li and F. S. Xiao, Langmuir, 22 (2006) 3068. [10] (a) R. Mokaya and W. Jones., J. Catal., 172 (1997) 211. (b) R. Mokaya and W. Jones, J. Mater. Chem., 8 (1998) 2819. (c) R. Mokaya, W. Jones, S. Moreno and G. Poncelet, Catal. Lett., 49 (1997) 87. (d) R. Mokaya, W. Jones, Chem. Commun., (1996) 981.


523 523

Synthesis of zeolitic mesoporous titanosilicate using mesoporous carbon as a hard template Haijiao Zhang, Yueming Liu, Mingyuan He and Peng Wu * Shanghai Key Laboratory of Green Chemistry and Chemical Processes, Department of Chemistry, East China Normal University, North Zhongshan Rd. 3663, Shanghai 200062, P .R.China

A crystalline MFI type titanosilicate showing mesoporous characteristics has been synthesized by crystallizing the zeolitic synthesis gel with the assistant of mesoporous carbon (CMK-3) using a dry gel conversion (DGC) method. The resulting zeolitic mesoporous titanosilicate (ZMTS) has been applied to the oxidation of alkenes with H2O2, and its catalytic properties have been compared with TS-1 and Ti-MCM-41. ZMTS proves to be superior in activity. 1. Introduction Recently, it is very attractive and desirable to synthesize catalytic materials which combine the advantages of crystalline zeolites and mesoporous materials from the viewpoint of processing large chemicals more effectively. Particular attentions have been focused on the nanocasting of mesopore-containing zeolites using various forms of carbon as templates [1, 2]. In this study, we have been trying to create mesopores within zeolite crystals by crystallizing the titanosilicate zeolite in and out of the pore system of well-ordered mesoporous carbon CMK-3. The mesoporous titanosilicate material with zeolitic characteristics has been synthesized successfully by using CMK-3 as the hard template with a dry gel conversion (DGC) method. The catalytic performance of ZMTS has been studied in the oxidation of alkenes and alkanes with H2O2 by comparing with conventional TS-1 [3] and Ti-MCM-41 [4] catalysts. 2. Experimental Section The synthesis of ZMTS was carried out using a DGC method. Mesoporous carbon CMK-3 was first prepared by nanocasting mesoporous silica SBA-15

524

following the literatures [5, 6]. CMK-3 was impregnated using incipient wetness method with a gel containing tetrapropylammonium hydroxide (TPAOH), tetrabutylorthotitanate (TBOT), water and ethanol. After evaporating ethanol slowly from the mixture at 40°C, tetrathylorthosilicate (TEOS) was added to the mixture to at a C/Si molar ratio of 3:1. The dry gel obtained gives a molar composition of TEOS/TBOT/TPAOH/H2O of 1 : 0.01 : 0.40 : 4. The dry gel was placed into a Teflon cup and was then transferred to a Teflon-lined autoclave. The gel was crystallized statically in the vapor of hydrofluoric acid or water at 180°C for 72 h. The final power was calcined in air at 550°C for 8 h to remove the CMK-3 template and organic additives to obtain ZMTS. The catalytic reactions for the oxidation of alkenes and cycloalkenes with H2O2 (30% wt) were run with CH3OH or CH3CN as a solvent in a 50 mL glass reactor. After stirred at 60°C for 2 h, the reaction mixture and remained H2O2 were analyzed on a gas chromatography (Shimadzu GC-14B) and determined by the titration method with a 0.1 M Ce(SO4)2 solution, respectively. 3. Results and Discussion Fig. 1 shows the XRD patterns of various samples. Similar to SBA-15, CMK3 obtained from SBA-15 template showed the typical pattern of hexagonal structure in the low angle range. The N2 adsorption isotherms of SBA-15 and CMK-3 were also characteristic of mesoporous materials (Fig. 2). In particular, the two samples showed the highly ordered mesostructures, which was also confirmed by means of FE-SEM (Fig. 3). The ZMTS prepared using CMK-3 as a hard template exhibited the typical diffraction peaks at 20 = 7.8, 8.8, 23.2, 23.8, 24.3° etc. due to MFI structure (Fig. lc and d), but no peaks due to hexagonal mesophase in lower angle region (not shown). These results indicate that ZMTS is essentially a crystalline material with zeolitic framework. Seen from the sorption isotherms

d

b

1 ..

c

a 0

11

2

3

22Theta/degree Theta/degree

44

5

5

10 10

15 15

2 0 2 255 3 030 20

35

2 Theta/degree

Fig. 1 XRD patterns of (a) SBA-15, (b) CMK-3, (c) As-syn.-ZMTS, (d) Cal.-ZMTS.

900

b

750

a

600 450 300 150 0 0.0

0.2

(U 0.4

0.6

0.8

1.0 1.0

Relative pressure (P/P0) (P/P0)

Amount adsorbed (cm3 STP g-1)

Amount adsorbed (cm3 STP g-1)

525 250

d 200

c 150

100 0.0

0.2 0.

0.44

0.6

0.8 08

1.0 L0

(P/P0) Relative pressure (P/P0

Fig. 2 Nitrogen adsorption-desorption isotherms of (a) SBA-15, (b) CMK-3, (c) ZMTS, (d) TS-1. a

b

Fig. 3 FE-SEM images of (a) SBA-15, (b) CMK-3. (Fig. 2), the ZMTS showed obvious hysteresis loops at P/Po = 0.05-0.20 and 0.45-0.80, probably due to the presence of mesopores within the zeolite crystals or inter-particle voilds after removing the CMK-3 carbon template. All samples showed the characteristic adasoprtion at 960 cm"1 in IR spectra and and mainly the 210 nm band in UV-visible spectra, which confirmed that the Ti atoms had been incorporated into the framework of zeolites. Table 1 summarizes the catalytic properties of TS-1, Ti-MCM-41 and ZMTS for Si/Ti = 100 (molar ratio) samples in oxidation of alkenes with H2O2. TiMCM-41 hardly showed catalytic activity in the oxidation of 1-Hexene because of its high hydropholicity related to silanol groups and the amorphous nature of its silicate framework wall. On the contrary, ZMTS and TS-1 showed a higher conversion. These results indicate that ZMTS contains the same type of Ti acid site as TS-1. For the oxidation of cycloalkene, an improved catalytic activity of

526 Table 1 Catalytic properties in oxidation of alkenes with H2O2

Cyclohexene /mol".Vo l-Hexene/mol% Oxide sel. H2O2 Conv. Oxide H2O2 conv. sel. conv. 11.0 21.0 6.1 42.6 20.7 ZMTS 96.5 TS-1 11.3 99.9 21.6 3.8 39.5 20.3 Ti-MCM-41 28.8 0.5 5.2 5.7 42.6 20.8 Reaction conditions: cat., 0.05 g; substrate, 10 mol; H2O2, 10 mmol; solvent, 10 mL; temp., 333 K; time, 2 h. Sample

Conv.

ZMTS was observed when compared with TS-1. This may be due to a result of the presence of mesopores in ZMTS which serves as an open reaction space suitable for bulky molecules. 4. Conclusion A novel titanosilicate molecular sieve microporous structures can be synthesized by (CMK-3) as a template with a DGC method. cycloalkenes with H2O2, the material showed MCM-41 andTS-1.

having both mesoporous and nanocasting mesoporous carbon In the oxidation of alkenes and superior catalytic activity to Ti-

5. Acknowledgement Financial supports by Program for New Century Excellent Talents in University (NCET-04-0423), Pujiang project (05PJ14041), 973 project (2006CB202508), STCSM (05DZ22306, 05JC14069) and NSFC (20473027 and 20233030) are appreciated. Z. H. J. thanks PhD Program Scholarship Fund ofECNU2006. 6. References [1] B. T. Holland, L. Abrams and L. A. Stein, J. Am. Chem. Soc, 121 (1999) 4308. [2] C. J. H. Jacobsen, C. Madsen, J. Houzvicka, I. Schmidt and A. Carlsson, J. Am. Chem. Soc, 122(2000)7116. [3] M. Taramasso, G. Perogo and B. Notari, US Pat., 4 410 501 (1983). [4] T. Blasco, A. Corma, M. T. Navarro and J. P. Pariente, J. Catal. 156 (1995) 65. [5] D. Y. Zhao, J. L. Feng, Q. S. Huo, N. Melosh, G. H. Fredrickson, B. F. Chmelka and G. D. Stucky, Science, 279 (1998) 548. [6] S. Jun, S. H. Joo, R. Ryoo, M. Kruk, M. Jaroniec, Z. Liu, T. Ohsuna and O. Terasaki, J. Am. Chem. Soc, 122 (2000) 10712.


527 527

Synthesis of micro- and mesoporous ZSM-5 composites and their catalytic application in glycerol dehydration to acrolein Chun-Jiao Zhoua, Cai-Juan Huanga, Wen-Gui Zhanga, He-Sheng Zhaib, HaiLong Wua and Zi-Sheng Chaoa* "College of Chemistry and Chemical Engineering, Key Laboratory ofChemometrics & Chemical Biological Sensing Technologies, Ministry of Education, Hunan University, Changsha 410082, P. R. China College of Chemistry and Chemical Engineering, Xiamen University, Xiamen, 361005, P. R. China

The micro- and mesoporous ZSM-5 composites were, for the first time, onestep synthesized, employing dual-templates. Influencing factors such as crystallization temperature, crystallization time, and pH were investigated. The composites were characterized by XRD, HRTEM and N2-adsorption. The studies on dehydration of glycerol to acrolein show that the micro- and mesoporous ZSM-5 composites provided a glycerol conversion of 98.27% with an acrolein yield of 73.64 mol%, the result being better than all those reported in literatures. 1. Introduction Zeolites have found versatile applications in separation and catalytic process due to their unique properties such as shape-selective effect, high thermal stability and intrinsic acidity [1]. On the other hand, transport limitation occurs, however, for the catalytic conversion of large molecules in zeolites, due to their microporosity. While mesoporous materials such as M41S, have emerged as promising catalytic materials in the conversion of large hydrocarbons [2], they are hard to find a practical application due to their low acidities and hydrothermal stabilities. Thus, the exploitation of novel materials with both microporous and mesoporous properties is of great interest. Recently, a few reports have dealt with the synthesis of this kind of materials using dual

528

templating method through a two-step process or zeolite seeding methods [3-7]. In this work, we address, for the first time, an one-step synthesis of micro- and mesoporous ZSM-5 composites, employing dual-templates, and also the catalytic application of the composites in the dehydration of glycerol to acrolein. 2. Experimental Section Synthesis A12(SO4)3 and TPAOH aqueous solutions were mixted at ice-water temperature and then TEOS was dropwise introduced under stirring. After that, the mixture formed was mixed with CTABr solution under strong agitation. To adjust the pH value of the batch, dilute H2SO4 solution was employed. Unless mentioned otherwise, the pH value of batches was adjusted to 9. The final gel had a molar composition of 60.4 SiO2 : A12O3 : 21.1 TPAOH : 9.8 CTABr : 2004.7 H2O and was subjected to a hydrothermal treatment for 1-8 d at given temperatures. The solid products were recovered by filtration, washing and drying. To remove the organic molecules, the specimens were calcined at 813 K in a N2 flow for 1 h and subsequently in air for 5 h. Characterization The specimens were characterized by XRD (Bruker D8 Advance Diffractometer; Cu Karl), HRTEM (JEM-3010; accelerating voltage 300 kV), N2 adsorption-desorption (Quantachrome Autosorb-1 MP) Catalytic reaction The catalysts tested included the micro- and mesoporous ZSM-5 composites, the pure ZSM-5 and MCM-41 as well as a mixture of the later two, all of which were prepared using same sources and Si/Al ratio in batches. Besides, a solid phosphoric acid catalyst, which was reported to possess the largest yield for the dehydration of glycerol to acrolein [8-9], was also prepared, according to the procedure in Ref. 8, and employed in this work. The catalytic experiments were performed in a fix-bed quartz reactor (0.9 x 25 cm), under the conditions of 588 K, 4 g catalyst, and 40 wt% glycerol aqueous solution. The products were analyzed by a Varian GC-Mass, equipped with a FID detector and a VF-5 capillary column (30m x 0.25mm, 0.25um). 3. Results and Discussion Fig. 1 to Fig. 3 show the XRD patterns of the specimens synthesized under S4

10 2

4

6

8

2 Theta

10

10

20

30

40

50

2 Theta

20 30 40 2 Theta

2 Theta

Fig. 1 XRD patterns of specimens synthesized at 8d and different temperatures. SI: 373 K; S2:398K;S3:418K

Fig. 2 XRD patterns of specimens synthesized at 398 K and different time. S4: 2d; S5: 4d; S6: 6d; S7: 8d

529

different conditions. Only a mesoporous phase could be identified for the specimen synthesized at 373 K (see Fig. 1 SI) or in a short period of crystallization time (see Fig. 2, S4 and S5), while both a mesoporous and a microporous phases were present for those at higher temperatures (see Fig. 1, S2 and S3 and Fig. 2, S6 and S7). The microporous phase was indexed to ZSM5 (JCPD 44-0003). With increasing temperature, the crystallinity of ZSM-5 increased and that of the mesoporous phase decreased, (see Fig. 1). The prolonging of crystallization time promoted the formation of the microporous phase ZSM-5 but hindered that of the mesoporous phase (see Fig. 2). With decresing the pH, the formation of the microporous phase ZSM-5 was hampered slightly and that of the mesoporous phase was promoted largely (see Fig. 3). The HRTEM of the specimen S8 synthesized under the condition of 398 K, 8 d and pH = 8 is shown in Fig. 4, which reveals the presence of the disordered mesoporous phase. The mesurement of N2 adsorption- desorption indicats that the scpecimen S8 has a BET specific surface area of 764.2 m2/g. The adsorption-desorption isotherm and BJH pore size distribution curve of the specimen S8 is shown in Fig. 5, which reveals the presence of both micropores and mesopores. Table 1 lists the catalytic reaction results. It indicates that the catalyst S8, among all the catalysts studied in both A S8 this work and literatures, presents the V. largest acrolein yield (73.64 mol%). It ^ S7 is suggested that the presence of both S9 microporous and mesoporous phases is ;=f^ 4 6 8 10 20 30 40 SO responsible for the well catalytic 2 Theta 2 Theta performance of the catalyst, may Fig. 3 XRD patterns of specimens synthesized being due to the high dispersion of at 8 days, 398 K and different pH value. S8: acidic sites and the decrease of the 8;S7:9;S9:10 resistance to diffusion.

3500 400-

|300 Tb-ZG>Tb-ZSM-5.

1.0

0.8

0.6

0.4

0.2

0.0 530

Tb-ZSM-5/MCM-41(200) 540

550

Tb-ZSM-5

Tb-ZG 560

530 530

540 540

550 550560

530 560 530

540

550

560

wavelength(nm) Figure 2. TRES of calcined Tb- ZSM-5, Tb-ZG and Tb- ZSM-5/MCM-41(200). Directions of arrows indicate delay times after laser pulse in range 1- 4200 us. With bold lines are represented TRES at 1 us delay after laser pulse

4. Conclusion The time-resolved photoluminescence spectra analysis indicated a single average terbium species in all hydrated Tb-zeolites with lifetimes varying between 474 us and 535 \is. For the calcined samples, lineshapes and TRES analysis correlated with terbium distribution that display a two species distribution in mesoporous materials with lifetimes centred on several hundreds of (j.s up to 2 ms while for ZSM-5 zeolite a distinct number of species could not be inferred indicating a more heterogeneous distribution. These data suggest that in mesoporous materials two distinct location of Tb exist, which might be correlated with two types of exchange sites: one on the external surface, the other inside the pores, while for ZSM-5 predominate the sites inside the pores. 5. References [1] Y. Liu, W. Zhang and T. J. Pinnavaia, J. Am. Chem. Soc. 122 (2000) 8791. [2] Z. Zhang, Y. Han, L. Zhu, R. Wang, Y. Yu, S. Qiu, D. Zhao and F.-S. Xiao, Angew. Chem. Int. Ed. 40 (2001) 1258. [3] D. T. On and S. Kaliaguine, Angew. Chem. Int. Ed. 40 (2001) 3248. [4] S. P. B. Kremer, C. E. A. Kirschhock, A. Aerts, K. Villani, J. A. Martens, O. I. Lebedev and G. van Tendeloo, Adv.Mater. 15 (2003) 1705. [5] M. P. Hehlen, N. J. Cockroft, A. J. Bruce and T.R Gosnell, Phys. Rev. B 56 (1997) 9302.


535 535

Acylation of fatty acids with amino-alcohols on ULMFI type materials M. Musteata3, V. Musteata3, A. Dinua, V.I. Parvulescu3*, V.T. Hoangb, D. Trong-Onb and S. Kaliaguineb "University of Bucharest, Department of Chemical Technology and Catalysis, 4—12 Regina Elisabeta Bvd., Bucharest 030016, Romania b Universite Laval, Ste-Foy, Quebec, G1K 7P4.

Acylation of oleic acid with ethanolamine was carried out using large mesoporous materials of UL-MFI-type. Mesostructured precursors having Si/Al ratios from 100 to 20, designated as Al-Meso-x were synthesized using SiCU and A1C13 as silicon and aluminum sources, and Pluronic PI23 in ethanol as surfactant. UL-ZSM-5 materials were obtained from surfactant containing the above precursors which were impregnated with an aqueous solution of tetrapropylammonium hydroxide followed by drying for several days. Chemoand regioselectivity was controlled via a strong correlation of temperature and solvent effects. 1. Introduction Acylation of fatty acids with amino-alcohols leads to valuable surfactants. In spite of this practical importance the literature is scarce, and the very few contributions in this subject refer to synthesis of pharmaceutical applications [1]. One of the major problems encountering in these syntheses is the regioselectivity, O- or N- acylation leading evidently to compounds with different properties [2]. To control O-acylation, Kihara et al. [3] suggested the use of trifluoromethanesulfonic acid as catalyst in the presence of a crown ether. Another serious problem concerns the conditions in which these reactions are carried out. All the reported acylations occur under very non-green conditions, using fatty acid chlorides and homogeneous acid Lewis catalysts. The aim of this study was to investigate a green route for the acylation of oleic acid with ethanolamine, with a good control of selectivity. Since these

536 536

molecules are very large, heterogeneous catalysis requires mesoporous materials. 2. Experimental Section UL-MFI materials were prepared according to the synthesis method described previously [4]. Mesostructured precursors having Si/Al ratio from 100 to 20, designated as Al-Meso-x (where x is the atomic Si/Al ratio), were synthesized using SiCLt and A1C13 as silicon and aluminum sources, respectively and Pluronic PI23 in ethanol as surfactant. UL-ZSM-5 materials were obtained from surfactant containing the above precursors which were impregnated with 10% aqueous solution of tetrapropylammonium hydroxide followed by drying for several days. The solid-state crystallization was performed at 120°C for different lengths of time in a Teflon-lined autoclave after the addition of a small quantity of water not contacting the sample. Table 1. Textural properties of the investigated catalysts

Sample

Si/Al ratio

SBET

Mesopore diameter

m2/g

Mesopore volume cm3/g

nm

Micropore volume cmVg

gel product

Crystallinity

%

AlMeso100 AlMeso50 AlMeso20 ULZSM5-100

100

100

800

1.6

6.9

-

50

50

745

1.5

6.2

-

20

20

680

1.4

5.4

0.008

-

100

100

440

1.2

30

0.127

58.0

ULZSM-550 ULZSM-520

50

51

470

1.2

32.5

0.133

60.0

20

21

395

1.2

27.0

0.110

40.0

The final partially crystalline products were dried in air at 80°C and calcined at 55O°C for 6 h to remove organics. The effect of crystallization conditions on the mesopore structure as well as the crystalline phase has been obtained from nitrogen adsorption experiments, transmission electron micrograph (TEM)

537

images, and from XRD patterns. Textural characteristics of these catalysts are given in Table 1. Batch catalytic tests were performed by reacting oleic acid (lmmole) with ethanolamine (1 mmole) in the presence of 30mg catalyst in the range of temperatures (rt-180°C) with (octane) and without solvents. The experiments were carried out in 50 mL teflon-lined autoclave, under a vigorous stirring. ZSM-5 have been also tested as reference catalysts. Products were analyzed by GC-MS and FTIR. 3. Results and Discussion Figures 1 and 2 describe the acylation of oleic acid at different temperatures without solvent and in octane. Scheme 1 describes the reactions occurred. The presence of the catalyst enhances the reaction rate, and controls the selectivity. This is a good evidence of the participation of the acid sites in this reaction. CH3(CH2)7CH=CH (CH2)7COOH + H2NCH2CH2OH -> -> CH3(CH2)7CH=CH(CH2)7COHNCH2CH2OH + CH3(CH2)7CH=CH(CH2)7COOCH2CH2NH2 Scheme 1. Reactions occurring in acylation of oleic acid with ethanolamine

• RT/24h • 80 80 °C/24h °C/24h

°C/24h • 120 120°C/24h 180 °C/24h 180°C/24h

y ield , %

100 90 80 70 s? 60 2 50 '?. 40 30 20 10 10 0

n UL-20/ester UL-20/amide Al-20/ester Al-20/amide Blank/ester Blank/amide

catalyst/product Figure 1. Acylation of oleic acid with ethanolamine without solvent

Till 80°C, the predominant reaction is the temperatures higher than 80°C the acylation predominate, and the NH acylated compound product. In octane, the yields are smaller than

esterification of the OH. For of the NH2 group starts to becomes the most important in the absence of the solvents

538

(Figure 2). In the investigated series, UL-ZSM-5-20 was by far the best catalyst, indicating that textural characteristics should be well correlated with the acidity. By using ZSM-5, the yields in the acylated compounds were much smaller, which is in a good agreement with the accessible surface of these catalysts. 100 90 80 70 60 3 s 60 50 3 50 40 40 30 30 20 20 10 10 0

y ield , %

0RT/octane/24h RT/octane/24h • 80 80°C/octane/24h °C/octane/24h 120°C/octane/24h 120 °C/octane/24h • 120 120°C/octane/24h °C/octane/24h

1 UL-20/ester

UL- Al-20/ester Al-20/amide Blank/ester Blank/amide UL20/amide catalyst/product

Figure 2. Acylation of oleic acid with ethanol amine in octane

4. Conclusion Large mesoporous materials are very effective catalysts for acylation of large acids with aminoalcohols. Chemo- and regioselectivity was controlled via a strong correlation of temperature and solvent effects. Depending on the conditions, this study demonstrates that it is possible to produce under very green conditions surfactants in which either OH or NH2 are fully accessible. 5. References [1] J. D. Riedel, DE Pat 181175(1903); S.Yano et al., JP 63216852(1988) for Kao Corp., Japan. [2] M. Bouzouba, G. Leclerc, J. D. Ehrhardt and G. Andermann, Bull. Soc. Chim. Fr. (1985) 1230. [3] N. Kihara, J.-I. Shin, Y. Ohga and T. Takata, Chem. Lett. (2001) 592. [4] D. Trong-On and S. Kaliaguine, Angew. Chem. Int. Ed. 40 (2001) 3248.


539 539

Creating mesopores in ZSM-5 for improving catalytic cracking of hydrocarbons Yingxu Wei, Fuxiang Chang, Yanli He, Shuanghe Meng, Yue Yang, Yue Qi and Zhongmin Liu* Applied Catalysis Laboratory, Dalian Institute of Chemical Physics, Chinese Academy of Sciences, P. O. Box 110, Dalian, P R China 116023.

Alkaline treatment method was employed in preparing high efficient catalytic cracking catalyst. The crystalline structure, morphology and new porosity formation was evidenced by XRD, SEM and N2 adsorption. The n-hexane catalytic cracking were carried out over the two sample prepared with and without alkaline treatment. The enhanced conversion was attributed to the coexistence of mesoporous and microporous surface. 1. Introduction The light olefins, ethylene and propylene, are the most important base chemicals among the petrochemical products. The main commercial technique for light olefins production is steam cracking of naphtha, which is known as the first energy-consuming process in petrochemical industry. Development of alternative and highly efficient route, such as catalytic cracking, is attracting considerable interest. Usually the cracking feedstock from crude oil is in a large boiling range and the target products are small molecular, so ideal catalyst will combine the mesopores for reactant diffusion and micropores for high selectiviey of light olefins. In recent years, preparing hierarchical material, with meso- and micro-pores attracts the interest from material preparation and catalytic process development [1, 2]. One of the method for preparing this kind of material is post-treatment with alkaline solution. In the present study, mesopores were created in ZSM-5 zeolite catalyst by alkaline treatment. The prepared sample was employed as the catalyst for catalytic cracking of n-hexane.

540

2. Experimental Section 2.1. Catalyst preparation The ZSM-5 (Si/Al = 60) was added to an aqueous NaOH solution of 0.1 M and stirred for 1 h under 80°C. After filtering and drying, the obtained sample was ion-exchanged with NH4NO3 solution and then calcined at 550°C to form H form catalyst. The ZSM-5 catalysts without and with alkaline treatment were denoted as Cat-1 and Cat-2. 2.2. Catalyst characterization The crystallinity was analyzed by powder X-ray diffraction (RIGAKU D/max-rb powder diffractometer) with CuKa radiation. The chemical composition of the samples was determined with Bruker SRS-3400 XRF spectrometer. Scan electron microscope (SEM) images were obtained on a KYKY-1000 instrument operated at 25 kV. N2 adsorption properties were measured with Micrometric2010 physical adsorption instrument. 2.3. Catalytic performance evaluation A pulse reaction system was used for n-hexane catalytic transformation. The catalyst (60-80 mesh) of 23 mg was loaded in the quartz reactor of 3 mm i.d. and heated at 500°C in a flow of N2 for 1 h. The reaction was performed at 400°C. The n-hexane vapor (1.98g/h) was generated in a saturator and injected automatically into the reactor. The products were analyzed by on-line Varian 3800 chromatograph with capillary column of Pona. The data was processed with DHA software. CAT-2 3. Results and discussion The XRD patterns of the two samples are shown in Fig. 1. The position of the diffraction peaks of alkaline treated sample CAT-2 are identical to those of the sample without alkaline treatment, CAT-1. High intensity of XRD lines and no any baseline drift indicate high crystallinity even

6

10

20

30

40

50

60

2 Theta (degree)

Fig. 1 XRD patterns of Cat-1 and Cat-2

70

541

Cat-1

Cat-2 Fig. 2 SEM photos of two samples

after treatment. No evident crystalline changes occur with alkaline treatment. Comparing the SEM photos given in Fig. 2, CAT-1 presents very uniform morphology, while some small particles appear in the photo of CAT-2. Even no change observed for crystalline with MFI structure, the morphology is different. Some of the ZSM-5 particles in a few microns were broken to the submicronsized nanoparticles by the alkaline solution treatment. The N2-adsorption isotherms of the two samples are shown in Fig. 3. The amount increase of N2 adsorption on Cat-2 is observed. The hysteresis loop on its desorption isotherm indicates the existence of mesopores. Textural properties listed in Table 1 show that alkaline treatment leads to a clear increase in BET specific area and pore volume, and especially the increases are from the mesopore of the sample, while the surface area and pore 0.170volumn of micropores decrease r> 160to some extent. ..:*• E 150The effect of the coexistence |140of mesopores and micropores on ;,.»*»•• n-hexane catalytic transfor< 120 - • - Cat-1 mation was investigated. The - • - Cat-2 I nopulse reaction tests were carried 's J out at low temperature and very > 100r 9(1short contact time to show the 1.0 0.0 0.2 0.4 0.6 0.8 catalyst activity difference. The Relative pressure (P/P ) conversion and product yield are compared in Fig. 4. Prodominent Fig. 3 N2-adsorption isotherm of the two samples conversion increase can be 01

f

542

Conversion and yield (%)

12 observed for CAT-2. The BTX* BTX* conversion is 4.05% over C5+ 10 10C5+ CAT-1, while the value is • C4H10 8 11.09% for the sample with C4H8 6 alkaline treat-ment. The yield • C3H8 enhancement of light olefins, 4 C3H6 4C3H6 ethylene, propylene and C2H6 2 butenes is also observed. The C2H4 0 improved catalytic CH4 Cat-1 Cat-2 performance may stem from the increased active sites and Fig. 4 Catalytic performance of the two samples optimized pore structure for *BTX:Benzene+Tolene+Xylene mass transfer caused by mesopores creation. Beside the yield increase in light olefins, more alkanes (methane, ethane, propane and butane) also generate over CAT-2. This indicates that the mesopores creation and enhanced surface activity also favor the second reactions, such as oligomerization and H-transfer.

Table 1 Textural properties of the prepared catalysts Sample

SBET

c . '-'micro

V tota i

mico

(m /g)

(cm /g)

(cm3/g)

Cat-1

394

282

0.23

0.13

Cat-2

414

252

0.28

0.11

2

3

V v

(m /g)

2

4. Conclusion Alkaline treatment can create mesopores in ZSM-5 catalyst with inherent micropores. The catalyst prepared in this way keeps the crystalline structure of ZSM-5 and has higher specific area and pore volume. The coexistence of mesopores could greatly improve the catalytic acitivity in n-hexane cracking compared with the untreated ZSM-5 catalyst. The yield of light olefins and alkane increase at the same time with CAT-2 as catalyst. The newly formed porosity favored the reactant diffusion and conversion. No obvious selectivity improvement for light olefins could be observed. 5. References [1] T. Suzuki and T. Okuhara, Micropor. Mesopor. Mater. 43 (2001) 83. [2] L. Su, L. Liu, J. Zhuang, H. Wang, Y. Li, W. Shen, Y. Xu and X. Bao, Catal. Lett., 91 (2003) 155.


543 543

Effect of surfactant on the morphology of TiMMM-2 mixed-phase materials Sean M. Solberg, Dharmesh Kumar and Christopher C. Landry* The University of Vermont, Department of Chemistry, Burlington, VT 05405

This paper presents a study on the synthesis of Ti-MMM-2 (Ti-MCM-48/TS1) mixed-phase materials prepared by a one-pot method using different gemini surfactants and TPA+ ions. Powder XRD and 29Si MAS-NMR reveal that materials prepared using longer chain gemini surfactants such as 22-12-22 favored the formation of TS-1 more strongly than the shorter 16-12-16 surfactant. N2 physisorption data shows a decrease in surface area and pore volume and an increase in pore diameter as the surfactant chain length is increased. 1. Introduction Significant efforts have been made in the last few years to overcome the drawbacks of mesoporous materials, particularly with respect to improvements in the crystalline nature and catalytic properties of these materials. One approach has been to introduce zeolitic order within the walls of the mesoporous materials, thereby leading to the formation of "mixed-phase" materials, containing both microporous and mesoporous phases [1-3]. Recently, we published a report on Ti-MMM-2 mixed-phase materials, in which the TS-1 microphase was shown to form within the walls of mesoporous Ti-MCM-48 [4]. The research used a one-pot synthesis of Ti-MMM-2 using the gemini surfactant 18-12-18 as the structure-directing agent for theMCM-48mesophase. These mixed-phase materials exhibited better activity for oxidation of cyclohexene than either pure TS-1 or pure Ti-MCM-48. 2. Experimental Section In continuation of this work, we report here on a comparative study of the synthesis of Ti-MMM-2, using gemini surfactants with different alkyl tail chain

544

lengths, which leads to overall changes in the porous properties of the mesophase and in the extent of microphase formed. The Ti-MMM-2 samples with different gemini surfactants were prepared per our earlier reported procedure [4] holding the molar ratios of reaction components constant among the three materials. The samples were crystallized for 30 h at 150°C using the gemini surfactants 16-12-16, 18-12-18 and 22-12-22, which were synthesized according to an earlier report [5] The Ti-MMM-2 samples prepared using these surfactants are hereby referred to as Ti-MMM-2(16), Ti-MMM-2(18) and TiMMM-2(22). 3. Results and Discussion

(x4) \j

c

&

Figure 1: Powder XRD patterns of calcined TiMMM-2 samples that were crystallized for 30 h: (a) Ti-MMM-2(16), (b) Ti-MMM-2-(18), and (c) Ti-MMM-2(22).

(x4)

b 10 nm, but occurs in smaller mesopores. An important result is further that the density of the confined krypton phase at 87.3 K corresponds to the density of supercooled liquid krypton, which is important for applying krypton adsorption for pore size analysis. We used the results of our systematic krypton adsorption studies to develop a method for the characterization of thin micro/mesoporous silica films based on krypton adsorption at liquid argon temperature (87.3 K). This method allows determining the pore size distribution of thin films in the pore diameter range from < 1 to ~ 9 nm. 1. Introduction Thin mesoporous (silica) films have important applications in many fields {e.g., sensors and low-k dielectrics). Detailed knowledge of the pore size and pore volume is crucial in order to optimize the application of such thin films for instance as low k-materials in microelectronic applications. However, the pore size analysis of such films is difficult, also because convenient methods such as nitrogen and argon adsorption at 77.4 and 87.3 K [1, 2] cannot be easily applied for the pore size analysis of thin films. Such films are only a couple of hundred nanometers thick (~ 100 - 900 nm), and the application of nitrogen and argon adsorption at 77.4 and 87.3 K, respectively, is (because of the high saturation pressure of 760 Torr) not sensitive enough to detect the small pressure changes

552

due to adsorption on thin films (deposited for instance on a Si wafer). Krypton adsorption provides in principle an alternative because krypton has very low saturation pressures at liquid nitrogen (77.4 K) and liquid argon temperature (87.3 K), i.e. 1.6 Torr and 13 Torr, respectively (these saturation pressures refer to solid krypton). Until now however, krypton adsorption has not been routinely used for pore size analysis at these temperatures because the sorption and phase behavior of krypton far below its triple point temperature (115.8 K) is still under investigation. Methods for pore size analysis based on the Kelvin equation (e.g., BJH approach) cannot be applied here, and the study of krypton adsorption by approaches based on statistical mechanics (such as nonlocal density functional theory (NLDFT) and molecular simulation) is still under development [4]. Hence, in order to address these problems we have performed systematic krypton adsorption experiments on selected zeolites and mesoporous silica molecular sieves (e.g., MCM-41, MCM-48 [2], SBA-15). This allowed us to study the effect of confinement on the sorption and phase behavior of krypton below its triple point temperature, and to use the set of krypton adsorption data to develop a procedure applicable for the pore size analysis of thin mesoporous films by krypton adsorption at 87.3 K [3]. 2. Results and Discussion The experimental adsorption studies of krypton at 87.3 K on micro and mesoporous molecular sieves revealed that pore filling (condensation) cannot be observed anymore in those cases the pore diameter exceeds ~ 9 nm, which reflects the upper limit of the application range of krypton for mesopore analysis [3]. However, for pore sizes below this threshold we observe pore condensation and hysteresis. Further, we suggest a novel method for the pore size analysis of thin films which is based on the development of a specific calibration curve at liquid argon temperature, 87.3 K. Liquid argon temperature is used rather than 77 K (liquid N2), because of two main considerations: (i) The available total pressure range for the adsorption experiments (before solidification of krypton occurs) extends up to -13 Torr, instead of only 1.6 Torr at 77.4 K. This increase in available pressure range makes it possible to resolve even microporosity (down to < 1 nm), [3b] with a sorption apparatus suitably equipped with turbomolecular pump and corresponding low-pressure transducers); (ii) There is evidence that within the mesopore diameter range from 2 - 9 nm both capillary condensation and solidification can occur as a function of pore size at 77.4 K, but it appears that at 87.3 K only gas-liquid phase transitions are observed up to a pore diameter of ~ 9 nm. Hence, contrary to the situation at 77.4 where the adsorbate density may depend on the pore size, the state of the adsorbed krypton phase is better defined at 87.3 K. The density of the confined krypton phase at 87.3 K could be calculated from our experimental data (i.e., 2.6 ± 0.1 g/cm3) and corresponds to the density of supercooled liquid krypton [3b]. A supercooled liquid krypton state at 87.3 K

553

was also found in very recent molecular simulations of krypton adsorption [4] in MCM-41 like systems, and in experimental studies on freezing and melting of krypton in MCM-41 silica [5]. This is a prerequisite in order to obtain a clearly defined relationship between pore filling pressure and pore size, and to determine the pore volume of a material from krypton adsorption data. The unique krypton calibration curve (i.e. the relation between the pore filling pressure of krypton at 87.3 K and the pore size) for pore size analysis of thin films of mesoporous silica of pore sizes between 2 and 10 nm is based on the following: (a) Krypton reference adsorption isotherms measured at liquid argon temperature (87.3 K) in highly ordered mesoporous molecular sieves of defined pore size and geometry (such as MCM-41, SBA-15, MCM-48, covering the pore diameter range from 2 - 1 0 nm. (b) Pore sizes and pore volumes of these mesoporous molecular sieves were obtained by applying Non-Local Density Functional Theory (NLDFT, which is considered to be the most accurate method currently available for pore size analysis), to nitrogen (at 77.4 K) and argon (at 87.3 K) sorption isotherms, which were measured on the same mesoporous molecular sieves used for obtaining the krypton reference isotherms. 300

0.625

Silica film450 mthick RUN 1 (ads) Silicafilm450mthickRUN1(ads) SilicaFilm, 450nmthick, RUN2(ads/des) Silica Film, 450 nmthick, RUN 2 (ads/des)

180

120

60

0

0

t \

0.502 0.502

Dv(logd) [cm3 g-1]

Volume [cm3 g-1 STP

240

•

0.256 0.256

0.133

0.2

0.4

0.6 P/P0

0.8

1

i

0.379

0.01

\ \

•J\

15

\

\

25

35

45

55 65 75 55 65 75 Pore Diam eter [Å] Diameter

85

95 95

105 105

Fig 1 (a) Plot of two krypton (87.3 K) sorption isotherms measured on a thin mesoporous silica film sample (thickness 400 nm, structure directing agent: Brij30), which was deposited on a Si wafer (b) Pore size distribution curve obtained from the krypton adsorption data shown in Fig l(a) by applying the new method.

Hence, pore sizes obtained for thin mesoporous silica films by applying this unique krypton calibration curve are traceable to NLDFT pore size analysis [3]. The novel krypton adsorption method at 87 K has been applied for the pore size analysis of thin ordered mesoporous silica films deposited on a Si wafer (see Fig. 1), which were synthesized as described in ref. [6]. In order to reveal details of the low pressure range of the krypton isotherm, we display in Fig.2 the isotherm data of Fig. la in form of a semi-logarithmic plot.

554 300

Silica film 450 m thick R U N 11 (A d s) RUN (Ads) Silica film 450 nm thick R U N 2 (A ds/D es) RUN (Ads/Des)

Volume [cm3 g-1 STP

240

180

120 I 120 S

I

60

60 0

-4 10 10-4

5

10 -3

5

10 -2 P/P 0

5

10 -1

5

10 0

Fig. 2 Semi-logarithmic plot of the krypton adsorption isotherm at 87.3 K shown in Figure l(a). (The steep increase in the adsorption isotherm at P/Po = 1 indicates sublimation of the bulk fluid)

Fig. 2 clearly shows that krypton adsorption at 87.3 K can be measured over a wide relative pressure range from below 10'5 up to 1. This demonstrates the potential of krypton adsorption at 87.3 K to assess micro- and mesoporosity in thin silica films. 3. References [1] M. Thommes, In: Nanoporous Materials Science and Engineering (edited by Max Lu and X. S. Zhao), World Scientific, 11 (2004) 317. [2] M. Thommes, R. Kohn and M. Froba, J. Phys. Chem. B 104 (2000) 7932. [3] (a) M. Thommes, E-MRS 2005 spring meeting, Symposium E, Poster PI-45; (b) M. Thommes et al, manuscript in preparation, (2006). [4] F. Hung, B. Coasne, K. Gubbins, F. Siperstein, M. Thommes and M. Sliwinska-Barkowiak, Studies in Surface Science and Catalysis, in press (2006). [5] K. Morishige, K. Kawano and T. Hayashigi, J. Phys. Chem. B 104(2000) 102898. [6] Y Oku, N. Nishiyama, S. Tanaka, K. Ueyama, N. Hata and T. Kikkawa, Mater. Res. Soc Symp. Proc716 (2002)587.

Mesostructured Materials Recent Progress in Mesostructured D. Zhao, S. Qiu, Y. Tang and C. Yu (Editors) © 2007 Published by Elsevier B.V.

555 555

Dynamics of xenon adsorbed in organically modified silica thin films using hyperpolarized 129 Xe 2D- exchange NMR M. Nader3, F. Guenneau3, C. Boissiereb, D. Grossob, C. Sanchezb and A.Gedeon3* "Laboratoire Systemes Interfaciaux a I'Echelle Nanometrique, CNRS-UMR 7142, Universite Pierre et Marie Curie, case 196, 4 place Jussieu, 75252 Paris cedex 05, France h LaboratoireChimie de la Matiere Condensee, CNRS-UMR 7574, Universite Pierre et Marie Curie, case 174, 4 place Jussieu, 75252 Paris cedex 05, France

Mesoporous silica thin films having 2D-hexagonal (p6m), 3D-hexagonal (P63/mmc) and 3D-cubic (Pm3n) structures were prepared via the sol-gel chemistry process using CTAB as surfactants. 2D exchange 129Xe spectroscopy (EXSY) of hyperpolarized (HP) xenon has been performed to probe the geometry of pores in organically modified siliceous thin films and to obtain exchange pathways and rates of xenon mobility between different zones. 1. Introduction 129

Xe NMR has been widely used for the characterization of nanometer-scale void spaces in solids, such as zeolites and clathrates [1]. It has been also applied for studies of mesoporous silicas, silica glasses and more recently for purely siliceous thin films [2]. Hyperpolarized (HP) xenon produced by optical pumping methods can attain spin polarizations 104 times larger than thermal ones and greatly facilitate the applications of xenon for the characterization of porous materials. In this study we report the first use of 2D exchange I29Xe spectroscopy (EXSY) of hyperpolarized (HP) xenon to probe the geometry of pores in organically modified siliceous thin films and to obtain exchange pathways and rates of xenon mobility between different zones.

556

2. Experimental Section The mesoporous silica thin films having 2D-hexagonal (p6m), 3D-hexagonal (P63/mmc) and 3D-cubic (Pm3n) structures were prepared via the sol-gel chemistry process using CTAB as surfactants. The thin films were deposited on a glass substrate via the dip-coating method. While the substrate was withdrawn, evaporation took place leading to a self assembly-condensation process. Thus, once the pure silica films are formed and consolidated at 130°C for 48 h in air, they were calcined at 450°C in order to eliminate the template and to form free silanols. After the 450°C thermal treatment, the films were transferred to a receptacle containing the organic function: (2-phenylethyl) trimethoxysilane (2 g, commercial product) dissolved in anhydrous toluene (20 g, commercial product), which will be closed and kept at 60°C for 24 h. In order to eliminate anhydrous toluene, a final washing of films by absolute ethanol is performed. 3. Results and Discussion 129

Xe 2D EXSY experiments allow determining whether exchange occurred between these different regions and how fast these exchange processes might be

PL (ppm)

(ppm)

8

8

16 16

16 16

24 (ppm)

160 160 120 120 80 80 40

0

Fig. 1: EXSY spectrum of 129Xe on phenyl SiO2 thin film (0.1) with mixing time at 1 ms.

24 (ppm)

160 120 120 80 40 160

0

Fig. 2: EXSY spectrum of 129Xe on phenyl SiO2 thin film (0.1) with mixing time at 10 ms.

In 2D-EXSY experiments, the exchange between regions with different chemical shifts manifests itself in the appearance of cross-peaks between the signals from the sites in exchange. Figure 1 shows the 2D spectra of phenyl grafted SiO2 thin film with loading at 0.1 using an exchange time tm of 1 ms. As expected, the signals appear only

557

on the main diagonal. Off-diagonal intensities, however, appear at 10 ms and become quite pronounced with tm > 10 ms (Fig. 2). The 2D EXSY spectra show that on a time scale of a few milliseconds there is exchange between all the adsorption regions and xenon in the gas phase. Fig. 3 shows the 2D spectra at T = 555 K for high SiO2 film with high phenyl loading (1.5) using an exchange time (/m) of 0.1 ms, respectively. The observed three diagonal peaks at ca. 0, 120, and 160 ppm are assigned to gaseous Xe, mobile Xe adsorbed in the mesopores, and Xe residing in the organic phase, respectively. In addition, the off-diagonal peaks intensified with increasing exchange times set in the experimental pulse sequence. Traces of cross peaks appeared at tm = 0.1 ms indicating that the exchange between the mobile (87 ppm) and gaseous (0 ppm) Xe occurred even on a time scale less than a fraction of 1 ms. As tm is increased to 5 ms, wherein such exchange became more pronounced, the exchange between mobile Xe adsorbed in the mesopores and Xe in the organic phase (98 ppm) began to take place. Eventually, the exchange between the organic phase and the gaseous Xe was also evident with tm = 100 ms, indicating that the exchange between Xe species in different adsorption regions and the gas phase appeared to be completed. Consequently, the observed evolution with 8 clearly indicates a hierarchical set of exchange processes. The exchange of Xe gas follows the sequence (from fastest to slowest): mesopores with free gas, mobile Xe in the mesopores and Xe residing in the organic free gas with -160 micropores, and finally, among (ppm) 120 40 gaseous- mobile Xe and gaseousorganic phase. Experiments carried out Fig. 3: EXSY spectrum of l29Xe on phenyl SiO 2 on SiO2 film with different structures at thin film (1.5) with mixing time at 0.1 ms. different phenyl loadings will be discussed. Exchange pathways and rates of xenon mobility between different zones are obtained. 4. Conclusion 129

Xe NMR has been applied for studies of purely and modified siliceous thin films mesoporous silicas. In this study we have shown for the first time that 2D exchange ' 9Xe spectroscopy (EXSY) of hyperpolarized (HP) xenon can be used to probe the geometry of pores to obtain exchange pathways and rates of xenon mobility between different zones.

558

5. References [1] a) T. Ito and J. Fraissard, Chem. Phys. Lett., 136 (1987) 314; b) J. Ripmeester and C. Ratcliffe, J. Phys. Chem. 94 (1990) 7652. [2] A. Nossov, E. Haddad, F. Guenneau, C. Mignon, A. Gede'on, D. Grosso, F. Babonneau, C. Bonhomme and C. Sanchez, Chem. Comm. (2002) 2476. [3] a) I. L. Moudrakovski, C. I. Ratcliffe and J. A. Ripmeester, Appl. Magn. Reson., 8 (1995) 385. b) K. Knagge, J. R. Smith, L. J. Smith, J. Buriak and D. Raftery, Solid State NMR 29 (2006) 85.

Progress in in Mesostructured Materials Recent Progress S. Qiu, Y. Tang and C. Yu (Editors) (Editors) D. Zhao, S. © 2007 2007 Published Published by Elsevier Elsevier B.V. B.V.

559 559

Nanocrystal-micelle: a new building block for facile self-assembly and integration of 2, 3-dimensional functional nanostructures Hongyou Fan1a,b* "Sandia National laboratories, Albuquerque, NM87106, USA Department of Chemical and Nuclearing Engineering, The University of New Mexico, Albuquerque, USA. h

1. Introduction Self-assembly has been testified to be one of the powerful and efficient methods to the synthesis of complex functional nanomaterials with precisely controlled dimension, function, and topology [1, 2]. Its combination with lithography and pattern techniques is an ideal tool kit that allows fabrication and integration of nanomaterial platforms providing functions and forms at multiple scales and locations, which emulates nature complex systems [3, 4]. Here I present our recent series of work on the synthesis of a new building block, NCmicelle and its use for further self-assembly and integration of 2, 3-D functional nanostructures [6-10]. 2. Results and Discussion Our concept is to consider monosized, organically-passivated NCs as large hydrophobic molecules that, if incorporated individually into the hydrophobic interiors of surfactant micelles, would result in the formation of monosized NC micelles composed of a metallic (or other) NC core and a hybrid bilayer shell with precisely defined primary and secondary layer thicknesses (see Fig. 1H). The hydrophilic NC micelle surfaces provide water-solubility and allow further assembly or derivatization as depicted in Fig. 1. The formation and stability of individual gold NC-micelles (as opposed to aggregated dimers, trimers etc.) was confirmed by ultraviolet/visible spectroscopy and TEM (Fig. ID), where we observed no difference between the positions and widths of the plasmon resonance bands (~ 510-nm) of the C12-alkanethiol stabilized gold NCs in

560 Biospecies tagging

Spin-coating

Films and devices fabrications

Fig 1. Schematic diagram for the synthesis of water-soluble gold nanocrystal-micelles and periodically ordered gold NC/silica superlattices.

chloroform and those of the corresponding water soluble NC-micelles. In addition, evaporation of the NC-micelle solutions resulted in self-assembly of hexagonally ordered NC arrays (Fig.lC) as expected for individual, monosized nanocrystals. Judging from UV/visible spectroscopy and TEM and the ability to make ordered arrays, these solutions were stable for over two years at room temperature. Formation of ordered gold NC/silica thin films is analog to that of selfassembly of surfactant and silica. Charge interaction and hydrogen bonding between hydrolyzed silica Fig 2. Representative transmission electron microscope (TEM) images of gold nanocrystal/silica superlattices. (A) [100] orientations of bulk samples prepared according to pathway i-ii-iii (Fig 1). Inset (al): high resolution TEM of sample (A) showing gold NC lattice fringes. Inset (a2): selected area diffraction pattern from the image in (A). (B) well-shaped superlattice solids. (C) Optical image of ordered gold NC/silica thin film spin-coated on glass. (D) TEM image of [21 l]-oriented NC/silica superlattice film. Inset (d) selected area diffraction pattern from image in (D). (E) Hierarchically ordered superlattice crystals on glass. (F) Patterned ordered gold NC/silica films through umolding.

561 561

and surfactant head groups on NC-micelle surface drive the formation of ordered gold NC/silica mesophase. However, the two systems exhibit distinct tendency to form mesostructures. Prior work on self-assembly of pure surfactant and silica indicated that a series of mesostructures can be formed including lamellar, 1-d hexagonal, cubic, and 3-d hexagonal periodic symmetries. In the case of self-assembly of NC-micelles and silica, only fee mesostructure are preferentially formed regardless of basic and acidic catalytic conditions. This is probably due to the fact that the gold NC-micelles are pre-formed in a homogeneous solution and behave rather like a "hard" sphere tending to form fee close packing than "soft" pure surfactant micelles that incline to undergo phase transformation. Vital to the formation of transparent, ordered gold NC/silica superlattice films is the use of stable and homogeneous spinning or casting solution that upon evaporation of water undergoes self-assembly of NCmicelles and soluble silica. For this purpose, we prepared oligomeric silica sols in NC-micelle aqueous solution at a low hydronium ion concentration (pH~2) designed to minimize the siloxane condensation rate, thereby enabling facile silica and NC-micelle self-assembly during spin-coating or casting. The aging experiments (Fig. 3, Cl to C5) unambiguously demonstrate that extensive silica condensation, that results in polymeric silica species, does not favor the selfassembly, leading to a less (111)

Fig. 3. A. Low-resolution scanning electron microscope (SEM) micrograph of ordered gold NC/silica superlattice thin film. B. Highresolution SEM from same specimen in A. C. cs XRD patterns of gold NC/silica superlattice films. Cl. Ordered gold/silica film prepared using a coating solution that was aged at ambient condition for 24 hours, and C2 for 5 hours. C3. Ordered gold/silica film prepared C3 using a coating solution without aging. C4. Ordered gold/silsesquioxane film prepared using a solution that was aged at ambient condition for 24 hours. C5. Ordered C1 gold/silsesquioxane film prepared using a 2 4 6 8 10 Two theta (degrees) solution without aging.

V

ordered film. In addition to silica, we have demonstrated the synthesis of ordered gold NC arrays inside organo-silsesquioxane framework. The ordered gold NC/ silsesquioxane was prepared by using ~3-nm DM-stabilizedgold NCs, CTAB, and BTEE. The corresponding XRD patterns (Fig. 3-C4&5) reveal that films exhibit ordered fee mesostructure. In addition, we observed from XRD results that the self-assembly when using BTEE is not strongly affected by solution aging unlike that when using TEOS. This is due to that organo-bridged

562

precursor has relatively slower hydrolysis and condensation rate than TEOS. The ability to form patterned films is essential for device fabrication. We have demonstrated the formation of patterned gold NC/silica superlattice films based on our previous work on patterning surfactant templated silica mesophases. Figure 2f shows the patterned stripes and dots containing ordered gold NC/silica superlattice fabricated using (i-molding techniques. The pattern sizes are determined by the feature sizes of the PDMS stamps 3. Conclusion The uniform The formation of water soluble NC micelles and their selfassembly into ordered 3D mesophases provides a new means to integrate model 3D NC arrays into robust devices. The arrays provide the ideal media for the study of the variety of transport and collective phenomena predicted to occur for such systems). Beyond transport, these robust, highly ordered NC arrays could be useful for catalysts and photonic devices such as lasers, and the watersoluble NC micelle intermediates have shown promise for biological labeling or sensors. 4. References [1] [2] [3] [4] [5] [6] [7] [8] [9] [10]

Y. N. Xia and G. M. Whitesides, Ann. Rev. Mater. Sci., 28 (1998) 153. N. B. Bowden, M. Week, I. S. Choi and G. M. Whitesides, Ace. Chem. Res., 34 (2001) 231. P. D. Yang et al., Science, 287 (2000) 465. H. Y. Fan, Y. Lu, A. Stump, S. T. Scott, T. Baer, R. Schunk, V. Perez-luna, G. P. Lopex and C. J. Brinker, Nature, 405 (2000) 56. H. Y. Fan, K. Yang, D. M. Boye, T. Sigmon, K. J. Malloy, H. Xu and C. J. Brinker, Science, 304 (2004) 567. H. Y. Fan, A. Wright, J. Gabaldon, A. Rodriguez, C. J. Brinker and Y. B. Jiang, Adv. Func. Mater. 16(2006)891. H. Y. Fan, E. W. Leve, C. Scullin, J. Gbaldon, D. Tallant, S. Bunge, T. Boyle, M. C. Wilson and C. J. Brinker, Nano Lett. 5 (2005) 645. H. Y. Fan, E. Leve, J. Gabaldon, A. Wright, R. E. Haddad and C. J. Brinker, Adv. Mater. 17(2005)2587. H. Y. Fan, Z. Chen, C. Brinker, J. Clawson and T. Alam, J. Am. Chem. Soc. 127, (2005) 13746. H. Y. Fan, J. Gbaldon, C. J. Brinker and Y. B. Jiang, Chem. Commun. 22 (2006) 2323.


563 563

Direct visualization of mesoporous structures in the framework of SBA-15 mesoporous films Jinlou Gua>b, Hangrong Chen b , Xiongping Dong b , Zhicheng Liu b and Jianlin Shi b

"Department of Chemical System Engineering, The University of Tokyo, 7-3-1 Hongo, Bunkyo-ku, Tokyo, 113-8654, Japan. b State Key Lab of High Performance Ceramics and Superfine Microstructure, Shanghai Institute of Ceramics, Chinese Academy of Science, Shanghai 200050, China.

Two separated experiment methods including electroless deposition and pulse electrochemical deposition were employed to incorporate high-density gold and platinum nanowire arrays into the pore channels of mesoporous thin films (MTFs). The incorporated metallic nanowires served as the inverse replicas to determine directly the structure properties of the SBA-15 mesoporous films. Both experiments support on the facts that the presence of mesopores structure rather than micropores in the framework of SBA-15 MTFs. 1. Introduction SBA-15 mesoporous silica, in the form of powder or films, has attracted much attention due to its current and potential applications [1,2]. This remarkable interest stems from the many desire features of SBA-15, including appealing textural properties, high surface area and appreciable thermal and hydrothermal stability [3,4]. Despite all this interest in the synthesis, modification and application of SBA-15, the very structure identification of this material was largely uncertain until recently [5-7]. The consensus was come to that the large uniform ordered pores of SBA-15 channels were actually accompanied by the smaller disordered pores that provided connectivity between adjacent large pore channels [8-10]. In the past few years, several attempts have been made to control directly the inter-connecting porosity since such control is particularly desirable for applications involving host-guest interactions and diffusion process [11-13]. High temperature hydrothermal treatment, even introducing TMB into embryo mesostructure, was employed by Zhao et al. [12] to generate three dimensional large-pore mesoporous networks.

564

The pore size and microporosity within the pore walls of ordered mesoporous silica SBA-15 could also be tuned by means of salt addition under microwave hydrothermal conditions [13]. Recently, Ryoo et al. [11,14] efficiently controlled the porous network connectivity of SBA-15 through optimizing synthesis conditions, such as synthesis temperature or TEOS/surfactant ratio. However, these investigations were mainly focused on mesoporous powder while few efforts were about, needless to say the control of, the structural properties of SBA-15 MTFs [15, 16]. Herein, we employed gold and platinum replicas, prepared by electroless deposition (ELD) and pulse electrochemical deposition (PED) methods, respectively, to directly visualize the mesoporous structures in the framework of MTFs. 2. Experimental Section 2.1. The procedure for the preparation of MTFs The MTFs were prepared as our recent reports [17]. Specifically, 7.68 mLof tetraethyl orthosilicate (TEOS, 98% Aldrich) were prehydrolyzed in a solution containing 3.71 g of dilute hydrochloric acid (PH~2, isoelectric point of silica) and 10 mL of THF under vigorous stirring at room temperature. Following 120 minutes of stirring, this prehydrolyzed silica solution was mixed with a solution containing 1.78 g of the poly (ethylene-oxide)-poly(propylene oxide)-poly (ethylene-oxide) block copolymer EO20PO70EO20 (Pluronic PI23, BASF) dissolved in 30 mL of THF. The two solutions were further stirred for 15 minutes. From this mixture with a final molar composition of TEOS : PI23 : H2O : HC1 : THF = 1 : 0.0094 : 5 : 0.0090 : 25, thin films were prepared by dip-coating onto cleaned glass slides at 75 mm min'1. The films were stored at room temperature for 24 hours and then extracted using ethanol with a little HC1 being added under refluxed condition to remove the surfactant. 2.2. The procedure of ELD Highly dispersed palladium nanoparticles within the pore channels of the MTFs were prepared as our previous work [18]. These Pd nanoparticles will serve as catalysis centers for the following ELD of gold nanowires. As-prepared Pd loaded MTFs were immersed into gold electroless plating bath [19] for 1-1.5 min. to obtain gold nanowires loaded MTFs. The silica template was removed by dropping 2% HF on the films. The template removal was confirmed by energy dispersive spectroscopy (EDS, not shown). In order to observe the nanobridges directly, sonic dispersion was used to obtain separated nanowires.

565

2.3. The procedure ofPED The PED was performed using a conventional three-electrode system in a glass cell with a mesoporous silica coated conductive glass slide as the working electrode, Pt wire as a counterelectrode and Ag/AgCl as a reference electrode [20]. Square wave pulses were applied with a duty cycle of 0.25, i.e.cathodic pulse time ton of 300 ms and time between pulses tOff of 900 ms based on our trial and error experiments. The deposited silica/platinum composite films were annealed at 400°C in a nitrogen atmosphere for at least 2 hours to enhance their structural strength and adhere more strongly to the conductive glass substrates. The silica template was removed by submersing the films in a 2M NaOH at 60 °C followed by rinsing with water. 3. Results and Discussion In the procedure of evaporation induced self-assembly [2, 21] to dip-coat the MTFs, PI23 surfactant enriches by solvent evaporation to exceed critical micelle concentration and therefore develops mesophases only during the last few seconds of film deposition, which suggests that the formation of films is very fast in kinetical conditions [22]. The inherent hydrophilic poly (ethyleneoxide) (PEO) blocks of the template are expected to be deeply occluded within the silica walls during the quick gelation of silica matrix and have limited time

Fig. 1 (a) TEM image of unsupported gold nanowires by removal of silica matrix with 2% HF aqueous solution. The arrows highlight the bridges between the nanowires. (b) The enlarged image of ellipse portion of image a.

566

to redistribute from silica framework to the region adjacent to the cores of micelles [23]. Thus, the calcined MTFs are likely to exhibit complementary pores in the parts of the framework where once the EO blocks are located [2]. In addition, the temperature used in the synthesis of MTFs is generally at room temperature [17, 24], which means EO blocks are substantially restrict in the silica framework since the degree of hydration of the EO blocks dramatically increases at low temperature [23]. Both of above mean MTFs may have the different structure from that of the SBA-15 powder. Firstly, high density gold nanowires as replicas were synthesized using our previous electroless deposition route [19] to determine directly the structure properties of MTFs. Fig. 1. shows the structure and morphology of unsupported nanowires after the silica film matrix is removed by 2% HF solution followed with sonic dispersion. The bridges between the two nanowires can be clearly seen as highlighted by arrows in the Fig. lb, which is the reflection of interconnections between pore channels in MTFs. This indicates that the synthesized gold nanowires are the replicas of the pore structure of the MTFs and we are able to detect defects and other structure variables within the channels. However, as enlarged in fig. lb, we find that the width of bridge is about 6 nm almost identical to the diameter of pore channels, which indicates IInt nteensity nsity ((a.u.) a.u.)

100

i

1

c

a

A 200 x10

B 22

3 3

2 θ (degree) 2θ (degree)

4

5

•b

in

/

m _

NUKE

SEI

•ft 2 •*<sa z? Lin

m K 28nT

Fig. 2 (a) XRD patterns of mesoporous silica/ metal composite films before (A) and after (B) removal of the silica template, (b) SEM top-view image of platinum nanowire arrays after the removal the silica, (c) TEM image of a bundle of platinum nanowires and the corresponding selected area diffraction.

567 567

the presence of mesopores rather than micropores in the framework of silica as SBA-15 powder demonstrated [4-10]. Since the deposited nanowires have no adhesion to the glass substrate, we could not characterize the ordered properties of synthesized nano arrays, thus a PED method as our previous reported [20] was also utilized to prepare high-density platinum nanowire arrays to confirm the structure properties. Fig. 2a shows the XRD patterns of a silica/platinum thin film before (A) and after (B) removal of the silica template by 2M NaOH. It should be point out that trace B in fig. 2a could only be obtained after the composite films were annealed at 400 °C for at least two hours to enhance their structural strength and adhere more strongly to the conductive glass substrates. Curve A shows the typical one dimensional hexagonal pattern with an intense (100) diffraction peak at 20=1.57 degree and relatively week (200) peak at 20=3.02 degree. Although the silica matrix is removed by NaOH, the ordered structure could be maintained from XRD patterns in curve B. The peak at ca. 20=1.6 degree, with slight broadened width and decreased strength, not only shows the synthesized nanowires had formed the arrays but also indicates the connectivity between the adjacent nanowires [15,20]. In fact, the top-view SEM image after the removal of silica, as shown in fig. 2b clearly shows the parallel nanowire arrays spread across the whole film plane. It is reasonable to conclude that both XRD and SEM show the presence of the connectivity between the adjacent nanowires, otherwise, these nanowires could not form the nanoarrays as reported for MCM-41 [21], which consisted of separated continuous walls. After the silica template was removed, large quantity of nanowire bundles were observed when we employed TEM to visualize directly the size of connectivity again. Fig 2c shows a bundle of self-standing platinum nanowires. This large bundle of parallel nanowires is of the uniform diameters consistent with the size of the ordered pores of SBA-15, and separated by the repeating distance corresponding to the silica framework in the structure of SBA-15 mesoporous porous films. If there is no connectivity between the adjacent nanowires, it is impossible to obtain so uniform repeating distance. As highlighted by the arrows in fig 2c, the bridges in the size range of 6-7 nm could be clearly seen again. These results further indicated that mesoporous rather than microporous voids were present in the framework of SBA-15 MTFs. 4. Conclusion Through the reverse replications of high density gold and platinum nanowire arrays, mesoporous structures in the framework of SBA-15 MTFs were visualized directly. This new finding of pore-pore communication by randomly distributional mesopores rather than micropors is very important in the fields of microreactors and sensors etc. wherein the diffusion is decisive to its success.

568

5. Acknowledgment The work was supported by National Natural Science Foundation of China, Grant No. 50232050 and Shanghai Special Project, Grant No.03DJ 14004. 6. References [1] D. Zhao, J. Feng, Q. Huo, N. Melosh, G. H. Frederickson, B. F. Chmelka and G. D. Stucky, Science, 279 (1998) 548. [2] D. Zhao, P.Yang, N. Melosh, J. Feng, B. F. Chmelka and G. D. Stucky, Adv. Mater., 10 (1998) 1380. [3] S. Andreas, Adv. Mater., 15 (2003) 763. [4] J. L. Gu, L. M. Xiong, J. L. Shi, Z. L. Hua, L. X. Zhang and L. Li, J. Solid State. Chem., 179(2006)1060. [5] W. Lukens, Jr., P. Schmidt-Winkel, D. Zhao, J. Feng and G. D. Stucky, Langmuir, 15 (1999) 5403. [6] R. Ryoo, C. H. Ko, M. Kruk, V. Antochshuk and M. Jaroniec, J. Phys. Chem. B, 104 (2000) 11465. [7] M. Imperor-Clerck, P. Davidson and A. Davidson, J. Am. Chem. Soc, 122 (2000) 11925. [8] K. Miyazawa and S. Inagaki, Chem. Commun., (2000) 2121. [9] P. L. Ravikovitch and A. V. Neimark, J. Phys. Chem. B, 105 (2001) 6817. [10] S. Jun, S. H. Joo, R. Ryoo, M. Kruk, M. Jaroniec, Z. Liu, T. Ohsuna and O. Terasaki, J. Am. Chem. Soc, 122 (2000) 10712. [11] H. J. Shin, R. Ryoo, M. Kruk and M. Jaroniec, Chem. Commun., (2001) 349. [12] J. Fan, C. Yu, L. Wang, B. Tu, D. Zhao, Y. Sakamoto and O. Terasaki, J. Am. Chem. Soc, 123(2001)12113. [13] J. R. Matos, L. P. Mercuri, M. Kruk and M. Jaroniec, Chem. Mater., 13 (2001) 1726. [14] M.Choi, W. Heo, F. Kleitz and R. Ryoo, Chem. Commun., (2003) 1340. [15] D. H. Wang, W. L. Zhou, B. F. McCaughy, J. E. Hampsey, X. L. Ji, Y. B. Jiang, H. F. Xu, J. K. Tang, R. H. Schmehl, C. O'Connor, C. J. Brinker and Y. F. Lu, Adv. Mater., 15(2003) 130. [16] M. P. Tate, B. W. Eggiman, J. D. Kowalski, and H. W. Hillhouse, Langmuir, 21 (2005) 10112. [17] J. L. Gu, G. J. You, J. L. Shi, L. M. Xiong, S. X. Qiang, Z. L. Hua and H. R. Chen, Adv. Mater., 17 (2005) 557. [18] J. L. Gu, J. L. Shi, L. M. Xiong, H. R. Chen and M. L. Ruan, Micro. Meso. Mater., 74 (2004) 199. [19] J. Gu, J. Shi, L. Xiong, W. Shen, M. Ruan, Y. Zhu and J. Liang, Solid State Sci., 7(2004) 747. [20] J. Gu, J. Shi, H. Chen, L. Xiong, W. Shen and M. L. Ruan, Chem. Lett., 33 (2004) 828. [21] Y. Lu, R. Gangull, C. A. Drewlen, M. T. Anderson, C. J. Brinker, W. Gong, Y. Guo, B. Dunn, M. H. Huang and J. I. Zink, Nature, 389 (1997) 364. [22] S. Besson, C. Ricollean, T. Gacion, C. Jacquiod and J. P. Boilot. J. Phys. Chem. B, 104 (2000) 12095. [23] G. S. Christine, Current Opinion in Colloid and Interface Science, 7 (2002) 173. [24] P. C. A Alberius, K. L. Frindell, R. C. Hayward, E. J. Kramer, G. D. Stucky and B. F. Chmelka, Chem. Mater., 14 (2002) 3284.


569 569

Preparation, texture and electrochemical properties of TiO2 films with highly ordered mesoporosity and controlled crystallinity D. Fattakhova Rohlfing,3 M. Wark,a J. Rathousky,b T. Brezesinski0 and B. Smarsly0 "Institute of Physical Chemistry and Electrochemistry, University Hannover, Callin Str. 3-3a, D-30167 Hanover, Germany h Academy of Sciences of the Czech Republic, J. Heyrovsky Institute of Physical Chemistry, Dolejskova 3, 18223 Prague, Czech Republic c Max Planck Institute of Colloids and Interfaces, 14 424 Potsdam, Germany

1. Introduction Mesoporous layers of TiO2 attract great attention owing to important applications in photocatalysis, solar cells, sensors and displays due to their large surface area, excellent accessibility of the inner surface and suitable morphological form in comparison with powders. A recently developed generalized procedure for the preparation of layers of mesoporous metal oxides is based on a mechanism combining block copolymer self-assembly with complexation of inorganic species [1, 2]. However, obtained materials suffer from important drawbacks, especially the relatively low thermal stability and robustness and only partial crystallinity of the mesoporous framework. Recently, we have demonstrated that a new type of diblock poly(ethylene-cobutylene)-b-poly(ethylene oxide) copolymers (KLE) enables to obtain mesoporous films of TiO2 with high crystallinity whilst maintaining the mesostructure up to 700 °C due to the thicker pore walls and generally much improved robustness [3, 4]. Based on the former work, the present communication aims at the systematic study into the electrochemical Li insertion into these films. This technique is highly sensitivity towards different TiC>2 phases enabling to detect crystalline phases even in trace amounts. The Li insertion process is characterized by the fundamental thermodynamic characteristics such as the specific insertion potential and the maximum insertion capacity, which differ for various TiO2 phases rendering them easily

570

recognizable. The fundamental process of Li insertion into anatase is the phase transition from tetragonal TiC>2 to orthorhombic Lio.5Ti02, taking place at formal potential Ef of 1.85 V. The maximum insertion capacity x of 0.5 mol of Li per 1 mol of anatase is given by the number of the vacant sites for the Li insertion. This enables quantification of the anatase fraction. Rutile has comparable insertion capacity but more negative insertion potential Efof 1.45 V. Layered TiO2(B) exhibits a pair of symmetric insertion/extraction peaks at potentials Ef of 1.5-1.6 V and the maximum insertion capacity x = 0.8. The amorphous forms of TiO2 show activity towards Li insertion in broad potential range without defined insertion/extraction potentials and insertion capacity of up to 1 mol/mol, but low stability towards multiple insertion/extraction cycles. 2. Experimental Section An isotropic solution containing 0.068 g KLE, 3 ml of ethanol and 0.5 ml of water was added to a solution of 0.6 g of TiCL, in 3 ml of ethanol, the resulting sol being stirred for 24h. The thin films were prepared by dip-coating onto FTO-coated glass slides in a controlled atmosphere of 20 % relative humidity at a withdrawal rate of 1 mm/s. The dried films were calcined in air at varying temperatures achieved at a ramp of 5°C/min. 2D-SAXS measurements were carried out on samples prepared on ultrathin silicon wafers with the variation of the angle of incidence p. WAXS measurements were performed in symmetric reflection using a D8 diffractometer from Bruker. Transmission electron microscopy images were taken with a Zeiss EM. The texture properties were determined from adsorption isotherms of Kr at 77 K using ASAP 2010 from Micromeritics. Electrochemical measurements were carried out using Autolab 12 potentiostat (Eco Chemie). The measurements were performed in 1 M LiN(SO2CF3)2 solution in 1 : 1 by weight mixture of ethylenecarbonate (EC) and 1,2-dimethoxyetane (DME). TiO2 films on FTO glass were used as working electrodes, Li foil as both auxiliary and reference electrodes. The efficiency of the Li insertion, actual amount of the material involved in the electrochemical reaction as well as relative fractions of contributing electrochemically active phases were characterized by insertion coefficient x = Q/Qtheor, which is calculated as the amount of charge Q consumed in the relation to the maximum theoretical amount Qtheor calculated according to Faraday's law Qtheor = zF m/M, where z is number of electrons in electrochemical reaction (here 1), F is the Faraday constant, m and M are mass and molar mass of electroactive compound.

571

3. Results and Discussion 3.1. Characterization of the structure and texture of the films 2D-SAXS experiments showed that all the films treated at 400-700 °C exhibit an oriented, highly-ordered mesoporous structure with a distorted bcc Im3m symmetry in the [110] orientation with respect to the substrate. The temperature treatment deforms the originally spherical mesopores into ellipsoids. TEM images of the films show a well-defined cubic arrangement of mesopores 14 nm in diameter distributed in a TiO2 matrix with pore walls 9-10 nm in thickness. WAXS analysis proves that the films are amorphous up to 450°C, while the treatment at 650°C leads to practically complete crystallization of the TiO2 framework. The crystallization starts at 500°C after the complete dehydration of the framework and provides practically completely crystalline material of exclusively one phase, namely anatase, without any X-ray detectable traces of rutile or brookite. Treatment at 650-700°C only slightly influences the crystal size and phase composition of the material. The Scherrer equation provides the nanocrystal size of 15 nm for the films treated at 550°C, which does not change with increasing the temperature up to 700°C. The adsorption isotherm of Kr at 77 K on the film calcined at 450°C significantly differs from those for samples calcined at higher temperature. As significant pore blocking during desorption was observed, the pores have access to the external gas phase only via narrow constrictions {e.g., ink-bottle pores). Film calcined at 550°C is characterized by developed mesoporosity, any pore blocking being removed due to the structure changes caused by the higher calcination temperature. In spite of the rather small thickness of the films, they exhibit large specific surface areas, ranging from 57 to 30 m2/g for films calcined at 450 to 650°C. The porosity of samples is similar of about 30 %. 3.2. Electrochemical measurements The film calcined at 450 °C exhibits broad and featureless insertion/extraction curves of amorphous TiO2 phase with some traces of anatase, which can be identified by characteristic insertion/extraction peaks (Fig. 1). Even if the peaks of crystalline anatase are clearly distinguishable, the corresponding charge fraction is practically negligible, which is ingreement with the X-ray amorphous character of the material. Calcination at 550-700°C causes a drastic change in the structure and corresponding electrochemical behavior. Films calcined at 550°C show pronounced anatase insertion and extraction peaks at 1.7 and 2.0 V, respectively (Fig. 1). The contribution from anatase is equal to 4 2 % of the theoretical insertion capacity, which corresponds to 85 % of anatase. The voltammograms of the films calcined at even higher temperature of 600 700°C correspond to pure crystalline anatase phase, sharp and symmetric insertion/extraction peaks characterizing the uniformity of insertion behavior for the whole material and evidencing the very narrow size distribution of the crystallites. Another feature of the Li insertion in the TiO2 films is the absence

572

of any detectable traces of other crystalline phases, which are typically present in varying amounts in almost all sol-gel prepared TiC>2 materials. The percentage of the anatase phase, determined precisely from the galvanostatic experiments, increases from 85 to 100 % for films calcined at 550 and 700°C.

E, Vvs. Li

E, Vvs. Ll

Figure 1. Cyclic voltammograms of TiO2 films calcined at 450-550 °C Scan rate 0.5 mV/s.

4. Conclusion The KLE-templated films have been shown to be practically amorphous if calcined at temperatures lower than 450°C. Above this temperature, complete crystallization occurs within relatively narrow temperature range. The films are distinguished by very high phase purity, consisting of uniform nanocrystals of anatase with easy and complete accessibility from the voids, and high temperature stability of both texture and structure properties. Due to their unique structure and texture properties, these novel films are very promising materials for a number of applications, the first test having confirmed their excellent photocatalytic performance for decomposition of wax layers and easily reachable and stable superhydrophilicity. 5. Acknowledgement The authors are grateful to the DFG (projects WA 1116/10 and 436 TSE/130/46/0-1), DAAD (D/04/25758), the Max Planck Society and the Ministry of Education, Youth and Sport of the Czech Republic (project 1M0577) for the financial support. 6. References [1] P. Yang, D. Zhao, D. I. Margolese, B. F. Chmelkaand G. D. Stucky, Nature 396 (1998) 152. [2] C. J. Brinker, Y. F. Lu, A. Sellinger and H. Y. Fan, Adv. Mater. 11 (1999) 579. [3] A. Thomas, H. Schlaad, B. Smarsly and M. Antonietti, Langmuir 19 (2003) 4455. [4] B. Smarsly, D. Grosso, T. Brezesinski, N. Pinna, C. Boissiere, M. Antonietti and C. Sanchez, Chem. Mater. 16 (2004) 2948.


573 573

Optimization of the silylation procedure of thin mesoporous SiO2 films with cationic trimethylaminopropylammonium groups Dina Fattakhova-Rohlfing,a Michael Warka and Jiri Rathouskyb "Institute of Physical Chemistry and Electrochemistry, Gottfried Wilhelm Leibniz Universitdt Hannover, D-30167 Hannover, Germany b J. Heyrovsky Institute of Physical Chemistry, Academy of Sciences of the Czech Republic, CZ-18223 Prague 8, Czech Republic

1. Introduction Mesoporous silicas are excellent hosts for incorporation of various guest molecules. The properties of the relatively inert silica surface can be drastically changed by the covalent grafting of functional groups, such as thiol-, amino- or alkylammonium ones, by silylation with chloro- or alkoxysilanes [1]. While the silylation procedure has been optimized for powdered mesoporous silica materials with differing porosity, it has not been developed for mesoporous silica thin films yet, even if the obvious differences in diffusion properties and pore accessibility of powders and films would imply the different conditions needed for their silylation. Recently we have faced a serious problem of poor reproducibility of silylation procedure of silica films when investigating their applicability as a matrix for anchoring electrochemically active species and dye molecules [2]. Therefore, the optimization of their silylation procedure has been aimed at in this communication. The procedure for the silylation of mesoporous silica films with trimethoxysilylpropyltrimethylamonium chloride (MAPTMS) bearing cationic trimethylammonium groups has been optimized. The introduced functional groups enable the ionic immobilization of anionic species, such as anionsubstituted dye molecules. The optimization criteria are (i) the reproducibility of the silylation reaction and (ii) the degree of surface modification providing the maximum incorporation of the guest species. The adsorption of Kr at 77 K was used as the checking method, combined with the UV/VIS analysis of the amount of incorporated dye molecules. Silica films used were prepared by

574

template-assisted procedure using commercial block copolymer Pluronic F127, yielding crack-free mesoporous films with 3D - worm hole like texture [3]. 2. Results and Discussion Kr adsorption data obtained for parent films reveal the highly pronounced mesoporosity with a narrow pore size distribution, the typical pore diameter, porosity and specific surface area being 6-7 nm, 60 % and 130-140 cm2/cm2 (corresponding to 435 m2/g) for films 340 nm in thickness. Fig. la clearly proves the excellent reproducibility of the texture properties of the parent films. 0.020 0.010 0.010b)

0.015

C/3

0.010

. • ^"

/ /

0.005

0.005

0.000 0.00

b)

VA / cm3/cm2 STP

VA / cm3/cm2 STP

a)

0.25

0.50

P/Po

0.75

1.00

0.000 0.00

0.25

0.50 0.250

0.75

1.00

P/Po

Figure 1. Adsorption isotherms of Kr at 77 K on five parent silica films (a) and on the same films silylated with MAPTMS in dichloromethane according to the non-optimized procedure (b)

The silylation with MAPTMS has been first attempted according to the recipe developed for mesoporous SiO2 powders, where long reaction times (12-16 hours) and aprotic solvent with relatively high dielectric constant (dichloromethane) were shown to give the best results [4]. This procedure, however, resulted in considerable scatter of the texture properties (Fig. lb). One of the reasons for different reactivity of powders and films is the difference in the accessibility of the silica surface for the silylation agent. For powders, even if some of the pores got stuck, there would be always enough free pathways at disposal for the sylilation agent to access virtually all the inner surface. Due the openness of a mesoporous particle to the diffusion from all the directions from the whole environment of the particle (Scheme la), the diffusion is fast and easy, enabling to use high concentrations of the sylilation agent. With a mesoporous film on a non-porous support, however, the inner surface is accessible only from one direction (Scheme lb), which makes it prone to blocking. In order to minimize this undesirable effect, the concentration of the sylilation agent should be substantially decreased.

575

Further, the total surface area of the sample to be sylilated vastly differs. For a film with mass of only few milligrams, it does not exceed one square meter, while for powders with almost arbitrary mass many hundreds of square meters are always at disposal. Of course, such large surface areas need much larger amount of the agent and much longer times to achieve complete modification than mesoporous films.

Scheme 1. Availability of surface for the silylation agents in mesoporous silica with cubic pore orientation (mesoporosity is not shown) in the form of particle (a) and thin film on a substrate (b)

The procedure was optimized with respect to the MAPTMS concentration, reaction time and reaction temperature as well as the polarity of the aprotic solvents used, namely toluene and dichloromethane. A low MAPTMS concentration in dichloromethane of 8 mmol/L and short reaction time of 4 hours provided the best results, while an increase in the temperature did not have practically any effect. Adsorption isotherms of Kr on the films silylated at given conditions are highly reproducible, showing the expected decrease in the pore size and film porosity (Fig. 2a). The use of toluene as a solvent leads just to a very slight change in the texture properties due to the low degree of the surface modification (Fig. 2a, B), which is not sufficient for the efficient immobilization of the guest species (Fig. 2b, B). Carrying out silylation in dichloromethane having higher dielectric constant somewhat increases the efficiency of silylation reflected in a slightly larger decrease in the pore volume (Fig. 2a, C) and the higher amount of the incorporated NiPc molecules (Fig. 2b, C). The higher efficiency of silylation reaction in dichloromethane can be due to the better solubility and reactivity of the MAPTMS bearing polar ammonium groups. Besides the choice of appropriate solvent, the efficiency of the coverage of the surface by alkoxysilanes requires also a sufficient concentration of free silanol groups on the silica surface, acting as the anchoring centers for the silylation. The lower efficiency of the silylation reaction can be caused by the partial deactivation of those groups due to the bonding of the products of the

576

template destruction or condensation leading to the formation of bridge -Si-OSi- groups due to the thermal treatment.

Q_ CO

0.00

0.4

0.8

500

600

700

P/Po Wavelength, nm Figure 2. (a) Typical Kr adsorption isotherms on the parent mesoporous silica films (A), after the optimized silylation procedure in toluene (B), dichloromethane (C) and dichloromethane including the pretreatment of the silica surface in mild alkaline solution (D). (b) Corresponding UV/VIS spectra of NiPc anchored on the surface of silylated silica films (the scattering patterns arise from the FTO substrate).

Thus, a short pretreatment of the surface of silica films in mild alkaline solution, which ensures the cleavage of the bridge siloxane groups and the activation of silica surface, allows reaching the optimum silylation efficiency. The pretreated films silylated in dichloromethane according to the optimized procedure exhibit the decrease in the pore size from 6.8 (for the parent film) to 6.3 nm, porosity from 56 to 37 % and specific surface area from 122 to 82 cm2/cm2. At the same time, the narrow pore size distribution without any pore blocking has been maintained, resulting in the maximum incorporated amount of guest NiPc molecules (Fig. 2, D). The anchoring of NiPc did not cause practically any change in the texture properties, the pore size decreasing and porosity decreasing by only 0.1 nm and 1 % abs., respectively. 3. Experimental Section Preparation of silica films according to a modified template-assisted procedure using Pluronic F127 is described elsewhere. Silylation with MAPTMS was carried out in a Schlenk flask equipped with a Teflon holder with magnetic stirrer. Prior to the silylation, the SiO2-coated glass slides were dried at 100 °C in air and activated in 0.3 % ethanolic solution of Et4NOH for 30 min. The optimum concentration of MAPTMS in dichloromethane or toluene and the duration of the silylation at room temperature were 8 mmol/L and 4 h. The samples were washed by repeated stirring in dichloromethane and ethanol. Tetrasodium salt of Ni(II) phthalocyanine tetrasulfonic acid (NiPc) was anchored from its 5 mmol/L solution in dimethylsulfoxide for 12 hours. After

577

the dye adsorption, the films were repeatedly washed in ethanol and dried in air. The intensity of the NiPc adsorption was determined from their UV/VIS spectra in the transmission mode using Varian 5000 spectrometer. Texture characteristics of the films were determined from the adsorption isotherms of Kr at the boiling point of liquid nitrogen (approx. 77 K) using an ASAP 2010 apparatus (Micromeritics). Minimum of 5 films was used for the statistical analysis of silylation reproducibility. 4. Conclusion The development of post-synthetic silylation procedure of mesoporous silica films with cationic trimethylaminopropylammonium groups, aimed at efficient reproducible incorporation of the anionic guest molecules, has clearly demonstrated different silylation reactivity of film and powder mesoporous materials. The major difference in case of the films is caused by the restricted accessibility of the silica surface to silylation agent, resulting in the proneness to the pore blocking after prolonged reaction times. A low concentration of silylation agent and a short reaction time are therefore needed for reproducible silylation of thin mesoporous films. Additionally, an activation of the silica surface by short pretreatment in mild alkaline allows achieving the optimum silylation efficiency. 5. Acknowledgement The authors are grateful to the DFG (projects WA 1116/10 and 436 TSE/130/46/0-1), DAAD (D/04/25758) and the Ministry of Education, Youth and Sport of the Czech Republic (project 1M0577) for the financial support. 6. References [1] E. F. Vansant, P. Van Der Voort and K. C. Vrancken, Characterization and chemical modification of the silica surface, Elsevier, Amsterdam (1995) [2] D. Fattakhova Rohlfing, J. Rathousky, Y. Rohlfing, O. Bartels and M. Wark, Langmuir, 21 (2005)11320. [3] D. Zhao, P. Yang, N. Melosh, J. Feng, B. Chmelka and G. Stucky, Adv. Mater., 10 (1998) 1380. [4] Y. Rohlfing, D. Woehrle, Y. Rathousky, A. Zukal and M. Wark, Stud. Surf. Sci. Catal. 142 (2002) 1067.



579 579

Synthesis of transparent mesoporous aluminum organophosphonate films through triblock copolymer templating Tatsuo Kimura and Kazumi Kato Advanced Manufacturing Research Institute, National Institute of Advanced Industrial Science and Technology (AIST), Shimoshidami, Moriyama-ku, Nagoya 463-8560, Japan

1. Introduction Morphological design of ordered mesoporous materials is one of the most important researches for their industrial uses in sensors, membranes, electronic, photonic, and optical devices. Although silica does not show photochemical and electrochemical properties, those properties can be given to ordered mesoporous silica by embedding organic groups in the framework. For example, hydrolysis and condensation of bridged silsesquioxanes in the presence of surfactants lead to the formation of periodic mesoporous organosilicas. Non-silica-based hybrid materials have attracted much attention because of the combination of properties due to the inorganic units and organic groups. Although a variety of non-silica-based mesoporous oxides and phosphates have been synthesized so far [1,2], there have been few reports on the preparation of non-silica-based hybrid mesoporous material [3-5]. Recently, a synthetic strategy of non-silica-based hybrid mesoporous materials by using organically bridged diphosphonic acids has been proposed [6]. Indeed, a successful preparation of mesoporous aluminum organophosphonates (AOPs) with 2-D hexagonal structures was reported by using alkylenediphosphonic acids [6-10]. Here, the synthesis of transparent mesoporous films composed of aluminophosphate-like units and alkylene groups was carried out in the presence of poly(ethylene glycol)-Z>/ocA:-poly(propylene glycol)-i/ocA:-poly(ethylene glycol) triblock copolymers (EOnPOmEOn).

580

2. Experimental Section In a typical synthesis, a triblock copolymer (EOgoPOsoEOgo, 1.2-1.6 g) was dissolved in a mixed solvent of water (30 mL) and ethanol (5 mL). Ethylenediphosphonic acid ((HO)2OPC2H4PO(OH)2, 0.96 g) was dissolved in the solution. The solution became cloudy at first during the gradual addition of aluminum chloride (A1C13, 0.67 g) to the solution under stirring (A1/2P = 1.00). After all of A1C13 was added to the solution and the stirring was continued, a clear solution can be obtained within several minutes. The clear solution was spin-coated on a glass substrate at a spinning rate of 4000 rpm. The transparent film was air-dried, dried at 100 °C, and calcined at 250°C for 3 h. 3. Results and Discussion The XRD pattern of a calcined mesoporous AOP film containing ethylene groups prepared in the presence of EOgoPCôEOgo is shown in Figure 1. A peak with the ^-spacing of 5.7 nm was maintained after calcination. Porosity of the film was checked by N2 adsorption of the corresponding bulk sample calcined at 250°C. The N2 adsorption isotherm was type IV. The BET surface area and the pore volume were 348 m2 g"1 and 0.84 cm3 g"1, respectively. The BJH pore diameter calculated using desorption branch was 7.5 nm. Although periodic structure of the transparent mesoporous AOP film cannot be defined from the XRD pattern, the TEM image (Figure 1) which was obtained by using a sample scrapped off from the grass substrate would reveal the presence of periodic mesostructure.

4 6 8 29 /°(FeKo)

12

Fig. 1. XRD pattern and TEM image of a calcined mesoporous AOP film containing ethylene groups prepared in the presence of EOgoPCôEOgo

On the basis of the high-resolution SEM image showing a direct observation of the mesopores (Figure 2), we have considered possible formation of cage-

581

type mesopores though distinct images due to the corresponding mesostructures such as 3-D hexagonal could not be taken by TEM. If the mesostructure is 3-D hexagonal, the XRD peak with the ^-spacing of 5.7 nm is assigned to the (002) plane due to a 3-D hexagonal structure (a = 11.4 nm) and the wall thickness is calculated to be 3.9 nm. However, the high-resolution SEM observation concluded that mesopores are present whole the transparent films but do not stack regularly. __^_^^

Fig. 2. High-resolution SEM image of a calcined mesoporous AOP film containing ethylene groups prepared in the presence of E080P03oE08o.

Solid-state NMR spectra of the calcined bulk sample showed the retaining of the hybrid framework structure (Figure 3). The P MAS NMR spectrum showed that broad peaks were observed at around 12.5 ppm, being assignable to P atoms in diphosphonate groups [6-8]. Only one peak due to carbon atoms in the ethylenediphophonate groups was observed at 21.5 ppm in the 13C CP/MAS NMR spectrum [9,10]. The NMR results indicate that ethylene groups within the hybrid framework are maintained after calcination at 250 °C. The results also revealed that P—C bonds in the diphosphonate groups are not decomposed during calcination. The 27A1 MAS NMR spectrum of the as-synthesized sample showed that all of the Al species are present as six-coordinated species. After calcination, a small amount of four-coordinated Al species were formed through condensation of the hybrid framework. Thus, it is considered that the hybrid framework is also maintained in the calcined film. The FT-IR spectra of the as-synthesized and calcined films also exhibited the successful removal of only triblock copolymers. Strong peaks assignable to CH stretching bands observed in the range of 2800-3000 c m 1 disappeared after calcination at 250°C and then small peaks due to C2H4 groups were observed in the same region. Ethylene groups in the diphosphonate groups are stable up to 400°C [7]. But complete removal of triblock copolymers was not confirmed by XPS. Although any peaks due to EOgoPOaoEOgo were not observed through the I3 C CP/MAS NMR measurement of the calcined bulk sample, the calcined film

582 (31P)

I

I I I I I I 100 0 -100 Chemical shift/ppm

ft

I I I I I 80 40 0 -40 -80 Chemical shift /ppm

(«CCP)

I I I I 150 100 50 0 Chemical shift /ppm

Fig. 3. Solid-state 27Al MAS, 31P MAS and 13C CP/MAS NMR spectra of a corresponding calcined bulk sample containing ethylene groups prepared in the presence of E08oP03oE08o.

contained ca. 22 mass % of carbon atoms (XPS). The value is somewhat larger than the calculated value (ca. 11 mass %, A1(O3PC2H4PO3) though the presence of OH groups and hydrated water molecules is not considered. A large number of water molecules were liganded to Al atoms in the hybrid frameworks (27A1 MAS NMR). The Al/P molar ratio of the film was 4.7 (XPS), being consistent with that in the precursor solution (0.5, A1/2P = 1.0). 4. Conclusion Mesoporous films whose frameworks are mainly composed of AOP can be synthesized by the reaction of aluminum chloride and ethylenediphosphonic acid in the presence of triblock copolymers. Triblock copolymers can be eliminated by calcination at low temperature (250 °C) without decomposition of the hybrid framework and mesopores formed whole the films with high surface areas. The insight contributes to further development of non-silica-based hybrid mesoporous films though further study is needed for developing methods to control mesostructural orderings of mesoporous AOP films. 5. References [1] C. Yu, B. Tian and D. Zhao, Curr. Opin. Solid State Mater. Sci., 7 (2003) 191. [2] B. Tian, X. Liu, B. Tu, C. Yu, J. Fan, L. Wang, S. Xie, G. D. Stucky and D. Zhao, Nature Mater., 2 (2003) 159. [3] T. Kimura, Chem. Lett., 31 (2002) 770. [4] T. Kimura and J. Mater. Chem., 13 (2003) 3072. [5] P. C. Angelome, S. Aldabe-Bilmes, M. E. Calvo, E. L. Crepaldi, D. Grosso, C. Sanchez and G. J. A. A. Soler-Illia, New J. Chem., 29 (2005) 59. [6] T. Kimura, Chem. Mater., 15 (2003) 3742. [7] T. Kimura, Chem. Mater., 17 (2005) 337. [8] T. Kimura, Chem. Mater., 17 (2005) 5521. [9] J. E. Haskouri, C. Guillem, J. Latorre, A. Beltran, D. Beltran and P. Amoros, Eur. J. Inorg. Chem., (2004) 1804. [10] J. E. Haskouri, C. Guillem, J. Latorre, A. Beltran, D. Beltran and P. Amoros, Chem. Mater., 16(2004)4359.


583 583

Electrical/Mechanical properties of nanoporous thin films by using various sized cyclodextrins Jin-Heong Yima Jong-Ki Jeonb and Young-Kwon Park "Division of Advanced Materials Engineering, Kongju National University, 182, Gongju, Chungnam, 314-701, Korea h Dept. of Chemical Engineering, Kongju National University, 182, Gongju, Chungnam, 314-701, Korea 'Faculty of Environmental Engineering, University of Seoul, 90, Jeonnong-dong, Seoul 130-743, Korea

1. Introduction As the dimension of integrated circuit decreases, it has been required a replacement of conventional Al/SiO2 interconnects to Cu/low-k (dielectric constant) to decrease RC (resistance and capacitance) delay. The predictions from the semiconductor industry indicate that inter level dielectric with a bulk dielectric constant (k) below 2.4 will be realized for 2007 [1]. This requirement would only be obtained by incorporation of nano voids into the matrix film. Many porous thin films have been demonstrated as low-k (low dielectric) materials in large scale integrated circuits (LSI) to reduce RC (resistance and capacitance) delay [2, 3]. One approach to generate nanoporous structures in thin films is to formulate a thermally stable low-k precursor with a pore generator (porogen) that can be decomposed and volatilized at the high temperature to leave pores in the film. It has been introduced the potentials to use cyclodextrin (CD) derivatives as a porogen. CD-based porogens have the attractive properties [3, 4]. Even though, several studies of nanoporous film, which templated by various types of CD based porogen have been performed [3-6], there has not been studied on the effect of core size of CD molecules. In this study, the electrical/mechanical properties of various sized CD (i.e. a-CD, P-CD and Y-CD) templated nanoporous films have been investigated to know the potential of low-k applications.

584

2. Experimental Section (a)

(b)

(c)

4-methyl-2-pentanone (Aldrich Chemical Co.) as solvent was used as-received without further purification. Hexakis (2,3,6-tri-Omethyl)-P-cyclodextrin (CYCLO LAB. Co.), heptakis (2,3,6-tri-O- Figure 1. PM3-optimized structures of various sized CD molecules; shows the front view of methyl)-P-cyclodextrin (CYCLO (a) a -tCD, (b) 3 -tCD, (c) y -tCD, Red LAB. Co.), and octakis (2,3,6-tri- sphere stands for a oxygen atom and gray O-methyl)-P-cyclodextrin sphere denotes a carbon atom.. (CYCLO LAB. Co.) were used as-received. In this study, MTMS(methyl trimethoxy silane) and TCS (2,4,6,8tetramethyl-2,4,6,8-tetrakis (trimethoxysilylethyl) cyclotetra siloxane) were used as monomers to synthesize the matrix precursor (mCSSQ) [7]. The spin-on coating solutions were prepared by properly mixing the SSQ precursor as a matrix with CD compounds as a porogen and propylene glycol methyl ether acetate (PGMEA) as a solvent. The porous films were prepared in accordance with our previous paper [4]. Depth-profiled PALS was used to determine the pore size and pore interconnectivity in these thin films [8]. The dielectric constant of each film with MIM (metal-insulator-metal) structure was measured by LCR meter (HP 4284) instrument at a frequency of 100 kHz. The hardness (H) and elastic modulus (E) of the thin films were measured by using the continuous stiffness measurement (CSM) of nano-indentation method. 15.7 Å

17.0 Å

19.1 Å


Weight loss (wt %)

The CDs are cyclic oligosac120 charides consisting of at least six Alpha_tCD Alpha t C D glucopyranose units that are joined 100 CD Beta_tCD Gamma_tCD Gamrr a_tCD together by a(l->4) linkages. The six 80 glucose unit containing CD is 1 specified as a-CD, while the CDs with 60 seven and eight glucose unit are I 40 designated as |3-CD and y-CD, 20 respectively. According to the molecular modeling based on the 0 250 300 350 400 450 500 semi-empirical quantum mechanic oC) Temperature ( (°C) theory (PM3), the methyl group substituted CD (tCD) compounds Figure 2. Thermogravimatric analysis (TGA) have three-dimensional structure with of various cyclodextrin compounds maximum diameter varying from 15.7 to 19.1 A as shown in Figure 1. The thermal decom-position of tCDs is observed around 350 ~ 400°C (Figure 2.). Considering that vitrification of the

I

A

V

585

Dielectric constant (k)

mCSSQ polymer almost complete up to 300°C, the tCDs could be 2.8 effectively used as porogen. The alpha-tCD • alpha-tCD range of thermal decomposition of alpha-tCD 2.6 • beta-tCD beta-tCD y-tCD is higher than that of 0-tCD beta-tCD and a-tCD as shown in Fig 2. Gamma-tCD • Gamma-tCD •£ 2.4 2.4 Gamma-tCD Refractive index decreased as expected and the porosity increased ' i 2.2 as a function of content of tCD in J_ the mixture as shown in Table 1. 2.0 I 2.0 . 5 Dielectric constant of the porous -J--J-iv-I1.8 thin film made from tCD varied from 2.4 to 1.9 as tCD content 1.6 increases from 10 to 50 wt% as can 0 10 20 30 40 50 60 be seen in Figure 3. Among the tCD (%) Porogen Concentration (%) based porogens, y -tCD templated porous film shows the lowest kvalue at the high content of porogen Figure 3. The variations of dielectric constant. (50 wt%). It is speculated that the most thermal stable porogen (y-tCD) may be favorable in the terms of dielectric constant of the film. Mechanical properties of the films decrease with increasing porosity in the evaluated range. Table 1. The mechanical properties of various CD templated porous thin films. Porogen content

Thickness (nm)

Refractive Index

a -tCD 10% a -tCD 30% a -tCD 50% B-tCD10% B -tCD 30% B -tCD 50% y -tCD 10% y -tCD 30% y -tCD 50%

1088 1187 937 673 1133 922 803 1136 959 710

1.4144 1.3715 1.3313 1.3169 1.3709 .3316 .3025 .3728 .3335 .3069

Porosities

9.2 18.1 21.4 9.4 18.1 24.7 8.9 17.6 23.7

0)

Elastic Modulus (GPa) (2)

Hardness (GPa)) 1TEOS: 0.007F127: 0.21HC1: 9.2H2O: 40EtOH. The drying was processed at Aging* below 50°C under decresed pressure T conditions. UV radiation was by the use Dryings of a deep-UV lamp whose wavelength is ~r UV Radiation. from 187 to 254 nm. For the phosphorous oxide-doped samples trimethyl , F ] o w cha[1 o f (he , js o f phosphate with the amount of 5-10 % silica . based monoliths. P/Si ratio was added. The samples were characterized using XRD (Philips, X Pert-MPD), N2sorption ( Quantachrome, Autosorb-1), AFM (Seiko II, SPA-300HV), and AC impedance spectroscopy (AC IS, Solartron, SI-1260). The proton conductivity was determined from the resistence, obtained from the AC impedance spectra, the thickness of the samples and the area of the Au electrodes. 3. Results and Discussion Fig. 2 shows the macro-morphology photographs of SBMMs. They are transparent and exhibit a considerable ductibility. The small-angle XRD (SAXRD) patterns of both the P-doped and undoped samples (Fig. 3) give the characteristic of ordered cubic mesostructures. The diffraction peaks can be indexed to (110), (220) and (222) reflections of this 3D cubic mesostructure [8]. For the doped sample (pattern b), its peaks were localized at larger 29 values than those of the undoped sample (pattern a), which indicates that Fig. 2 Macromorphology photographs of SBMM the doped sample had a smaller

Fig. 5 AFM image of SBMM.

a:

dd (nm) 10.64 10.64 7.52 4.34

222

220

b: h kk ll 11 11 00 2 22 0 2 22

dd (nm) (nm) 11.32 11.32 8.00 8.00 4.62

110

a

220

X5

1

222

Intensity /a.u.

h k ll 1 11 00 2 2 00 2 22 2

b

2

3

4

5

6

22θ/° θ /o CuK

α

Fig. 3 SAXRD patterns of SBMMs: (a) the undoped and (b) the P-doped samples. 350 350

—•—Undoped, Undoped, Abs —•—Undoped, Undoped, Des —•— P-doped, P-doped, Abs —o—P-doped, P-doped, Des

300 300 250 250

V (cc/g, STP)

200 ? 200 r> ri>150 150-

! 38.12 38.I2MM!

! -B-Uruopea Undoped

! !

P-doped

I

•

100 J" 10050 50

s j i l l j iiiii 10

0 0.0

!

38.23 o

8

A Dv(d) [cc/A/g]

unit cell parameter than the undoped sample. The unit cell parameters of both the doped and undoped samples were calculated to be about 150.4 A and 160.0 A, respectively, following Bragg Equation. This fact shows that the doping of phosphorous oxides affected the mesostructure of the monoliths. The N2-sorption isotherms for the (circles) doped and (squares) undoped monoliths (Fig. 4) are both of type IV character and exhibited distinct capillary condensation steps at a relative pressure P/Po of 0.4-0.8 and a H2 hysteresis loop, which is typical of sorption for mesoporous solids. Both samples exhibited almost the same narrow pore size distributions between 2-4 nm. Both the SAXRD and N2-sorption results indicated the meostructure of SBMMs is similar to that ot SBA16 with a space group Im3m. An accessible porous structure open to surface sides is very important for proton-condcuting membrane, which is beneficial for its proton transfer. A tipycal AFM image of SBMM (Fig. 5) illustrated the rough surface nature, where mesopore structure was accessible, open to the surface.

110

593

0.2

0.4

M M iiiii

100

-,

•

0.6

i ii

1000 o

MIUHÎIUU.HPI Pore Diameter [A]

0.8

,

1.0

Relative Pressure, Pressure, P/P P/P00 Relative

Fig. 4 N2-sorption isotherms and pore size distribution curves (inset) of the (circles) doped and (squares) undoped monoliths.

These SBMMs were support-free and facile to be coated with Au electrodes on both surface sides for the collection of AC impedance spectrum. Fig. 6 illustrates the typical complex impedance responses (Nyquist plots) of the (•) doped and (o) undoped monoliths at 98 °C under 82% RH conditions. The different shapes of the plots suggest different equivalent circuses for proton conduction in the doped and undoped monoliths. The proton conductivity (o) of the

594 594 -2000

sample is obtained following Doped -1800 Undoped the formula: a = L/(AR), -1600 where A is the area of Au -1400 electrode, L is the distance -1200 between the electrodes, and -1000 R can be detemined from the -800 diameter of the semi-circles -600 Z' (real) / in Fig. 6. The calculated -400 3 conductivities are up to 10" -200 and 10"4 S cm'1 for the doped 0 0 200 200 400 400 600 600 800 800 1000 1000 1200 1200 1400 1400 1600 1600 1800 1800 2000 2000 and undoped monoliths at 98 Z' (real) /Ω (real)/Ω °C under 82% RH conditions, respectively. This indicates that the doping of phosphorous oxides led to a Fig. 6 A.C. impedance responses of the (•) doped and (o) undoped monoliths at 98 °C under 82% RH higher conductivity for the conditions. mesostructured monolith. Moreover, both temperature and RH increase the conductivity of both samples. -200

Z'' (imaginary) / Ω

Z'' (imaginary) / Ω

-150

-100

1 MHz

1 Hz

-50

0

0

50

100

150

200

250

300

Ω

4. Conclusion In summary, we proposed a preparation of 3D cubic SBMMs and investigated into their proton conductivity. The conductivity of the P-doped samples was higher and up to 10"3 S cm"1 under 82% RH, compared to that of the undoped. 5. Acknowledgement This work was supported by the 21st Century COE Program in Nagoya Institute of Technology, Japan and National Fundmental Research Programm of China (Grant No. 2002CB613305). 6. References [1] [2] [3] [4] [5] [6] [7] [8]

K. D. Kreuer, Solid State Ionics, 97 (1997) 1. M. Nogami, R. Nagao and C. Wong, J. Phys. Chem. B, 102 (1998) 5772. M. Yamada, D. Li, I. Honmaand H. Zhou, J. Am. Chem. Soc, 127 (2005) 13092. W. H. J. Hogarth, J. C. D. da Costa, J. Drennan and G. D. Max Lu, J. Mater. Chem., 15 (2005) 754. H. Li and M. Nogami, Adv. Mater., 14 (2002) 912. L. Xiong and M. Nogami, Chem. Lett., 35 (2006) 972. H. Yang, Q. Shi, B. Tian, S. Xie, F. Zhang, Y. Yan, B. Tu and D. Zhao, Chem. Mater., 15 (2003) 536. D. Zhao, P. Yang, N. Melosh, J. Feng, B. F. Chmelka and G. D. Stuky, Adv. Mater., 10 (1998), 1380.


595 595

Vapor phase preparations of mesoporous silica thin films for ultra-low-A: dielectrics Shunsuke Tanaka,ac* Takanori Maruo,a Norikazu Nishiyama,a Korekazu Ueyarna3 and Hugh W. Hillhouseb "Division of Chemical Engineering, Graduate School of Engineering Science, Osaka University, 1-3 Machikaneyama, Toyonaka, Osaka 560-8531 Japan h School of Chemical Engineering, Purdue University, 480 Stadium Mall Drive, West Lafayette, Indiana 47907 USA 'Current Address; Department of Chemical Engineering, Faculty of Engineering, Kansai University, 3-3-35 Yamate-cho, Suita-shi, Osaka 564-8680

1. Introduction Low dielectric constant (low-&) materials are a central development target in the electronics industry. For example, microchip device densities continue to increase, generating much demand for insulators with a lower dielectric constant. In 45 nm technology node for ultralarge-scale integrated circuits, it is essentially inevitable to attain the film with the dielectric constant of less than 2.0. Introduction of nanoscale pores in the dielectric film is an efficient way to reduce the dielectric constant. Surfacatant-templated ordered mesoporous silicas may be a promising material for low-& films because the film has extremely high porosity, uniform pores, and ordered structure [1-3]. Thin films made of mesoporous silica have conventionally been fabricated using dip or spin coating via evaporation-induced self-assembly (EISA) [2-5]. On the contrary, we have previously synthesized mesoporous silica thin films by the vapor phase preparations [6-8]. In this study, we have characterized the detailed structure (space group, lattice constants, and orientation) and dielectric constant of the films prepared by the vapor phase method using PEO106-PPO70-PEO106 (Pluronic F127). The films were characterized using grazing-angle of incidence small-angle X-ray scattering (GISAXS), high-resolution field emission scanning electron microscope (FESEM), Fourier transform infrared spectroscopy (FTIR), and N2 adsorption/desorption measurements.

596

2. Experimental Section First, the polymer films were prepared on the silicon wafer by spin-coating using a starting solution with a molar ratio of 0.02 Pluronic F127: 100 EtOH: 100 H 2 O. The polymer films were placed in a closed vessel along with a separate, small amount of TEOS and HC1 (5 N). The vessel was then placed in an oven at 90°C for 60 min. Thus, the polymer films were exposed to a saturated TEOS vapor under autogenous pressure. The film was calcined at 400°C in air for 5 h. End-capping of residual silanols was conducted by silylation using trimethylchlorosilane at 150°C for 1 h after calcination. The GISAXS experiments were performed at the Advanced Photon Source at Argonne National Laboratory on the 1-BM-C beamline using synchrotron source. The spot patterns at various angles of incidence were simulated using NANOCELL, a Mathematica-based program [5,9]. FESEM images were recorded on a Hitachi S-5000L microscope. The N 2 adsorption/desorption isotherms of products were measured using a Quantachrome AUTOSORB-1 instrument. The dielectric constant of the films was measured at room temperature with a Solatron SI 1260 impedance analyzer. Platinum electrodes were deposited on the films with the ULVAC QUICK COATER VPS-20. 3. Results and Discussion Complete removal of copolymer by calcination at 400°C was confirmed by the FTIR spectrum of the calcined films. The FTIR spectra for the films prepared by vapor phase method show that the concentration of residual silanol group is lower than that of conventional sol-gel films (data not shown). 3.0

αf (deg.)

2.0 0) "D

^ -

„:

o o0 O o o o o o o o 1.0 1.0 o o o o o 1 oo 1 Q o o QD O O OO j 0 –2.0 -2.0

–1.0 -1.0

:

o

o

O

0 0

o

O

o

l°l II 11 o

{

° O

O O

0 (deg.) 2θf (deg.)

0 0

o

0 0

o o

0

oo o

o

o o o |

1.0 1.0

2.0 2.0

0 0 0 OO oo ao |

Figure 1 GISAXS pattern collected from synchrotron source (<Xi= 0.21°) for the mesoporous silica film with overlays showing simulated spot pattern by NANOCELL.

GISAXS pattern shown in Figure 1 has the large number of well resolved peaks, indicating that the film is highly ordered. Note that the spots not overlaid

597

1000 800 600 400 200 0

0

0.2

0.4 0.6 P/P P/P0

0.8

1

Pore volume (cc/nm/g)

Volume adsorbed (cc/g)

by the white circles can be simulated by NANOCELL. Several spots not overlaid arise from diffraction of the transmitted then reflected incident beam. The GISAXS pattern was described by the rhombohedral space group R-3m oriented with the (111) axis perpendicular to the substrate. The lattice constants for the film were determined to be a = 16.8 nm and a = 70°. The d\u spacing, the periodic distance perpendicular to the substrate, is 12.6 nm. At a relative N2 pressure of 0.7-0.8, a steep increase in the amount of adsorbed N2 with a hysteresis loop corresponds to the filling of ordered mesopores (Figure 2). The pore size distribution was obtained using the BJH model for the desorption isotherm. The BET surface area and pore diameter were 720 m2/g and 7.2 nm, respectively. 1.0 0.8 0.6 0.4 0.2 0 0

10 5 10 Pore diameter (nm) (nm) Pore

15 15

Figure 2 N 2 adsorption/desorption isotherms and a pore size distribution for a calcined film. The measurements were performed with the powdery sample which was peeled from the substrate. (b) (b)

10 9 8 7 6 5 4 3 2 1• i 1 0 1.00E+04 1.00E+04

Dielectric constant

(a) (a)

1

1.00E+05 1.00E+05 Frequency (Hz) (Hz) Frequency

1.00E+06 1.00E+06

Figure 3 FESEM image of the cross-section of mesoporous silica film (Scale bar; 60 nm). The portion of the enclosed with dotted lines is platinum electrode, (a) Dielectric constant (at 10 kHz1 MHz) of MIS (Pt/film/Si) structure fabricated using the mesoporous silica film.

No shrinkage was observed in the pore size after heating at 650°C and immersing in water at 180°C in a closed vessel for 3 h. These results show high thermal and hydrothermal stability. Mechanical strength was investigated by pressurizing the films for 5 min using a pressing apparatus. The ordered structure of the films was maintained even after compression at 3500 kg/cm2. It was found from FESEM observations that the mesoporous silica films have silicate layers with ordered pillars. The dielectric constant was measured using

598

the 150 nm thick film, which has thirteen layers. After the silylation, new bands appeared at 760 and 1260 cm"1 in the FTIR spectra, indicating that the residual silanol groups were replaced with the methylsilyl groups. The upper platinum film was prepared by sputter deposition as electrode (Figure 3a). The electric constant of 1.8 was obtained (Figure 3b). The result suggests that the porosity of the film was approximately 60%. 4. Conclusion The mesoporous silica thin films have two-dimensionally connected cagelike mesopores and are indexed with (111) oriented R-3m structure. The silica layers play a role as passivating films, capping of the mesopores on the film surface. The structure, high thermal and hydrothermal stability, and low dielectric constnat of the films are of advantage for next-generation \ow-k films. 5. Acknowledgement The authors wish to acknowledge use of the NSF funded facility for In-situ X-ray Scattering from Nanomaterials and Catalysts (MRI program award 0321118-CTS) and the use of the Advanced Photon Source supported by the U. 5. Department of Energy, Office of Science, Office of Basic Energy Sciences, under Contract No. W-31-109-ENG-38. The authors gratefully acknowledge the assistance of the GHAS laboratory and Mr. M. Kawashimaat Osaka University with the FE-SEM measurements. S. Tanaka acknowledges the Japan Society for the Promotion of Science (JSPS) Research Fellowships. 6. References [1] C. T. Kresge, M. E. Leonowicz, W. J. Roth, J. C. Vartuli and J. S. Beck, Nature, 359 (1992)710. [2] F. Schuth and W. Schmidt, Adv. Mater., 14 (2002) 629. [3] R. C. Hayward, P. C. A. Alberius, E. J. Kramer and B. F. Chmelka, Langmuir, 20 (2004) 5998. [4] C. J. Brinker, Y. F. Lu, A. Sellinger and H. Y. Fan, Adv. Mater., 11 (1999) 579. [5] M. P. Tate, B. W. Eggiman, J. D. Kowalski and H. W. Hillhouse, Langmuir, 21 (2005) 10112. [6] N. Nishiyama, S. Tanaka, Y. Egashira, Y. Oku and K. Ueyama, Chem. Mater., 15 (2003) 1006. [7] S. Tanaka, N. Nishiyama, Y. Egashira, Y. Oku and K. Ueyama, J. Am. Chem. Soc, 126 (2004) 4854. [8] S. Tanaka, N. Nishiyama, Y. Hayashi, Y. Egashira and K. Ueyama, Chem. Lett., 33 (2004) 1408. [9] M. P. Tate, V. N. Urade, J. D. Kowalski, T. -C. Wei, B. D. Hamilton, B. W. Eggiman and H. W. Hillhouse, J. Phys. Chem. B, 110 (2006) 9882.


599 599

Synthesis of silica nanospheres with well-ordered mesopores assisted by amino acids Toshiyuki Yokoia*, Marie Iwamab, Tatsuya Okubob, Yasuhiro Sakamoto0, Osamu Terasaki0, Yoshihiro Kubotad and Takashi Tatsumf " Chemical Resources Laboratory, Tokyo Institute of Technology, 4259 Nagatsuta, Midori-ku, Yokohama 226-8503 Japan Department of Chemical System Engineering, The University of Tokyo, 7-3-1 Hongo,Bunkyo-ku, Tokyo 113-8656, Japan. c Structural Chemistry, Arrhenius Laboratory, Stockholm University, 10691 Stockholm, Sweden d Division of Materials Science and Chemical Engineering, Graduate School of Engineering, Yokohama National University 79-5 Tokiwadai, Hodogaya-ku, Yokohama 240-8501, Japan.

1. Introduction The realm of nanoparticles has been extended by the emergence of innovative synthetic method, the Stober method, which was reported in 1968 [1]. The need for monodispersed colloidal silica spheres with two or three-dimensionally well-ordered arrangement is thus constantly increasing because high-tech industries provide a tremendous demand for such well-ordered and nano-sized silica spheres [2]. Bio-inspired and biomimetic chemistries have demonstrated the marvelous power for assembling and structure-directing small species into unique materials [3-5]. Recently, unique anionic surfactants derived from diverse amino acids have been applied to the synthesis of mesoporous materials [6]. In particular, the development of an anionic surfactant Af-myristoyl-L-alanine sodium salt enabled us to obtain a chiral mesoporous silica with a twisted hexagonal-rod-like morphology [7]. The use of polypeptide as a template for assembling inorganic materials with a unique structure has also been reported [8, 9]. Here we report a novel and simple liquid-phase method for crystallizing uniform-sized SNS (Silica NanoSpheres) by using tetraethyl orthosilicate (TEOS) and a basic amino acid, L-lysine.

600

2. Experimental Section SNS was synthesized by using tetraethyl orthosilicate (TEOS) as a silica source in the presence of a basic amino acid, L-lysine. In a typical synthesis, Llysine was dissolved in the solution containing deionized water and octane with stirring. After the mixture was stirred for 1 h, TEOS was added to the mixture with stirring (the final molar composition; 1 TEOS: x L-lysine: 1.3 C8H!8: 154.4 H2O; x = 0 - 0.5). The resulting mixture was stirred for 20 h followed by being kept statically at 373 K for 20 h. Finally, the solution was directly evaporated in an oven at 373 K, resulting in the formation of the silica nanospheres. Thus obtained silica was calcined in an oven at 873 K to remove organic components. The silica materials prepared by using L-lysine were designated as n-L-Lys.-SNS. SEM images were taken on a Hitachi S-5200 microscope. The samples were observed without any metal coating. TEM images were taken on a JEM-3010 microscope operating at an accelerating voltage of 300 kV. The XRD were recorded on a M03X-HF22 powder diffractometer equipped with Cu-Ka radiation (40 kV, 40 mA). Nitrogen adsorption-desorption measurements were conducted at 77 K on a Bell Japan Belsorp 28SA sorptionmeter. The pore size distributions were calculated by the DH (Dollimore-Heal) method using the adsorption branch. 3. Results and Discussion High-resolution scanning electron microscopic (HRSEM) images of the 0.02L-Lys.-SNS sample revealed that the micro-sized silica block consisted of uniform-sized nanospheres, and that silica nanospheres with a uniform size of around 12 nm were well ordered (Fig. 1). This HRSEM image also revealed that there was a uniform nanospace between the nanospheres and that its size was estimated to be around 3 nm. Although silica spheres with sizes of 100 - 200 nm have been easily obtained by the Stober method, to the best of our

500 nm

vrf

100 IB nm

Fig. 1 Representative high-resolution scanning electron microscopic (HRSEM) images of the calcined 0.02-L-Lys.-SNS sample.

knowledge, silica nanospheres with a size of the level of 10 nm arranged in a highly regular order is unprecedented. High-resolution transmission electron

601

dVp / dRp

3

V ol ume a ds or be d / cm g

-1

Int e ns i ty / a .u.

microscopic (HRTEM) images of the 0.02-L-Lys.-SNS sample also demonstrated that the spheres of this sample were well ordered. The XRD pattern of the calcined 0.02-L-Lys.-SNS sample is shown in Fig. 2, which shows marked three diffraction peaks in the region of 26 = 0.5 - 2.0 °. These peaks can be indexed as the 111, 220 and 331 reflections based on the cubic closed pack (ccp) structure. When x was 0 or 0.01, no precipitate was formed even after aging at 373 K for 10 h, likely due to the lack of catalysis for the hydrolysis of TEOS followed by condensation of the resultant products. On the other hand, when x was increased up to 0.5, the diffraction peaks became | unresolved, and the position of the first main peak was broadened, and was shifted to higher angle with an increase in x; the dm spacing values at x = 0.02 and 0.5 were found to be 11.9 and 7.7 nm, respectively. The HRSEM image revealed that the 0.5-L-Lys.-SNS s ample 0 1 2 3 4 5 6 was merely aggregates of silica particles without regularity. It is 22theta/deg. theta / deg. concluded that the optimum x to Fig. 2 XRD pattern of the calcined 0.02-Lobtain the mesos tructured Lys.-SNS sample. product is 0.02. The nitrogen adsorptiondesorption isotherms of the 0.02200 L-Lys.-SNS sample after the removal of the organic moieties by calcination exhibit the type IV pattern, indicating the 100 presence of uniform mesopores (Fig. 3); the BET (BrunauerEmmett-Teller) surface area and the average pore size were found 0 5 10 15 20 Pore size / nm to be 228 m 2 g 4 and 3.2 nm, 0 0 0.5 1 respectively. The presence of Relative pressure Relative pressure uniform mesopores is attributed to the crystallization of the wellFig. 3 Nitrogen adsorption-desorption isotherms ordered silica nanospheres. with corresponding pore size distributions of the Combining the data from the calcined 0.02-L-Lys.-SNS sample. CHN elemental analysis and the TG-DTA measurement of the 0.02-L-Lys.-SNS sample before the calcination, the contents of silica and L-lysine were estimated to be 15.02 and 0.33 mmolg"1,

602

respectively; the molar ratio of L-lysine / SiO2 was found to be 0.022, which is consistent with the starting molar gel composition. Since the pKa of a -COOH, a-NH 3 + and a -(CH2)4NH3+ in L-lysine molecule is estimated to be 2.18, 8.90 and 10.28, respectively and the isoelectric point of L-lysine is 9.74, about 92 % of a -(CH2)4NH2 and 33 % of a -NH2 in L-lysine molecule would be protonated under the synthesis conditions (pH 9.2). Therefore, two kinds of interaction comprising the electrostatic one between anionic silicates ( = SiO") and protonated amino groups in L-lysine, and hydrogen-bonding between L-lysine molecules could be operative. They might result in the formation of the wellordered SNS. L-lysine, L-histidine and L-arginine are categorized as basic amino acids. We found that the use of L-arginine led to the formation of similar well-ordered SNS under the same conditions. On the other hand, the use of L-histidine was unsuccessful probably due to the low basicity. Even when the pH of the solution containing L-histidine was increased by means of addition of aqueous NH3 solution, well-ordered SNS was not formed. 4. Conclusion The uniform and nano-sized SNS (silica nanospheres) assisted by basic amino acids, which can work as an inducement to three-dimensional arrangement as well as a catalyst for the formation of silica were successfully synthesized. Thus simple basic amino acids show a talent for assembling silica nanospheres, leading to their crystallization. Our approach for preparing mesostructured materials by means of assembling nanospheres with regularity is not a general liquid-crystal templating method and will stimulate the development of a new family of ordered mesoporous materials. 5. References [1] W. Stober and A. Fink, J. Colloid Interface Sci., 26 (1968) 62. [2] S.-M. Yang, S. G. Jang, D.-G. Choi, S. Kim and H. K.Yu, Small, 2 (2006) 458. [3] Y. Lu, Y.Yang, A.Sellinger, M. Lu, J. Huang, H. Fan, R. Haddad, G. P. Lopez, A. R. Bums, D. Y.Sasaki, J. Shelnutt and C. J. Brinker, Nature, 410 (2001) 913. [4] K. J. C. van Bommel, A. Friggeri and S. Shinkai, Angew. Chem. Int. Ed., 42 (2003) 980. [5] E. Dujardin and S. Mann, Adv. Mater., 14 (2002) 775. [6] S. Che, A. E. Garcia-Bennett, T. Yokoi, K. Sakamoto, H. Kunieda, O. Terasaki and T. Tatsumi, Nature Materials, 2 (2003) 801. [7] S. Che, Z. Liu, T. Ohsuna, K. Sakamoto, O. Terasaki and T. Tatsumi, Nature, 429 (2004) 281. [8] J. N. Cha, G. D.Stucky, D. E. Morse and T. J. Deming, Nature 403 (2000) 289. [9] K. M. Hawkins, S. S.-S. Wang, D. M. Ford and D. F. Shantz, J. Am. Chem. Soc, 126 (2004)9112.


603 603

Size and morphology control in the synthesis of SBA-15 Huanling Xie ac , Ranbo Yub, Dan Wang0*, Jianxi Yaoc, Xianran Xingb and Wenguo Xua "The Institute for chemical physics, Beijing institute of Technology, Beijing 100081, China Department of physical Chemistry, University of Science & Technology Beijing, Beijing 100083, China c Key Laboratory of Multi-phase Reaction, Institute of Process Engineering, Chinese Academy of Sciences, Beijing 100080, P. R. China

1. Introduction It has been about two decades since the discovery of large-pore periodic mesoporous silica [1]. Recent developments have been reported on their versatile applications in catalysis, separation, adsorption and host materials [2]. For the purpose of these applications to industry, the synthesis of mesoporous molecular sieves with controllable morphologies and size is one of the main areas of interest in materials chemistry. And, extensive work was devoted to the morphology and size control mesoporous silicas [3-9]. In this work, we report a size and morphology control technique by using different mixing method and tuning the molar ratios of tetraethyl orthosilicate (TEOS) to the surfactants to form crystal-like sphere- and gyroid- particles of mesoporous silica SBA-15. 2. Experimental Section In a typical experiment, a certain amount of triblock copolymer Pluronic P123 (P123) and potassium chloride (KCl) were dissolved in 2 M hydrochloric acid (HC1) aqueous solution, and then TEOS was added to this solution under ultrasonic irradiation or magnetic stirring. The final molar raio of TEOS: PI23: KCl: HC1: H2O was 1: 0.0052-0.0172: 1.48: 6.6: 170. Eight minutes later, this mixture was sealed in Teflon-lined stainless steel autoclaves, and kept under

604

static conditions at 30°C for 24 h, followed by heating at 100°C for 24 h. The synthetic conditions for the typical samples are shown in Table 1. The solid products were collected by filtration, washed with water and dried. The assynthesized SBA-15 samples were calcined in air at 550°C for 6 h to remove the surfactant. SEM images were achieved by JEOL JSM-35CF. HRTEM images were recorded on a JEOL JEM-2010. Small-angle X-ray powder diffraction were taken on an X' Pert PRO diffractometer (PANalytical, Netherlands). N2 adsorption-desorption isotherms were measured with a QUANTACHROM analyzer (Autosorb-1, USA) Table 1 . Different synthetic conditions and physical properties for materials c i

nno

Spl v

PI23

1 2 3 4 5 6 7

0.0052 0.0086 0.0121 0.0172 0.0086 0.0121 0.0172

Mixing

iU j method ultrasonic ultrasonic ultrasonic ultrasonic stirring stirring stirring

TEOS

mi_.

/PI 23 192 116 83 58 116 83 58

dioo

, \ (nm) 8.81 9.32 9.39 9.68 8.79 8.93 9.16

»,,

. i

Morphology v bJ Irregular particles Sphere (d = 5um) Sphere (d = 7 urn) Larger gyroid Sphere (d = 4um) Smaller gyroid Gyroid-like

3. Results and Discussion The reactant molar ratio of TEOS/P123 plays an important role in the morphology and size of the as-synthesized samples. In the SEM image of sample 1 (not shown here), a lot of particles with a kind of irregular shape and few spherical particles could be observed. Decreasing the molar ratio to 116 and 83 (sample 2, 3), large and uniform spheres with the mean size about 5 urn and 7um, respectively, could be clearly observed in the SEM images of (Fig. 1.(1) and (2)). SEM images of the sample 4 prepared with the TEOS/P123 molar ratio of 58 is shown in Fig. 1. (3). As can be seen, Gyroid particles with about lOum were obtained. To investigate the effect of mixing method on the morphology of the samples, the magnetic stirring was used to mix precursor solution. The SEM images of sample 5 prepared at the same TEOS/P123 molar ratio as sample 2 showed that the magnetic stirring resulted in the formation of sphere with the samller mean size of 4 um (Fig. 1. (4)). With the decrease of the TEOS/P123 molar ratio to 83 and 58, the gyroid particles with much smaller mean size and wider size distribution, respectively, could be obtained (Fig. 1 (5) and (6)). The SEM results indicated that the morphology and the size of the assynthesized sample could be easily controlled by means of the synergetic effects of the reactant molar ratio of TEOS/P123 and the mixing method for the

605

precursor solution. The HRTEM image of the typical samples displays a wellordered 2D mesostructure (not shown here).

Figure 1. SEM images of (1) sample 2, (2) sample 3, (3) sample 4 synthesized by ultrasonic irradiation; (4) sample 5, (5) sample 6, (6) sample 7 prepared under magnetic stirring.

sample 5 and 6, which display

200000

150000

Relatively Intensity (a.u.)

Fig. 2 shows the small-angle XRD patterns of the samples calcined at 55O°C for 6h. The three obvious peaks in the XRD patterns could be indexed as (100), (110), and (200) reflection. The values of d spacing between the (100) planes of the arrays were summarized in table 1. It could be seen that the dioo value slightly increases with the decrease of the TEOS/P123 molar ratios. On the condition of using the same TEOS/P123 molar ratio, the samples prepared under ultrasonic irradiation showed larger d1Oo value compared with that of the samples prepared under magnetic stirring. Apart from

J

\

X

^,

100000 100 110

0

(6)

×5 x5

(5) (5)

×5

(4)

300 ×4 ×4

(3) (3)

×5

(2) (2)

×5

(1) (1)

\

T

~2-

×5

A

200

-

V__

2210 10

50000

0

rr

0

1

2

2

2 2 θθ (( °°) )

3

4

Figure 2. Small-angle X-ray diffraction of (1) sample 2, (2) sample 3, (3) sample 4, (4) sample 5, (5) sample 6, (6) sample 7.

5

606

broad and weak (110) and (200) peaks, sample 2 and 3 exhibit higher (110) and (200) peaks. XRD pattern of sample 4 showed well-resolved (210) and (300) peaks, whereas, such reflections were not seen on the sample 7. It indicated that materials prepared by ultrasonic irradiation have relatively good mesostructure ordering. The nitrogen adsorption-desorption isotherms of the materials basically show type IV in IUPAC nomenclature. From BJH pore size distribution, it can be seen that the pore size increased with the decrease of TEOS/P123, in accord with XRD patterns results. 4. Conclusion Sphere and gyroid of SBA-15 mesoporous silicas with different size were successfully synthesized under hydrothermal condition. The result showed that the mixing method for the precursor solution and the reactant molar ratios of TEOS/P123 have great effects on the morphology and size of the mesoporous silicas SBA-15. The morphology and size control in the synthesis of SBA-15 introduces more flexibility and diversity into the designed synthesis of shaped mesoporous silicas. Such morphological SBA-15 mesoprous silicas are promising for applications in industry. 5. Acknowledgment This work was partially supported by National Natural Science Foundation of China (NSFC) (No. 20401015, 50574082), Foundation of University of Science & Technology Beijing (Grant No.: 2004214890 and 20050214890) and CNPC Innovation Foundation (No. 04E7018). 6. References [1] D. Zhao, J. Feng, Q. Huo, N. Melosh, G. H. Fredrickson, B. F. Chmelka and G. D. Stucky, Science, 279 (1998) 548. [2] H. Song, R. M. Rioux, J. D. Hoefelmeyer, R. Komor, K. Niesz, M. Grass, P. Yang and G.A. Somorjai, J. Am. Chem. Soc, 128 (2006) 3027. [3] J. Fan, J. Lei, L. Wang, C. Yu, B. Tu and D. Zhao, Chem. Commun., (2003) 2140. [4] D. Zhao, J. Sun, Q. Li and G. D. Stucky, Chem. Mater., 12 (2000) 275. [5] K. Kosuge, T. Sato, N. Kikukawa and M. Takemori, Chem. Mater., 16 (2004) 899. [6] Sayari, B. Han, Y. Yang and J. Am. Chem. Soc, 126 (2004) 14348. [7] Z. Yu, J. Fan, B. Z. Tian and D. Y. Zhao, Chem. Mater., 16 (2004) 889. [8] S. K. Lee, J. Lee, J. Joo, T. Hyeon, W. S. Ahn, H. I. Lee, C. H. Lee and W. Choi, J. Ind. Eng. Chem., 9 (2003) 83. [9] X. Y. Bao and X. S. Zhao, J. Phys. Chem. B, 109 (2005) 10727.


607 607

Synthesis and characterization of mesostructured silica sphere particles with core space Jung-Sik Choi3, Kyung-Ku Kangb and Wha-Seung Ann3* "Department of Chemical Engineering, Inha University, Incheon, 402-751, Korea Research Institute of Chemicals and Electronic Materials, Cheil Industries, INC. Gyeonggi-do, 437-711, Korea

Spherical mesostructured silica particles with inner core space were prepared under acidic condition using TEOS and a block copolymer template in an aqueous/butanol emulsion system. Mesoporous silica particles obtained were highly uniform in 125 um - 1 mm size range with core space in 100 - 170 um depending on the synthesis condition. The sphere diameter was directly proportional to the concentrations of TEOS and butanol. Butanol plays an important role of making the silica particles hollow and spherical as well as being involved in mesopore formation; an increase in butanol concentration produced mesoporous silica with larger pore diameter. 1. Introduction The preparation of mesoporous silica materials has evolved to a new stage in which the hierarchical structures having at least two length scales of micro- and nanometer can be achieved [1]. The controlling of structures in both length scales has important impacts on design of nanomaterials and their potential applications such as catalyst/supports, drug release, micro reactor, separation, and chromatography packing materials. Making spherical silica particles with mesopore structure by chemical and hydrodynamic approach has advantages on cost and performance. In this work, spherical mesoporous silica particles with core space were prepared by promoting condensation of silica/surfactant assembly around an organic phase in an aqueous/butanol emulsion system. Synthesis process is very simple and uses cheaper reagents than the previous report by Stucky's group on a similar material [2].

608

2. Expermental Section TEOS was used as silica source and 1-butanol with Pluronic 123 dissolved in water was used to form an O/W emulsion. In a typical synthesis, surfactant solution was prepared by adding P123 to 2 M HCl solution and stirred at room temperature. Independently, TEOS was added in 1-butanol with stirring and this solution was added to the surfactant solution. The substrate mixture was then stirred for 24 h at 35°C. Particles obtained were recovered by filtration, washed, and dried. Finally, the product was carefully calcined in air at 550°C. The morphology of the samples was examined by SEM (Hitachi S-4300) and TEM (Philips, CM 200). The specific surface area and average pore diameters were determined by N2 physisorption using a Micromeretics ASAP 2000 automatic analyzer. 3. Results and Dicussion In this work, spherical mesoporous silica particles were synthesized by solgel method under acidic condition with controlled morphology, using butanol as the organic phase in O/W emulsion. Scheme 1 represents the formation process of the sphere particles as suggested by Schacht et al. [1]. In our synthesis, TEOS mixed with butanol was added to acidic surfactant solution with stirring.

Direction of silica growth

r c?s> v

Surfactant as emulsion

stabilizer

Organic phase (Emulsion)

>{

Surfactant as rjoiêj) template with random orientation

Aqueous phase Scheme 1. Proposed growth mechanism of spherical mesoporous silica [1].

Surfactant plays an important role both as emulsion stabilizer and as micelle template. TEOS also contributes to the stabilization of this emulsion phase after partial hydrolysis. TEOS is eventually fully hydrolyzed under acidic conditions at the organic/water interface and forms the mesostructure under the influence of the surfactant.

609

1^ (a)

y^

Macro pore

(b)

V

100 µm 100

1 mm

µmy

Core Core space space Fig. 1. SEM micrographs of the spherical mesoporous silica and the particle cross section.

Amount of adsorption (cc/g, STP)

SEM image (Fig. la) shows uniform spherical particles with ca. 500 urn in diameter. It was also possible to prepare particles up to 1 mm by controlling the synthesis condition. Fig. lb is a cross section image of a spherical mesoporous silica particle with ca. 200 um in diameter, which are made of 3 different types of pores: core space with 100-170 urn, macro pores with 1-5 um and mesopores as measured by nitrogen adsorption-desorption isotherm. Spherical particle size and core space could be controlled by changes in stirring rate and concentrations of TEOS and butanol. Increasingly large particles were obtained as the stirring speed decreased from 1200 to 300 rpm. At a fixed amount of butanol, increases of TEOS amount led to increases in particle size and also increased the particle thickness. TEOS concentration did not sensitively govern the particle size as butanol concentration. At a fixed amount of TEOS, increases of butanol/TEOS molar ratio led to particle size increase from 125 urn to 1 mm. Increase of butanol concentration was 800 related not to only particle size but also to mesostructure formation. Pore 600 diameter was increased from 3.2 to 4.9 nm with increasing concentration of butanol. 400 Pore diameter As shown in Fig. 2, nitrogen adsorption-desorption isotherm of 200 type IV for mesopore structure and hysteresis loop of type H2 was 0 0.0 0.2 0.4 0.6 0.8 1.0 observed, which is known due to the Relative Pressure (P/Po) presence of pores with narrow mouths (cage-like pores). The isotherm Fig. 2. Nitrogen adsorption-desorption isotherm inflection point for the spherical plot and BJH desorption pore size distribution mesoporous silica particles was (inset) of spherical mesopore silica. 10

100

1000

610

located at relatively high P/Po between 0.6 and 0.7, which indicates larger pore diameter than other mesoporous materials such as MCM-41 and HMS. BET surface area was ca. 890 m /g, single point total pore volume at relative pressure of 0.98 was 0.96 cm3/g, and the BJH desorption pore diameter was 4.9 nm. Fig. 3 shows the TEM micrograph of the spherical silica material prepared. Disordered pore structure but with uniform diameters similar to the disordered mesoporous silica materials obtained using nonionic surfactant or in the presence of organic salt [3,4] was observed. Ordered pore structures are seldom found in the case of spherical particles for which an oil phase is employed to control the morphology. It seems that its mesostructure was disordered because of the presence of butanol in the synthesis mixture. Increasing amount of butanol added to the synthesis batch for SBA-15 in acidic condition led to transition from 20 nm 2D hexagonal to the cubic Ia3d mesophase and finally to the disordered phase through the smaller Fig. 3. TEM micrograph of the spherical domains of intermediate mixed phase mesoporous silica. [5]. 4. Conclusion Spherical mesostructured silica particles with core space were synthesized under acidic condition in an aqueous/butanol emulsion system. Concentration of TEOS or butanol was directly proportional to the sphere diameter in such a manner that high concentration of both TEOS and butanol resulted in particle size increases. Butanol, however, was the more critical variable controlling the particle size and also found to affect the pore diameter of the silica obtained. 5. References [1] S. Schacht, Q. Huo, I. G. Voigt-Martin, G. D. Stucky and F. Schuth, Science, 273 (1996) 768. [2] Q. Huo, J. Feng, F. Schuth and G. D. Stucky, Chem. Mater., 9 (1997) 14. [3] P. Tanev and T. Pinnavia, Science, 269 (1995) 1242. [4] R. Ryoo, J. Kim, C. Ko and C. Shin, J. Phys. Chem., 100 (1996) 17718. [5] T. Kim, F. Kleitz, B. Paul and R. Ryoo, J. Am. Chem. Soc, 127 (2005) 7601.


611 611

Synthesis of highly ordered large pore mesoporous silica SBA-16 spheres Hongxiao Jina, Qingyin Wua*, Chao Chenb, Daliang Zhang1 and Wenqin Pangab* "Department of Chemistry, Zhejiang University, Hangzhou 310027, P. R. China h State Key Lab of Inorganic Synthesis and Preparative Chemistry, Jilin University, Changchun 130023, P. R. China

1. Introduction It is well-known that the morphology of mesoporous materials plays one of the key roles for their advanced applications [1]. This is because that the applications of these materials depend on not only the intra-particle structures but also the inter-particles mass transport process. Mesoporous materials with spherical morphology have attracted considerable attention due to the potential applications in macromolecular separation, drug deliveries, catalysis supports and template agents for photonic crystals [2]. Sine e the first report of the synthesis of mesoporous silica spheres through a modification of Stober's procedure [3], several synthetic methods, including solution self-assemble aero sol spraying [4, 5], hard template and evaporation-induced self-assemble process were developed [6, 7]. Compared with other process, the solution selfassemble route was relatively technologically simple. The diameter of these products is less than Ca. 10 um excluding a few examples. Recently, Kosuge K. and co-workers reported the forming of porous silica spheres over 100 um in diameter using triblock copolymer as template. But the quality of the intraparticle mesostructure is still limited. Herein, we present a facile synthesis of highly ordered SBA-16 spheres with diameter of 2~6 um in a ternary F127H2O-HC1-TEOS system.

612

2. Experimental Section 2.1. Synthesis of Materials The preparation procedure was as follow: triblock copolymer Pluronic F127 was added to HC1 aqueous solution and allowed to stir at a certain temperature overnight. Then, TEOS was added to this solution under vigorous stirring. After 10 min stirring, the mixture was kept under static conditions at aforementioned temperature for 3 ~ 72 h. The solid products were collected by filtration, washed with ethanol, dried, and calcined at 550°C in air for 5 h. The preparation of SBA-16 single crystals relies on the control of the reaction temperature and the reactants ratio. 2.2. Characterization of Materials XRD patterns were recorded on a SIEMENS D8 ADVANCE powder diffraction system using Cu Ka (1=1.5418 A) radiation (40 kV and 40 mA). The Scanning electron micrographs (SEM) were taken on FEI SIRJON electron microscope with an acceleration voltage of 5 KV. The samples were deposited on a sample holder with an adhesive carbon foil and sputtered with gold prior to imaging. Transmission electron microscopy (TEM) measurements were taken on a JEM-3010 electron microscope (JEOL Japan) with an acceleration voltage of 300 KV. The nitrogen sorption experiments were performed at -196 °C on Micromeritics ASAP 2010M systems. The samples were outgassed at 300 °C for 10 h before the measurement. The pore diameter was calculated from the analysis of desorption branch of the isotherm by the BJH (Barrett-JoynerHalenda) method. 3. Results and Discussion As revealed by field emission scanning electron microscopy (FE-SEM), mesoporous silica SBA-16 of decaoctaheron shape consists of a large quantity of cubic structure with typical diameter of 2~6 micrometers (part a and b in Figure 1). The evidences for the mesostructure are provided by a combination of TEM, XRD and N2 adsorption/desorption measurement. Part c in figure 1 show TEM image taken along 100 incidence, which reveals a lattice constant of ao = 10 nra. Low-angle X-ray diffraction (XRD) measurements (part d in Figure 1) show that the calcined powder exhibits 3 diffraction peaks in the region of 20 = 0.9 -1.8 degree, which are indexed to the 110, 200 and 211 diffractions of cubic symetery with a lattice constant of ao = 11 nm [8]. The lattice value is in accordance with the TEM result. The corresponding nitrogen adsorption/ desorption measurement give type-IV isotherms with a H2 hysteresis loop (part e in figure 1), which suggests that the mesopores are cage like. The average

613

pore diameter was calculated to be 7.2 nm from the adsorption branch of the isotherm by using the Barrett-Joyner-Halenda (BJH) method. The results give a pore volume of 0.5 crnVg, a BET surface area of 700 m2/g. Recently, a time-resolved in-situ study of the formation of SBA-16 suggests that globular micelles in a silica matrix involves in early stage, which directly transforms into cubic structure in final. Moreover, to visualize the selforganization of spherical micelles, a "colloidal phase separation" mechanism was proposed [9]. Thus, the formation of mesoporous spheres could be considered as meso-scaled self-organization of spherical micelles and inorganic species into micrometer structured domains. To maintain the high curvature spherical building block, various parameters which can greatly influence the final mesostructure and morphology of the products, such as reaction temperature the surfactant/silica ratio, and anions present in the reaction, should be carefully controlled.

Fig. 1 Calcined SBA-16 spheres: (a), (b) FE-SEM image; (c) TEM image taken along 100 incidence; (d) XRD pattern; (e) N2 adsorption/ desorption isotherm.

Various synthesis conditions were investigated as shown in Figure 2. Part a, b and c show the effect of HCl concentration under the synthetic condition: 1.00

614

TEOS: 0.049 F127: X HC1: 182.4 H2O at 30°C, where X=1.6, 4.8 and 8.0. Part d, e and f show the effect of the surfactant ratio under the synthetic condition: 1.00 TEOS: Y F127: 4.8 HC1: 182.4 H2O at 30°C, where Y=0.016, 0.033 and 0.057. Part g, h and i in show the effect of the reaction temperature under the synthetic condition: 1.00 TEOS: 0.049 F127: 4.8 HC1: 182.4 H2O at 24, 28 and 34 °C, respectively. The results showed that a middle surfactant concentration (TEOS/F 127=0.016-0.057), strong acidic conditions (1.0-2.5M HC1) and a moderate reaction temperature (24~32°C) were necessary for the syntheses. Moreover, lower surfactant concentration leads to amorphous porous powder with poor structure order; higher concentration would not promote the surfactant/silicates condensation. Stronger acidity or higher temperature would promote a rapid, uncontrolled hydrolysis/condensation of silica species which would not lead to the formation of spheres. Weaker acidity with an HC1 concentration less than 1.2 M would lead to the formation of other mesoporous structure, and lower reaction temperature would result in materials with amor-

Fig. 2 SEM micrographs of samples synthesized under various conditions of which more details are presented in text: HC1 = a) 0.5 M, b) 1.5 M and c) 2.5 M; TEOS/F127 molecular ratio = d) 0.016, e) 0.033, f) 0.057; reaction temperature = g) 24 °C, h) 28 °C, i) 34 °C. Scale bar: 5 j i m .

phous morphology and poorly ordered mesostructures. It should also be noted that mesoporous SBA-16 single crystals (part h) could be obtained by a more carefully control of the synthetic condition. It was reported that the addition of co-surfactant, cosolvents and inorganic salts are beneficial to the synthesis of mesoporous silica spheres. In that case PI23 was used as template; however, F127 was used in our case. The difference

615

of the solution behavior between PI23 and F127 cause the result spheres different in both morphology and intrinsic mesostructure: ~luxn VS 2~6 urn in size, hexagonal VS cubic in structure. Moreover, Kosuge K. and co-workers reported the forming of porous silica spheres which over 100 um in diameters and less order in structure using various triblock copolymers as template and sodium silicate solution as silica source. In this study, TEOS was used as silica source under similar other synthetic conditions. 4. Conclusion Highly ordered large pore mesoporous silica SBA-16 spheres with 2-6 \im in diameter were synthesized in a ternary F127-H2O-HC1-TEOS system. The effect of various synthetic conditions such as HC1 concentration, TEOS/surfactant ratio, silica and template source, and reaction temperature were investigated. The results show that the TEOS which results in more dispersed silicate under hydrolysis in acid solution favors the formation of highly ordered small mesoporous spheres, while sodium silicate which possesses poly condensed silicate drives larger spheres with less structural order. 5. Acknowledgement The financial support of the State Basic Research Project of China (G200077507), the National Natural Science Foundation of China (Grant No. 20233030, 20271045), and the State Key Laboratory of Inorganic Synthesis and Preparative Chemistry of Jilin University for this work is greatly appreciated. 6. References [1] [2] [3] [4] [5] [6]

L. Li, Q. Y. Wu, Y. H. Guo and C. W. Hu, Microporous Mesoporous Mater., 87 (2005) 1. A. Stein, Adv. Mater., 15 (2003) 763. M. Grttn, I. Lauer and K. K. Unger, Adv. Mater., 9 (1997)254. K. Kosuge, N. Kikukawaand M. Takemori, Chem. Mater., 6 (2004) 4181. Y. Lu, H. Fan, A. Stump, T. L.Ward, T. Rieker and C. J. Brinker, Nature, 398 (1999) 223. M. L. Breen, A. D. Dinsmore, R. H. Pink and S. B. Qadri, B. R. Ranta, Langmuir, 17 (2001) 90. [7] C. J. Brinker, Y. Lu, A. Sellinger and H. Fan, Adv. Mater., 11 (1999) 579. [8] D. Zhao, Q. Huo, J. Feng, B. F. Chmelka and G. D. Stucky, J. Am. Chem. Soc.,120 (1998) 6024. [9] C. Yu, B. Tian, J. Fan and D. Zhao, Chem. Mater., 16 (2004) 880.



617 617

Effects of the different amount of phosphoric acid on the resulting morphology of SBA-15 Yun Li ab , Jihong Sun a \ Fu Ma ab and Shijie Luoa "Department of Chemistry and Chemical Engineering, College of Environmental & Energy Engineering, Beijing University of Technology, Beijing, 100022, P. R. China Key Laboratory of Energy and Chemical Engineering, NingXia University, Yinchuan, 750021, P. R. China

1. Introduction For the synthesis of the SBA-15 with controllable morphology, most approaches were based on changes in synthesis conditions including the silica source [2], the nature of surfactants, co-surfactants and co-solvent [3], additive of organic substances, inorganic salts [4], acids and bases as well as the overall composition of the synthesis mixture. While, SBA-15 film can be grown at solid-liquid and liquid-vapor interfaces through an interface silica-surfactant self-assembly process [5]. All of these films were formed by using acidic condition, and low molecular weight surfactants. Up to now, only few contributions have been published on the synthesis of large mesoporous silica free standing film by using non-ionic triblock copolymer as template at the interface of air/water [1]. A simple method is reported to synthesize SBA-15 with controlled distinct morphologies. Well ordered transparent mesoporous silica freestanding film and cake-like structure were produced by using nonionic surfactant (PI23) in the presence of phosphoric acid under static conditions. In this experiment, in order to further our understanding of the fundamental mechanism by using the mild phosphoric acid replacing the commonly strong hydrochloric acid, we also investigated in detail the influence of adding different amount of phosphoric acid on the resulting morphology of SBA-15.

618

2. Experimental Section SBA-15 samples were prepared by using triblock copolymer P]23 (EO20PO70EO20, MW 5800, Aldrich) as template, tetraethyl orthosilicate (TEOS) as silica source and phosphoric acid (H3PO4, 85%) as acid source through hydrothermal synthesis. The synthesis approach is based on the hydrothermal route reported by Coppens and co-workers [1]. X-ray diffraction (XRD) of the samples was recorded using a Brucker-AXS D8 Advance X-ray diffractometer using Cu K a radiation (X Ka : =0.154056nm). Scanning electron microscopy (SEM) images were obtained with a JEOL JSM6500 microscope. Transmission electron microscope (TEM) images were recorded on a JEOL JME-2010. Nitrogen adsorption-desorption isotherms were measured using a Micromeritics ASAP 2010 system, and pore size distributions were obtained from the N2 desorption branch isotherm using BJH method. 3. Results and Discussion (100)

(100) (100)

(110)

a

b

(110) (200)

0

2

4

6

2θ/°

8

10

0

2

4

6

2θ/°

8

10

Fig. 1 The typical XRD patterns of calcined solid product (a) and film (b) of SBA-15

It can be seen that the pattern of the solid product in Figure la shows a series of well-defined reflections, which could be assigned to the (100), (110), and (200) planes of SBA-15, demonstrating a long-range ordered 2-D hexagonal space group (P6mm), similar to traditional hexagonal phase SBA-15 [1, 11]. While the pattern of film in Figure lb, shows only two low-angle peaks assigned to (100) and (110) reflections of the hexagonal symmetry. Very interestingly, we also found that, for the SBA-15 film, the intensity of (100) peak of XRD pattern in Figure lb is less than that of (110) peak. The SBA-15 particles are randomly oriented, while the pores in the film run parallel to the surface [1]. It should also be mentioned that these findings are in agreement with [1]. Compared with that of the random hexagonal SBA-15 particle, both the weak intensity of the (100) reflection and strong intensity of

619

(110) peak for the film imply that the effects of phosphoric acid on the processing of between inorganic species and surfactant in the solution play an important rule in limiting the growth of film along with (100) dimensional arrays. TEM for film SBA-15 (Figure 2a) shows the parallel one-dimensional nanochannels of uniform diameter around 6nm running along the long axis (110) of the bundles, in good agreement with that as observed with XRD patterns in Figure lb.

a

b

20nm Fig. 2 TEM (a) and SEM (b) images of SBA-15 film

SEM image of the calcined SBA-15 film shows that the film is continuous and composed of the randomly aggregated uniform particles. Whereas, enlarged image for film SBA-15 (Figure 2b) reveals that each individual is composed of a well-defined nanopatricle with a uniform diameter around lOOnm. 14

1000

f e

800

d

600

12 12

dv / dlog (D) (cm3 / g)

Volume Adsorbed (cm3 / g STP)

1200

-»

c b a

400

o

8

f\

6fi

il

1 jk *^ Ax

A

>

0 0. 4 0.4

d c

4

| \

2

b

^ ^ ^ * ^ v^

0 0. 2 0.2

ee

^y\^v

O>

200 0 0

^f

M—

10 10

0. 6 0.6

0. 8 0.8

Relative 0) Relative Pressure Pressure (P/P (P/P0)

1

1

aa

10

B 100

Pore Diameter Diameter (nm) (nm) Pore

Fig. 3 Nitrogen adsorption-desorption isotherms (A) and corresponding to the pore size distribution plots (B) for solid SBA-15 prepared using different amount of phosphoric acid. The molar composition of H3PO4/TEOS in the starting reactant solution was (a) 0.5, (b) 1, (c) 2, (d) 4, (e) 6, (f) 8

620

Meantime, we investigated in detail the influence of adding different amount of phosphoric acid on the resulting texture properties of solid product. Figure 3 shows the nitrogen adsorption/desorption isotherms and corresponding to the pore size distribution plots for series of SB A-15 solid prepared with increasing the amount of phosphoric acid in the starting reactant solution. All of the isotherms for the different calcined SBA-15 solid (Figure 3a) show the typical type IV isotherm with HI type hysteresis loop, indicative of an ordered, welldefined mesoporosity. The position of the inflection point is relative to pore size, and the sharpness of these steps indicates the uniformity of the pore size distribution. The shift of the capillary condensation step to lower relative pressures with increasing the amount of phosphoric acid (n (H3PO4) /n (TEOS> =0.5-8.0 suggests a decrease in the pore size, which was changed from around 3.5nm to 6.5nm in Figure 3b. The other factors such as reaction temperature, aging time and inorganic salt are under way recently. 4. Conclusion In the XRD pattern of SBA-15 film, the intensity of (100) peak is lower than that of (110) peak indicates that the effect of phosphoric acid on limiting the growth of film along with (100) dimensional arrays during the period processing of between silicate species and surfactant PI23. SEM image of the SBA-15 film shows that the film is continuous and composed of a well-defined nanopatricle with a uniform diameter (100 nm). The mean pore size of SBA-15 solid was decreased from around 3.5 ~ 6.5nm with increasing the molar ration of n (H3PO4) /n (TEOS) from 0.5 to 8.0. 5. Acknowledgement This work was supported by the Doctoral Science Fundation of BJUT and the Natural Science Fundation of Ningxia Hui Autonomous Region (ZD02). 6. References [1] [2] [3] [4] [5]

R. Pitchumani, W. J. Li and M. O. Coppens, Catalysis Today, 105 (2005) 618. K. Kosuge, T. Sato, N. Kikukawa and M. Takemori, Chem. Mater., 16 (2004) 899. D. Y. Zhao, J. Y. Sun, Q. Z. Li and G. D. Stucky, Chem. Mater., 12 (2000) 275. D. Y. Zhao, P. D. Yang, B. F. Chmelka and G. D. Stucky, Chem. Mater., 11 (1999) 1174. I. A. Aksay, M. Trau, I. Honma, N. Yao, L. Zhou, P. Fenter, P.M. Eisenberger and S. M. Gruner, Science, 273 (1996) 892.

Mesostructured Materials Recent Progress in Mesostructured D. Zhao, S. Qiu, Y. Tang and C. Yu (Editors) © 2007 Elsevier B.V. All rights reserved.

621 621

Morphology control of SBA-15 in chiral organic acid media Shengrong Ye, Yueming Liu, Mingyuan He and Peng Wu* Shanghai Key Laboratory of Green Chemistry and Chemical Processes, Department of Chemistry, East China Normal University, North Zhongshan Rd. 3663, Shanghai 200062, P. R. China

SBA-15 siliceous materials have been synthesized in chiral organic acid media, and their physicochemical properties have been characterized by various techniques. The resultant materials exhibited distinctive macroscopic morphologies and textural properties different to conventional SBA-15. By changing the aging temperature, a range of mesoporous silica with independently tailored mesopores were obtained. 1. Introduction SBA-15 is a mesoporous SiO2 with a hexagonal arrangement of channels with diameters in the range of 6-30 nm, templated by nonionic triblock copolymers EOnPOmEOn via a hydrogen bonding [S H+][X"I+] assembly pathway [1, 2]. Because of its promising applications to catalyst supports, hostguest assembling materials and adsorbents etc., it is important to control its morphologies. Mesoporous materials in the form of sphere, fibber, doughnut, rope, egg-sausage, and gyroid have been obtained by controlling the synthesis conditions and varying the nature of surfactants [3]. In the present work, we report a simple approach to selectively synthesize unique morphologies of SBA-15 with highly ordered large mesopore hexagonal structures in the media of chiral organic acids of tartaric acids, D-(-)-TA and L-(+)-TA. 2. Experimental Section The SBA-15* materials have been synthesized by modifying the methods described in the literature [1] from typical synthesis batches with the gel composition of Pluronic PI 23 or Pluronic F68, aqueous solution of tartaric acid,

622

and tetraethyl orthosilicate (TEOS) (Table 1). XRD, SEM, TEM, and N2 adsorption were used to characterize these materials. 3. Results and Discussion SBA-15* materials are very well-defined and characteristic of ordered hexagonal materials (Fig. 1). After calcination, a 2 % contraction is observed for samples synthesized at 120 °C, giving cell parameters around 12.0 nm (Table 1, No. 1-4). For samples synthesized at temperatures between 35 and 90 °C, the cell parameter of calcined samples are in ranges from 10.1 to 12.2 nm, revealing a much heavier contraction (10-12 %) (Table 1, No. 9-20). In the case of the samples synthesized at 0 °C, the calcination caused a less contraction (4 %) and the solids retained their cell-unit sizes (ca. 12.0nm) (Table 1, No. 22-24). Table 1 Preparation Conditions and Physicochemical Properties of Calcined SBA-15* b V e Template/Acid/Aging Unit Cell3 n td SBET vtc mi 2 Temperature (nm) (nm) (m /g) (crnVg) (nm) 1 P123/D-(-)-TA/120°C 0.9 0.06 12.2(12.4) 11.3 673 1.6 2 P123/L-(+)-TA/120°C 12.2(12.3) 11.3 2.0 0.9 0.06 731 3 F68/D-(-)-TA/120°C 12.1(12.4) 11.3 614 1.6 0.8 0.05 4 F68/L-(+)-TA/120°C 754 1.8 0.5 0.04 11.8(12.0) 11.3 P123/D-(-)-TA/100°C 5 11.7(12.7) 10.2 892 1.6 1.5 0.09 P123/L-(+)-TA/100°C 11.6(12.6) 10.0 1.6 0.07 706 1.3 6 F68/D-(-)-TA/100°C 11.6(12.6) 9.9 818 1.6 1.7 0.07 7 F68/L-(+)-TA/100°C 9.9 869 .6 1.5 0.07 11.4(12.6) 8 9 P123/D-(-)-TA/90°C 1125 .8 2.1 0.13 12.1(12.7) 10.0 10 P123/L-(+)-TA/90°C 0.14 12.2(12.9) 9.9 1089 .8 2.3 11 F68/D-(-)-TA/90°C .6 1.9 0.11 11.9(12.6) 10.0 1007 12 F68/L-(+)-TA/90°C 0.12 11.9(12.5) 9.9 929 .6 2.0 13 P123/D-(-)-TA/60°C 0.14 10.1(11.7) 6.1 711 0.8 4.0 14 P123/L-(+)-TA/60°C 4.2 10.2(11.6) 6.0 796 0.9 0.15 F68/D-(-)-TA/60°C 0.22 15 10.6(11.2) 6.1 1210 1.5 4.5 16 F68/L-(+)-TA/60°C 780 1.1 3.8 0.16 10.5(11.6) 6.7 17 P123/D-(-)-TA/35°C 1.2 3.9 0.14 10.6(12.0) 6.7 895 18 P123/L-(+)-TA/35°C 4.0 0.13 10.7(12.1) 6.7 789 1.1 19 F68/D-(-)-TA/35°C 10.2(12.0) 6.2 601 0.8 4.0 0.15 20 F68/L-(+)-TA/35°C 10.8(12.2) 696 1.0 3.5 0.13 7.3 21 P123/D-(-)-TA/0°C 10.2(12.2) 0.8 3.5 0.11 6.7 690 22 P123/L-(+)-TA/0°C 0.16 12.0(12.3) 8.1 920 1.1 3.9 0.14 23 F68/D-(-)-TA/0°C 783 1.0 4.0 12.0(12.5) 8.0 24 F68/L-(+)-TA/0°C 5.4 0.25 12.2(12.7) 6.8 111 0.7 a The numbers in parentheses indicate the unit cell dimension of as-synthesized samples. b Pore size obtained from adsorption isotherm.c Total pore volume. d Wall thickness. e Micropore volume.

No.

v

623 (100) (100)

A(100) (100)

A

(110) (200)

110)(200) 1 A

a b

h-

a b c

c d

A j\

f 2

3 2Theta/°o 2Theta/

d

•A

e

1

B

(110)(200)

4

5

1

e f 2

3 o 2Theta/ 2Theta/°

4

Fig. 1 Powder XRD patterns of as-synthesized (A) and calcined (B) SBA-15* synthesized at 120°C (a), 100°C (b), 90°C (c), 60°C (d), 35°C (e) and 0°C (f). The difference between the cell parameter and the pore size, namely the pore wall thickness (/), became thicker at lower temperatures but it did not increase at temperatures below 60°C; in contrast, the samples prepared at 60°C, 35°C, 0°C possessed nearly the same pore wall thickness (Table l,No. 13-24). Fig. 2 shows several representative SEM and TEM images for SBA-15*. The mesoporous channels running parallel to the long axis were ca. 10 nm in diameter and had a uniform 2D hexagonal array (P6mm) (Fig. 2a-c). The presence of the roughness in the pore windows was observed. Here, the use of the chiral tartaric acids resulted in the well-defined rodlike aggregates (Fig. 2d-g). It seems that the different counterions of acids have a large effect on the macroscopic morphology. The main reason is that the tartaric acid is not a strong acid (pKal = 3.2; pKa2 = 4.8); which led to the pH value of about 1.1. Increasing the pH value decreases the .. , .. r^, .... .. aggregation velocity of the silicic acid. SBA-15 tends to form more curved

Fi

8- 2 T E M ( a ' c ) a n d S E M i m a 8 e s (d-§> " * PrePared in the media of D( } TA at 9 C -°° < c ) , ™ d ^ ^ l f i e d images off (b) and (d). SBA-15 prepared in typica , m e t h o d (HC1) is for c o m p a r i s o n (h) . o f SBA 15

5

624

morphology such as the ropelike ones according to the literature [3]. However, the morphology of SBA-15* is unexpectedly close to rodlike one with a low curvature. The nitrogen sorption isotherms of SBA-15* materials with different pore size distribution are shown in Fig. 3. All the N2 adsorption-desorption isotherms are of type IV. A shift to higher relative pressure of the pore-filling step was observed in the isotherms with increasing synthesis temperature, indicating that hydrothermal synthesis at higher temperatures leads to an increase of pore diameter. It is also in agreement with the pore size distribution calculated by BJH method (Fig. 4 and Table 1, No. 1-16). 0.09 0.09

e

0.08

a

2000

b

1500

c

1000

d e

500 0 0.0

0.07

a

6 0.06

3

2500

dV/dD (cm /(nm g))

3

Vol Adsorbed (cm /g STP)

3000

I

-o

f 0.2

0.4

0.6

0.8

1.0 1.0

Relative Pressure (P/P (P/P00)

Fig. 3 The isotherms of SBA-15* prepared at different synthesis temperatures. For a-f, same in Fig. 1.

•

fi c lf\

f

0.05

d

0.04 0.03 0.02 0.01 -

1b

11/^ ^

1 ft

0.00 00

55

10 10

15 15

20 20

25 25

30

Pore Diameter (nm)

Fig. 4 BJH pore size distribution of SBA-15* prepared at different synthesis temperatures. For a-f, same in Fig. 1.

4. Conclusion SBA-15 materials with unique morphology and pore properties have been synthesized in chiral acid media. The weak acidity of acetic acids tends to lead to rodlike shape with larger crystal sizes. 5. Acknowledgement Financial supports by NCET-04-0423, Pujiang project (05PJ14041), 973 project (2003CB615801), STCSM (05DZ22306, 05JC14069) and NSFC (20473027 and 20233030) are appreciated. 6. References [1] D. Y. Zhao, J. L. Feng, Q. S. Huo, N. Melosh, G. H. Fredrickson, B. F. Chmelka and G. D. Stucky, Science, 279 (1998) 548. [2] D. Y. Zhao, Q. S. Huo, J. L. Feng, B. F. Chmelka and G. D. Stucky, J. Am. Chem. Soc, 120 (1998) 6024. [3] D. Y. Zhao, J. Y. Sun, Q. Z. Li and G. D. Stucky, Chem. Mater. 12 (2000) 275.


625 625

Synthesis of the mesoporous TiO2 films and their application to dye-sensitized solar cells Dong-Hyun Cha, Young-Suk Kim, Jia Hong Pan, Yoon Hee Lee, Wan In Lee* Nano Materials and Devices Lab., Department of Chemistry, Inha University, lncheon 402-751, Korea.

Mesoporous titania films with worm-like structure have been fabricated on the FTO substrates by evaporation-induced self-assembly (EISA) process using triblock copolymer as a structure-directing agent. The prepared mesoporous films were applied to the electrode material in the dye-sensitized solar cells (DSSCs). SAXRD patterns and TEM images show that the mesoporous structure was thermally stable at least up to 450 °C. The DSSC fabricated from these mesoporous films showed 1.7 times of photovoltaic current (Jsc) than those from the nanocrystalline films in the same thickness. It is deduced that the high Jsc is caused by the efficient transport of electrons due to far less grain boundaries in the mesoporous TiO2 structure, and by the fast diffusion of electrolytes with the high uniformity in the mesopore size. 1. Introduction Recently, DSSC draws great attention with low production cost of electricity and high energy conversion efficiency. One of the highest photoconversion efficiency of DSSCs derived from the nanocrystalline titania is 10.4%, as reported by GratzeFs group [1]. Typically for the construction of DSSC, the TiO2 nanoparticles are deposited as a thick film layer on the transparent conductive oxide (TCO). Then, the dye molecules are anchored on its surface, and the redox couples and electrolytes are filled between two electrodes. The photo-excited electrons from the dye molecules are injected to the conduction band of TiO2 and transferred to the TCO. Recently, the tailoring of TiO2 nanostructures in the DSSC has been studied for the purpose of efficient transfer of the injected electrons [2,3]. The mesoporous TiO2 films would be a promising candidate with high surface area and uniform pore diameter. In this work, the 1.2 fxm-thick the mesoporous titania films were deposited on the TCO,

626

and they were applied to the DSSC. The advantage of the mesoporous titania films on the photoconversion efficiency of DSSCs was also discussed. 2. Experimental section The mesoporous TiO2 films were prepared by spin-coating the Ti-sol on a pre-cleaned FTO glass [4]. The molar composition TTIP: F127: HC1: H2O: EtOH was 1: 0.005: 1.7: 10: 24. The deposited films were aged for 3 days in the closed chamber, whose relative humidity was maintained to 60% by a saturated Mg(NO3)2 aqueous solution. The nanocrystalline TiO2 films were prepared by screen-printing method. Both films were calcined at 450 °C for 30 min, and immersed into the dye solution (N3, Solarnonix Inc.) for 24 hr. The dye/TiO2 layer/FTO and Pt/FTO were used as working and counter electrodes, respectively, and the electrolyte was filled into the interval between these two electrodes. The photovoltaic properties of the DSSCs were measured by a Keithley 2400 source meter under the AM 1.5 direct illumination provided by a Thermo Oriel Xenon 300 W lamp fitted with AM 1.5D filters. 3. Results and discussion It was found that the periodic texture of the prepared mesoporous titania films was greatly dependent on the nature of substrates. With the given EISA condition, the highly organized cubic mesoporous structures in the thickness of 300 nm could be grown on the Pyrex glass, but the worm-like mesostructure was obtained by on the (a) (b) ITO or FTO glass, as indicated in the Planview TEM images of Fig. 1. The structure of the Meso-Ti02 films was stable up to 450 °C, which is a typical heattreatment temperature 50nm for the fabrication of DSSCs. Fig. 1. TEM images of the Meso-TiO2 films in about 300 nm For the application thickness, (a) A cubic mesoporous structure grown on Pyrex of mesoporous TiO2 glass, (b) A worm-like structure grown on FTO substrate. films to DSSC, the 1.2 (im-thick films (Meso-TiO2) were fabricated on FTO glass, by applying the four times of EISA process, since the thickness of the mesoporous titania films obtained by the single EISA process is only 300 nm. For the comparison, 1.8 u.m-thick nanocrystalline TiO2 films (NC-TiO2) were formed by screen-printing method. 1.00 g of 7 nm-sized TiO2 nanoparticles was suspended in 8 ml of ethanol/H2O solution (50: 50 in volume), and then 0.30 g of polyethylene glycol

627

20,000 (Fluka Co.) and 0.10 g of polyethylene glycol 500,000 (Wako Pure Chemical Co.) were added to obtain highly viscous paste for the screen printing. Fig. 2 shows the cross-sectional SEM images for the 1.2 |wn-thick Meso-TiO2 and the 1.8 (am-thick NC-TiO2 films annealed at 450 °C. Both films do not have cracks, and seem to have good contact with the FTO substrate.

(b)

(a)

1

1

Fig. 2. Cross-sectional SEM images for the Meso-TiO2 (a) and NC-TiO2 (b) films.

Fig. 3 shows the photocurrent versus voltage curves for the DSSCs derived from Meso-TiO2 and NC-TiO2 films. The Jsc of the DSSC derived from the Meso-TiO2 film was 15% higher than that of the DSSC from NC-TiO2 films, even though the thickness of the Meso-TiO2 film is only 2/3 of that of the NCTiO2 film. This indicates that the Jsc of DSSC from the Meso-TiO2 film is 1.7 times, when it is compared at the same thickness. Furthermore, the Voc was increased from 0.615 V to 0.645 V. It was observed that the Meso-TiO2 film was very tightly bound to the FTO substrate. This may induce the appreciable increase of Voc due to the low contact resistance between the TiO2 layer and the FTO substrate. From the BET measurements, the surface area of the Meso-TiO2 was determined to 142 m2/g, while that of the NC-TiO2 was 108 m2/g. Considering the thickness difference in these two films, the surface area of the Meso-TiO2 film was only 0.51 times of that of NC-TiO2 film. The amount of the adsorbed N3 dye in the both films was analyzed in this work. That is, the adsorbed dye in the TiO2 films was retrieved by the addition of 0.1 M NaOH ethanol solution, 5

voc

F.F

n [%]

Jsc (mA/cm2)

4

3

NC-TiO2

3.07

615

0.69

1.92

Meso-TiO2

3.52

645

0.69

2.32

2

NC-TiO NC-TKX,2 Meso-TiO2

1

0 0

200

400

Applied Voltage (mV)

600

Fig 3.1-V curves for the DSSCs derived from the Meso-TiO2 and NC-TiO2 films. The thicknesses of films were controlled to 1.2 and 1.8 |im, respectively. The measured results are summarized in the table.

628

Absorbance (a.u.)

and the concentration of the eluted dye was estimated by UV-Visible absorption spectra, as shown in Fig. 4. The absorption maxima at around 500 nm indicate the characteristic absorption peak of N3 dye. The peak height for the MesoTiO2 sample was 0.54 times that for the NC-TiC>2 film. This suggests that the adsorption amount of N3 dye is simply proportional to the surface area of TiO2 regardless of the film structure. Herein we found the Meso-TiO2 film containing 54% of N3 dye NC-TiO2 showed 115% of photovoltaic current Meso-TiO2 0.2 than the NC-TiO2 film. Then why does the mesoporous film show 8 higher photovoltaic current? First, the mesoporous TiO2 structure have 0.1 much less grain boundary. Thus the injected electrons to the conduction band of TiO2 from the photo-excited 0.0 N3 dye can be efficiently transported 400 500 600 700 800 500 600 700 to the TCO without the back Wavelength (nm) transport to the HOMO of the dye. Fig. 4. The absorption peaks of N3 dye eluted Second, the mesopore of Meso-TiO2 from the Meso-TiO2 and the NC-TiO2 films, respectively. film is highly uniform in size and have good connectivity without blind ally. Thus the diffusion of the electrolyte is expected to be greatly efficient. The optimum thickness of nanoporous TiO2 films providing the highest photovoltaic efficiency in the DSSC is higher than 10 m in general. Therefore, the preparation of very thick mesoporous TiO2 film is prerequisite for the realization of high efficiency solar cell. More attention is necessary in this issue. 4. Acknowledgement The authors gratefully acknowledge the financial support of the Korean Science and Engineering Foundation (KOSEF R01-2003-000-10667-0). 5. References [1] M. Gratzel, (2001). Photoelectrochemical Cells. Nature 414 (2001) 338. [2] L. I.. Halaoui, N. M. Abrams and T. E. Mallouk,. Increasing the Conversion Efficiency of Dye-Sensitized TiO2 Photoelectrochemical Cells by Coupling to Photonic Crystals. J. Phys. Chem. B 109 (2005) 6334. [3] M. Zukalova, A. Zukal, L. Kavan, M. K. Nazeeruddin, P. Liska and M. Gratzel, Organized Mesoporous TiO2 Films Exhibiting Greatly Enhanced Performance in Dye-Sensitized Solar Cells. Nano Lett. 5, (2005) 1789. [4] J. H. Pan and W. I. Lee, Selective Control of Cubic and Hexagonal Mesophases for Titania and Silica Thin Films with Spin-Coating. New J. Chem. 29(2005) 841.


629 629

Formation mechanism of monodispersed mesoporous silica spheres and its application to the synthesis of core/shell particles Hiroshi Nozaki, Noritomo Suzuki, Tadashi Nakamura, Yuusuke Akimoto and Kazuhisa Yano Toyota Central Research & Development Labs. Inc., Nagakute, Aichi, 480-1192, Japan. 1. Introduction

After the discovery of the M41S family [1], considerable amounts of research have been made on the synthesis of mesoporous silicas possessing uniform mesopores and high specific surface areas [2-4]. Many researchers have investigated the formation mechanism of mesoporous silicas so far [5-8], no simple mechanism exists because it greatly depends on the synthesis conditions. Recently, we have successfully synthesized monodispersed mesoporous silica spheres (MMSS) possessing highly ordered hexagonal regularity from tetramethoxysilane and alkyltrimethylammonium halide in very diluting conditions [9-13]. During the reaction, a clear solution turned opaque suddenly, a white precipitate appearing. It is very important to study the formation mechanism of MMSS to control particles size and monodispersity precisely. In order to address the mechanism, in situ particle size development was measured by means of TEM. A newly developed method for MMSS with core/shell structure based on the proposed mechanism will be also described. 2. Experimental Section Synthesis was conducted according to the literature [11]. Core/shell particles were obtained by adding TMOS/mercaptopropyltrimethoxysilane (MPTMS) mixture 30 min after the commencement of the experiment. Transmission electron microscopy (TEM) was performed on a Jeol-200CX TEM using an acceleration voltage of 100 kV. A small amount of a reaction solution was dropped on a carbon-coated copper grid at every half minute for ten minutes during the synthesis. Liquid portion immediately passed through the membrane,

630

and only solid particles remained on the grid, quenching particle growth. Scanning electron micrographs (SEMs) were obtained using a SIGMA-V (Akashi Seisakusho). The average particle diameter was calculated from the diameters of 50 particles observed in a SEM picture. 3. Results and Discussion In order to investigate the formation mechanism of MMSS, particles size development was captured on TEM images at every 30 sec during the synthesis. Fig. 1 shows some of the images. After 150 sec experimental started, small particles (ca. 200 nm) emerged suddenly, and grew to the final size (ca. 500 nm) in 600 sec. It was confirmed by TEM observation that primary generated small particles grew homogeneously into larger particles, leading to the formation of monodispersed spherical particles.

Fig. 1 Transmission electron micrographs of samples obtained at different time, (a) 130, (b) 150, (c) 200, and (d) 360 sec after the synthesis had started. Scale bar represents 500 nm.

From the above results, it is assumed that residual silica precursors in solution preferentially reacted with existing particle surface silanols, preventing generation of new particles. This leads to the formation of MMSS. To confirm this assumption, TMOS was added different number of times after the completion of the initial reaction. Fig. 2 shows SEM images of particles obtained upon two and four additions of TMOS to the initial reaction mixture.

0.61 jim (5.1%) 1.1 lum

0.80 urn (3.1%) 1.Hum

1.21 |im (2.8%) 1.09um

Fig. 2 SEM images of particles obtained by the different TMOS addition times: (a) 0, (b) 2 and (c) 4.

631

The diameter of the particles was clearly increased upon the addition of TMOS, while retaining the monodispersion characteristic (standard deviation in parenthesis). This result indicates that additional TMOS prefers to react with the surface silanol of existing particles rather than generates new particles. It was confirmed by nitrogen adsorption measurement that pore volume (ca. 0.7 ml/g) and specific surface area (ca. 1100 m2/g) were unchanged upon the further addition of TMOS. On the basis of the above results, it MPTMS-TMOS is assumed that MMSS with TMOS TMOS core/shell structure can be obtained by adding different type of silica i MPTMS MPTMS -TMOS precursor from the original one to the addition pre-existing particles, as illustrated in Fig. 3. Synthesis was conducted in which double the molar amount of Fig. 3 Schematic illustration of the formation mercaptopropyltrimethoxysilane of core/shell MMSS. (MPTMS)/TMOS (=20/80 mol/mol) mixture was added to the solution including pre-existing particles obtained with TMOS. Fig 4 (a) shows a SEM image of the particles obtained. The average diameter was 0.73 um, and the standard deviation was 4.3 %, indicating that the particles were highly monodispersed. In addition, specific surface area and pore volume determined by nitrogen adsorption measurement were 998 m2/g and 0.49 ml/g, respectively. It was confirmed that mesoporous structure was retained in core/shell particles. It is anticipated that the particles possess a silica core/mercaptopropyl-modified silica shell structure, more specifically, a hydrophilic core /hydrophobic shell structure. To confirm this, platinum was incorporated into the particles. An egg type structure is clearly seen in Fig. 4 (b).

T

(b)

(a)

1.11 µm

nm 200 nm

Fig. 4 (a) SEM image of the silica/mercaptopropyl-modified silica core/shell MMSS. (b) TEM image of the platinum incorporated silica/mercaptopropyl-modified silica core/shell MMSS.

Platinum (dark portion) is concentrated in the hydrophilic core part. Because

632

platinum was incorporated into mesopores by using an aqueous solution of tetra ammine complex as a precursor, platinum particles (black part) existed in only hydrophilic core portions. From these results it is obvious that MMSS with core/shell structure was successfully synthesized by changing the type of additive silica precursor. 4. Conclusion In conclusion, it was found that small particles emerged suddenly during the synthesis of monodispersed mesoporous silica spheres (MMSS). The primary generated small particles grew homogeneously into larger particles, leading to the formation of MMSS. Furthermore, MMSS with core/shell structure have been successfully obtained for the first time by adding different type of silica precursor to pre-existing particles. Work is underway to explore new potential applications for these unique materials, which possess both monodispersed shape and mesoporous core/shell structure. 5. Acknowledgement This research was partially supported by Japan Society for the Promotion of Science, Grant-in-Aid for Scientific Research (B), 17310079, 2005. 6. References [1] C. T. Kresge, M. E. Leonowicz, W. J. Roth, J. C. Vartuli and J. S. Beck, Nature 359 (1992) 710. [2] J. S. Beck, J. C. Vartuli, W. J. Roth, M. E. Leonowicz, C. T. Kresge, K. D. Schmitt, C. TW. Chu, D. H. Olson, E. W. Sheppard, S. B. McCullen, J. B. Higgins and J. L. Schlenker, J. Am. Chem. Soc. 114 (1992) 10834. [3] P. Yang, D. Zhao, B. F. Chmelka and G. D. Stucky, Chem. Mater. 10 (1998) 2033. [4] P. J. Bruinsma, A.Y. Kim, J. Liu and S. Baskaran, Chem. Mater. 9 (1997) 2507. [5] J. C. Vartuli, K. D. Schmitt, C. T. Kresge, W. J. Roth, M. E. Leonowicz, S. B. McCullen, S. D. Hellring, J. S. Beck, J. L. Schlenker, D. H. Olson and E. W. Sheppard, Chem. Mater. 6 (1994)2317. [6] A. Firouzi, F. Atef, A. G. Oertli, G. D. Stucky and G. G. Chmelka, J. Am. Chem. Soc. 119 (1997)3596. [7] J. Frasch, B. Lebeau, M. Soulard, J. Patarin and R. Zana, Langmuir 16 (2000) 9049. [8] J. Morell, C. V. Teixeira, M. Cornelius, V. Rebbin, M. Tiemann, H. Amenitsch, M. Froba and M. Linden, Chem. Mater. 16 (2004) 5564. [9] K. Yano, N. Suzuki, Y. Akimoto and Y. Fukushima, Bull. Chem. Soc. Jpn. 75 (2002) 1977. [10] K. Yano and Y. Fukushima, J. Mater. Chem. 13 (2003) 2577. [11] K. Yano and Y. Fukushima, J. Mater. Chem. 14 (2004) 1579. [12] Y. Yamada, T. Nakamura, M. Ishii and K. Yano, Langmuir, 22 (2006) 2444. [13] Y. Yamada and K. Yano, Microporous Mesoporous Mater. 93 (2006) 190.


633 633

Controllable synthesis of cubic MCM-48 with different morphologies by using ternary surfactant templating route Lingdong Konga, Su Liub, Yi Wanga, Xuewu Yana, Heyong Hea and Quanzhi Lia " Department of Chemistry and Shanghai Key Laboratory of Molecular Catalysis and Innovative Materials, Fudan University, Shanghai 200433, P. R. China. Department of Environmental Science and Engineering, Fudan University.

Cubic MCM-48 with different morphologies, such as cube shape, vesicle-like, microtubule-like and spherical particles was synthesized in the same ternary mixed surfactants system. This system not only make high-quality cubic phase MCM-48 prepared at extremely low surfactant concentration (1.76 ~ 2.4 wt%) but also facilitate the formation of various morphologies, which is closely correlated to the strong synergistic effects of the ternary mixed surfactants system and the amount of ethanol coming from the hydrolysis of TEOS. Keywords: synergistic effect, MCM-48, surface tension, morphology 1. Introduction Cubic MCM-48, a member of M41S mesoporous family [1], has attracted much attention for its interwoven bicontinuous pore structure. In the past over ten years, many methods for the synthesis of MCM-48 were developed by using the single cationic surfactant systems [1, 2] and binary mixed surfactants systems [3-5]. Recently, we developed a ternary mixture of cationic surfactant, anionic surfactant and non-ionic surfactant as template for the synthesis of MCM-48 with various morphologies under alkaline conditions. This is the first observation for the existence of so many morphologies in the same synthesis system of cubic MCM-48.

634

2. Experimental Section The typical ternary mixed surfactants were composed of cationic surfactant, cetyltrimethylammonium bromide (CTAB), anionic surfactant, sodium laurate (SL) and nonionic surfactant, poly (ethylenglycol) monooctylphenyl ether (OP10). The detail synthetic procedures have been reported elsewhere [6, 7]. In a typical synthesis, 1.458 g of CTAB, 0.095 g of SL, 0.173 g of OP-10 and 1.504 g of NaOH were dissolved in 70 g of distilled water in an open beaker by stirring at 311 K to give a clear solution, and then 15.2 mL of TEOS was added dropwise to the solution. The molar composition of the resulting synthesis gel was 1.0SiO2: 0.06CTAB: 0.004OP-10: 0.0064SL: 0.282Na2O: 58H2O. The different morphologies of MCM-48 were obtained through controlling the hydrolysis rate of TEOS and ethanol amounts produced by TEOS' hydrolysis with changing the stirred time before the synthesis gels were transferred into the Teflon-lined stainless steel autoclave for the hydrothermal treatment. The assynthesized samples are designated as sample A, B, C and D, corresponding to the stirred time of 1, 1.5, 3.5 and 6h, respectively. Different amount of water was added for compensating for the loss of water which evaporated from the synthetic system corresponding to the different stirred time. 3. Results and Discussion The first observation of our experimental results demonstrated that the "cmc" and surface tension of the ternary surfactants system can be dropped more greatly than that of binary surfactants system. From Table 1 one can see that the strong synergism effects in the mixture of the ternary surfactants can make high-quality cubic phase MCM-48 be prepared at extremely low surfactant concentration, which is only 1/10 that of in single cationic surfactant synthesis system and 1/3-1/2 that of in binary mixed surfactants synthesis system. Table 1. "cmc" and corresponding surface tension of the different surfactants mixtures (298K), and the molar ratios of total surfactant to silicon (Sur/Si) of the different systems for the synthesis of MCM-48 Surfactant systems CTAB a CTAB+OP-10 b CTAB+SL C CTAB+OP-10+SL

cmc (mol/L)

1.09X10" 3 4.35 X10" 4 3.89X10" 4 2.45 XI0" 4 a. see ref. [2]. b. see ref. [3]. c. ref. [4].

Surface tension (mN/m) 39.6 41.0 37.4 29.5

Total Sur/Si 0.55 0.144 0.168 0.07

The small-angle X-ray diffraction patterns for as-synthesized samples are shown in Figure 1. As can be seen from Figure 1, besides intense 211 and 220

635 635

diffraction peaks, several well-resolved Bragg diffraction peaks that can be indexed as 321, 400, 420, 332 and 422 reflections associated with cubic symmetry can be observed, which is typical for MCM-48. Figure 2a shows that the particles of sample A have various hollow morphologies, such as spherical and cocoon-like shapes with micron size covered by MCM-48 particles of nano or submicron size. The ternary surfactants' strong synergistic effects create an extremely dilute surfactants concentration offering an environment for meeting the co-existence of vesicles and MCM-48. Thus, the hollow morphologies come from the result that vesicles act as soft template.

29 /degree

Figure 1. XRD patterns of as-synthesized samples: (a) sample A, (b) sample B, (c) sample C; (d) sample D.

Figure 2. SEM images of the as-synthesized MCM-48: (a) sample A; (b) sample B; (c) sample C; (d) sample D.

636

The as-synthesized sample B possesses cube shapes, consisting of 6 welldefined crystal faces (see Figure 2b). This is the first synthesis of MCM-48 with such less crystal faces. The synergism effects, the low "cmc" of forming micelles, and the residual ethanol produced by the hydrolysis of TEOS delaying the condensation of silicate-surfactant aggregates, all may benefit the formation of cube morphology in the ternary mixed surfactant synthesis system. With the decrease of the amount of ethanol, the particles of sample C exhibit another unique morphology shown in Figure 2c, which consists of well-defined irregularly flat spherical particles with concave, and seem to be growing in pairs or growing up on each other. While sample D has more round and smaller spherical particles (Figure 2d) than that of sample C when the ethanol amount further decreases with the increase of stirred time of synthesis gel before crystallization. These diverse morphologies of MCM-48 would have potential applications for various fields. 4. Conclusion We have synthesized mesoporous MCM-48 with various morphologies by employing the ternary mixed surfactants templating method. This synthesis method provides a better control over particle morphologies compared with the other methods, which will further deepen the understanding of the morphology control during the synthesis of mesoporous materials. 5. Acknowledgement Financial support from National Science Foundation of China (Project 20303005) is greatly acknowledged. 6. References [1] C. T. Kresge, M. E . Leonowicz, W. J. Roth, J. C. Vartuli and J. S. Beck, Nature, 359 (1992)710. [2] J. Xu, Z. Luan, H. He, W. Zhou and L. Kevan, Chem. Mater., 10 (1998) 3690. [3] W. Zhao, J. D. Yao, X. D. Huang and Q. Z. Li, Chinese Science Bulletin, 46 (2001) 1436. [4] F. X. Chen, L. M. Huang and Q. Z. Li, Chem. Mater., 9 (1997) 2685. [5] R. Ryoo, J. M. Kim and S. H. Joo, J. Phys. Chem., 103 (1999) 7435. [6] L. D. Kong, S. Liu, X. W. Yan, H. He and Q. Z. Li, Stud. Surf. Sci. Catal., 154 (2004) 468. [7] L. D. Kong, S. Liu, X. W. Yan, Q. Z. Li and H. He, Microporous Mesoporous Mater., 81 (2005)251.


637 637

Mesoporous silica hosts for polyenzymatic catalysis Anne Galarneau, Lai Truong Phuoc, Aude Falcimaigne, Gilbert Renard and Francois Fajula Laboratoire de Materiaux Catalytiques et Catalyse en Chimie Organique, UMR 5618 CNRS/ENSCM/UM1, Institut Gerhardt FR 1878, ENSCM, 8 rue del'Ecole Normale, 34296 Montpellier Cedex 5, France. E-mail: [email protected]

Lipases, oxidase and peroxidase have been immobilized or coimmobilized in mesoporous silica hosts by using a novel sol-gel procedure based on the use of lecithin as surfactant and lactose as enzyme protector. The resulting biocatalysts demonstrate high activities in various model reactions. Furthermore, the preparation procedure allows to generate in-situ hydrogen peroxide from glucose and oxygen, opening new perspectives for soft oxidation reactions. 1. Introduction The immobilization of enzymes in/on solid supports is expected to provide breakthroughs in the area of heterogeneous catalysis. Biological molecules such as enzymes are outstanding catalysts combining very high activity with very high specificity. However they are only barely used to date because of their fragility. Appropiate immobilization should preserve their quaternary structure -to protect them against the external environment- while permitting easy recovery of the products and, ultimately, develop continous flow processes. According to Whitesides and Wong [1] enzymes can be classified in five types: very stable enzymes, enzymes with self-regenerated co-factor, enzymes with sacrificial co-factor, very fragile enzymes and polyenzymatic systems. Generally, their immobilization in/on a solid support either by adsorption, covalent tethering or encapsulation leads to denaturation, with a severe loss of activity, and necessitates specific preparation procedures. We present here a simple and versatile enzyme encapsulation method giving access to very efficient biocatalysts.

638

2. Materials and Reactions 2.1. Monoenzymatic biocatalysts Several solid biocatalysts have been prepared by immobilization of a lipase (from Mucor miehei, obtained from Gist-Brocades) via encapsulation in porous silicas. Materials loaded with 3 to 9 mg of enzyme per gram of silica were prepared by using either conventional methods, such as adsorption on mesostructured silicas of varying pore sizes and surface polarities (MCM-41type, 3.7-10 nm, as-made, calcined, dimethylbutyl-grafted) [2] and sol-gel encapsulation [3], or via a new direct encapsulation procedure enabling control of both the textural and surface characteristics of the porous host [4]. Two different new types of nanostructures were thus prepared by the latter method: a three dimensional isotropic structure with cavities of 6 nm in diameter, named Sponge Mesoporous Silicas (SMS, 622 m2/g, 1 mL/g), and 20 nm Silica Porous Nanocapsules (SPN, 400 m7g, 0.62 mL/g). The preparation of SMS and SPN biocatalysts is based on an improved sol-gel synthesis involving: i) a natural phospholipid surfactant (egg lecithin) to avoid direct interaction between silanol groups and the enzyme which may denaturate its activity by changing its conformation, ii) amines, to generate a porous structure thanks to their curvature effect on the phospholipid bilayer and iii) lactose to preserve the enzyme activity by replacing the conformational water of the protein. The activity of the immobilized lipases was evaluated in aqueous medium at RT and pH = 8 for the hydrolysis of ethyl thiodecanoate and of the esters of p-nitrophenol bearing acyl chains with 2 to 16 carbon atoms, hereafter C2-C16. 2.2. Poly enzymatic biocatalysts The system chosen to investigate the possibility to design polyenzymatic solid biocatalysts from SMS and SPN combines a Glucose Oxidase (GOD, from Aspergillus niger, Sigma) and a Horse Radish Peroxidase (HRP, from Horseradish, Sigma). The reaction is performed at RT, pH= 7, under conditions chosen so that the overall activity (measured by the generation of quinoneimine, a red dye, which is titrated by UV-Vis at 508 nm [5]) is controlled by the production of hydrogen peroxide from glucose and oxygen. 3. Results and Discussion 3.1. Monoenzymatic biocatalysts Figure 1 summarizes typical activity data expressed as the % of specific activity of the biocatalysts (IU per mg of protein) compared to the specific

639

SMS

activity of the enzyme in solution for the hydrolysis of ethyl thiodecanoate. Materials prepared by adsorption on MCM-41 developped a moderate activity, regardless of the polarity of the surface (hydrophilic in calcined solids, hydrophobic in grafted ones, intermediate in as-made solids) and pore size. The sol-gel procedure, which provides a balanced hydrophobic/ hydrophilic environment to the enzyme [3] generates a better catalyst but the most active system was the one prepared via the SMS route. The efficiency of SMS-type biocatalysts was also demonstrated in the reaction of hydrolysis of esters of p-nitrophenols susbituted with C2-C16 chains. In this reaction the native enzymes in solution shows a very high specificity for long alkyl chain esters [2]. As shown in Figure 2, upon encapsulation a dramatic change in typoselectivity is observed, probably on account of the unfolding of the entrapped enzyme. As a consequence the SMS biocatalyst demonstrates a specific activity for the C2 and C3 esters of

< CM

tr

I i

. 5

~

ci ~n3

QJ *•=

o

2

i—i,-^-,

/I-41

ICM

ss.

CD

cn "o

en

o

c to CO 03

-syn.

J3 CD

1-41

•41

T—'

CO CO

2 Biocatalysts

Fig.l: Percentage of relative specific activity (IU lipasesoHd/IU lipaseSO|ulion x 100) in ethyl thiodecanoate hydrolysis

3 8 12 Ester chain length, Cn

Fig. 2: Relative specific activity for the hydrolysis of esters of p-nitrophenol as a function of acyl chain length

the p-nitrophenol six and nine times higher, respectively, than the activity of the native enzyme. Here again, direct SMS encapsulation generates a much active catalyst than adsoprtion in a pre-formed solid (MCM-41, 10 nm). These results clearly illustrate the synergistic influence of surface polarity and porosity in enzyme silicate hosts. 3.2. Poly enzymatic systems The SMS and SPN synthesis procedure has been applied to the coimmobilization of Horse Raddish Peroxidase (HRP) with Glucose Oxidase

640

(GOD). In this system hydrogen peroxide is generated in situ and immediately consumed quantitatively preventing the peroxidase denaturation [5, 6]. Glucose + H2O + O2 H2O2 +PhOH + 4-AAP

GOD

HRP

Gluconic acid + H2O2

(1)

Quinoneimine + H2O

(2)

(with PhOH: phenol, 4-AAP: 4-aminoantipyrine) The HRP and GOD enzymes catalyse two independent but consecutive reactions and the activity of HRP is regulated by the rate of formation of hydrogen peroxide (deliberately limited in all experiments by the amount of glucose and GOD engaged in the system). Figure 3 shows the relationship between the ratio of activities of HRP to GOD determined separately (UHRP/UGOD) and the relative activity (respective to the maximum GOD activity) of the catalytic systems consisting of the native enzymes (Fig. 3a), of the two enzymes encasulpated individually in different SPN hosts (Fig. 3b, • ) and of the two enzymes coimmobilized is SPNs (Fig. 3b, o). In the case of the native enzymes in solution, the maximum GOD activity (68 umol.min'.mg'1) is reached for a ratio UHRP/UGOD close to 2. The immobilized and coimmobilized enzymes produce a catalytic system which is less effective (the activity of the encapsulated GOD is decreased to 15 umol.mhf'.mg"1). The overall activity increases to ca 80% of the nominal value for UHRP/UGOD ratios higher than 10. Such a behaviour could be well related to the loss of activity of the fragile HRP upon encapsulation (from 165 in solution to 12 umol.mhv'.mg"1 in the solid)and to a restricted diffusion of the substrates and oxidant in the confined space of the silica hosts. Further optimization of this biosystem is in progress. However, the most remarkable conclusion drawn from these preliminary experiments is the high level of activity that can be reached with these easy-to-prepare bienzymatic biocatalysts.

Fig. 3: Relative activity of the HRP /GOD systems versus the maximum activity that could be reached if all H2O2 produced by GOD be consumed by HRD, ie for well balanced reactions (1) and (2). (a: free enzymes in solution, b: enzymes immobilized separately, • or coimmobilized,o)

641

4. Conclusion Lipases as well as HRP and GOD have been immobilized individually or in association in porous silicate hosts prepared by using a combination of natural phospholipid and lactose in order to control both the textural and surface properties of the rigid matrix. The resulting biocatalysts exhibit relatively high enzymatic activity with, in some cases, unique typoselectivities. The synthesis procedure we introduce is attractive by its simplicity and versatility. 5. References [1] G. M. Whitesides and C-H, Wong, Angew. Chem., Intern. Ed. Eng., 24 (1985) 617. [2] A. Galarneau, M. Mureseanu, S. Atger, G. Renard and F. Fajula, New J. Chem, 30 (2006) 532. [3] M. T. Reetz, A. Zonta and J. Simpelkamp, J. Biotechnol. Bioeng., 49 (1996) 527. [4] M. Mureseanu, A. Galarneau, G. Renard and F. Fajula, Langmuir, 21 (2005)4648. [5] Y. Wei, H. Dong, J. Xu and Q. Feng, Chem. Phys. Chem., 9 (2002) 802, US 2004/0014189 Al (2004). [6] F. van de Velde, N. D. Lourenco, M. Bakker, F. van Rantwijk and R. A. Sheldon, Biotechnol. Bioeng., 69 (2000) 286.


643 643


Mesoporous silica-supported chiral norephedrine ligands for asymmetric transfer hydrogenation Myung-Jong Jina*, M. S. Sarkara and Sang-Eon Parkb " School of Chemical Science and Engineering, Inha University, Incheon, 402-751, Korea h Department of Chemistry, Inha University, Incheon, 402-751, Korea

Optically active norephedrine was anchored on three different mesoporous silica materials. The immobilized norephedrines could be served as enantioselective ligands in the asymmetric transfer hydrogenation of ketones. The heterogeneous catalysts gave satisfactory enantioselectivity as well as high levels of catalytic activity in the transfer hydrogenation. 1. Introduction Asymmetric transfer hydrogenation of ketones is known to be one of the most attractive methods for the synthesis of optically active secondary alcohols [1]. Efficient chiral ligands have been developed for the homogeneous catalysis. Successful development of homogeneous ligands has been sometimes followed by attempts to attach the ligands on an insoluble polymeric support. This strategy offers practical advantages such as simplified separation, easy recovery of catalyst, and potential reuse [2]. Recently, mesoporous silica materials with OH Si OH OH

1a. SBA-15 1a.SBA-15 1b. SBA-16 SBA-16 1c. MCM-48

Scheme 1

i)

O Si O O

ii) Si

Cl

O Si O

Si

O

2a-c

2 a - c

H3C

Ph

N

OH

H

3a-c

i)i) (C22H C, 10 C, 48 H55O) O)33Si(CH Si(CH22))33Cl Cl,, toluene, 105 105 o°C, 10 h. h. ii) ii) (-)-norephedrine, DIPEA, toluene, 105 105 o°C, 48 h

644

uniform pore diameters and high specific surface areas have become of high interest as inorganic supports [3]. Our interest in the field led to prepare mesoporous silica-supported norephedrine ligands. Herein, we describe the application of the immobilized ligands 3 for the asymmetric transfer hydrogenation of ketones. 2. Experimental Section 2.1. Preparation of mesoporous silicas la-c All the supporting silica la-c were prepared according to the reported methods [4]. 2.2. Preparation of 3-chloropropylated mesoporous silicas 2a-c To a solution of 3-(chloropropyl)triethoxysilane (0.11 g, 0.45 mmol) in toluene (8 mL) was added mesoporous silica la (1.0 g). The mixture was stirred at 105 °C for 10 h. The modified silica was collected by filtration and washed with CH2CI2. After drying in vacuo at 80°C, 3-chloropropylated silica 2a was obtained. The modified silicas 2b and 2c were prepared by the same procedure. Weight gain showed that 0.40 mmol, 0.37 mmol, and 0.40 mmol of 3-(chloropropyl)triethoxysilane were immobilized on 1.0 g of mesoporous silicas 2a-c respectively. 2.3. Preparation of mesoporous silicas-supported norephedrine 3a-c To a solution of (-)-norephedrine (0.151 g, 1.0 mmol) and diisopropylethyl amine (0.142 g, 1.1 mmol) in toluene (10 mL) was added 3-chloropropylated silica 2a (1.0 g). The mixture was gradually heated at 105°C and allowed to react for 48 h. The silica powder 3a was collected by filtration and successively washed with H2O, methanol and CH2CI2. Mesoporous silica-supported norephedrine 3a was obtained after drying in vacuo at 70°C. The supported ligands 3b and 3c were prepared by the same procedure. Elemental analysis and weight gain showed that 0.35 mmol, 0.31 mmol and 0.36 mmol of norephedrine were anchored on 1.0 g of 3-chloropropyl silicas 3a-c respectively. 2.4. General procedure for the Ru-catalyzed asymmetric transfer hydrogenation with immobilized ligands 3a-c A suspension was formed by the mixture of [RuCl2(p-cymene)]2 (5 mg 0.008 mmol) and mesoporous silica-supported norephedrine 3 (0.016 mmol) in 2propanol (5 mL). The mixture was heated at 80°C for 30 min under nitrogen atmosphere. To this resulting solution, a degassed solution of ketone (0.83 mmol)

645

with KOH (2.3 mg, 0.04 mmol) in 2-propanol (10 mL) was added and the mixture was stirred at RT for 3~6 h. The reaction was monitored by TLC and neutralized with aqueous NH4CI. The immobilized ligand 3 was separated by centrifugation from the reaction mixture. Excess 2-propanol was removed under reduced pressure and the residue was extracted with ethyl acetate. Organic layer was washed with brine and dried over MgSO4. The crude product was purified by short-column chromatography (hexane-ethyl acetate, 95:5, as eluent). Enantiomeric excess of the product was determined by HPLC analysis using Chiralcel OD-H column (3% 2-propanol in hexane, 1 ml/min). 3. Results and Discussion The immobilization of norephedrine onto three mesoporous silicas SBA-15 la, SBA-16 lb and MCM-48 lc were performed in two steps (Scheme 1). Reaction of mesoporous silicas la-c with (3-chloropropyl)triethoxysilane in refluxing toluene gave chloropropylsilanized silicas 2a-c with loading ratio of 0.37-0.4 mmol/g. Subsequent treatment of 2a-c with an excess of (-)-norephedrine in refluxing toluene in the presence of diisopropylethylamine afforded the heterogenized norephedrine Iigands 3a-c. The mesoporous silica-supported chiral Ru(II) complexes were prepared in situ by heating a mixture of the Iigands 3 and [RuCl2(p-cymene)]2 in 2-propanol. Asymmetric transfer hydrogenation of ketones with isopropanol as a hydrogen source was examined in the presence of the supported Ru(II) complexes as chiral catalysts. As indicated in Table 1, the ketones were reduced to (7?)-secondary alcohols with satisfactory enantioselectivities in high conversions. It is noteworthy that the mesoporous silica-supported norephedrines 3 are comparable to the homogeneous counterpart (-)-ephedrine in terms of enantioselectivity [5]. 4. Conclusion In conclusion, the immobilized norephedrines 3 could be served as efficient enantioselective Iigands in the asymmetric transfer hydrogenation of ketones. We have proven that mesoporous silicas SBA-15, SBA-16 and MCM-48 can be served as suitable supports for the immobilization of chiral Iigands. Further synthesis of mesoporous silica-supported chiral Iigands and their use to asymmetric catalysis are underway in our laboratory.

646 646 Table 1 Asymmetric transfer hydrogenation of ketones using immobilized ligands 3 a

R

O

OH

)|n

o II

[Ru(arene)Cl2]2 chiral ligand 3, j-PrOK OH

A

0

A

Entry

Ketoneb

Ligand

Time (h)

Conv. (%)c

E.e. (%) d

1

Acp

3a

6

85

80

2

Acp

3b

4

86

81

3

Acp

3c

3

96

77

4

Pp

3a

6

80

72

5

Pp

3b

5

87

70

6

Pp

3c

3

94

70

7

3'-OMe-Acp

3a

6

90

77

8

3'-OMe-Acp

3b

3

95

80

9

3 '-OMe-Acp

3c

3

98

75

10

4'-Cl-Acp

3b

4

99

85

11

4'-Cl-Acp

3c

3

99

71

e

82 12 4'-Cl-Acp 4 92 3c "The reactions were carried out at RT in 2-propanol; ketone : Ru : ligand : KOH = 100 : 1 : 2 : 5. b Acp = acetophenone, Pp = propiophenone. cDetermined by GC analysis. dDetermined by HPLC analysis using Chiralcel OD-H column (3% 2-propanol in hexane, 1 ml/min). e [RuCl2(hexamethylbenzene)]2 was used instead of [RuCl2(p-cymene)]2

5. References [1] [2] [3] [4] [5]

R. Noyori and S. Hashiguchi, Ace. Chem. Res. 30 (1997) 97. N. E. Leadbeater and M. Marco, Chem. Rev. 102 (2002) 3217. A. P. Wright and M. E. Davies, Chem. Rev. 102 (2002) 3589. J. Y. Ying, C. P. Mehnert and M. S. Wong, Angew. Chem. Int. Ed. 38 (1999) 56. J. Takehara, S. Hashiguchi, A. Fujii, S.-I. Inoue, T. Ikariyaand R. Noyori, Chem. Commun. (1996)233.


647 647

Facile heterogenization of homogeneous ferrocene catalyst on SBA-16 David Raju Burri, Isak Rajjak Shaikh, Sang-Cheol Han and Sang-Eon Park* Laboratory ofNano-Green Catalysis andNano Center for Fine Chemicals Fusion Technology, Department of Chemistry, Inha University, Incheon, 402-751, Korea

1. Introduction Heterogenization of homogeneous catalysts has been an indispensable requirement for the green and sustainable chemistry. Ferrocene is one of the important homogeneous catalysts for the oxidation and hydroxylation of aromatic compounds due to its redox centre, ^-conjugation system and exclusive electron transfer ability [1]. Recently, ferrocene has been heterogenized on SBA-15 support via multi-step post-synthetic grafting method [2]. A versatile synthetic methodology has recently been reported for the condensation of primary amine that attached to the SiC>2 support with one of the aldehyde groups of terepthaldicarboxaldehyde. Based on this methodology ferrocene has been heterogenized on SBA-16 support in a simple and an environmentally benign technique with Schiff s base attachment (C = N). Of late, it has been reported that the Schiff s base attached cobalt (III) immobilized SiO2 catalysts are highly stable and active for the oxidation reactions than that of cobalt (III) immobilized SiC>2 catalysts without Schiff s base attachment [3]. Recently, there has been increasing interest for the direct hydroxylation of benzene to phenol [4] aiming at the replacement of complex conventional threestep cumene process [5], To the best of our knowledge, the reports on ferrocene functionalized mesoporous oxidation / hydroxylation catalysts are very rare [2] and in particular, ferrocene functionalized SBA-16 catalysts are nil. Hence, in the present work, a simplified technique of Schiff s base containing ferrocene heterogenized SBA-16 synthesis and its catalytic application for the direct hydroxylation of benzene to phenol have been delineated.

648

2. Experimental Section 2.1. Synthesis of ferrocene heterogenized SBA-16 Propylamine functionalized SBA-16 was synthesized by direct cocondensation technique under strong acidic conditions (2 M HC1) similar to pure SBA-16 synthesis [6]. In a typical synthesis, 10 g of pluronic F127 (E0106P07oEOio6, Mav=12600) was dispersed in 256 g of H2O and added 29.4 g of sodium metasilicate nonahydrate (Na2SiO3.9H2O). Prehydrolysis was conducted for 1 h at 40°C under vigorous stirring prior to the addition of 1.86 g of 3- aminopropyltrimethoxysilane. The hydrolysis was continued for further 3 h and then, the reaction mixture was subjected to hydrothermal treatment at 100 °C for 12 h under static conditions. The solid product was separated by filtration under reduced pressures and dried at room temperature for 12 h. The template was extracted from this as-synthesized material by using acidified boiling ethanol for 24 h. Ferrocenecarboxaldehyde (Aldrich) was dissolved in absolute ethanol / toluene and added to aminopropyl functionalized SBA-16 under stirring at room temperature for 4 h. The solid product was recovered by filtration and washed with diethyl ether and dried at 60°C for 12 h. 2.2. Characterization of ferrocene heterogenized SBA-16 Nitrogen adsorption-desorption isotherms were generated at liquid nitrogen temperature with an ASAP 2020 adsorption analyzer supplied by Micromeritics. The pore size distribution curves were calculated using BJH equation from the analysis of adsorption branch of isotherm. X-ray diffraction patterns were recorded using a Rigaku, Multiflex, diffractometer with a nickel filtered CuKa radiation in the 29 ranges from 0.5 to 3° for the estimation of SBA-16 textural parameters. The FT-IR spectra for propylamine and ferrocene functionalized SBA-16 samples were obtained over a range of 400-4000 cm "' on a Shimadzu FT-IR spectrophotometer. 2.3. Catalytic activity studies Benzene hydroxylation reactions were performed in a sealed glass reactor at room temperature, as described by Li et al [2]. In a typical experiment, 0.5 g of catalyst, 12.84 mmol of benzene, 4.28 mmol of 30% aq. H2O2 (H2O2/Benzene = 3) and 25 ml of 0.025 M H2SO4 were loaded prior to seal the reactor. The product samples were collected every 1 h and analyzed by gas chromatography equipped with a capillary column (DB-1). The product identification was made by GC-MS.

649

3. Results and Discussion The designed Schiff s base containing ferrocene heterogenized SBA-16 was synthesized as shown in Scheme 1, wherein the propylamine functionalized SBA-16 was directly synthesized by using F127 as structure directing agent, sodium metasilicate nonahydrate as silica source and 3-aminopropyltrimethoxy silane as the source of propylamine anchoring group.

NH2

N O

F127 H2O HCl SMS APTMS

Fe

Fe Toluene *Room Room Temp. Temp.

+ Si

Si O

O

C H

O

O

O O

SBA-16 Silica Wall

SBA-16 Silica Wall

Scheme 1: Schematic representation of ferrocene heterogenization, SMS: Sodium metasilicate, APTMS: Aminopropyltrimethoxysilane

(a)

(B) (B)

Inntens tensity (a. u)

(A)

l'

CD

(b)

Ail

1 ——-——'(b)b)

dV / dD

V o l u m e o f N2 a d s o r b e d ( c m 3/ g , S T P )

Ferrocene heterogenized SBA16 was obtained by tethering of amine and aldehyde groups of propylamine functionalized SBA-16 and ferrocenecarboxaldehyde respectively (Scheme 1). The nitrogen adsorptiondesorption isotherms of type IV with HI hysteresis loops and the highly intense low angle XRD patterns revealed the high quality of propylamine functionalized and ferrocene heterogenized SBA-16 materials.

(a)

(a)

(b) 0

50

100

150

200

Pore diameter (Angstrom)

0.0

0.2

0.4

0.6

0.8

Relative Relative Pressure Pressure (p/Po) (p/Po)

1.0 1.0

0.5

1.0

1.5

2.0

2.5 2.5

3.0

ao

22theta(degree) theta (degree)

Fig. 1 (A) N2 sorption isotherms (B) low angle XRD patterns (a) propylamine (b) Ferrocene functionalized SBA-16

650 (b) -CH2-

Intensity (a. u.)

The propyl chain attachment in propylamine functionalized SBA-16 and ferrocene heterogenized SBA-16 was confirmed by IR spectroscopy. The well resolved C-H stretching band at 2927 and 2857 cm "" represent the aminopropyl functional group attachment, which are shown in Fig. 2. Similarly, the presence of aminopropyl groups have been identified by several authors by the appearance of these absorption bands[7, 8].

(a) -CH2-

0

1000 1000

2000 2000

3000 3000

4000 4000

Wavenumber cm cm-1 -1

Fig. 2: FT-IR Spectra of (a) propyl amine and (b) ferrocene functionalized SBA-16

4. Conclusion Ferrocene heterogenized SBA-16 catalyst has successfully been synthesized in a single step using aminopropyl functionalized SBA-16 and ferrocenecarboxaldehyde and it was found that this novel heterogeneous catalyst is highly active towards the direct hydroxylation of benzene to phenol. 5. Acknowledgement The authors gratefully acknowledge the Asia 3 (A3: Korea, Japan and China) foresight program of Korea Science and Engineering Federation (KOSEF) 6. References [1] H. Yang, X. Chen, W. Jiang and Y. Lu, Inorg. Chem. Commun., 8 (2005) 853. [2] L. Li, J. Shi, J. Yan, X. Zhao and H. Chen, Appl. Catal. A, 263 (2004) 213. [3] I. C. Chisem, J. Chisen, J. S. Rafelt, D. J. Macquarrie, J. H. Clark and K. A. Utting, J. Chem. Technol. Biotechnol 74 (1999) 923. [4] J. He, H. Ma, Z. Guo, D. G. Evans and X. Duan, Topics in Catal. 22 (2003) 41. [5] A. K. Uriarte, M. A. Rodkin, M. J. Gross, A. S. Kharithonov, G. I. Panov, Stud. Surf. Sci. Catal. 110(1997)857. [6] Y. K. Hwang, J. S. Chang, Y. U. Kwon and S. E. Park Micropor. Mesopor. Mater. 68(2004) 21. [7] T. Ishikawa, M. Matsuda, A. Yasukawa, K. Kandori, S. Inagaki,T. Fukushima and S. Kondo, J. Chem. Soc, Faraday Trans. 92 (1996) 1985. [8] Z. Luan, J. A. Fournier, J. B. Wooten and D. E. Miser, Micropor. Mesopor. Mater. 83 (2005) 150.


651 651

Naphthalene alkylation with i-PrOH over bimodal mesoporous catalysts containing alumina Fang Liua'b, Jihong Suna* ,Quansheng Liub and Haibo Jinc "Department of Chemistry and Chemical Engineering, College of Environmental & Energy Engineering, Beijing University of Technology, Beijing, 100022, P. R. China 1 'Applied Chemistry,college of Chemical Engineering, Inner Mongolia University of Technology, Huhhot,Inner Mongolia, 010062, P. R. China 1 Beijing Institute of Petrochemical Technology

1. Introduction 2, 6-naphthalene dicarboxylic acid (2, 6-NDCA) can be obtained by oxidizing 2, 6-diisopropylnaphthalene (2, 6-DIPN), which can be used to make high quality polyester and thermo-tropic liquid polymer (LCP) [1, 2]. 2, 6-DIPN can be synthesized by naphthalene and i-PrOH over zeolites. But products of the isopropylation of naphthalene are very complicated, and the selectivity of 2, 6-DIPN is usually lower than other products. Therefore, it is very important to research the increasing of the selectivity of 2,6-DIPN and search for a new chemical material as the catalyst of appropriate operation conditions in order to improve the quality of naphthalene alkylation which have a better activity and stability. The usually used zeolites are easily to lose its activity for coking. So people are looking for a new catalyst to overcome the limitations. Wellconnected pores and a combination of independently controlled smaller and larger pore sizes would be very beneficial in, for example, reducing or eliminating transport limitations in catalysis, while simultaneously taking full advantage of the high intrinsic reaction rates per unit catalyst mass [3]. In this paper, the novel bimodal mesoporous molecular sieves (BMMs) incorporated of aluminum into the framework has been synthesized, and naphthalene alkylation with z-PrOH over Al-BMMs has been investigated.

652

2. Experimental Section First, the BMMs were synthesized according to the literature [3]. For postsynthesis modification, BMMs were reacted with different Al salt, namely AICI3, A12(SO4)3, A1(NO3)3, A1(OC3H7)3. we carried out as follows: 2 g BMMs were dried by air at 120°C for 2 h, then transferred into a 500 ml roundbottomed flask about 100 ml of a solution which contained the necessary amount of the Al ion. The mixture was stirred for 24 h. After filtered off, washed with distilled water, and dried at 150°C for 2h, the final materials containing Al ion were prepared. Nitrogen adsorption-desorption isotherms were measured using a Micromeritics ASAP 2010 system. Pore size distributions were obtained from the N2 desorption branch isotherm using BJH method. The Temperatureprogrammed desorption of ammonia (TPD) of samples was carried out in a CHEM BET-3000 instrument. The catalytic activities of the prepared samples with different Al loadings were tested for naphthalene alkylation with /-PrOH. 3. Results and Discussion cb

a

A

B d

b

e f

c a

d 1

3

5

θ /° 2 26/°

7

9

1

3

5 5

7

9

2 θ /° 26/°

Fig. 1. XRD patterns of BMMs. (A) different Al source: a: A1C13, b: A12(SO4)3, c: A1(NO3)3, d: AI(PiO)3; (B) different Si/Al molar ratio: a: pure SiO2, b: 20, c: 40, d: 60, e: 80, f: 100.

As shown in Figure 1, all samples appeared two diffraction peaks at two theta of around 2° and 4 ~ 6°, indicating the typical hexagonal mesoporous structure. For all samples, the decreasing in intensity of lower angle peaks with different Al salt in Fig.lA was as following order: A1C13> A12(SO4)3> A1(NO3)3> AIP, showing that the degree of long-scale order was decreased. On the other hand,

653 653

b

A

B

b

a

a

c

c d

d e

0

100 100 200 200 300 300 400 400 500 500600 600 T(°C) T(°C)

00

200 100

300 200

400 300

500 400

600 500

100 600

T(°C)

Fig. 2. TPD patterns of BMMs. (A) different Al source: a: AlCl3, b: AI(PiO)3, c: Al(NO3)3, d: A12(SO4)3; (B) different Si/Al molar ratio: a: pure SiO2, b: 20, c: 40, d: 60, e: 80, f: 100.

intensity of the diffracting peaks of two theta of around 2° in Figure IB decreased gradually with increasing Al content, implying the decrease of the long-distance order. On the basis analysis of nitrogen adsorption/desorption isotherms of BMMs and corresponding pore size distributions (not shown), it clearly indicates that there are two pores of Al-BMMs: around 3nm and 20nm respectively. Because the type of acid site could affect the catalytic Table 1 Catalysis data of all samples for reactions, it is preferable to naphthalene alkylation with i-PrOH measure these acid sites Yield(%) of individually. The measured TPD Sample was shown in Figure 2 2, 6-DIPN quantitatively. The BMMs AIP/BMMs-20 6.95 containing different Al source (in Figure 2A) and different Al A1(NO3)3/ BMMs -20 5.01 content (in Figure 2B) showed a A1 (SO ) / BMMs -20 5.07 2 4 3 broad peak at below 500 °C, 7.30 which was characteristic of AlCy BMMs -20 ammonia desorption from acidic A1C13/ BMMs -40 5.12 centers, however, desorption peak 4.49 at any high temperature was not AICI3/ BMMs -60 shown. Further, the two peaks A1C13/ BMMs -80 4.11 were centered at about 250°C and AICI3/ BMMs -100 3.48 440°C, respectively, which

654

indicated that acid sites of two different strengths were present on the catalyst surface with different Al amounts. As shown in Table 1, the BMMs of different aluminum source synthesized have greatly difference on Naphthalene alkylation with i-PrOH. The sequence of activity of samples was as following that: A1C1 3 /BMMS>A1P/BMMS> Al2(SO4)3/BMMs ~ Al(NO3)3/BMMs, on the other hand, obviously, the yields of 2,6-DIPN product were increasing with the increasing aluminum content of BMMs. It indicated that the activity of catalyst not only depend on its acid amount but also its porous structure and acid distribution. The influence of various reaction parameters such as reaction temperature, reactant feed ratio and catalyst amount, and the affecting activity of Al-BMMs, are being investigated 4. Conclusion The Al-BMMs with different nSi/nAl ratios and different salts as alumina source have been synthesized. The Al-BMMs catalyst by using A1C13 salt as Al source and, Si/Al of 20 shows the best activity for naphthalene alkylation. The influence of various reaction parameters and related mechanism are under way. 5. Acknowledgement We thank the Natural Science Fundation of Beijing (No.2063024), the Excellent Oversea Chinese Scholars Fundation of the Personal Ministry of the Chinese Government and the Natural Science Fundation of Ningxia Hui Autonomous Region (ZD02) for the financial support. 6. References [1] A. D. Schmitz and C. Song, Prepr. pap.-Am. Chem. Div. Fuel. Chem., 39 (1994) 985. [2] S. F. Newman, Pantent No. US5000312 (1991). [3] J. H. Sun, Z. Shan, J. A. Moujin and M. O. Coppens, Langmuir, 19 (2003) 8395.


655 655

Synthesis and application of MCM-41 molecular sieves modified by lanthanum in oxidation of cyclohexane Wangcheng Zhan, Yanglong Guo*, Yanqin Wang, Yun Guo and Guanzhong Lu* Lab for Advanced Materials, Research Institute of Industrial Catalysis, East China University of Science and Technology, Shanghai 200237, P.R. China

1. Introduction Since the scientists in Mobile Corporation synthesized the M41S molecular sieves in 1992 [1], the mesoporous MCM-41 materials has attracted much attention on their interesting structures and potential applications in various fields. However, the purely siliceous molecular sieve is hardly effective for the catalytic reactions, so it is essential to functionalize the purely siliceous molecular sieves by the introduction of heteroatoms, such as B, Ga, Ti, V, Cr and Co [2-4]. However, the structural and catalytic properties of mesoporous molecular sieves modified by La are unclear. In this paper, MCM-41 molecular sieves modified by La were synthesized and characterized by XRD, UV-Vis, N2 adsorption, and 2 Si MAS NMR. Their catalytic behaviors for the cyclohexane oxidation by molecular oxygen as oxidant were firstly investigated in detail. 2. Experimental Section The synthesis procedures of MCM-41 molecular sieves modified by La were similar to those described in the literature [5], and ethamine was used as alkaline source. The molar composition of the synthesis solution was SiO2: 0.2CTAB: xLa: 0.6EA: 120H2O (where JC=0.02, 0.04 or 0.06). The samples prepared were denoted as La-MCM-41-x, where x is the La/Si molar ratio in the synthesis solution. In the oxidation of cyclohexane, 9 g cyclohexane and 0.3 mmol H2O2 (used as initiator) were mixed with La-MCM-41 catalyst, and heated to 140°C at 0.5 MPa O2. The reaction products were analyzed by Perkin-Elmer Clarus 500 gas

656

chromatograph (PE-2, 25m>2, MCM41 and La-MCM41 supported

796 796

catalysts were prepared by impregnation with an aqueous solution of Ni(NO3)2. The catalysts were dried in air at 103-105°C for 14 h after evaporation of water and calcinated at 500°C for 4 h in air. The textural structure of supports, SiO2 and MCM41 and their supported Ni catalysts was determined by N2 adsorption. Chemical phases were determined by XRD. The mean crystallite diameters of nickel were estimated from application of the Scherrer equation. CO2 adsorption was used for acid/base measurement. The carbon deposition was investigated by a temperature programmed oxidation (TPO) using TGA. Catalytic reactions were carried out on a fixed-bed quartz reactor at atmospheric pressure with 0.2 g catalysts. The reactant stream consisting of CH4:CO2=1:1 is fed in at 60 ml/min. Before reaction, the catalysts were reduced in H2 at 500°C for 3 h and then the temperature was increased to the desired reaction temperature (800°C). 3. Results and Discussion The physicochemical properties of silica, prepared mesoporous silica (MCM41) and the supported Ni catalysts are presented in Table 1. As shown that mesoporous silica has much higher surface area than comericial silica mainly contributed by mesopores. Impregnation of Ni reduces the total surface area and mesoporous surface area while resulting in the increase in micropore. La substitution further decreases the surface area and pore volume. For three supports, mesoporous silica can produce high Ni dispersion and La substituted Si-MCM41 induces the highest dispersion of Ni particles on the support. Table 1 Characteristics of MCM-41 and its supported Ni catalysts Catalyst

SBET(m2/g)

SiO2

90

Ni/SiO2

64

Smicro ( m 2 / g )

S meS o(m 2 /!g)

V (cmVg)

DNi(nm) 15.5

MCM-41

737

0.706

-

806

69

Ni/MCM41

642

164

478

0.685

9.8

Ni/La-MCM41

410

87

323

0.545

8.7

Fig.l shows CO2 adsorption on Ni/MCM-41 and Ni/La-MCM-41 catalysts. It is seen that Ni/La-MCM-41 exhibits higher CO2 adsorption than Ni/MCM-41, suggesting strong basicity of Ni/La-MCM-41. Catalyst testing shows that Ni/SiO2 exhibits low catalytic activity than mesoporous silica supported catalysts. At 800°C, initial CH4 conversion on Ni/SiO2 is only 7% while other two catalysts can produce about 90% methane conversion and Ni/La-MCM41 gives a higher methane conversion than Ni/MCM41. This can be ascribed to the

797

higher dispersion of Ni and stronger basicity of Ni/La-MCM41. The catalytic stability of two mesoporous Ni catalysts is displayed in Fig. 2. As seen that they exhibit different patterns of deactivation. Methane conversion on Ni/MCM41 shows a decreasing trend during the initial 20 h performance and can maintain the catalytic activity at 80 % methane conversion without further deactivation for 100 h. On the contrary, Ni/La-MCM41 shows a behaviour of continuing deactivation within 100 h. The methane conversion decreases from 94 % to 75 % after 100 h.

• O

Ni/MCM-41 Ni/La-MCM-41

O O

0 D

0.000

0.005

0.010

0.015

0.020

0.025

0.030

Ni/La-MCM41 Ni/MCM41

0.035

Relative pressure (p/pQ)

Fig.l CO2 adsorption isotherm on Ni catalysts at 0 °C.

Time(h) 2

J ^ Catalytic performance of Ni/MCM41 and Ni/La-MCM41 in CO2 reforming of methane at 800 °C.

XRD analyses (Fig. 3) show that a small carbon peak occurring on Ni/MCM41 but a higher intensity of Ni peaks, suggesting the less carbon deposition and higher sintering of Ni particles on this catalyst. For Ni/LaMCM41, the carbon peak is much stronger than that on the Ni/Si-MCM41, indicative of higher amount of carbon deposition on this catalyst, which is confirmed by the experimental results of TPO. Temperature programmed oxidation shows that two peaks occurring at 600 and 680°C on Ni/MCM41, attributed to carbon whisker and graphite [6], while a strong oxidation peak occurs on Ni/La-MCM41 centred at 700°C. Thus, it is believed that the lower oxidation activity of the graphite carbon contributes to the deactivation of Ni/La-MCM41. Previous investigations have shown that two or three carbon species can form on catalyst surface in CO2 reforming of methane and that the reactivity of carbon determines the catalyst stability [1].

798

Ni/MCM-41 Ni/La-MCM-41

e

0.15

E

gijr

^™H0

I

500

A/ /\A

600

700

Temperature (°C)

Fig. 3 XRD patterns of reacted catalysts M/MCM41 and Ni/La-MCM41 in C0 2 reforming of methane at 800°C.

Fig. 4 Temperature programmed oxidation of carbon deposited on Ni catalysts after reaction.

4. Conclusion Ni supported on MCM41 and La exchanged MCM41 mesoporous materials have been employed as catalysts for CO2 reforming of methane. Both catalysts present high catalytic activity but the catalytic stability are quite different. Due to high coking problem, Ni/La-MCM41 exhibit faster deactivation while Ni/MCM41 will maintain the catalytic activity after initial deactivation. Two types of carbon species will form on the catalysts during the reaction. 5. References [1] S. B. Wang, G. Q. M. Lu and G. J. Millar, Energ. Fuel 10 (1996) 896. [2] H. V. Fajardo, A. O. Martins, R. M. de Almeida, L. K. Noda, L. F. D. Probst, N. L. V. Carreno and A. Valentini, Mater. Lett. 59 (2005) 3963. [3] Z. P. Hao, H. Y. Zhu and G. Q. Lu, Appl. Catal. A. 242 (2003) 275. [4] Z. P. Hao, C. Hu, Z. Jiang and G. Q. Lu, J. Environ. Sci.-China 16 (2004) 316. [5] S. B. Wang, H. Y. Zhu and G. Q. Lu, J. Colloid. Interf. Sci. 204 (1998) 128. [6] S. B. Wang and G. Q. Lu, Ind. Eng. Chem. Res. 38 (1999) 2615.


799 799

SBA-15 mesoporous molecular sieve as an appropriate support for highly active HDS catalysts prepared using Mo and W heteropolyacids Lilia Lizamaa, Juan C. Amezcuaa, Ramon Resendiza, Sergio Guzmana, Gustavo A. Fuentesb and Tatiana Klimovaa* a

Facultad de Quimica, Universidad National Autonoma de Mexico (UNAM), Cd. Universitaria, Coyoacan, Mexico D.F. (04510) Mexico h Area de Ingenieria Quimica, Universidad Autonoma Metropolitana - Iztapalapa, Av. Michoacdny Purisima, Iztapalapa, Mexico D.F. (09340) Mexico

A series of Mo/W HDS catalysts promoted by Ni/Co, supported on SBA-15 were prepared using Keggin-type heteropolyacids as active phase precursors to study the activity of different catalytic formulations in the 4, 6dimethyldibenzothiophene (4, 6-DMDBT) hydrodesulfurization (HDS). Catalysts' characterization showed that SBA-15-supported heteropolyacids were well-dispersed and maintained their characteristic Keggin structure after calcination at 623 K for 2 h. NiPW and NiPMo catalysts supported on SBA-15 resulted to be highly active in HDS of hindered dibenzothiophenes. 1. Introduction A growing interest in the removal of sulfur from gasoline and diesel oil by means of deep hydrodesulfurization is due to the implementation of more stringent fuel specifications in many countries. Many efforts are aimed to improve HDS catalysts by using new materials as catalytic supports, changing the promoter and the precursor of the active phase. To date, there have been very few reports on the application of heteropolyacids (HPAs) in the preparation of HDS catalysts [1,2]. Different carriers have been used to support HPAs. It was found that, when HPAs are deposited on alumina, very strong interaction with the support leads to the destruction of the characteristic heteropolyanion precursor structure [3], and, consequently, catalytic behavior of the catalysts prepared from HPAs and other traditional Mo/W precursors resulted to be similar. New mesoporous molecular sieves such as SBA-15 [4],

800

highly stable and with better textural properties compared to the traditional yalumina support, seem to be especially suitable for depositing large HPA precursors. The aim of the present work is to demonstrate that SBA-15supported heteropolyacids are good oxidic precursors for the preparation of highly active HDS catalysts and to analyze the effect of different promoters (Co, Ni) on catalysts' behavior in HDS of hindered dibenzothiophenes. 2. Experimental Section The pure siliceous hexagonal p6mm SBA-15 was prepared according to literature [4] using Pluronic PI23 as structure-directing agent and TEOS as the silica source. Mo/W, as well as P, were incorporated to the SBA-15 support by incipient wetness impregnation of methanol solutions of Keggin-type heteropolyacids (H3PM012O40 or H3PW12O40). After the impregnation, the catalysts were dried (373 K, 12 h) and calcined (623 K, 2 h) in air. Ni or Co were incorporated to calcined Mo/W catalysts by the same impregnation technique using corresponding nitrates as promoter sources. After promoter impregnation, catalysts were dried and calcined again as described above. The nominal composition of the catalysts was 12 wt % of MoO3 or WO3 and 3 wt % of NiO or CoO. The samples were designated as HPW(HPMo)/SBA-15 for unpromoted catalysts and MPW(MPMo)/SBA-15, where M is Ni, Co, for promoted catalysts. The support and catalysts were characterized by N2 physisorption, small- and wide-angle XRD, UV-Vis DRS, 31P MAS-NMR, and TPR, and tested in the 4, 6-DMDBT HDS reaction. Catalysts' activation was carried out ex situ in a tubular reactor at 673 K for 4 h in a stream of H2S (15 vol. %) in H2 under atmospheric pressure. The HDS activity tests were performed in a batch reactor at 573 K and 7.3 MPa total pressure for 8 h. 3. Results and Discussion The nitrogen adsorption-desorption isotherms, as well as the small-angle XRD patterns (Fig. 1) show that W and Mo heteropolycompounds can be supported on SBA-15 without substantial loss of the support's characteristics (texture and structural order). Results from textural characterization of the catalysts (Table 1) 1.0 indicate that the incorporation of HPW or HPMo on the SBA-15 surface produces a decrease in Fig. 1. Small-angle XRD patterns the textural properties (Sg, S^, Vp), which of SBA-15 (a); NiPMo/SBA-15 (b); becomes stronger for the Ni- or Co-promoted NiPW/SBA-15 (c); C0PM0/SBAsamples. This decrease can be explained taking 15 (d); and CoPW/SBA-15 (e). into account the weight of the deposited metal species. Wide-angle XRD of the catalysts (not shown) demonstrated that

801

deposited metal oxidic species were well-dispersed in all catalysts. The formation of any crystalline phase was not detected. Table 1. Textural and structural characteristics of SB A-15 support and catalysts Dp

ao

8

(m /g)

vP (cmVg)

(A)

(A)

(A)

881

121

1.22

66

106

40

HPW/SBA-15

733

104

1.04

67

106

39

NiPW/SBA-15

690

88

0.96

66

106

40

HPMo/SBA-15

780

112

1.10

66

106

40

NiPMo/SBA-15

734

88

1.05

67

105

38

Sample

Sg 2

(m /g) SBA-15

2

The solid state 31P MAS-NMR spectra of Mo catalysts are shown in Fig. 2. In all these spectra a peak at -3.5 ppm, characteristic of the Keggin structure of the parent HPMo, can be observed. Similar results were obtained for the catalysts of the W series, where the signal of HPW structure was observed at -15 ppm. These results, as well as the absence of a signal at 0 ppm (a phosphate formed from HPA decomposition), indicate that the characteristic Keggin structure was preserved in the oxidic precursors supported on SBA-15. An increase in the dispersion of octahedral Mo and W species supported on SBA-15 in comparison with bulk HPMo and HPW precursors was observed by UV-Vis DRS (Fig. 3). Addition of promoters (Ni, Co) results in a further increase of catalysts' dispersion. Unpromoted and Co-promoted catalysts showed high reduction temperatures (Fig. 4) and low catalytic activities (Table 2).

a 2 0 - 2 - 4 -6 -8 5, ppm Fig. 2. 31 P NMR spectra of dried (a) and calcined (b) HPMo/SBA-15 catalysts and calcined NiPMo/SBA-15 s a m p l e d .

Table 2. 4,6-DMDBT conversions obtained over different catalysts at 8 h reaction time Catalyst Conv. (%)

HPW/ SBA-15 29

CoPW/ SBA-15 30

NiPW/ SBA-15 91

HPMo/ SBA-15 46

CoPMo/ SBA-15 55

NiPMo/ SBA-15 79

NiMo/ A12O3 61

However, Ni-promoted catalysts showed a significant decrease in the temperature of reduction of metal oxide species. Both, Mo and W, Ni-promoted

802

catalysts showed high activity in 4,6-DMDBT HDS, which was substantially higher than that of the NiMo/Al2O3 analog. The 4,6-DMDBT reaction products were methylcyclohexyltoluene (the principal product), dimethylbiphenyl and dimethylbicyclohexyl. Catalysts' deactivation after HDS catalytic tests was not detected.

400 600 Wavelength (ran)

800

Fig. 3. UV-Vis DRS spectra of parent bulk HPMo (a); HPMo/SBA-15 (b); NiPMo/SBA15 (c) and CoPMo/SBA-15 (d).

200

400

600 800 Temperature (°C)

1000

Fig. 4. TPR profiles of mechanical mixture of HPMo and SBA-15 (a); HPMo/SBA-15 (b); CoPMo/SBA-15 (c); and NiPMo/SBA-15 (d).

4. Conclusion The use of SBA-15 materials as supports together with Keggin-type Mo or W heteropolyacids as HDS active phase precursors show promising features for the preparation of Mo and W-based Ni-promoted catalysts, active for HDS of hindered dibenzothiophenes. 5. Acknowledgement Financial support for this work by DGAPA-UNAM (Mexico, grant IN104106) is gratefully acknowledged. The authors wish to thank M. Aguilar and C. Salcedo for technical assistance with XRD characterizations. 6. References [1] B. Pawelec, S. Damyanova, R. Mariscal, J. L. G. Fierro, I. Sobrados, J. Sanz and L. Petrov, J. Catal., 223 (2004) 86. [2] R. Shafi, M. R. H. Siddiqui, G. J. Hutchings, E. G. Derouane and I. V. Kozhevnikov, Appl. Catal. A: General, 204 (2000) 251. [3] A. Griboval, P. Blanchard, E. Payen, M. Fournier and J. L. Dubois, Catal. Today, 45 (1998) 277. [4] D. Zhao, Q. Huo, J. Feng, B. Chmelka and G. Stucky, J. Am. Chem. Soc, 120 (1998) 6024.


803 803

SBA-15 mesoporous molecular sieves doped with ZrO2 or TiO2 as supports for Mo HDS catalysts Oliver Y. Gutierrez3, Fernando Pereza, Cecilia Salcedoa, Gustavo A. Fuentesb, Manuel Aguilarc, Xim Bokhimic and Tatiana Klimovaa* "Facultad de Quimica and3Institute) de Fisica, UniversidadNational Autonoma de Mexico (UNAM), Cd. Universitaria, Coyoacdn, Mexico D.F. (04510) Mexico b Area de Ingenieria Quimica, Universidad Autonoma Metropolitana - Iztapalapa, Av. Michoacdny Purisima, Iztapalapa, Mexico D.F. (09340) Mexico

SBA-15 materials with different TiO2 or ZrO2 loadings were prepared by chemical grafting procedure and used as supports for Mo hydrodesulfurization (HDS) catalysts. Ti and Zr oxide species were found to be well-dispersed on SBA-15 surface (DRS, XRD). In the catalysts supported on the TiO2 or ZrO2 modified materials, the dispersion of Mo oxide species increased with TiO2 or ZrO2 loading in the SBA-15 support. Catalytic activity tests in hydrodesulfurization of 4,6-dimethyldibenzothiophene (4,6-DMDBT) showed that the modification of SBA-15 supports with Ti and Zr species significantly improves the performance of unpromoted Mo catalysts in HDS of refractory dibenzothiophenes. 1. Introduction Hydrodesulfurization is a key process for producing clean engine fuels. Nowadays, many efforts are aimed to improve the HDS catalysts by using new materials as catalytic supports. Among them, mesoporous molecular sieve SBA15 has attracted much interest. However, up to now only purely siliceous SBA15 materials were tested in HDS and published information is limited to a few papers [1-3]. The incorporation of heteroatoms (Al, Ti, Zr, etc.) on the SBA-15 surface should modify dispersion and coordination of the deposited active metal species (Mo, W) and therefore their efficiency and selectivity in HDS reaction. In the present work, a series of Mo catalysts supported on TiO2 or ZrO2modified SBA-15 was prepared, characterized and tested in 4,6-DMDBT HDS.

804

2. Experimental Section Purely siliceous SBA-15 was synthesized according to the well-known procedure [4]. T1O2 and ZrC>2 incorporation was made by grafting of titanium or zirconium alkoxides on SBA-15 surface according to the previously reported procedure [5]. Supports with 11 and 19 wt % of TiO2 (Ti-SBA-15(ll) and TiSBA-15(19), respectively) and with 16 and 22 wt % of ZrO2 (Zr-SBA-15(16) and Zr-SBA-15(22)) were prepared. Mo/M-SBA-15 catalysts (where M is Ti or Zr) were prepared by impregnation of (NH4)6Mo7O24 aqueous solutions. The nominal composition of the catalysts was 12 wt % MoO3. The 4,6-DMDBT HDS activity tests were performed in a batch reactor at 300°C and 7.3 MPa total pressure for 8 h. 3. Results and Discussion Results from textural characterization of the supports indicate that the incorporation of Zr or Ti oxides in the SBA-15 surface produces a decrease in the SBA-15 textural properties (Table 1). This decrease is larger for the Zr-containing material because of higher zirconia weight loading. However, the characteristic shape of N2 adsorption isotherms (type IV in Brunauer classification) and small-angle XRD patterns (Fig. 1) are still maintained after titania or zirconia incorporation. TiC>2 and ZrC>2 surface species were found to be well-dispersed. In the DRS spectra of Ti- and Zr-containing SBA-15 samples (Fig. 2), absorption bands at 225 and 200 nm, respectively, are observed, which correspond to the presence of isolated Ti(IV) or Zr(IV) species in tetrahedral coordination. This result is in line with powder XRD observations, where the formation of any kind of TiO2 or ZrO2 bulk crystalline phases was not detected. A significant decrease in the textural properties was observed after Mo incorporation to the supports (Table 1). This decrease indicates the possibility of some obstruction of the support pores by deposited Mo oxidic species.

5

•v/

1

20 (°) Fig. 1. XRD patterns of SBA-15 (a); TiSBA-15(19) (b); and Zr-SBA-15(22) (c) supports.

200

300

400

500

A. (nm) Fig. 2. UV-Vis DRS spectra of supports: SBA-15 (a); Ti-SBA-15(ll) (b); Ti-SBA-15(19) (c); Zr-SBA-15(16) (d): and Zr-SBA-15(22) (e).

805 Table 1. Textural characteristics of supports and catalysts Sample 2

2

(m /g)

(m /g)

VP

Dp

a0

5

(cmVg)

(A)

(A)

(A)

SBA-15

863

139

1.16

56

100

44

Ti-SBA-15(19)

649

121

0.85

57

102

45

Zr-SBA-15(22)

583

105

0.77

57

100

43

Mo/SBA-15

601

82

0.85

55

102

47

Mo/Ti-SBA-15(19)

466

69

0.66

52

102

50

Mo/Zr-SBA-15(22)

394

49

0.60

50

102

52

The formation of crystalline MOO3 phase was detected by XRD for Mo catalysts supported on pure siliceous SBA-15 and Ti-containing supports (Fig. 3). The dispersion of Mo oxide species increases with TiO2 or ZrO2 loading in the SBA-15 support. Thus, the size of MOO3 crystallites decreases from 825 A (Mo/SBA-15) to 500 A for Mo/Ti-SBA-15(19) catalyst, and it becomes smaller than 50 A for the catalysts supported on Zr-SBA-15. This may be due to the stronger interaction of Mo species with Ti- or Zr-containing supports. The size of MoO3 crystallites detected by XRD compared to the pore diameter of the used SBA-15 materials makes evident that they should be located on the external surface of the support particles being responsible for pore entrance blocking and textural properties decrease after Mo deposition. The TPR results for Mo catalysts are shown in Fig. 4. The TPR profile of Mo/SBA-15 catalyst exhibits two main reduction peaks at 560°C (the first step of reduction of polymeric octahedral Mo species (Mo(Oh)) weakly bound to the silica surface) and 730°C (the second step of reduction of Mo(Oh) species and the first step of reduction of

10

15

20

25

30

35

40

45

50

Fig. 3. Powder XRD patterns of Mo catalysts supported on SBA-15 (a); Ti-SBA-15(l 1) (b); Ti-SBA-15(19) (c); Zr-SBA-15(16) (d); and Zr-SBA-15(22) (e). * MoO3 400

200

400 600 800 1000 Tern peratu re (°C )

Fig. 4. TPR of Mo catalysts supported on SBA-15 (a); Zr-SBA-15(22) (b) and TiSBA-15(19)(c).

806

tetrahedral Mo species). The shoulder at 6OO0C can be assigned to the reduction of crystalline MoO 3 detected by XRD. TiO 2 or ZrO 2 grafting on SBA-15 surface leads to a decrease in both: the proportion of tetrahedral Mo species, difficult to reduce, and the temperature of reduction of Mo(Oh) species evidencing their better dispersion. T ui 1 A a T-.n^r.-r Table 2. 4,6-DMDBT conver' ., , , . . , . sion over Mo catalysts (at 8 h)

Table 2 vpresents the 4,6-DMDBT . * o u t ! i conversions over A/r Mo catalysts at 8 h .g ^ ^ ^ reactk)n tjme ft

Catalyst

incorporation of Ti or Zr atoms on the SBA-15 surface significantly increases (almost twice) the activity of unpromoted Mo catalysts in the HDS reaction of 4,6DMDBT. Observed activities of the sulfided catalysts were closely related with coordination and dispersion of Mo species in the oxide-state materials.

Conv (%)

Mo/SBA-15 Mo/Ti-SBA-15(ll)

28 45

Mo/Ti-SBA-15(19) Mo/Zr-SBA-15(16) Mo/Zr-SBA-15(22)

52 47 57

4. Conclusion It can be concluded that the interaction of Mo species with the SBA-15 support becomes stronger with TiO 2 or ZrO 2 loading which increases the dispersion of oxidic Mo species especially for Zr-containing SBA-15 supports. Mo catalysts supported on Ti- and Zr-containing SBA-15 molecular sieves are active for the elimination of hindered dibenzothiophenes. Catalyst activity increases with an increase in the proportion of octahedral Mo species and their dispersion. 5. Acknowledgement Financial support by CONACyT-Mexico (grant 46354-Y) is acknowledged. 6. References [1] L. Vradman, M.V. Landau, M. Herskowitz, V. Ezersky, M. Talianker, S. Nikitenko, Y. Koltypin and A. Gedanken, J. Catal., 213 (2003) 163. [2] G. M. Dhar, G. M. Kumaran, M. Kumar, K. S. Rawat, L. D. Sharma, B. D. Raju and K. S. R. Rao, Catal. Today, 99 (2005) 309. [3] A. Sampieri, S. Pronier, J. Blanchard, M. Breysse, S. Brunet, K. Fajerwerg, C. Louis and G. Perot, Catal. Today, 107-108 (2005) 537. [4] D. Zhao, Q. Huo, J. Feng, B. Chmelka and G. Stucky, J. Am. Chem. Soc, 120 (1998) 6024. [5] Z. Yongzhong, S. Jaenicke and G. Chuah, J. Catal., 218 (2003) 396.


807 807

Isopropylation of naphthalene over mesostructured aluminosilicate nanoparticles with wormhole framework structures Shang-Ru Zhaia*, Chang-Sik Hab, Yong Liuc, Hua-Yu Qiuc, Dong Wud, Yu-Han Sund, Shao-Jun Wanga and Bin Zhaia "Department of Chemical Engineering and Materials, Dalian Institute of Light Industry, Dalian 116034, China b National Research Laboratory ofNano-lnformation Materials, Department of Polymer Science and Engineering, Pusan National University, Busan 609-735, South Korea "Key Laboratory of Organosilicon Chemistry and Material Technology of Education Ministry, Hangzhou Teachers College, Hangzhou 310012, China d State Key Laboratory of Coal Conversion, Institute of Coal Chemistry, Chinese Academy of Sciences, Taiyuan 030001, China

The preparation and catalytic properties in isopropylation of naphthalene of nanosized mesostructured alumiosilicate with worm-like framework structures were presented in this work. Catalytic results showed that, under optmium conditions, the present nanocatalyst exhibited high activity making ca. 90 mol% of naphthalene conversion into mono-, di- and triisopropyl substituted derivatives. It should be mentioned that, however, the present nanocatalyst showed no considerable selectivity to objective products, and this may be attributed to its somewhat large mesopores in comparsion with microporous alkylating catalysts. 1. Introduction The fabrication of nanoscale devices and the preparation of structures with ordered mesoporosity are two hotspot of current research in materials chemistry. As is known, materials with length scales between 1 and 100 nm possessing uncommon catalytic, magnetic, optical and semi-conducting properties. Similarly, mesostructured materials, such as the M41S, SBA-n, MSU-n and AMS-n family of silicas, are important new classes of inorganic oxides with enormous potentials in molecular sieving, catalysis (e.g. for large molecule

808

transformations) and adsorption processes [1-4]. Thus, it is scientifically interesting to combine the methods for nanomaterials synthesis with those leading to the templating of open framework mesoporous materials to produce nanosized objects with both external (surface) and internal (bulk) functionalization. In the present work, we present a route to the production of highly catalytic mesoporous alumiosilicate nano-particles with particle size in 40-60 nm range, and experimental results show that the material with wormlike but uniform mesostructured interiors exihibted much high reaction activity in isopropylation naphthalene. 2. Experimental Section The present nanocatalyst was prepared from TEOS and A1(NO3)3«9H2O as inorganic source and CTAB as template, respectively, and all chemicas were industral grade as received without further treatment. The comphrensive preparation procedures have been introduced in our previous work [5], and thus will not be repeated here. Utilizing this method, about 2 kg nanocatalyst was prepared and used as alkylating catalyst. Isopropylation of naphthalene was carried out in a 100 mL stainless steel autogneous reactor with a stirrer. Reaction conditions are: reaction time = 4 h, naphthalene/isopropanol = 1/2, catalyst = 0.5 g, solvent (decahydronaphthalene) = 15 mL. Prior to the reaction, N2 was introduced into the reaction mixture to eliminate air. At the required reaction temperature and the reaction time, the reaction mixture was sampled and then centrifuged to remove catalyst particles, followed by GC analysis using a SE30 capillary column (50mx0.2mm) fitted with FID. The calculation of naphthalene conversion and products selectivity can be referenced to the previous literature [6]. Besides, IPN, DIPN and PIPN stand for mono-, di- and polyisopropylnaphthalene, respectively, and the selectivity to p and P'(Sp.p) substitued derivatives was used as an indicator for selective performance of catalyst. 4 00

1 .2

-1

dV/dlog(D) (cmg nm )


3 -1

0 .4

3

(cm /g)

0 .8

2200 00

0 .0

1

10

100

ads

D(nm)

V

The sorption isotherms and pore size distribution for the catalyst are shown in Fig. 1. Clearly, the isotherm exhibits a complicated form not only with a definite step in the low relative pressure 0.15 to 0.3, typical of capillary condensation of N2 into framework mesopores, but also with another clearer hystersis above 0.8, which may be related to the presence of larger mesopores

3300 00

11 0 00

0 00.0 .0

0 .2

0 .4 0 .6 P /P0

0 .8

Fig. 1 N2 sorption isotherms and pore size distribution (inset) for nanocatalyst.

11.0 .0

809

formed by aggregation of nanosized particles [5, 7]. Indeed, this speculation is instantly proved by the pore size distribution that there exist two distinct mesopores at 2.4 and 30 nm, respectively, and this may be repsonsible for the complicated sorption isotherms. The 27A1 MAS NMR of as-synthesized nanocatalyst indicates that all aluminum was -5.6 1 i A* incorporated into the framework skeleton, even 53 — \ /'\ with a much low Si/Al (gel) ratio as 7.5. In 27 contrast, the A1-NMR spectrum for calcined V \ nanoparticles shows three distinct signals center \ Cal. at-5.6, 21 and 53 ppm, respectively. Of interest is the presence of the line at 21 ppm, which can be assigned to five-coordinated aluminum. It is reported that, although five-coordinated As-syn. J aluminum has been identified under certain 150 100 50 0 -50 -100 synthesis conditions, it can not generally be ppm observed in calcined aluminum-rich A1MCM-41 27 materials even for very low Si/Al ratios. This Fig. 2 A1 MAS NMR for the fact indicates that the quick addition of ammonia nanocatalyst. water for inorganic precursors condensation might play an unfavorable role, owing to the fast increase of pH from mild acidic to much basic [8]. Meanwhile, the presence of large amount of five- and six-coordinate aluminum centers is especially noteworthy, though uncommon for directly prepared aluminosilicate mesostructures, as they may be used as Lewis solid acids in many organic reactions. Commercially, alkyl naphthalenes are produced by alkylation of naphthalene with an alcohol or alkene over solid acid catalysts, and many zeolites as Hmordenite, H-beta, HY, HZSM-5 and HMCM-22 have been extensively investigated. Relative to instenive studies on zeolitic catalysts, however, there are only a few papers reported on naphthalene isopropylation over mesocatalysts [6, 9]. Following structural charactrization on the nanocatalyst, its alkylating performance in naphthalene isopropylation was investigated in detail. Firstly, the dependence of naphthalene conversion and product selectivities on the reaction temperature over nanocatalyst and comparative results of Y and USY were shown in Figs.3 and 4, respectively. With increasing reaction temperature, the naphthalene conversion increased dependently and amounted to the maximum value at around 270°C. Similarly, other reacton parameters also significantly changed with the reaction temperature. It is revealed that, based on comphrensive calculation, the optmium reaction temperature is about 280°C, when naphthalene conversion and Sp.p- are about 92.0% and 74.1%, respectively. Besides, the present mesostructured nanocatalyst showed comparable reactivity in comparison with microporous zeolites Y and USY as evidenced by results in Fig. 4, once again indicating its superior reactivity, and this may be issociated • .

J

V

810

with its integrated effects of high density of active sites and facilitated transport of guest molecules in the bimodal pore arrays [5]. 100 80H o 6040 -Niph.conv. -Sel.lPN -5al.DIPN -Snl.PIPN -5el.B-B -2.&V2.7-DIPN

20200

220

240 260 280 Temperature (°C)

300

320

Fig.3 Reaction results over nanocatalyst as a function of reaction temperature.

Nano

USY Catalyst

Fig.4 Catalytic results over different catalysts.

4. Conclusion Catalytic results in the alkylation reaction showed that, although naphthalene conversion over the present nanoparticles was high amounting up to 90%, indicating the nanocatalyst possessing excellent reaction activity, the selectivity to the objective products was not unexpectedly high as its relatively large mesopores. 5. References [1] C. T. Kresge, M. E. Leonowiez, W. J. Roth, J. C. Vartuli and J. S. Beck, Nature, 359 (1992) 710. [2] S. A. Bagshaw, E. Prouzet and T. J. Pinnavaia, Science, 269 (1995) 1242. [3] D. Y. Zhao, J. Feng, Q. Huo, N. Melsoh, G. H. Fredrickso, B. F. Chemelka and G. D. Stucky, Science, 279 (1998) 548. [4] S. Che, Z. Liu, T. Ohsuna, K. Sakamoto, O. Terasaki and T. Tatsumi, Nature, 429 (2004) 281. [5] S. R. Zhai, Y. Zhang, X. Shi, D. Wu, Y. Sun, Y. Shan and M. He, Catal. Lett., 93 (2004) 225. [6] Q. Y. Liu, W. L. Wu, J. Wang, X. Q. Ren and Y. R. Wang, Micropor. Mesopor. Mater., 76(2004)51. [7] K. Suzuki, K. Ikari and H. Imai, J. Am. Chem. Soc, 126 (2004) 462. [8] C. Boissiere, M. A. U. Martine, M. Tokumoto, A. Larbot and E. Pouzet, Chem. Mater., 15(2003)509. [9] X. S. Zhao, G. Q. Lu and C. Song, J. Mol. Catal. A: Chem, 191 (2003) 67.


811 811

Adsorption desulfurization from gasoline by silver loaded on mesoporous aluminum oxide Wenzhong Shenab*, Xiangping Yanga, Qingjie Guoa, Yihong Liua and Yanru Songa a

State Key Laboratory of Heavy Oil, China University of Petroleum, Dongying, 257061, P. R. China b Key Laboratory of Carbon Material, Chinese Academy Sciences, Institute of Coal Chemistry, Taiyuan, Shanxi, 030001, P. R. China

1. Introduction Deep desurization has become more difficult because the lower and lower limit of sulfur content in fuel products is required by regulatory specifications, and the higher and higher sulfur contents is in the crude oils. The hydrodesulfurization (HDS) process is an efficient method of removing thiols, sulfides, and disulfides but it is not adequate for the removal of aromatic thiophenes and their derivatives. The remained sulfur compounds after the HDS process are thiophene, benzothiophene, and so on. The sulfide content could be higher than several hundred ppm even after hydrodesulfurization. The adsorption is a promising method to reach deep desulfurization due to the adjustable pore structure and alterable surface function groups of adsorbents. The adsorption mechanism is based on the property of sulfur compounds in fuel. Adsorption desulfurization could be improved to remove the thiophene compounds if chemical force is taken place between the molecules containing thiophene rings and adsorbents and the force is also easy to rupture[l-4]. The porous materials are always selected as the adsorbents, and some metals compounds or ions were impregnated to improve its adsorption properties [4, 5]. Thiophenic sulfur compounds could be separed from aromatic compounds based on n -complexation using Cu- and Ag-exchanged Y zeolites [6]. In this work, the HDS and FCC gasoline were selected as the objects; the adsorption desulfurization of mesoporous aluminum oxide loaded with silver/oxide was investigated. The adsorption property was compared and discussed.

812

2. Experimental Section The mesoporous aluminum oxide was sythesized at lab and nominated as A-0; it was impregnated with the aqueous solution of silver nitrate by equal volume for 4 h. The loaded molar amount of silver nitrates was 0.006 and 0.030 on a gram aluminum oxide and were denoted as A-1 and A-5, respectively. The samples were then dried at 353 K for overnight and heated at 473 K for 60 min under nitrogen flow. The structures of samples were characterized by nitrogen adsorption, XRD patterns, FTIR spectra and SEM images. 0.25 g A-0, A-1 and A-5 were filled in a glass column to investigate its adsorption capacity for sulfides from HDS and FCC gasoline, respectively. The gasoline flew from top at 1 milliliter per minute; the total treated amount was 10 milliliter. The sulfur contents and kinds in HDS and FCC gasoline were determined using a microcoulomb sulfur analyzer and Hewlett-Packard 5890 series II gas chromatograph. 3. Results and Discussion 1 .8 1 .6

400

A -1 A -5 A -0

1 .4 1 .2

3

dV/dlog(D) (cm /g)

3

Volume adsorbed (cm /g)

The primary structure parameters of samples were listed in Table 1. The micropore volume markedly decreased with the sliver nitrate loaded amount. The nitrogen adsorption-desorption isotherms and pore size distributions were drawn in Fig. 1; the mesopore size of samples mainly ranged from 5 nm to 20 nm. The silver ion could enter the micropore and blocked it after heating treatment, so the micropore volume decreased with silver nitrate loading amount; the micropore could be total blocked for A-5.

300

200

1 .0 0 .8 0 .6 0 .4 0 .2 0 .0 1

10

100

100

P o re s iz e ( n m )

0 0 .0

0 .2

0 .4

0 .6

0 .8

1 .0

P /P 0

Fig. 1 the nitrogen adsorption-desorption isotherms and pore size distributions of samoles (inset)

Table 1: the structure parameters of adsorbents and its adsorption of organosulfur Sample

SBET

Pore volume (cm3/g)

2

(m /g)

'total

v v

V • v meso

micro

HDS (35Oppm S)

FCC (843ppm S)

(ppm)

Adsored amount(mg/g)

(ppm)

Adsored amount(mg/g)

S Residue

" Residue

A-0

161

0.672

0.668

0.003

336

0.56

778

2.7

A-1

138

0.569

0.567

0.001

234

4.64

675

6.72

A-5

120

0.509

0.509

—

141

8.36

441

16.08

The XRD patterns of samples, which were heated at 473 K for 60 min, were shown in Fig. 2. The characteristic peaks of aluminum oxide were at 66.73, 45.9,

d -

>•

'•

CD

s-

1.

A-5

V>

.A

A-1 A-0 A-0

00

3 aqueous solution, followed by H2 reduction. In a typical synthesis, a mixture containing 0.25 g AgNO3, 20 ml water, 20 ml ethanol and 2 g SBA-15 was stirred for 24 h at room temperature. Then, the solid was dried at 353 K and reduced at 573 K or 773 K under a nitrogen flow containing 10% hydrogen gas for 3h. All the as-prepared samples are denoted as Ag(x)/SBA-15-y, where x and y is Ag loading (wt.%) and reduction temperature, respectively. For example, Ag(6.4)/SBA-15-573 refers to a Ag/SBA-15 sample with 6.4 wt.% Ag obtained by reduction at 573 K. E. coli (ATCC 25922) was selected as indicators for antibacterial test to confirm the minimal inhibiting concentration (MIC). X-ray diffraction (XRD) measurements were performed on a Rigaku D/max.B diffractometer with CuKa. Transmission electron microscopy (TEM) images were obtained on a JEOL JEM2011 electron microscope. Nitrogen sorption isotherms were measured on a Quantachrome NOVA 4000e analyzer. FT-IR transmission spectra were determined in transmission mode using a Nicolet Omnic 405 Model spectrometer. 3. Results and Discussion Figure 1 shows the low-angle and wide-angle XRD patterns of pristine SBA15 and Ag/SBA-15 materials^ Three well-resolved diffraction peaks with 28 value of 0.83, 1.45 and 1.69° are observed in the pristine SBA-15 material,

843

which can be indexed as 10, 11 and 20 Bragg reflections of a 2-D hexagonal (p6m) structure [10] . The cell parameter is calculated to be 11.1 nm. The Ag(6.4)/SBA-15-573 exhibits a similar low-angle XRD pattern to the pristine SBA-15 with a minor decrease in cell parameter. The Ag(6.4)/SBA-15-573 exhibits A more resolved diffraction peaks and a further smaller cell parameter to 10.7 nm. From the wide-angle XRD patterns, one could see that, besides a broad peak around 26 = 23 °, the Figure 1 Small-angle(A) and wide angle(B) XRD patterns of (a) SBAAg(6.4)/SBA-15-573 exhibits four new 15, (b) Ag(6.4)/SBA-15-573 and (c) diffraction peaks with 26 values around 37.9°, 44.2 , 64.3 and 77.3°, respectively, corres- Ag(6.4)/SBA-15-773 samples ponding 111, 200, 220, and 311 reflections of Ag metal [4]. No significant peaks indicative of oxidized Ag species were observed. The TEM images (Figure 2) of the Ag(6.4)/SBA-15-573 sample display a typical hexagonally stripe-like morphology recorded along 01 and 10 incidences, suggesting a highly ordered 2-D hexagonal p6m mesostructure. Almost no wires or particles are Figure 2 TEM images of Ag(6.4)/SBA-15-573 observed on the external surface of recorded along [01] and [10] directions SBA-15, implying that the silver nanowires are totally immobilized inside the channels and the distribution of these nanowires is very uniform. The estimated cell parameter is 10.9 nm, in good agreement with the XRD result. Table 1 lists the textural parameters of different Ag(x)/SBA-15-y samples. It is reasonable to conclude the successful immobilization of silver nanowires inside the SBA-15 channels. According to FT-IR spectra, the Ag(6.4)/SBA-15 exhibits a strong and relatively broad peak around 3458 cm" which is assigned to the hydroxyl stretching of surface silanols. Several bands observed at 1094, 798 and 460 cm"1 are associated with the Si-O-Si asymmetric stretching, symmetric stretching and bending vibrations, respectively. The bands at 970 and 571 cm"1 are attributed to the stretching and bending vibrations of Si-OH [4]. These results demonstrate the formation of Si-O-Si framework with abundant hydroxyl groups. The other two bands at 1390 and 1450 cm"1 are attributed to NO3" ions [11], indicating the presence of trace nitrate salt in the channels. These two bands disappear after annealing the material at a temperature above 573 K under a nitrogen atmosphere containing hydrogen owing to the complete decomposition. A

844

continuous decrease of the bands at 970 and 571 cm'1 is observed in the Ag(6.4)/SBA-15 materials with the increase of reduction temperature, possibly due to the polycondensation between silanols. Based on above experimental results, a possible mechanism for the formation of Ag nanowires in the mesochannels of SBA-15 is discussed Firstly, the aqueous solutio-n of silver nitrate diffused into the mesopores of SBA-15. Because of the interaction of silver ions with - Si Table 1 Textural parameters of Ag(x)/SBA-15-y samples Sample

SBET(m2/g)

D(nm)

SBA-15

111

7.5

1.56

Ag(1.6)/SBA-15-573

671

5.5

1.04

Ag(3.2)/SBA-15-573

682

5.4

1.06

Ag(6.4)/SBA-15-573

640

5.5

0.78

Ag(6.4)/SBA-15-773

602

5.5

0.67

V(cmVg)

-OH groups on the internal surfaces of silica framework, a equilibrium is established between the free silver ions in solution and those adsorbed in the mesochannels. During the H2 reduction at high temperature, the nitrate salt is decomposed and the silver ions are reduced to silver metal within the pore channels. Improvement of AgNO3 solution immigration process into the mesochannels is extraordinarily important to obtain uniform Ag nanowires. Otherwise, partial silver particles are probably formed on the external surface if silver ions are not completely trapped in the silica matrix [4]. One important factor is the solvent since only Ag nanoparticles were obtained by using AgNO3 solution in pure water or a mixture of ethanol and water with the volume ratios of 3:7 and 8:2, while a blend of nanoparticles and nanowires was formed when AgNO3 precursor was dissolved in an equivalent ethanol and water solution. This effect can be assigned to the quite different surface tension of H2O and ethanol at room temperature, namely 71.99 and 21.97 mN m"1, respectively. Selection of a mixture of ethanol of water with the volume of Scheme 1. Possible mechanism for 1:1 as the solvent may lead to a rapid transfer the formation of Ag nanowires in of silver ions into the SBA-15 mesochannels the mesochannels of SBA-15. since a suitable surface tension influences the immigration rate [12]. Besides, the ultrasonic treatment is favorable to enhance the immigration of silver ions into the mesopores in SBA-15 and interaction

845

MIC (p p m)

with the surface Si-OH groups. During the thermal treatment under 10% H2/N2, the adjacent Ag+-SiO species are in situ reduced to silver nanowires. Figure 3 gives the activities of Ag/SBA-15 samples in killing E. coli, estimated by MIC values. The Ag can kill E. coli via its reaction 350 with protein molecules through 300 the combination with the -SH 250 groups, which leads to the 200 inactivation of bacterial proteins 150 [13]. The enrichment of E. coli 100 species in mesopores also 50 facilitates the contact of silver 0 metals with E. coli and thus, Ag(1.6)/SBA-15- Ag(3.2)/SBA-15- Ag(6.4)/SBA-15- Ag(3.2)/SBA-15- Ag(6.4)/SBA-15573 573 573 773 773 enhances the combination Ag/SBA-15 Ag(SB 5ssamples *' ~pb reaction. The MIC value reduces from 300 to 90 ppm with the increase of silver loading on Figure 3. Antibacterial activity over Ag/SBA-15 SBA-15 support from 1.6 % to sam les P 6.4 %, indicating that silver is the active center. In addition, the increase of reduction temperature also shows an great improvement on the antibacterial activity, especially for the Ag(3.2)/SBA15. On one hand, the increasing reduction temperature may enhance the reduction degree of Ag/SBA-15 samples, which may supply more active sites. On the other hand, the increase of reduction temperature may also enhance combination strength between the silver nanowires and the SBA-15 support, which may inhibit the leaching of Ag particles from the SBA-15 support during reaction with E. coli in aqueous solution. It is expected that the as-prepared Ag/SBA-15 samples can be used in killing other kinds of microorganisms besides E. coli. Detailed studies are being underway. Ag(1.6)/SBA-15-

Ag(3.2)/SBA-15-

Ag(6.4)/SBA-15-

Ag(3.2)/SBA-1 5-

Ag(6.4)/SBA-15-

573

573

573

773

773

4. Conclusion A new Ag/SBA-15 sample with uniform distribution of Ag nanowires in the pore channels of SBA-15 support is prepared by simple method including the impregnation of silver nitrate dissolved in a solution comprised of equivalent ethanol and water, ultrasonic dispersion, solvent evaporation and reduction in 10% H2/N2 atmosphere. Such Ag/SBA-15 exhibits high activity in killing Escherichia coli (ATCC 25922). The MIC value could be reduces from 300 to 90 ppm with the silver loading increasing from 1.6 % to 6.4 %, possibly owing to the ordered mesostructure and large surface area of of SBA-15 which may ensure the high and homogeneous distribution of Ag particles in the pore channels. The reduction temperature also plays important role in enhancing the bacterial activity owing to the improvement of reduction degree of the Ag/SBA15 and interaction strength between Ag particles and SBA-15 support.

846

5. Acknowledgment This work was supported by the National Natural Science Foundation of China (20377031, 20407014 and 20521140450), Shanghai Municipal Scientific Commission (03DJ14005 and 03QF14037) and Shanghai Municipal Educational Commission (04DB05). 6. References [1] J. H. He, W. S. Ma, S. Z. Tan and J. Q. Zhao, Appl. Surf. Sci. 241 (2005) 279. [2] H. Y. Kang and Y. K. Jeong , J. Biotechnol. Bioeng. 15 (2000) 521. [3] M. Rivera-Garza, M. T. Olguin, I. Garcia-Sosa, D. Alcantara and G. Rodriguez-Fuentes, Micropor. Mesopor. Mater. 39 (2000) 431. [4] H. J. Jeon, S. C. Yi and S. G. Oh, Biomaterial 24 (2003) 4921. [5] A. Oya, S. Yoshida, Y. Abe, T. Iizuka and N. Makiyama, Carbon 31 (1993) 71. [6] Y. L. Wang, Y.Z. Wan, X. H. Dong, G. X. Cheng, H. M. Tao and T. Y. Wen, Carbon 36 (1998) 1567. [7] S. J. Park and Y. S. Jang, J. Coll. Inter. Sci. 261 (2003) 238. [8] P. V. Adhyapak, P. Karandikar, K. Vijayamohanan, A. A. Athawale and A. Chandwadkar, J. Mater. Lett. 58(2004)1168. [9] Y. J. Han, J. M. Kim and G. D. Stucky, Chem. Mater. 12 (2000) 2068. [10] D. Zhao, J. Feng, Q. Huo, N. Melosh, G. H. Fredrickson, B. F. Chmelka and G. D. Stucky, Science 279 (1998) 548. [11] N. B. Colthup, L. H. Daly and S. E. Wiberiey, Introduction to infrared and Raman spectroscopy, 2nd ed. New York: Academic Press; 1975. [12] M. H. Huang, A. Choudrey and P. D. Yang, Chem. Commun. (2000) 1063. [13] Q. L. Feng, J. Wu, G. Q. Chen, F.Z. Cui, T. N. Kim and J.O. Kim, J Biomed. Mater. Res. 52 (2000) 662.


847 847

Preparation and conductivity of decatungstomolybdovanado-germanic heteropoly acid supported on mesoporous silica SBA-15, SBA16, MCM-41 and MCM-48 Qingyin Wua*, Hongxiao Jina, Wenqi Fenga and Wenqin Pang a,b* "Department of Chemistry, Zhejiang University, Hangzhou 310027, P. R. China 1 State Key Lab of Inorganic Synthesis and Preparative Chemistry, Jilin University, Changchun 130023, P. R. China

1. Introduction Heteropoly acids (HPA) with Keggin structure have been attracted a lot of attention because of their high proton conductivity [1] and their potential application as solid electrolyte in hydrogen-oxygen fuel cells, electrochromic displays, desiccators, ¥t sensors at low temperature, solid modified electrodes, etc. [2, 3]. Mesoporous silica (MPS) materials are known as excellent supporter for HPAs, and have been extensively studied for their use of catalysts [4]. Because of the existence of large, uniform mesopore and the abundance of silanol (SiOH) groups, HPAs supported on mesoporous materials are also of solid highproton conductor, however, limited research papers were published in this field. Therefore, research on the conductivity of HPAs supported on MPS was significant. As a further study of our previous works which were mainly on decatungstomolybdovanadogermanic heteropoly acid and polyvinyl alcohol (PVA) doped decatungstomolybdovanadogermanic heteropoly acid [5, 6], we report here the preparation and conductivity of decatungstomolybdovanadogermanic heteropoly acid supported on mesoporous silica SBA-15, SBA-16, MCM-41 and MCM-48.

848

2. Experimental Section 2.1 Synthesis Decatungstomolybdovanadogermanic acid, H5GeWioMoV04o'21H20 was prepared according to the literature method [5]. SBA-15, SBA-16, MCM-41 and MCM-48 were synthesized according to the literature methods [7-9]. Preparation of MPS (MPS= SBA-15, SBA-16, MCM-41 and MCM-48) containing 75 wt% of H5GeW10MoVO40 (HPA/MPS): HPA (1.125 g) was dissolved in 20 ml of boiling water, then 0.375 g MPS were added to the solution with stirring. The stirring was continued for 2h and then kept static at 40°C over night, drying in vacuum oven. 2.1. Characterization IR spectra were recorded on a Nicolet Nexus 470 FT-IR spectrometer using KBr pellets and X-ray diffraction patterns were obtained with a Siemens D5005 diffractometer using Cu Ka radiation (A, = 0.15418 nm). The conductivity was determined by complex impedance spectroscopy using an M273 electrochemical impedance analyzer over the frequency range from 99.9 kHz to 12Hz at room temperature. The compound was pressed at 20 MPa into a compact pellet with 10.00 mm in diameter. The conductivity was calculated as o = (1/R) • (L/S), where L is the pellet thickness, and S is the area of the pellet. 3. Results and Discussion 3.1. Infrared Spectra Fig. 1 compares the infrared (IR) spectra of the H5GeWioMoV04o (HPA) and HPA/MPS. The Keggin structure of GeM1204o5" (M=W, Mo, or V) consists of one GeO4 tetrahedron surrounded by four M3O13 sets formed by three edgesharing octahedra. There are six characteristic bands in the IR spectrum of H5GeW10MoV04o: 978 cm"1, vas (M-Od); 877 cm"1, vas (M-Ob-M); 767 cm"1, vfl, (M-Oc-M); 816 cm"1, vas (Ge-Oa); 458 cm"1, 6(O-Ge-O), all of which correspond to the spectrum of the heteropoly complex of Keggin structure previously reported. In 3800-1200 cm"1 region the absorptions associated with OH modes (stretching v and bending S) are also present: 3434.7 cm"1, v(OHXieiS.Ocm"1, SBA18.35 20%-Eu-MCM-41 1.14 16.10 15>HMS (shown in Table 0.44 5%-Eu- SBA-15 8.51 19.34 10%-Eu-SBA-15 0.56 6.50 11.63 2). The PL of Eu3+ in 9.03 20%-Eu-SBA-15 0.78 11.58 MCM-41 was quenched

892

by the silanol groups [5, 7]. The silanol group number of MCM-41 was more than that of HMS but less than that of SBA-15 [14-15], i.e., one has an order from the smallest HMS to the largest SBA-15 in term of the silanol content. The PL intensity per Eu atom of MCM-41 is greater than that of SBA-15, which could be attributed to the less silanol group number in MCM-41 than in SBA-15. HMS exhibits less silanol group number than that of MCM-41 and that of SBA15, but the PL intensity per europium of the impregnated HMS samples are the weakest. This may be due to the narrow pore size distribution of the latter has effect on the microenvironment of the Eu3+ [6, 16] and needs study in depth. 20%-Eu-MCM-41 and 20%-Eu-SBA-15 samples show high PL intensity per europium. As MCM-41 shows poor stability, SBA-15 should be a better support for the encapsulation of the europium complexes. 4. Conclusion [Eu(bpy)2]3+was incorporated into mesopores of HMS, MCM-41 and SBA15, respectively. The silanol group and pore size distribution of samples provide effect on the Eu atom microenvironment which influence PL intensity. Although the impregnated SBA-15 exhibited a little weak PL intensity per europium than MCM-41 sample, SBA-15 is stable and may become an interesting medium to encapsulate the europium complex. 5. References [1] C. T. Kresge, M. E. Leonowicz, W. J. Roth, J. C. Vartuli and J. S. Beck, Nature, 359 (1992) 710. [2] P. Yang, D. Zhao, D. I. Margolese, B. F. Chmelka and G. D. Stucky, Nature, 396 (1998) 152. [3] H. Maas, A. Currao and G. Calzaferri, Angew. Chem. Int. Edit., 41 (2002) 2495. [4] G. Vicentini, L. B. Zinner, J. Zukerman-Schpector and K. Zinner. Coord. Chem. Rev., 196 (2000) 353. [5] L. Bian, H. Xi, X. Qian, J. Yin, Z. Zhu and Q. Lu, Mater. Res. Bull., 37 (2002) 2293. [6] Q. Xu, L. Li, B. Li, J. Yu and R. Xu, Micropor. Mesopor. Mat., 38 (2000) 351. [7] S. Ge, N. He, C. Yang, J. Cao, H. Chen and M. Gu, Stud. Surf. Sci. Catal., 156 (2005) 711. [8] Q. Xu, L. Li, X. Liu and R. Xu, Chem. Mater., 14 (2) (2002) 549. [9] S. Ge, N. He, C. Yang and M. Gu and J. Cao, J. Nanosci. Nanotechnol., 5 (2005) 1305. [10] C. Yang, S. X. Ge and N. Y. He, Stud. Surf. Sci. Catal., 146 (2002) 129. [11] C. Yang, X. P. Jia, Y. D. Cao and N. Y. He, Stud. Surf. Sci. Catal., 146 (2002) 485. [12] N. He, C. Yuan, Z. Lu, C. Yang, S. Bao and Q. Xu, Supramol. Sci., 5 (1998) 523. [13] K. Cassiers, T. Linssen, M. Mathieu, M. Benjelloun, K. Schrijnemakers, P. Van Der Voort, P. Cool and E. F. Vansant, Chem. Mater., 14 (2002) 2317. [14] W. Z. Zhang, Design, synthesis and catalytic applications of mesoporous silica molecular sieves (dissertation). East Lansing (MI): Michigan State University, Chapter 2 27(1999)56. [15] I. G. Shenderovich, G. Buntkowsky, A. Schreiber, E. Gedat, S. Sharif, J. Albrecht, N.S. Golubev, G.H. Findenegg and H.H. Limbach, J. Phys. Chem. B, 107 (2003) 11924. [16] A. F. Kirby, D. Foster and F. S. Richardson, Chem. Phys. Lett., 95 (1983) 507.


893 893

Benzene sensors based on surface photo voltage of mesoporous organo-silica hybrid thin films Brian Yuliarto,a Yoko Kumai,b Itaru Honma,a Shinji Inagakib and Haoshen Zhoua "Energy Technology Research Institute, National Institute of Advanced Industrial Science and Technology (AIST), Tsukuba 305-8568, Japan h Toyota Central R&D Laboratories, Inc., Nagakute, Aichi, 480-1192, Japan

1. Introduction Detection of VOCs such as benzene, toluene and methanol is a very important aim in sensor technology. In the last few years many research groups have been focusing their attention in this type of sensors towards environmental applications, electronic noses, food or chemical industry. Benzene has been classified by the Environmental Protection Agency as a Group A, known human carcinogen of medium carcinogenic hazard. [1] Benzene, together with toluene, and xylenes can be found in motor gasoline as light high-octane aromatic hydrocarbons. As the variety using of benzene in many chemical processes, the measurement of benzene concentration is of significance important to control the benzene affect for human and environmental dangerous. The use of mesoporous silica material for separation and sensor devices is interesting because the large surface area of mesoporous material, which can be as high as 1100 m2g"', allows especially good gas access. The large surface area created by mesoporous materials enables an improvement in the gas adsorption properties of SPV devices. In this work, an ordered organo-silica hybrid thin film [2] is used as a sensitive layer in the MIS sensor structure. An ordered mesoporous organo-silica hybrid thin film is used as a sensitive layer in the MIS sensor structure [3]. The sensing performance is measured using surface photovoltage (SPV) technique for VOC detection at room temperature.

894

2. Experimental Section The ordered organo-silica hybrid material was prepared from alternating hydrophilic and hydrophobic, composed of silica and phenol, respectively. The sensor device is constructed following the previous method on our publications. [2] The n-type silicon (n-Si), with SiO2 and Si3N4 layers was used as the substrate. The mesoporous organo-silica hybrid thin film was prepared on the Si3N4 layer of the substrate, as a VOC adsorption insulator layer. The film preparation method has been detailed explained in the previous publications [3]. After deposition of mesoporous organo-silica hybrid, the Au electrode was deposited on the mesoporous film by sputtering while an Al electrode was fabricated on the backside of the n-Si surface by vacuum vapor deposition. The complete structure of the SPV sensor device based on MIS structure is Au/ mesoporous phenol-silica/ Si3N4/ SiCV n-Si/ Al as shown in Figure 1. 1.E+05

1.E+04

Au Mesoporous Int e ns it y

Si3 SiO A

n-Si

n-Si V VB

LED

1.E+03

1.E+02

1.E+01

1.E+00 1.0

2.0

3.8nm 4.0

3.0

2θ / θ

5.0

6.0 .0

7.0 7.0

8.0

Fig. 1 A mesoporous organo-silica hybrid SPV sensor with MIS structure, and the XRD of mesoporous organo-silica hybrid.

The gas sensing properties were characterized using automatic gas sensor characterization based on SPV system. The structure of the sensor consisted of four layers that formed a MIS structure. The sensor system consisted of a computer that controlled a lock in amplifier. An alternating modulated LED (930 nm, 1 kHz) beam was irradiated on the reverse side of the semiconductor to induce an ac photocurrent. A volume flow controller and multi-port valve controlled the VOC compounds during measurement. A two channels volume flow controller has been used to vary VOC compound concentration from 100 to 800 ppm. 3. Results and Discussion The XRD pattern of mesoporous organo-silica hybrid (Fig. 1) shows the peaks at low angle, indicating that the mesostructure is exist in the thin films.

895

The typical transient response of 195 mesoporous organo-silica hybrid is 190 shown in Figure 2. The figures show the photocurrents output variation of 185 the SPV sensor versus time for 180 increasing VOC concentrations. Measurements performed upon certain 175 bias voltage application showed clear 170 photocurrent variations related to 0 20 40 60 80 100 100 120 120 140 140 160 160 180 180 exposure in environments containing Time (minutes) N2 and VOC compounds. The Fig. 2 The response dynamic of benzene on photocurrent signals response increases mesoporous organo-silica SPV sensor. upon a given concentration of benzene due to any chemical and physical interaction of VOC molecules adsorbed into mesoporous silica layer. Moreover, after switching to recovery ambient of nitrogen, the sensors signal turn to decrease to the baseline and then returns to a stable reference level. The change in both the dielectric constant and the charge of the gas sensitive layer, due to physical adsorption and interaction between benzene compound and mesoporous silica layer with phenol chain produce a clear photocurrent shift. The sensitivity (Sen) of each concentration of VOC compound can be calculated from the Figure 1 using the definition of sensitivity as follow: Photo currents (nA)

f: r.

J

en VOC

i \

x 100%

N2

Vol adsorpt ion (ml STP/ gr)

Where Ivoc is the photocurrent after exposure of VOC and IN2 is the photocurrent under N2 condition. 300 250 200 150

Benzene

100 50 0 0

0.1

0.2 0.3 Relative pressure Relative pressure (P/ (P/ Po) Po)

0.4 0.4

0.5

Fig. 3 The benzene absorption-desorption on the SPV sensor

The increasing of photo-capacitive current indicates that the positive surface potential has changed due to reaction between benzene compound and the

896

mesoporous layer. The sensitivity for 100, 200, 400 and 800 ppm of benzene are 1.7, 3.3, 6.3 and 11.7% respectively. The response time for all concentrations of VOC compounds is less than 1 minutes providing clear evidence that both type of sensors can absorb and react easily with benzene compounds. This response time is much faster than the time response of NO2 SPV gas sensors based on a MCM-41 structure. Figures 2 also show that the photocurrent returns to its starting value after the gas is switched to N2. This proves that the absorption process is reversible. The recovery time is also much better than that of NO2 SPV gas sensor. The accessibility of benzene to the organo-silica hybrid mesoporous film is confirmed by the benzene adsorption-desorption measurement as show in Figure 3. It is clear that the benzene compound can be adsorbed and desorbed on the organo-silica mesoporous layer. In the organo-silica hybrid mesoporous, which consist of the phenol chain, the densities of Si-O- and silanol (-Si-OH) bonds would be replaced by the phenol-silica in a crystalline super lattice structure. The inner surface of the phenol-silica hybrid mesoporous transfers from hydrophilic into hydrophobic, which makes the mesoporous structure could be easy to be accessed by the organic molecules comparing to the inorganic compound. As a result, the benzene which is organic molecules would be easily absorbed 4. Conclusion The mesoporous organo-silica hybrid thin film was successfully prepared as benzene sensors. Good response properties have shown that the device can be used, at room temperature, as a detector of benzene compound in the range of 100-800 ppm. 5. References [1] Y. H. Lanyon, G. Marrazza, I. E. Tothill and M. Mascini, Biosensors and Bioelectronics 20 (2005) 2089.

[2] S. Inagaki, S. Guan, T. Ohsuna and O. Terasaki, Nature 416 (2002) 304. [3] B. Yuliarto, I. Honma, Y. Katsumura and H. S. Zhou, Sens. Actuators. B 114 (2006) 109.


897 897

Lipase immobilization in ordered mesoporous materials Elias Serraa, Alvaro Mayoralb, Yasuhiro Sakamotob, Rosa M. Blancoa and Isabel Diaz3* "Institute de Catdlisis y Petroleoquimica, CSIC. C/ Marie Curie 2, Cantoblanco (Madrid) 28049. Spain. Arrenhius Laboratory, University of Stockholm. Stockholm S-10691. Sweden

1. Introduction Enzyme immobilization in solid supports is an increasing technology. Lipase immobilization in amorphous mesoporous silicas has been achieved with high loadings and good retention of activity [1]. However sol-gel materials lack of precise mesopore size control and display small surface areas, limiting their application as suitable hosts. Ordered Mesoporous Materials (OMM) possess high surface areas, narrow pore size distribution and well defined connectivity that may solve problems related to diffusion and accessibility to the bulk material. Hexagonal two-dimensional (p6mm) OMM such as SBA-15 and MCM-41 have been tested as lipase carriers in recent years [2]. Although valuable loadings have been achieved, leaching problems have not been solved yet [2d, 2e], and the total solid surface is used only in a small percentage. The influence of the porous structure in the immobilization process has not been assessed yet. Here we present a systematic study in which a variety of OMM with different structures and pore sizes have been tested as lipase (CALB) carriers. The candidates include materials with cylindrical pores as well as cagelike systems. Due to lipase dimensions (9.92 x 5.05 x 8.67 nm), too close to the range of conventional OMMs, recent developments to enhance and control pore diameters have been applied [3-5]. 2. Experimental Section A variety of surfactants, synthesis conditions and additives were used to obtain p6mm (MCM-41 [6]), la-Id (KIT-6 [3]), Im-3m (SBA-16 [4]) and Fm-

898

3m (FDU-12 [5]) structures. Powder X-ray diffraction (XRD) patterns of the solids were obtained with a Seifert XRD 3000P diffractometer using monochromatic Cu Ka radiation. Thermogravimetric analysis (TGA) was performed using a Perkin-Elmer TGA7 instrument, from 20 to 900°C at a heating rate of 20°C/min. N2 adsorption isotherms were obtained on a Micromeritics ASAP apparatus. Surface areas were calculated through the BET procedure. Pore sizes were estimated applying the BJH analysis to the adsorption branch of the isotherm. SEM images were obtained with a JEOL JSM 6400 Phillips XL30 microscope operating at 20 kV. TEM images were obtained in JEOL 2000FX (200 kV) and JEOL JEM 3010 (300 kV) microscopes. Immobilization of CALB was performed by suspending 100 mg of solid in 20 mL of a solution of enzyme in phosphate buffer with different enzyme concentrations at pH = 5. The immobilization yield was monitored by measuring the amount of enzyme in the supernatant using UV-Vis absorption at 348 nm, with p-nitrophenyl acetate (p-NPA) as substrate. As-made materials were also tested in order to quantify enzyme adsorption on the external surface. 3. Results and Discussion The structure of all the OMM was initially evaluated by XRD, and further confirmed to be in good agreement with the literature by TEM/SAED. As an example, Figure 1 shows the XRD patterns of KJT-6 and FDU-12-a. The main peaks can be indexed to the corresponding reflexions of the expected space groups (la-Id and Fm-3m, respectively). Besides, TEM tilting series allowed doubtlessly assessment of the expected space groups. SEM micrographs supplies information about the morphology of the particles and are also in good agreement with the literature. Figure 1 shows an example of TEM and SEM images of SBA-15 and SBA-16. As it can be observed, Figure le reveals the 100 direction of SBA-15 and Figure lg the perpendicular orientation, demonstrating a hexagonal and well ordered p6mm structure. SEM image shows the typical morphology of SBA-15, consisting of rod-like particles associated into wheat-like macrostructures [7]. Cage-like structures (SBA-16 and FDU-12) show globular type of particles with different faceted termination depending on the space group. Table 1 collects the textural properties of the solids. All of them present surface areas above 500 m2/g, excepting the sample FDU-12-a, probably due to a major presence of intergrowths. The materials cover a pore range of 4.7 - 27.9 nm, including amorphous silica with large mesopores that was used as reference. The immobilization results (Table 1) indicate that cage-like solids require extremely longer times to achieve maximum loading than cylindrical-pore systems. This can be explained because the enzyme (9.92 x 5.05 x 8.67 nm) has to diffuse in an adequate orientation to be able to pass through the pore entrances and access the cages. To evaluate this effect, different synthetic attempts led to samples with at least two different pore windows. However,

899 899

there are no straightforward techniques to estimate accurately the entrance/cage size and it is only possible to assure that systems with larger cages lead to higher loadings (FDU-12-a > FDU-12-b > SBA-16). In the case of the SBA-16 sample, the loading was identical for the as-made and calcined materials, clearly 2U

Intensity (a.u.)

1 211 '

a

) \ 220 22C

b

A 111 111

'\

311 311 1

22θ θ 2

3

SOnm

50nm

Figure 1. XRD patterns of a) KIT-6, and b) FDU-12-a. SEM images of c) SBA-15 and d) SBA16. TEM images of SBA-15 along e) [100] and g) perpendicular orientations. TEM images of SBA-16 along f) [100] and h) [111] zone axes.

indicating that the enzyme is not able to pass through the window and hence the immobilization takes place only on the external surface. Enzyme immobilization can therefore provide an indirect evidence of the size of the pore entrances. In any case, further 3D reconstruction based on Electron Crystallography has to be applied in order to have an accurate cage systemlipase sketch. When CALB is immobilized in OMM with hexagonal arrangement of cylindrical pores (MCM-41 and SBA-15), a clear increase of enzyme loading with pore diameter is observed. MCM-41, with 4.7 nm pore size, exhibits lower enzyme content and at longer contact time than SBA-15 with a 8.8 nm pore size (see Table 1). By comparing as-made and calcined MCM-41 samples it can be concluded that 50% of the immobilization is on the external surface, and only 5 mgE/g penetrates inside the channels. Amorphous silica exhibits the highest values (45.3 mg/g in 120min), however it is remarkable that such a big pore size difference (27.9 in SiO2 and 8.8 nm in SBA-15) showed almost the same loading in very similar times (see Table 1). This seems to indicate that, above a minimum value, pore size might not be the only limiting step for a larger enzyme loading to be reached, not even when increasing the enzyme concentration. On the other hand, it was expected that KIT-6 material (MCM-48 type of structure) would show better performance than SBA-15 in terms of diffusion properties. However it exhibits an intermediate behaviour, with lower loading and higher contact time than SBA15, probably due to a slightly smaller pore diameter (8.4 nm). This seems to

900

indicate that pore diameter, window size in cage-type mesostructures, is a crucial factor for the immobilization process. However, it has to be highlighted that crystal morphology and textural properties of the mesophase affect the immobilization properties so the results should be view with some caution. Table 1. OMM textural properties and immobilization results Mesoporous support

Enzyme-Mesoporous support

Name

Structure

Pore size (nm)

SBET (m2/g)

V mesop (m3/g)

Contact time (h)

Enzymatic loading* (mgE/g support)

Organic content (nig/g support)**

S1O2

Amorphous p6mm

27.9 4.7

305 595

2.70 0.82

2 24

45.3 10

50.9 14.9

SBA-15 KIT-6

poTwn

la-Zd

8.8 8.4

890 917

1.31 1.20

~2 ~4

44 37

57 45.2

SBA-16 asmade-SBA-16 FDU-12-a as-made FDU-12-a FDU-12-b

Im-3m Im-3m Fm-3m Fm-im Fm-3m

10.2 10.4 9.2

658 . 261 501.2

. 0.38 _ 0.62

24 24 48 48 48

5 5 28 5 21

8.6 10.7 36.3 10.1 30

as-made FDU-12-b

Fm-3m

-

-

48

5

8.8

MCM-41

'Determined by the activity assay. **Determined by Thermogravimetric Analysis of the solid once filtered and dried.

4. Acknowledgement The authors acknowledge Comunidad Autonoma de Madrid (CAM) for financial support within the Project GR/MAT/0694/2004. E. Serra acknowledges the support of a CAM PhD fellowship. 5. References [1] R. M. Blanco, P. Terreros, M. Fernandez-Perez, C. Otero and G. Diaz-Gonzalez, J. Mol. Catal. B: Enzimatic 30 (2004) 83. [2] a) A. Macario, V. Calabro, S. Curcio, M. De Paola, G. Giordano, G. Iorio and A. Katovic, Stud. Surf. Sci. Catal. 142 (2002) 1561; b) E. L. Pires, E. A. Miranda and G. P. Valenca, Appl. Biochem. Biotechnol. 98 (2002) 963; c) Z. Z. Chen, Y. M. Li, X. Peng, F. R. Huang and Y. F. Zhao, J. Mol. Catal. B: Enzym. 18 (2002) 243; d) H. Ma, J. He, D. G. Evans and X. Duan, J. Mol. Catal. B: Enzim. 30 (2004) 209; e) A. Salis, D. Meloni, S. Ligas, M. F. Casula, M. Monduzzi, V. Solinas and E. Dumitriu, Langmuir 21 (2005) 5511. [3] K. Tae-Wan, F. Kleitz, B. Paul, and R. Ryoo, J. Am. Chem. Soc. 127 (2005) 7601. [4] T. W. Kim, R. Ryoo, M. Kruk, K. P. Gierszal, M. Jaroniec, S. Kamiya and O. Terasaki J. Phys. Chem. B 108 (2004) 11480. [5] J. Fan, C. Z. Yu, T. Gao, J. Lei, B. Z. Tian, L. M. Wang, Q. Luo, B. Tu, W. Z. Zhou and D.Y. Zhao, Angew. Chem. Int. Ed. 42 (2005) 3146. [6] M. Boveri, J. Agundez, I. Diaz, J. P6rez-Pariente, E. Sastre and Collect. Czech. Chem. Commun. 68 (2003) 1914. [7] D. Y. Zhao, J. Sun, Q. Li and G. D. Stucky, Chem. Mater. 12 (2000) 275.


901 901

Microwave synthesis of Zr incorporated SBA-16 mesoporous silica as a catalyst for MeerweinPonndorf-Verley (MPV) reduction Nanzhe Jiang, Kwang-Min Choi, Sang-Cheol Han, Jeong-Boon Koo and Sang-Eon Park* Lab. ofNano-Green Catalysis andNano Center for Fine Chemicals Fusion Technology, Dept. of Chemistry, Inha University, Incheon, 402-751, Korea

Zr incorporated and pure SBA-16 were prepared by microwave synthesis method. These microwave synthesized Zr-SBA-16 played a role as Lewis acid sites for the Meerwein-Ponndorf-Verly reduction of ketones giving almost 100 % selectivities with high activities. 1. Introduction Metal incorporation into nanoporous materials could give birth to Lewis acid sites through the framework substitution onto silica matrix. The supported Lewis acid sites can offer several advantages in various heterogeneous catalytic systems such as Baeyer-Villiger reactions [1], and Meerwein-Ponndorf-Verley (MPV) reduction reactions [2]. The MPV reductions of carbonyl compounds using secondary alcohols as hydrogen donor are one of the highly selective transfer hydrogenation reactions [3]. Zr is an important element which it is being increasingly used in catalysis, because the addition of Zr in catalysts led to the improvements in activity and selectivity. The incorporated Zr could played a role as the active Lewis acid sites through the activation of C=O groups of the ketone [2]. For the incorporation of Zr into the silica framework, microwave-assisted synthesis method could offer many distinct advantages over conventional hydrothermal method. Besides the rapid and homogeneous nucleation, direct intrusion of metallic components forced by microwave was expected. It is caused by the difference in the electronegativities of Zr-0 bonding and Si-0 bonding which could absorb microwave energy selectively [4].

902

Herein, we report a successful synthesis of Zr substituted SBA-16 materials by microwave method. Those incorporated Zr species have tetragonal structure which were confirmed by the UV-vis spectroscopy. The generated Lewis acidic sites by the framework Zr were investigated by the pyridine adsorption in FT-IR measurements. These active sites played a role as Lewis acid sites in the MPV reduction of cyclohexanone giving almost 100% selectivities with high activities as well. 2. Experimental Section 2.1. Synthesis In a typical synthesis, 16 g of a 10 % aqueous solution of F127, 26 g of distilled water and 4.71 g of Na2SiO3»9H2O was mixed at 313 K. To this solution, 13.6 g of HC1 (35 %) with ZrOCl2»8H2O were added quickly under vigorous stirring to obtain a gel. The gel solution was stirred for 120 min before loaded into a microwave digestion system (CEM Corporation, MAR-5), and microwave was irradiated for 120 min at 100°C. The solid product was calcined at 500°C. Pure siliceous SBA-16 was synthesized with the same procedure except that no Zr was added. 2.2. Characterization XRD patterns were recorded on a Rigaku Multiflex diffractometer with a monochromated high-intensity Cu Ka radiation (X = 0.15418 nm). Nitrogen adsorption/desorption isotherms were measured at 77 K on a ASAP 2020 apparatus.The UV diffuse reflectance spectra were measured with a Solidspec 3700 UV-Vis-NIR spectrometer of Shimazu. A BaSO4 was used as a standard. FT-IR spectroscopy was carried out on a Nicolet Magna-AEM FT-IR spectrometer using KBr windows. The samples were preheated at 450°C for 15h, and pyridine was adsorbed at 150 °C for 30 min followed, desorbing at 150°C for 20 min before measurement. The samples were measured at 25°C. SEM images were obtained from a SEM (JEOL 630-F) instrument. 2.3. Catalytic reaction 0.127 g (1.3 mmol) of the cyclohexanone and 5 g (83 mmol) of 2-propanol were placed in the tube and heated to 82°C. A quantity of 100 mg of catalyst was added to the reaction mixture. The products were analyzed by gas chromatography. The o-xylene was used as internal standard.

903


5 X

0 5 X

X

a 1

0.005 5

5 2 2 Theta

0.008 0.01 0 .0.02 02 3

750

1.6

6.1 nm

4.7 nm

1.2 0.8

"T" i0

g

1 b)

3 Pore Volume ( cm /g)

Zr/Si X

AdsorbbedV ed Volume ( cm3/g)

Fig. la illustrates the XRD patterns of calcined pure and Zr containing SBA16. It showed that the Im3m structures were obtained when the Zr/Si atomic

500

i

250

0.4 0.0

0

50

100

150

Pore Diameter

C^^ 0.0

0.2

0.4

" 0.6

0.8

1.0 1.0

P/P P0 0

Fig. 1 a) Small-angle X-ray diffraction patterns of calcined Zr-SBA-16 with varid Zr/Si atomic ratios (in gel), b) N2 sorption isotherms and the pore size distributions of 0.01 ZrSBA-16 and pure SB A-16

ratios lower than 0.01. They were identified with sharp ( 1 1 0 ) and small (2 0 0) reflections [5]. The lattice parameters were calculated as about 88A which was smaller to those reported in the literature [6, 7]. It might be due to the incorporation of zirconium which caused the more closed condensation. The textural ordering of the Zr- SBA-16 decreased as the Zr/Si was 0.02. It indicated that maximum Zr content was lower than 2 % under such synthesis condition. The physical properties of the 0.01 Zr-SBA-16 and pure SBA-16 samples were characterized by N2 sorption studies (Fig. lb). The pore volume and BET decreased apparently from 6.1 to 4.7 nm and 948 to 537 m2/g, respectively. It indicates the incorporation of Zr leeds to the more closed condensation of silica framework. Fig 2a presents the UV-visible spectra of the calcined Zr-SBA-16 samples. Zr containing samples exhibited a band around 210 nm which was ascribed to an oxygen to Zr(IV) charge-transfer transition. Sharp band at 210 nm showed the presence of isolated Zr4+ ions in the framework of silica. Increases in Zr contents resulted in the increases in intensities. But Zr/Si ratios of higher than 0.01, the ZrC>2 phase might be formed which gave band at about 230 nm [7]. Fig 2b shows infrared spectra of pyridine adsorbed on the varied content of ZrSBA-16. The peak at 1447 cm'1 indicated the presence of Lewis acid sites and the absence of a peak at 1540 cm'1 showed the absence of any strong Bransted acid sites. The weak peaks at 1480 and 1580 cm"1 could be ascribed to Hbonded pyridine [8]. It means, in the framework of directly synthesized ZrSBA-16, most of incorporated Zr shows Lewis acid sites, because of these Zr species have tetragonal structure in the silica framework. MPV reduction of cyclohexanone on Zr-SBA-16 with different contents of Zr are presented in Figure 2c. The selectivities on cyclohexanol were higher than

904

98 % for all samples. It was due to the moderate acidity of Zr active sites in the SBA-16 framework. And reaction results showed the 0.01 (Zr/Si) is the best ratio for MPV reduction. 4. Conclusion From above results, we could conclude that direct synthesis of zirconium substituted SBA-16 mesoporous silica (with the best molar ratio Zr/Si = 0.01) have been achieved using zirconyl chloride octahydrate as a zirconium source under microwave irradiation without any loss in textural properties. Such obtained Zr-SBA-16 had Lewis acidity which had played highly selective catalysts for the MPV reduction of cyclohexanone. a

b Zr/Si

1580 1580

J

1480 1480

1448 1448

1__A.

Zr/Si 0.005 0.005

cc

100 100 90

0.02

%

0.008 0.008

0.01 0.008 0.005

200

250

300

350 400450500 400 450

Wavelength nm Wavelength / nm

——^^— ^\

A 0.01 0.02

500 1700 1700 1650 1650 1600 1600 1550 1550 1500 1500 1450 1450 1400 1400 -1 Wavenumber/Cm Wavenumber / Cm- 1

80 70 008Conversion Conversion of cyclohexanone - • - Selectivity Selectivity of cyclohexanol cyclohexanol

60 0.005

0.010

0.015

0.020

Zr/Si (mol / mol) (mol/mol)

Figure 2. a) UV spectra of Zr-SBA-16 with various Zr/Si atomic ratios (in gel), b) FT-IR spectra of chemisorbed pyridine on Zr-SBA-16 at 150 °C, and c) Effect of Zirconium content on MPV reduction of cyclohexanone.

5. Acknowledgement This work was supported by KOSEF A3 Foresight Program (33426-1) 6. References [1] [2] [3] [4] [5]

A. Corma, L. T. Nemeth, M. Renz and S. Valencia, Nature, 412 (2001), 425. Y. Z. Zhu, G. Chuah and S. Jaenicke, J. Cat., 227 (2004) 1. C. F. de Graauw, J. A. Peters, H. van Bekkum and J. Huskens. Synthesis, 10 (1994) 1007. Young Kyu Hwang, J. S. Chang and S. E. Park, Angew. Chem. Int. Ed., 44 (2005) 556. Y. K. Hwang, J. S. Chang, Y. U. Kwon and S. E. Park, Microporous and Mesoporous Materials, 68(2004)21. [6] D. Zhao, Q. Huo, J. Feng, B. F. Chemlka and G. D. Stucky, J. Am.Chem. Soc, 120 (1998) 6024. [7] M. S. Morey, S. Schwarz, M. Froba and G. D. Stucky, J. Phys. Chem. B, 103 (1999) 2037. [8] G. G. Juttu and R. F. Lobo, Catalysis Letters, 62 (1999) 99.


905 905

One and three dimensional mesoporous carbon nitride molecular sieves with tunable pore diameters Ajayan Vinua*, Toshiyuki Moria, Sunichi Hishitaa, Srinivasan Anandana, Veerappan Vaithilingam Balasubramanianb and Katsuhiko Arigac "Fuel Cell Materials Center, National Institute for Materials Science, 1-1 Namiki, Tsukuba 305-0044, Ibaraki, Japan; Email: [email protected] b Department of Marine Biotechnology, Asan-City 336-745, Chungnam, Soonchunhyang University, South Korea c Supermolecules Group, National Institute for Materials Science, 1-1 Namiki, Tsukuba 305-0044, Ibaraki, Japan One- and three-dimensional mesoporous carbon nitride materials have been synthesized using SBA-15 and SBA-16 mesoporous silica hard templates, respectively. The obtained materials have been unambiguously characterized by sophisticated techniques such as XRD, HRTEM, EELS, XPS, FT-IR and nitrogen adsorption. The pore diameter of the above materials can easily be tuned by changing the pore diameter of mesoporous silica template with keeping the weight ratio of carbon and nitrogen source constant. 1. Introduction Mesoporous carbon materials [1-2] with nanoscale pore sizes prepared from periodic inorganic silica templates have been receiving much attention because of their versatile uses in size and shape selective adsorption media, chromatographic separation, catalysts, nanoreactors, battery electrodes, capacitors, energy storage and biomedical engineering. Mesoporous carbon nitride materials (MCN) with one and three dimensional pore systems promise access to an even-wider range of application possibilities because of their unique properties such as semi-conductivity, intercalation ability, hardness, etc. Until now no such materials have been reported. However, there are lots of report on the synthesis and characterization of nonporous carbon nitride materials [3]. These materials can be prepared either from molecular or chemical precursors at very high temperatures. Very recently, Gao and Giu have reported the chemical synthesis of nonporous turbostratic carbon nitride crystallites from polymerized ethylenediamine and carbon tetrachloride [4]. Here, we used the similar chemical method for the preparation of the highly ordered one and three dimensional mesoporous carbon nitride material, designated as MCN, having pores with various diameters, high specific surface area and specific pore volume [5].

906

2. Experimental Section In a typical synthesis, the calcined mesoporous silica SBA-15 or SBA-16 was added to a mixture of ethylenediamine (EDA) and carbon tetrachloride (CTC). The resultant mixture was refluxed and stirred at 90°C for 6 h. The materials prepared using SBA-15 and SBA-16 as templates were named as MCN-1 and MCN-2, respectively. Another set of samples was prepared using SBA-15 materials synthesized at different temperature and the samples were labeled as MCN-1-T where T indicates the synthesis temperature of mesoporous silica. The template-carbon nitride polymer composites were then heat treated in a nitrogen flow to carbonize the polymer. The MCN was recovered after dissolution of the silica framework in 5 wt% hydrofluoric acid. The powder X-ray diffraction (XRD) patterns of mesoporous carbon nitride materials were collected on a Rigaku diffractometer using CuKoc (A, = 0.154 nm) radiation. The specific surface area was calculated using the Brunauer-Emmett-Teller (BET) method. HRTEM images were obtained with TEM JEOL JEM-2000EX2. The preparation of samples for HRTEM analysis involved sonication in ethanol for 2 to 5 min and deposition on a copper grid. The accelerating voltage of the electron beam was 200 kV. 3. Results and Discussion The ordered one-dimensional (1-D) mesoporous carbon nitride MCN-1 structure was investigated by powder XRD and nitrogen gas adsorption measurements. The XRD pattern of MCN-1 material shows three, clear peaks, which can be assigned to 100, 110, and 200 diffractions of 2-D hexagonal lattice (space group p6mm) with a lattice constant a1Oo = 9.52 nm, similar to the XRD pattern of parent template SBA-15 which consists of the hexagonal arrangement of cylindrical pores and the pores are interlinked by the micropores present in the walls, as shown in Fig. la. Such materials with 1-D mesopores are arranged in a hexagonal net are defined as 2-D mesostructure because the XRD pattern shows 2-D p6mm symmetry. The powder XRD pattern of MCN-1 before carbonization also exhibits the pattern similar to SBA-15, consisting of a week 100 reflection at low angle and two small peaks at a higher angle (not shown). However, the intensity of the low angle (100) and high angle peaks (110 and 200) decreases as compared to the parent SBA-15 material upon loading the CN matrix inside the mesopores. This can not be interpreted as a severe loss of structural order, but it is likely that larger contrast in density between the silica walls and the open pores relative to that between the silica walls and the CN matrix inside the pores is responsible for the observed decrease in intensity. Moreover, the unit cell constant of the MCN-1 material before carbonization (10.7 nm) is higher than the respective carbonized sample.

907

This can be ascribed to the condensation reaction between the free carbon and nitrogen in the walls resulting in a lattice contraction. The powder XRD pattern and HRTEM of 2-D mesoporous carbon nitride materials synthesized using SBA-15 with different pore diameters prepared at different synthesis temperature are also shown in Fig. la and lb, respectively. All the materials possess a sharp 100 reflection at very low angle which is typical for hexagonally ordered mesoporous materials. It is interesting to note that the d-spacing and the unit cell size of the MCN-1 materials synthesized using different pore diameters of SBA-15 materials as templates increase in the following order : MCN-1-150 > MCN-1-130 > MCN-1-100. This is a direct evidence of pore size enlargement in the MCN-1 materials. The overall carbon to nitrogen ratio of all the materials obtained from the CHN and EELS is almost same and is found to be 4.35. EEL spectra exhibit C and N K-edges located at 284 and 401 eV. The fine structure of the edges, in particular, their left-hand 2 shoulders revealing ls-Jt* electron transitions, is a fingerprint of a sp hybridization. The FT-IR and XPS data also confirm that the materials are mainly composed of C and N with a small amount of hydrogen. The trace of H comes either from the moisture or ethanol adsorbed on the surface or NH group on the MCN-1 matrix. Higher angle XRD pattern shows that the materials are partially amorphous and possess turbostratic ordering of carbon and nitrogen atoms in the CN graphene layers. 100 100

aa -

Intensity (a.u)

10.7 10.7 nm nm

b

MCN-1-150 MCN-1-150

(0

I

110

MCN-1-130 MCN-1-130 9.51 9.51 nm nm

200

00

22

MCN-1-100 MCN-1-100

44

66

Angle θ (theta) Angle 22θ (theta)

88

10 10

Fig. 1 (a) Powder XRD patterns of mesoporous carbon nitride materials with different pore diameters and (b) HRTEM of MCN-1-130. The powder XRD pattern of MCN-2 shows a sharp 110 reflection with a broad 200 reflection and is almost similar to that for SBA-16 template (Fig. 2a), demonstrating that 3-D mesoporous cage structure is successfully replicated to the MCN-2 sample. The intensity of the 110 peak of MCN-2 is much higher than that of the silica template, indicating that the enhancement in the structural order is occurred during the replication process. The unit cell

908

3e+4

600 500

MCN-2

b

3

Intensity (cps)

-1

a

3e+4

Amount Adsorbed (cm .g STP)

parameter of the MCN-2 is calculated using the formula 2 2 dnoand is found to be 13.4 nm. The nitrogen adsorption isotherm of MCN-2 in comparison to that of the parent silica template is shown in Figure 2b. Both the materials exhibit type IV isotherm with a broad hysteresis loop which is typical for the well ordered cage type mesoporous material. It should be also noted that the specific surface area and the specific pore volume of MCN-2 are much higher than those of the template and the 2-D mesoporous carbon nitride, MCN-1, prepared from the SBA-15 template. It is also important to note that the preparation of MCN-2 failed when our previous synthesis procedure for MCN-1 was used in this study. This could mainly be attributed to difference in the pore structure and the diameter of SBA-16 as compared to SBA-15 template.

2e+4 2e+4

MCN-2

1e+4 5e+3 SBA-16

0 2

4 4

2 θ (degrees) 2θ

6 6

8

400

SBA-16

300 200 100 0 0.0

0.2

0.4

0.6

0.8

1.0

1.2


Fig. 2 (a) powder XRD pattern and (b) nitrogen adsorption isotherms of MCN-2 in comparison with SBA-16

4. Conclusions Novel mesoporous carbon nitride materials with different structures have been synthesized using SBA-15 and SBA-16 hard templates, respectively. The obtained materials have been unambiguously characterized by various sophisticated techniques. Moreover, the pore diameter of the above materials can easily be tuned by changing the pore diameter of mesoporous silica template with keeping the weight ratio of carbon and nitrogen source constant. 5. References 1. R. Ryoo, S. H. Joo, S. Jun, J. Phys. Chem. B, 103 (1999), 7743. 2. A. Vinu, C. Streb, V. Murugesan, M. Hartmann, J. Phys. Chem. B, 107 (2003), 8297. 3. A. Vinu, M. Miyahara, K. Ariga, J. Phys. Chem. B, 109 (2005), 6436. 4. Y. Qiu, L. Gao, Chem. Commun., (2003), 2378; E. Kroke, M. Schwarz, Coordin. Chem. Rev., 248 (2004), 493. 5. A. Vinu, K. Ariga, T. Mori, T. Nakanishi, S. Hishita, D. Golberg, Y. Bando, Adv. Mater., 17(2005), 1648.


909 909

Synthesis of well-ordered carboxyl group functionalized mesoporous carbon using non-toxic oxidant, Ajayan Vinua*, Kazi Zahir Hossainb, Sunichi Hishitaa, Toshiyuki Moria, Narasimhan Gokulakrishnan0, Veerappan Vaithilingam Balasubramanianc and Katsuhiko Arigab "Fuel Cell Materials Center, National Institute for Materials Science, 1-1 Namiki, Tsukuba 305-0044, Ibaraki, Japan; Email: [email protected] b Supermolecules Group, National Institute for Materials Science, 1-1 Namiki, Tsukuba 305-0044, Ibaraki, Japan 'Department of Marine Biotechnology, Asan-City 336-745, Chungnam, Soonchunhyang University, South Korea Carboxyl group substituted mesoporous carbons were synthesized by oxidation of well-ordered mesoporous carbon materials with a solution of (NH4)2S2Og for a different periods of time and temperature. The effect of the oxidation treatment on the textural parameters of the mesoporous carbons was studied. The amount of carboxyl groups on the pore surface of the mesoporous carbon with very high structural order can be easily tuned by changing the oxidation conditions such as oxidation time, oxidant concentration and the oxidation temperature. 1. Introduction Mesoporous carbon materials with very high surface area, pore volume and uniform pore size distribution synthesized from periodic mesoporous silica templates are quite useful in many applications such as gas separation, catalysis, water and air purification and energy storage. However, the hydrophobic and inert nature of mesoporous carbons can be unfavourable for several applications. Surface modification or functionalization of porous carbon surface is crucial for the development and application of hybrid nanoporous materials and to make new adsorbent or catalyst for the selective removal of organic contaminants and biomaterials adsorption [1]. However, there have been only a limited number of studies on the functionalization of mesoporous carbon. Variety of functionalities can be introduced upon oxidising the surface of mesoporous carbons by various oxidation agents. This would also help to enhance the wettability for polar solvents and making the surface more reactive. Very recently, Ryoo and his coworkers have reported that COOH groups can easily be introduced on the surface of the mesoporous carbon by simple HNO3 oxidation [2]. It is expected that the COOH functionalized mesoporous carbon could have a great potential for high enzyme immobilization or low leaching because the size of the pore is much larger than the molecular size of the protein and can easily be tuned to the size of proteins for selective adsorption, and the

910

anchoring ability of COOH groups on the pore entrances. Unfortunately, to our knowledge, the preparation of -COOH functionalized mesoporous carbons by (NH4)2S2Og (APDS) as an oxidant and its great potential advantage in the enzyme immobilization have not been yet realized. 2. Experimental Section Mesoporous carbon material (CMK-3) was synthesized using a reported procedure elsewhere [3,4] and was oxidized using a solution of APDS with different concentration (0 to 1.75 M) in 2 M H2SO4, different periods of time up to a maximum of 48 h, and different temperatures starting from 0 to 60°C. All the oxidized samples were washed with several times with distilled water until there was an absence of sulphates in the washing water. However, a trace amount of sulphur was detected in the oxidized samples when they were analyzed using CHNS and EDS analysis. The nature and the amount of surface functional groups on the surface of mesoporous carbon were determined using FT-IR spectroscopy. The powder XRD patterns of mesoporous carbon materials after the APDS treatment were collected on a Rigaku diffractometer. The textural parameters of the mesoporous carbon after oxidation were calculated from the nitrogen adsorption and desorption isotherm using a Quantachrome Autosorb-lC instrument.

3. Results and Discussion Fig. la shows the FT-IR spectra of mesoporous carbon samples (CMK-3) treated with APDS at different reaction times. The efficiency of the oxidation treatment to create the carboxyl groups on the surface of the CMK-3 material using APDS is clearly reflected on the FT-IR spectra. All the samples after the oxidation treatment show four bands centered around 1723, 1587, 1400 and 1250 cm"1. Such peaks are not observed for the sample without the oxidation treatment. The band at 1723 c m 1 can be attributed to C=O stretching vibration of non-aromatic carboxyl groups while the band at 1587 c m 1 may be assigned to aromatic ring stretching coupled to highly conjugated keto groups. The band at 1400 cm"1 could be assigned either to carboxyl-carbonate structures or to aromatic C=C bond. It is interesting to note that the intensity ratio of the bands corresponding to the carboxyl and keto groups increases with increasing the oxidation time. The above results reveal that the prolonged treatment of mesoporous carbon with APDS could help the easy conversion of a large number of surface carbon atoms into keto groups and then to carboxyl groups on the surface of CMK-3. In order to study the changes on the textural parameters and structural order of the CMK-3 after APDS treatment, the materials were thoroughly characterized

911

by powder XRD, nitrogen adsorption and HRSEM measurements. Fig. lb shows the powder XRD patterns of CMK-3 treated with APDS solution at different reaction times. It can be clearly seen from Fig. lb that the structural order of the CMK-3 materials is almost maintained upto the reaction time of 24 h, while the structure is completely collapsed with a further increase from 24 to 48 h. The unit cell parameter of CMK-3 increases with increasing the oxidation time, suggesting that the oxidation can remove several layers of carbon from the pore walls and makes the walls thinner, resulting in an increase of pore size. The powder XRD results reveal that the structure of the CMK-3 materials is quite stable after the APDS treatment for 24 h. Though the mesoporous structure of the functionalized CMK-3 remained intact, the specific surface area, and pore volume of the material decrease with the severity of oxidation treatment. At one stage, i.e., above 24 h of reaction time, the pore walls are completely destroyed by the oxidation treatment which is clearly seen on the Figure lb.

1.4

b

a

1.42

48H

1.04

Intensity [a.u]

Absorbance (a.u)

1.6

24H

1.2

0.53

6H

0.48

0.8 0.6 0.6

12H

0.75

1.0

2H

24H 48H

0H

•

2000

2H 6H 12H

1800 1800

1600

1400 1400

1 -1 wavenumber /cm/cm 1

1200 1200

1000

0

2

4

6

Angle [2θ]

8

10

Fig. 1 (a) FT-IR spectra (inset numbers: Left-intensity ratio between the carboxyl and keto groups; Right-oxidation time) and (b) Powder XRD patterns of CMK-3 materials treated with APDS at different oxidation time. The surface morphology mainly the particle size, shape and structure of the CMK-3 materials after the APDS treatment was thoroughly studied by HRSEM technique. It is very interesting to note that the surface morphology of the materials except CMK-3-48H was completely retained after the APDS treatment. The observation of morphological disorder in the CMK-3-48H is consistent with the results obtained from the XRD and nitrogen adsorption measurements. All the above results clearly indicate that the oxidation time of 24 h is the best condition to functionalize mesoporous carbon without affecting its structural order and has been followed in the rest of our investigation. The effect of the concentration of the APDS on the degree of functionalization, structural order and the textural parameters of CMK-3 was also investigated. The degree of COOH functionalization increases with increasing the concentration of APDS as shown in Fig. 2a. It should be noted that the amount of COO groups calculated from the IR and HRSEM-EDX data increases from

912

0.5M

0.26M None

'.

1

2000 2000

.

1800 1800

1600 1600

1400 1400

1200 1200 -1

Wavenumber [cm ]

'

1000

0.8

800 0.6 600 0.4

400

0.2

200 0 0.0

0.5

1.0

1.5 1.5

0.0 2.0

-1 3

1.0

1000

5 4 3 2 1

Pore Diameter [nm]

0.52 '"X_/\^

1200

Mesopore Volume [cm .g ]

ioiir^ ^ " 0.5M

1.0M

*^^ ^

1.2

-1

1.75M 0.89

1400

Surface Area [m .g ]

Absorbance [a.u]

1.05

2

1.463 to 5.307 mmol.g"1 with increasing the oxidation time from 0 to 48 h. It can be also seen from the Fig. 2b that the pore diameter of the carbon materials after the APDS treatment is slightly larger than that of the sample before the treatment. The large reduction in the surface area and specific pore volume of the CMK-3 after APDS treatment could not be attributed as a severe loss of structural order as powder XRD pattern of all the materials exhibit strong 100 reflection after the treatment (not shown), but, however, could be mainly due to the formation of COOH groups inside the micropores of the mesoporous carbon as these micropores are mainly responsible for its very high specific surface area and specific pore volume. The effect of the temperature on the degree of functionalization has also been studied. It has been found that the structure of the CMK-3 was completely collapsed after the APDS treatment at 60°C for 24 h though the degree of functionalization is higher at 60°C.

0

Concentration of Oxidant [M]

Fig. 2 (a) FT-IR spectra and (b) textural parameters of mesoporous carbons treated with different concentration of APDS for 24 h. 4. Conclusions COOH functionalization on mesoporous carbon materials has been successfully achieved using a novel non-toxic oxidant, APDS. The effect of the oxidation treatment on the textural parameters of the mesoporous carbons was reported. The amount of carboxyl groups on the pore surface of the mesoporous carbon with very high structural order can be easily tuned by changing the oxidation conditions such as oxidation time, oxidant concentration and the oxidation temperature. 5. References 1. A. Vinu, C. Streb, V. Murugesan, M. Hartmann, J. Phys. Chem. B, 107 (2003), 8297. 2. S. Jun, M. Choi, S. Ryu, H-Y. Lee, R. Ryoo, Stud. Surf. Sci. Catal, 146 (2003), 37. 3. A. Vinu, M. Miyahara, K. Ariga, J. Phys. Chem. B, 109 (2005), 6436. 4. S. Jun, S. H. Joo, R. Ryoo, M. Kruk, M. Jaroniec, Z. Liu, T. Ohsuna, O. Terasaki, J. Am. Chem. Soc, 122 (2000), 10712.

913 STUDIES IN SURFACE SCIENCE AND CATALYSIS Advisory Editors: B. Delmon, Universite Catholique de Louvain, Louvain-la-Neuve, Belgium J.T. Yates, University of Pittsburgh, Pittsburgh, PA, U.S.A.

Volume 1

Volume 2

Volume 3

Volume 4

Volume 5

Volume 6

Volume 7

Volume 8 Volume 9

Volume 1 0

Volume 1 1

Volume 1 2

Volume 1 3 Volume 1 4

Volume 1 5

Preparation of Catalysts I. Scientific Bases for the Preparation of Heterogeneous Catalysts. Proceedings of the First International Symposium, Brussels, October 1 4 - 1 7 , 1 9 7 5 edited by B. Delmon, P.A. Jacobs and G. Poncelet The Control of the Reactivity of Solids. A Critical Survey of the Factors that Influence the Reactivity of Solids, w i t h Special Emphasis on the Control of the Chemical Processes in Relation to Practical Applications by V.V. Boldyrev, M. Bulens and B. Delmon Preparation of Catalysts ll.Scientific Bases for the Preparation of Heterogeneous Catalysts. Proceedings of the Second International Symposium, Louvain-laNeuve, September 4 - 7 , 1978 edited by B. Delmon, P. Grange, P. Jacobs and G. Poncelet Growth and Properties of Metal Clusters. Applications to Catalysis and the Photographic Process. Proceedings of the 32 n d International Meeting of the Societe de Chimie Physique, Villeurbanne, September 2 4 - 2 8 , 1979 edited by J. Bourdon Catalysis by Zeolites.Proceedings of an International Symposium, Ecully {Lyon), September 9 - 1 1, 1980 edited by B. Imelik, C. Naccache,Y. BenTaarit, J.C.Vedrine, G. Coudurier and H. Praliaud Catalyst Deactivation. Proceedings of an International Symposium, A n t w e r p , October 1 3 - 1 5 , 1 9 8 0 edited by B. Delmon and G.F. Froment New Horizons in Catalysis. Proceedings of the 7 th International Congress on Catalysis, Tokyo, June 3 0 - J u l y 4 , 1980. Parts A and B edited by T. Seiyama and KJanabe Catalysis by Supported Complexes by Yu.l.Yermakov, B.N. Kuinetsov and V.A. Zakharov Physics of Solid Surfaces. Proceedings of a Symposium, Bechyne, September 2 9 - O c t o b e r 3 , 1 9 8 0 edited by M. Laznicka Adsorption at the Gas-Solid and Liquid-Solid Interface. Proceedings of an International Symposium, Aix-en-Provence, September 2 1 - 2 3 , 1981 edited by J. Rouquerol and K.S.W. Sing Metal-Support and Metal-Additive Effects in Catalysis. Proceedings of an International Symposium, Ecully (Lyon), September 1 4 - 1 6 , 1982 edited by B. Imelik, C. Naccache, G. Coudurier, H. Praliaud, P. Meriaudeau, P. Gallezot, G.A.Martin and J.C.Vedrine Metal Microstructures in Zeolites. Preparation - Properties - Applications. Proceedings of a Workshop, Bremen, September 2 2 - 2 4 , 1982 edited by P.A. Jacobs, N.I. Jaeger, P. Jiru and G. Schulz-Ekloff Adsorption on Metal Surfaces. An Integrated Approach edited by J. Benard Vibrations at Surfaces. Proceedings of the Third International Conference, Asilomar, CA, September 1 - 4 , 1982 edited by C.R. Brundle and H.Morawitz Heterogeneous Catalytic Reactions Involving Molecular Oxygen by G.I. Golodets

914 Volume 16

Volume 1 7

Volume 18

Volume 1 9

Volume 20

Volume 21

Volume 22 Volume 23 Volume 24

Volume 25

Volume 26

Volume 27 Volume 28

Volume 29 Volume 30

Volume 31


Volume 35

Preparation of Catalysts III. Scientific Bases for the Preparation of Heterogeneous Catalysts. Proceedings of the Third International Symposium, Louvain-la-Neuve, September 6 - 9 , 1982 edited by G. Poncelet, P. Grange and PA. Jacobs Spillover of Adsorbed Species. Proceedings of an International Symposium, Lyon-Villeurbanne, September 12-16, 1983 edited by G.M. Pajonk.S.J.Teichner and J.E. Germain Structure and Reactivity of Modified Zeolites. Proceedings of an International Conference, Prague, July 9 - 1 3 , 1984 edited b y PA. Jacobs, N.I. Jaeger, P. Jiru, V.B. Kazansky and G. Schulz-Ekloff Catalysis on the Energy Scene. Proceedings of the 9'h Canadian Symposium on Catalysis, Quebec, P.Q., September 30-October 3, 1984 edited by S. Kaliaguine and A.Mahay Catalysis by Acids and Bases. Proceedings of an International Symposium, Villeurbanne (Lyon), September 2 5 - 2 7 , 1984 edited by B. Imelik, C. Naccache, G. Coudurier.Y. Ben Taarit and J.C.Vedrine Adsorption and Catalysis on Oxide Surfaces. Proceedings of a S y m p o s i u m , Uxbridge, June 2 8 - 2 9 , 1984 edited b y M. Che and G.C.Bond Unsteady Processes in Catalytic Reactors by Yu.Sh. Matros Physics of Solid Surfaces 1984 edited by J.Koukal Zeolites:Synthesis, Structurejechnology and Application. Proceedings of an International Symposium, Portoroz -Portorose, September 3 - 8 , 1984 edited by B.Driaj.S. Hocevar and S. Pejovnik Catalytic Polymerization of Olefins. Proceedings of the International Symposium on Future Aspects of Olefin Polymerization, Tokyo, July 4 - 6 , 1985 edited by T.Keii and K.Soga Vibrations at Surfaces I98S. Proceedings of the Fourth International Conference, Bowness-on-Windermere, September 15-19, 1985 edited by DA. King, N.V. Richardson and S. Holloway Catalytic Hydrogenation edited b y L. Cerveny New Developments in Zeolite Science and Technology. Proceedings o f t h e 7 th International Zeolite Conference, Tokyo, August 1 7-22, 1 986 edited by Y.Murakami.A. lijima and J.W.Ward Metal Clusters in Catalysis edited by B.C. Gates, L. Guczi and H. Knozinger Catalysis and Automotive Pollution Control. Proceedings of t h e First International Symposium, Brussels, September 8 - 1 1 , 1986 edited by A. Crucq and A. Frennet Preparation of Catalysts IV. Scientific Bases for the Preparation of Heterogeneous Catalysts. Proceedings of the Fourth International Symposium, Louvain-laNeuve, September 1-4, 1986 edited by B. Delmon, P. Grange, PA. Jacobs and G. Poncelet Thin Metal Films and Gas Chemisorption edited by P.Wissmann Synthesis of High-silica Aluminosilicate Zeolites edited b y P A Jacobs and J.A.Martens Catalyst Deactivation 1987. Proceedings of the 4"1 International Symposium, Antwerp, September 29-October 1, 1987 edited by B. Delmon and G.F. Froment Keynotes in Energy-Related Catalysis edited by S. Kaliaguine

915 915 Volume 36

Volume 37

Volume 38

Volume 39

Volume 40

Volume 41


Volume 45 Volume 46

Volume 47 Volume 48

Volume 49

Volume 50

Volume 51 Volume 52

Volume 53

Volume 54

Methane Conversion. Proceedings of a Symposium on the Production of Fuels and Chemicals from Natural Gas, Auckland, April 2 7 - 3 0 , 1987 edited by DM. Bibby, C.D.Chang, R.F.Howe and S.Yurchak Innovation in Zeolite Materials Science. Proceedings of an International Symposium, Nieuwpoort, September 13-17, 1987 edited by P.). Grobet, W.J.Mortier, E.F.Vansant and G. Schulz-Ekloff Catalysis l987.Proceedings of the 1 0 * North American Meeting of the Catalysis Society, San Diego, CA, May 17-22, 1987 edited by J.W.Ward Characterization of Porous Solids. Proceedings of t h e IUPAC S y m p o s i u m (COPS I), Bad Soden a, Ts., April 26-29,1987 edited by K.K.Unger, J. Rouquerol, K.S.W.Sing and H. Krai Physics of Solid Surfaces 1987. Proceedings of the Fourth Symposium on Surface Physics, Bechyne Castle, September 7 - 1 1 , 1987 edited by J.Koukal Heterogeneous Catalysis and Fine Chemicals. Proceedings of an International Symposium, Poitiers, March 15-17, 1988 edited by M. Guisnet, J. Barrault, C. Bouchoule.D. Duprez, C. Montassier and G. Perot Laboratory Studies of Heterogeneous Catalytic Processes by E.G. Christoffel, revised and edited by Z. Paal Catalytic Processes under Unsteady-State Conditions by Yu. Sh. Matros Successful Design of Catalysts. Future Requirements and Development. Proceedings of the Worldwide Catalysis Seminars, July, 1988, on the Occasion of the 30 th Anniversary of the Catalysis Society of Japan edited by T. Inui Transition Metal Oxides. Surface Chemistry and Catalysis by H.H.Kung Zeolites as Catalysts, Sorbents and Detergent Builders. Applications and Innovations. Proceedings of an International Symposium, Wiirzburg, September 4-8,1988 edited by H.G. Karge and ].Weitkamp Photochemistry on Solid Surfaces e d i t e d by M.Anpo and T. Matsuura Structure and Reactivity of Surfaces. Proceedings of a European Conference, Trieste, September 13-16, 1988 edited by C.Morterra.A. Zecchina and G. Costa Zeolites: Facts, Figures, Future. Proceedings of the 8Ih International Zeolite Conference, Amsterdam, July 10-14, 1989. Parts A and B edited by P.A. Jacobs and R.A. van Santen Hydrotreating Catalysts. Preparation, Characterization and Performance. Proceedings of the Annual International AlChE Meeting, Washington, DC, November 27-December 2, 1988 edited by ML. Occelli and R.G.Anthony New Solid Acids and Bases.Their Catalytic Properties by K.Tanabe, M. Misono.Y. Ono and H. Hattori Recent Advances in Zeolite Science. Proceedings of the 1989 Meeting of the British Zeolite Association, Cambridge, April 17-19, 1989 edited by ]. Klinowsky and P.J. Barrie Catalyst in Petroleum Refining 1989. Proceedings of the First International Conference on Catalysts in Petroleum Refining, Kuwait, March 5 - 8 , 1989 edited by D.L.Trimm,S.Akashah, M.Absi-Halabi and A. Bishara Future Opportunities in Catalytic and Separation Technology edited b y M. Misono,Y.Moro-oka and S. Kimura

916 916 Volume 55

Volume 56

Volume 57A

Volume 57B

Volume 58 Volume 59

Volume 60

Volume 61

Volume 62

Volume 63

Volume 64 Volume 65

Volume 66

Volume 67

Volume 68

Volume 69

Volume 70

Hew Developments in Selective Oxidation. Proceedings o f an International Symposium, Rimini, Italy, September 18-22, 1989 edited by G. Centi and F.Trifiro Olefin Polymerization Catalysts. Proceedings of the International Symposium on Recent Developments in Olefin Polymerization Catalysts, Tokyo, October 2 3 - 2 5 , 1989 edited by T.Keii and K.Soga Spectroscopic Analysis of Heterogeneous Catalysts. Part A: Methods of Surface Analysis edited by J.L.G. Fierro Spectroscopic Analysis of Heterogeneous Catalysts. Part B: Chemisorption of Probe Molecules edited by J.L.G. Fierro Introduction to Zeolite Science and Practice edited by H. van Bekkum, E.M. Flanigen and J.C. Jansen Heterogeneous Catalysis and Fine Chemicals II. Proceedings o f t h e 2 n d International Symposium, Poitiers, October 2 - 6 , 1990 edited by M. Guisnet, J. Barrault, C. Bouchouie.D. Duprez, G. Perot, R.Maurel and C. Montassier Chemistry of Microporous Crystals. Proceedings of the International Symposium on Chemistry of Microporous Crystals, Tokyo, June 26-29, 1990 edited by T. Inui.S. Namba and T.Tatsumi Natural Gas Conversion. Proceedings of the Symposium on Natural Gas Conversion, Oslo, August 12-17, 1990 edited by A. Holmen, K.-J, Jens and S.Kolboe Characterization of Porous Solids II. Proceedings of t h e IUPAC S y m p o s i u m (COPS II), Alicante, May 6 - 9 , 1990 edited by F. Rodriguez-Reinoso, J. Rouquerol, K.S.W. Sing and K.K.Unger Preparation of Catalysts V. Scientific Bases for the Preparation of Heterogeneous Catalysts. Proceedings of the Fifth International Symposium, Louvain-la-Neuve, September 3 - 6 , 1990 edited by G. Poncelet, PA. Jacobs, P. Grange and B. Delmon New Trends in CO Activation edited by L. Guczi Catalysis and Adsorption by Zeolites. Proceedings o f ZEOCAT 9 0 , Leipzig, August 20-23, 1990 edited by G . Ohlmann, H. Pfeifer and R. Fricke Dioxygen Activation and Homogeneous Catalytic Oxidation. Proceedings of t h e Fourth International Symposium on Dioxygen Activation and Homogeneous Catalytic Oxidation, Balatonf ured, September 10-14, 1990 edited by L.I. Simandi Structure-Activity and Selectivity Relationships in Heterogeneous Catalysis. Proceedings of the ACS Symposium on Structure-Activity Relationships in Heterogeneous Catalysis, Boston, MA, April 22-27', 1990 edited by R.K. Grasselli and A.W.SIeight Catalyst Deactivation 1991. Proceedings of the Fifth International Symposium, Evanston, IL, June 2 4 - 2 6 , 1991 edited by C.H. Bartholomew and J.B. Butt Zeolite Chemistry and Catalysis. Proceedings of an International Symposium, Prague, Czechoslovakia, September 8-13, 1991 edited by PA.Jacobs, N.I.Jaeger, LKubelkovaand B.Wichterlova Poisoning and Promotion in Catalysis based on Surface Science Concepts and Experiments by M. Kiskinova

917 917 Volume 71

Volume 72

Volume 73

Volume 74 Volume 75

Volume 76 Volume 77

Volume 78

Volume 79

Volume 80

Volume 81

Volume 82

Volume 83

Volume 84


Catalysis and Automotive Pollution Control II. Proceedings of t h e 2 n d International Symposium (CAPoC 2), Brussels, Belgium, September 10-13, 1990 edited by A. Crucq New Developments in Selective Oxidation by Heterogeneous Catalysis. Proceedings of the 3rd European Workshop Meeting on New Developments in Selective Oxidation by Heterogeneous Catalysis, Louvain-la-Neuve, Belgium, April 8 - 1 0 , 1991 edited by P. Ruiz and B. Delmon Progress in Catalysis. Proceedings of the 12 th Canadian Symposium on Catalysis, Banff, Alberta, Canada, May 25-28, 1992 edited by K.J. Smith and EX. Sanford Angle-Resolved Photoemission.Theory and Current Applications edited by S.D. Kevan New Frontiers in Catalysis, Parts A-C. Proceedings of the 10th International Congress on Catalysis, Budapest, Hungary, 19-24 July, 1992 edited by L. Guczi, F. Solymosi and P.Tetenyi Fluid Catalytic Cracking: Science and Technology edited b y J.S.Mageeand M M . Mitchell,jr. New Aspects of Spillover Effect in Catalysis. For Development of Highly Active Catalysts. Proceedings of the Third International Conference on Spillover, Kyoto, Japan, August 17-20, 1993 edited by T. Inui, K. Fujimoto.T.Uchijima and M. Masai Heterogeneous Catalysis and Fine Chemicals III. Proceedings of the 3rd International Symposium, Poitiers, April 5 - 8, 1 993 edited b y M. Guisnet, J. Barbier, J. Barrault, C. Bouchoule.D. Duprez, G. Perot and C. Montassier Catalysis: An Integrated Approach to Homogeneous, Heterogeneous and Industrial Catalysis edited by J.A. Moulijn, P.W.N.M. van Leeuwen and R.A. van Santen Fundamentals of Adsorption. Proceedings of the Fourth International Conference on Fundamentals of Adsorption, Kyoto, Japan, May 17-22, 1992 edited by M. Suzuki Natural Gas Conversion II. Proceedings of the Third Natural Gas Conversion Symposium, Sydney, July 4 - 9 , 1993 edited by H.E. Curry-Hyde and R.F.Howe New Developments in Selective Oxidation II. Proceedings of t h e Second W o r l d Congress and Fourth European Workshop Meeting, Benalmadena, Spain, September 2 0 - 2 4 , 1993 edited by V. Cortes Corberan and S.Vic Bellon Zeolites and Microporous Crystals. Proceedings of the International Symposium on Zeolites and Microporous Crystals, Nagoya, Japan, August 2 2 - 2 5 , 1993 edited byT. Hattori and T.Yashima Zeolites and Related Microporous Materials: State of the Art I994. Proceedings of the 10th International Zeolite Conference, Garmisch-Partenkirchen, Germany, July 17-22, 1994 edited b y J.Weitkamp, H.G. Karge.H. Pfeifer and W. Holderich Advanced Zeolite Science and Applications edited b y J.C. Jansen, M. Stocker, H.G. Karge and J.Weitkamp Oscillating Heterogeneous Catalytic Systems by M M . Slinko and N.I. Jaeger Characterization of Porous Solids III. Proceedings of t h e IUPAC S y m p o s i u m (COPS III), Marseille, France, May 9 - 1 2 , 1993 edited by J.Rouquerol, F. Rodriguez-Rdnoso, K.S.W. Sing and K.K.Unger

918 Volume 88

Volume 89

Volume 90

Volume 91

Volume 92

Volume 93 Volume 94

Volume 95 Volume 96

Volume 97

Volume 98

Volume 99 Volume 100

Volume 101

Volume 102 Volume 1 03 Volume 104 Volume 1 05

Catalyst Deactivation 1994. Proceedings of the 6 * International Symposium, Ostend, Belgium, October 3 - 5 , 1994 edited by B. Delmon and G.F. Froment Catalyst Design for Tailor-made Polyolefins. Proceedings o f t h e International Symposium on Catalyst Design for Tailor-made Polyolefins, Kanazawa, Japan, March 10-12, 1994 edited by K.Soga and M.Terano Acid-Base Catalysis II. Proceedings of the International Symposium on Acid-Base Catalysis II, Sapporo, Japan, December 2 - 4 , 1 993 edited b y H. Hattori.M. Misono and Y.Ono Preparation of Catalysts VI. Scientific Bases for the Preparation of Heterogeneous Catalysts. Proceedings of the Sixth International Symposium, Louvain-La-Neuve, September 5-8, 1994 edited by G. Poncelet, J.Martens.B. Delmon, P.A. Jacobs and P. Grange Science and Technology in Catalysis I994. Proceedings o f t h e Second T o k y o Conference on Advanced Catalytic Science and Technology, Tokyo, August 21-26, 1994 edited by Y. Izumi, H.Arai and M. Iwamoto Characterization and Chemical Modification of the Silica Surface by E.F.Vansant, P.Van Der Voort and K.C.Vrancken Catalysis by Microporous Materials. Proceedings of ZEOCAT'95, Szombathely, Hungary, July 9-13, 1995 e d i t e d by H.K. Beyer, H.G.Karge, I. Kiricsi and J.B.Nagy Catalysis by Metals and Alloys by V. Ponec and G.C.Bond Catalysis and Automotive Pollution Control III. Proceedings o f the Third International Symposium (CAPoC3), Brussels, Belgium, April 2 0 - 2 2 , 1994 edited by A. Frennet and J.-M. Bastin Zeolites:A Refined Tool for Designing Catalytic Sites. Proceedings of the International Symposium, Quebec, Canada, October 15-20, 1995 edited by L. Bonneviot and S. Kaliaguine Zeolite Science I994: Recent Progress and Discussions. Supplementary Materials t o t h e 10th International Zeolite Conference, Garmisch-Partenkirchen, Germany, July 17-22, 1994 edited b y H.G. Karge and J.Weitkamp Adsorption on New and Modified Inorganic Sorbents edited by A.Dabrowski and V.A.Tertykh Catalysts in Petroleum Refining and Petrochemical Industries 1995. Proceedings of the 2nd International Conference on Catalysts in Petroleum Refining and Petrochemical Industries, Kuwait, April 22-26, 1995 edited by M.Absi-Halabi, J. Beshara, H. Qabazard and A. Stanislaus II th International Congress on Catalysis - 4 0 * Anniversary. Proceedings of the 11 t h ICC, Baltimore, MD, USA, June 30-July 5, 1996 edited by J.W. Hightower.W.N. Delgass, E. Iglesiaand A.T. Bell Recent Advances and New Horizons in Zeolite Science and Technology edited by H. Chon.S.I.Woo and S. -E. Park Semiconductor Nanodusters - Physical, Chemical, and Catalytic Aspects edited by P.V. Kamat and D. Meisel Equilibria and Dynamics of Gas Adsorption on Heterogeneous Solid Surfaces edited by W. Rudziriski.W.A. Steele and G. Zgrablich Progress in Zeolite and Microporous Materials Proceedings of the 11 t h International Zeolite Conference, Seoul, Korea, August 12-17, 1996 edited by H. Chon,S.-K. Ihm and Y.S.Uh

919 Volume 106

Volume 107

Volume 108

Volume 109

Volume 110

Volume 1 11

Volume 112

Volume 1 1 3

Volume 1 14

Volume 115

Volume 1 1 6

Volume 117

Volume 1 1 8

Volume 11 9

Volume 1 2 0 A

Hydrotreatment and Hydrocracking of Oil Fractions Proceedings of the 1 s t International Symposium / 6' h European Workshop, Oostende, Belgium, February 17-19, 1997 edited by G.F. Froment.B. Deimon and P. Grange Natural Gas Conversion IV Proceedings of the 4 t h International Natural Gas Conversion Symposium, Kruger Park, South Africa, November 19-23, 1995 edited by M. de Pontes, R.L. Espinoia, C.P. Nicolaides, J.H. Scholtz and M.S. Scurrell Heterogeneous Catalysis and Fine Chemicals IV Proceedings of the 4 t h International Symposium on Heterogeneous Catalysis and Fine Chemicals, Basel, Switzerland, September 8-12, 1996 edited by H.U. Blaser, A. Baiker and R. Prins Dynamics of Surfaces and Reaction Kinetics in Heterogeneous Catalysis. Proceedings of the International Symposium, Antwerp, Belgium, September 15-17, 1997 edited by G.F. Froment and K.C.Waugh Third World Congress on Oxidation Catalysis. Proceedings of the Third World Congress on Oxidation Catalysis, San Diego, CA, U.S.A., 21-26 September 1997 edited by R.K. Grasselli.S.T.Oyama, A.M. Gaffney and J.E. Lyons Catalyst Deactivation 1997. Proceedings of the 7 th International Symposium, Cancun, Mexico, October 5-8, 1997 edited by C.H. Bartholomew and G.A. Fuentes Spillover and Migration of Surface Species on Catalysts. Proceedings of the 4 t h International Conference on Spillover, Dalian, China, September 15-18, 1997 edited by Can Li and Qin Xin Recent Advances in Basic and Applied Aspects of Industrial Catalysis. Proceedings of the 1 3 th National Symposium and Silver Jubilee Symposium of Catalysis of India, Dehradun, India, April 2-4, 1997 edited by T.S.R. Prasada Rao and G.Murali Dhar Advances in Chemical Conversions for Mitigating Carbon Dioxide. Proceedings of the 4 t h International Conference on Carbon Dioxide Utilization, Kyoto, Japan, September 7 - 1 1 , 1997 edited by T. Inui, M.Anpo.K. lzui,S.Yanagida and T.Yamaguchi Methods for Monitoring and Diagnosing the Efficiency of Catalytic Converters. A patent-oriented survey by M. Sideris Catalysis and Automotive Pollution Control IV. Proceedings of the 4 t h International Symposium (CAPoC4), Brussels, Belgium, April 9 - 1 1 , 1997 edited by N. Kruse, A. Frennet and J.-M. Bastin Mesoporous Molecular Sieves 1998 Proceedings of the 1 s ' International Symposium, Baltimore, MD, U.S.A., July 10-12, 1998 edited by L.Bonneviot, F. Beland, C.Danumah, S. Giasson and S. Kaliaguine Preparation of Catalysts VII Proceedings of the 7 l h International Symposium on Scientific Bases for the Preparation of Heterogeneous Catalysts, Louvain-la-Neuve, Belgium, September 1-4, 1998 edited by B. Deimon, PA. Jacobs, R. Maggi, J.A.Martens, P. Grange and G. Poncelet Natural Gas Conversion V Proceedings of the 5 t h International Gas Conversion Symposium, Giardini-Naxos, Taormina, Italy, September 20-25, 1998 edited by A. Parmaliana, D. Sanfilippo, F. Frusteri, A.Vaccari and F.Arena Adsorption and its Applications in Industry and Environmental Protection. Vol I: Applications in Industry edited by A. Dqbrowski

920 920 Volume 120B

Adsorption and its Applications in Industry and Environmental Protection.

Vol II: Applications in Environmental Protection Volume 121

edited by A. D;|browski Science and Technology in Catalysis I998

Proceedings of the Third Tokyo Conference in Advanced Catalytic Science and Technology, Tokyo, July 19-24, 1998 Volume 122

edited by H. Hattori and K. Otsuka Reaction Kinetics and the Development of Catalytic Processes

Proceedings of the International Symposium, Brugge, Belgium, April 19-21, 1999 Volume 123

edited by G.F. Froment and K.C.Waugh Catalysis:An Integrated Approach

Second, Revised and Enlarged Edition Volume 124 Volume 125

edited by R.A. van Santen, P.W.N.M. van Leeuwen, J.A. Moulijn and B.A.Averill Experiments in Catalytic Reaction Engineering by J.M. Berty Porous Materials in Environmentally Friendly Processes

Proceedings of the 1S1 International FEZA Conference, Eger, Hungary, September 1-4, 1999 Volume 126

edited by I. Kiricsi, G. Pal-Borbely, J.B.Nagy and H.G. Karge Catalyst Deactivation 1999

Proceedings of the 8th International Symposium, Brugge, Belgium, October 10-13, 1999 Volume 127

edited by B. Delmon and G.F. Froment Hydrotreatment and Hydrocracking of Oil Fractions

Proceedings of the 2nd International Symposium/7th European Workshop, Antwerpen, Belgium, November 14-17, 1999 Volume 128

edited by B. Delmon, G.F. Froment and P. Grange Characterisation of Porous Solids V

Proceedings of the 5th International Symposium on the Characterisation of Porous Solids (COPS-V), Heidelberg, Germany, May 30- June 2, 1999 Volume 129

edited by K.K.Unger.G.Kreysa and ).P. Baselt Nanoporous Materials II

Proceedings of the 2nd Conference on Access in Nanoporous Materials, Banff, Alberta, Canada, May 25-30, 2000 Volume 130

edited byA. Sayari.M. Jaroniec and T.J. Pinnavaia 12th International Congress on Catalysis

Volume 131

edited byA. Corma, F.V. Melo.S. Mendioroz and J.L.G. Fierro Catalytic Polymerization of Cycloolefins

Proceedings of the 12 th ICC, Granada, Spain, July 9-14, 2000

Ionic, Ziegler-Natta and Ring-Opening Metathesis Polymerization Volume 132

By V. Dragutan and R. Streck Proceedings of the International Conference on Colloid and Surface Science, Tokyo, Japan, November 5-8,2000

25 'h Anniversary of the Division of Colloid and Surface Chemistry, The Chemical Society of Japan Volume 1 33

edited by Y. Iwasawa, N.Oyama and H.Kunieda Reaction Kinetics and the Development and Operation of Catalytic Processes

Proceedings of the 3 rd International Symposium, Oostende, Belgium, April 2225, 2001 Volume 134

edited by G.F. Froment and K.C.Waugh Fluid Catalytic Cracking V

Materials and Technological Innovations edited by M L Occelli and P. O'Connor

921 Volume 135

Volume 136

Volume 137 Volume 138 Vol ume 139 Volume 140 Volume 141

Volume 142

Volume 143

Volume 144

Volume 145

Volume 146

Volume 147

Volume 148

Volume 149

Zeolites and Mesoporous Materials at the Dawn of the 21st Century. Proceedings of the 13lh International Zeolite Conference, Montpellier, France, 8-13 July 2001 edited by A. Galameau, F. di Renso, F. Fajula ans J. Vedrine Natural Gas Conversion VI Proceedings of the 6m Natural Gas Conversion Symposium, June 17-22, 2001, Alaska, USA. edited by J.J. Spivey, E. Iglesia and T.H. Fleisch Introduction to Zeolite Science and Practice. 2nd completely revised and expanded edition edited by H. van Bekkum, E.M. Flanigen, P.A. Jacobs and J.C. Jansen Spillover and Mobility of Species on Solid Surfaces edited by A. Guerrero-Ruiz and I. Rodriquez-Ramos Catalyst Deactivation 2001 Proceedings of the 9lh International Symposium, Lexington, KY, USA, October 2001 edited by J.J. Spivey, G.W. Roberts and B.H. Davis Oxide-based Systems at the Crossroads of Chemistry. Second International Workshop, October 8-11, 2000, Como, Italy. Edited by A. Gamba, C. Colella and S. Coluccia Nanoporous Materials III Proceedings of the 3"1 International Symposium on Nanoporous Materials, Ottawa, Ontario, Canada, June 12-15, 2002 edited by A. Sayari and M. Jaroniec Impact of Zeolites and Other Porous Materials on the New Technologies at the Beginning of the New Millennium Proceedings of the 2nd International FEZA (Federation of the European Zeolite Associations) Conference, Taormina, Italy, September 1-5, 2002 edited by R. Aiello, G. Giordano and F.Testa Scientific Bases for the Preparation of Heterogeneous Catalysts Proceedings of the 8th International Symposium, Louvain-la-Neuve, Leuven, Belgium, September 9-12, 2002 edited by E. Gaigneaux, D.E. De Vos, P. Grange, P.A. Jacobs, J.A. Martens, P. Ruiz and G. Poncelet Characterization of Porous Solids VI Proceedings of the 6lh International Symposium on the Characterization of Porous Solids (COPS-VI), Alicante, Spain, May 8-11, 2002 edited by F. Rodriguez-Reinoso, B. McEnaney, J. Rouquerol and K. Unger Science and Technology in Catalysis 2002 Proceedings of the Fourth Tokyo Conference on Advanced Catalytic Science and Technology, Tokyo, July 14-19, 2002 edited by M. Anpo, M. Onaka and H. Yamashita Nanotechnology in Mesostructured Materials Proceedings of the 3rd International Mesostructured Materials Symposium, Jeju, Korea, July 8-11, 2002 edited by Sang-Eon Park, Ryong Ryoo, Wha-Seung Ahn, Chul Wee Lee and Jong-San Chang Natural Gas Conversion VII Proceedings of the 7th Natural Gas Conversion Symposium, Dalian, China, June 6-10, 2004 edited by X. Bao and Y. Xu Mesoporous Crystals and Related Nano-Structured Materials Proceedings of the Meeting on Mesoporous Crystals and Related Nano-Structured Materials, Stockholm, Sweden, 1-5 June, 2004 edited by O. Terasaki Fluid Catalytic Cracking VI: Preparation and Characterization of Catalysts Proceedings of the 6th International Symposium on Advances in Fluid Cracking Catalysts (FCCs), New York, September 7 - 1 1 , 2003 edited by M. Occelli

922 Volume 150

Volume 151

Coal and Coal-Related Compounds Structures, Reactivity and Catalytic Reactions Reactions edited by T. Kabe, A. Ishihara, E.W. Qian, Kabe I.P. Sutrisna and Y. Kabe Petroleum Biotechnology Biotechnology Developments and Perspectives Perspectives edited by R. Vazquez-Duhalt and R. Quintero-Ramirez Quintero-Ramirez

Volume 152

Fisher-Tropsch technology edited by A.P. Steynberg and M.E. Dry

Volume 153

Carbon Dioxide Utilization for Global Sustainability Sustainability Proceedings Proceedings of the 7th International Conference on Carbon Dioxide 12-16, 2003 Seoul, Korea Utilization (ICCDU VII), October 12–16, K.-W. Lee edited by S.-E. Park, J.-S. Chang and K.-W.

Volume 154

Recent Advances in the Science and Technology of Zeolites and Related Materials Proceedings Proceedings of the 14th International Zeolite Conference, 25-30th April 2004 Cape Town, South Africa, 25–30th edited by E. van Steen, L.H. Callanan and M. Claeys

Volume 155

Oxide Based Materials Materials New Sources, Novel Phases, New Applications edited by A. Gamba, C. Colella and S. Coluccia

Volume 156

Nanoporous Materials IV edited by A. Sayari and M. Jaroniec

Volume 157

Zeolites and Ordered Mesoporous Materials Materials Progress and and Prospects Prospects Progress edited by J. Cejka and H. van Bekkum

Volume 158

Molecular Sieves: From Basic Research to Industrial Applications rd rd International Zeolite Symposium (3rd FEZA), Proceedings Proceedings of the 3rd Prague, Czech Republic, August 23-26, 2005 Prague, Nachtigall edited by J. Cejka, N. Zilková and P. Nachtigall

Volume 159

Engineering New Developments and Application in Chemical Reaction Engineering Proceedings Proceedings of the 4th Asia-Pacific Chemical Reaction Engineering Engineering (APCRE'05), Syeongju, Korea, June 12-15, 12-15, 2005 Symposium (APCRE’05), edited by H.-K. Rhee, I.-S. Nam and J.M. Park

Volume 160

Characterization of Porous Solids VII Proceedings Proceedings of the 7th International Symposium on the Characterization Characterization Porous Solids (COPS-VII), Aix-en-Provence, France, France, May 26-28, 2005 of Porous Rouqerol edited by Ph.L. Llewellyn, F. Rodríquez-Reinoso, J. Rouqerol and N. Seaton

Volume 161

Progress in Olefin Polymerization Catalysts and Polyolefin Materials Proceedings Proceedings of the First Asian Polyolefin Polyolefin Workshop, Nara, Japan, December 7-9, 2005 edited by T. Shiono, K. K. Nomura and M. Terano

Volume 162

Scientific Bases for the Preparation of Heterogeneous Catalysts Proceedings of the 9th International Symposium, Louvain-la-Neuve, Belgium, Proceedings September 10-14, 2006 edited by E.M. Gaigneaux, M. Devillers, D.E. De Vos, S. Hermans, P.A. Jacobs, J.A. Martens and P. Ruiz

Volume 163

Fischer-Tropsch Synthesis, Catalysts and Catalysis edited by B.H. Davis and M.L. Occelli

Volume 164

Biocatalysis in Oil Refining edited by M.M. Ramirez-Corredores Ramirez-Corredores and A.P. Borole

Recent Progress in Mesostructured Materials, Volume 165: Proceedings of the 5th International Mesostructured Materials Symposium (IMMS 2006) Shanghai, ... (Studies in Surface Science and Catalysis)

Nanotechnology in Mesostructured Materials

Progress in Zeolite and Microporous Materials (Studies in Surface Science and Catalysis)

Progress in Zeolite and Microporous Materials (Studies in Surface Science and Catalysis)

Catalysis by Zeolites: International Symposium Proceedings (Studies in surface science and catalysis)

Preparation of Catalysts: 2nd: International Symposium Proceedings (Studies in Surface Science and Catalysis)

Fluid Catalytic Cracking VII:, Volume 166: Materials, Methods and Process Innovations (Studies in Surface Science and Catalysis) (Studies in Surface Science and Catalysis)

Catalysts for Upgrading Heavy Petroleum Feeds, Volume 169 (Studies in Surface Science and Catalysis) (Studies in Surface Science and Catalysis)

Mesoporous Crystals and Related Nano-Structured Materials, Volume 148: Proceedings of the Meeting on Mesoporous Crystals and Related Nano-Structured Materials, ... (Studies in Surface Science and Catalysis)

Waste Materials in Construction: Proceedings (Studies in Environmental Science)

New Developments in Selective Oxidation by Heterogeneous Catalysis: Proceedings (Studies in Surface Science and Catalysis)

Crosslinking In Materials Science

Catalytic Polymerization of Olefins (Studies in Surface Science and Catalysis)

Preparation of Catalysts VII (Studies in Surface Science and Catalysis)

Past and Present in DeNOx Catalysis: From Molecular Modelling to Chemical Engineering, Volume 171 (Studies in Surface Science and Catalysis) (Studies in Surface Science and Catalysis)

Polymeric Materials in Organic Synthesis and Catalysis

Polymeric Materials in Organic Synthesis and Catalysis

Recent Advances and New Horizons in Zeolite Science and Technology (Studies in Surface Science and Catalysis, Volume 102)

Progress in Electrorheology: Science and Technology of Electrorheological Materials

Materials and Surface Engineering in Tribology

Materials and Surface Engineering in Tribology

Catalysis and Automotive Pollution Control III (Studies in Surface Science and Catalysis, Volume 96)

Progress in Zeolite and Microporous Materials

Fluid Catalytic Cracking V (Studies in Surface Science and Catalysis)

Photochemistry on Solid Surfaces (Studies in Surface Science and Catalysis)

Fluid Catalytic Cracking V (Studies in Surface Science and Catalysis)

12th International Congress on Catalysis (Studies in Surface Science and Catalysis)

Acid-Base Catalysis II: Proceedings of the International Symposium on Acid-Base Catalysis Ii, Sapporo, December 2-4, 1993 (Studies in Surface Science and Catalysis)

Characterization of Porous Solids III: Proceedings of the Iupac Symposium (Studies in Surface Science and Catalysis) (v. 3)

Catalysis: An Integrated Approach to Homogenous, Heterogenous and Industrial Catalysis (Studies in Surface Science and Catalysis)

Theory of laminated plates (Progress in materials science series)

Recent Progress in Mesostructured Materials, Volume 165: Proceedings of the 5th International Mesostructured Materials Symposium (IMMS 2006) Shanghai, ... (Studies in Surface Science and Catalysis)

Nanotechnology in Mesostructured Materials

Progress in Zeolite and Microporous Materials (Studies in Surface Science and Catalysis)

Progress in Zeolite and Microporous Materials (Studies in Surface Science and Catalysis)

Catalysis by Zeolites: International Symposium Proceedings (Studies in surface science and catalysis)

Preparation of Catalysts: 2nd: International Symposium Proceedings (Studies in Surface Science and Catalysis)

Fluid Catalytic Cracking VII:, Volume 166: Materials, Methods and Process Innovations (Studies in Surface Science and Catalysis) (Studies in Surface Science and Catalysis)

Catalysts for Upgrading Heavy Petroleum Feeds, Volume 169 (Studies in Surface Science and Catalysis) (Studies in Surface Science and Catalysis)

Mesoporous Crystals and Related Nano-Structured Materials, Volume 148: Proceedings of the Meeting on Mesoporous Crystals and Related Nano-Structured Materials, ... (Studies in Surface Science and Catalysis)

Waste Materials in Construction: Proceedings (Studies in Environmental Science)

New Developments in Selective Oxidation by Heterogeneous Catalysis: Proceedings (Studies in Surface Science and Catalysis)

Crosslinking In Materials Science

Catalytic Polymerization of Olefins (Studies in Surface Science and Catalysis)

Preparation of Catalysts VII (Studies in Surface Science and Catalysis)

Past and Present in DeNOx Catalysis: From Molecular Modelling to Chemical Engineering, Volume 171 (Studies in Surface Science and Catalysis) (Studies in Surface Science and Catalysis)

Polymeric Materials in Organic Synthesis and Catalysis

Polymeric Materials in Organic Synthesis and Catalysis

Recent Advances and New Horizons in Zeolite Science and Technology (Studies in Surface Science and Catalysis, Volume 102)

Progress in Electrorheology: Science and Technology of Electrorheological Materials

Materials and Surface Engineering in Tribology

Materials and Surface Engineering in Tribology

Catalysis and Automotive Pollution Control III (Studies in Surface Science and Catalysis, Volume 96)

Progress in Zeolite and Microporous Materials

Fluid Catalytic Cracking V (Studies in Surface Science and Catalysis)

Photochemistry on Solid Surfaces (Studies in Surface Science and Catalysis)

Fluid Catalytic Cracking V (Studies in Surface Science and Catalysis)

12th International Congress on Catalysis (Studies in Surface Science and Catalysis)

Acid-Base Catalysis II: Proceedings of the International Symposium on Acid-Base Catalysis Ii, Sapporo, December 2-4, 1993 (Studies in Surface Science and Catalysis)

Characterization of Porous Solids III: Proceedings of the Iupac Symposium (Studies in Surface Science and Catalysis) (v. 3)

Catalysis: An Integrated Approach to Homogenous, Heterogenous and Industrial Catalysis (Studies in Surface Science and Catalysis)

Theory of laminated plates (Progress in materials science series)

Recommend Documents