Langmuir Monolayers in Thin Film Technology

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CHEMICAL ENGINEERING METHODS AND TECHNOLOGY

LANGMUIR MONOLAYERS IN THIN FILM TECHNOLOGY

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CHEMICAL ENGINEERING METHODS AND TECHNOLOGY

LANGMUIR MONOLAYERS IN THIN FILM TECHNOLOGY

JENNIFER A. SHERWIN EDITOR

Nova Science Publishers, Inc. New York

Copyright © 2011 by Nova Science Publishers, Inc. All rights reserved. No part of this book may be reproduced, stored in a retrieval system or transmitted in any form or by any means: electronic, electrostatic, magnetic, tape, mechanical photocopying, recording or otherwise without the written permission of the Publisher. For permission to use material from this book please contact us: Telephone 631-231-7269; Fax 631-231-8175 Web Site: http://www.novapublishers.com

NOTICE TO THE READER The Publisher has taken reasonable care in the preparation of this book, but makes no expressed or implied warranty of any kind and assumes no responsibility for any errors or omissions. No liability is assumed for incidental or consequential damages in connection with or arising out of information contained in this book. The Publisher shall not be liable for any special, consequential, or exemplary damages resulting, in whole or in part, from the readers‟ use of, or reliance upon, this material. Any parts of this book based on government reports are so indicated and copyright is claimed for those parts to the extent applicable to compilations of such works. Independent verification should be sought for any data, advice or recommendations contained in this book. In addition, no responsibility is assumed by the publisher for any injury and/or damage to persons or property arising from any methods, products, instructions, ideas or otherwise contained in this publication. This publication is designed to provide accurate and authoritative information with regard to the subject matter covered herein. It is sold with the clear understanding that the Publisher is not engaged in rendering legal or any other professional services. If legal or any other expert assistance is required, the services of a competent person should be sought. FROM A DECLARATION OF PARTICIPANTS JOINTLY ADOPTED BY A COMMITTEE OF THE AMERICAN BAR ASSOCIATION AND A COMMITTEE OF PUBLISHERS. Additional color graphics may be available in the e-book version of this book.

LIBRARY OF CONGRESS CATALOGING-IN-PUBLICATION DATA Langmuir monolayers in thin film technology / editors, Jennifer A. Sherwin. p. cm. Includes bibliographical references and index. ISBN 978-1-61209-188-4 (eBook) 1. Thin films, Multilayered. I. Sherwin, Jennifer A. QC176.9.M84L365 2010 621.3815'2--dc22 2010041312

Published by Nova Science Publishers, Inc. † New York

CONTENTS Preface

vii

Chapter 1

Carbons and Clays for Heavy Metals Removal – A Review of Latest Literature John U. Kennedy Oubagaranadin and Z.V.P. Murthy

Chapter 2

Molecular Organization of Thermotropic Liquid Crystals and Their Mixtures with Azo Dyes in Langmuir and Langmuir-Blodgett Films Danuta Bauman, Anna Modlińska, and Krzysztof Inglot

Chapter 3

Atomic Force Microscopy Characterization of Lipid/ Protein Nanostructures Formed in Langmuir-Blodgett Films Yih Horng Tan and Keith J. Stine

Chapter 4

Langmuir Monolayers in Biosensors Jadwiga Sołoducho and Joanna Cabaj

Chapter 5

Adsorptive Characteristics of Bovine Serum Albumin onto Cationic Langmuir Monolayers of Sulfonated Poly (Glycidylmethacrylate)Grafted Cellulose: Mass Transfer Analysis, Isotherm Modeling and Thermodynamics T. S. Anirudhan and P. Senan

Chapter 6

Index

Electrochemistry of Polymeric Thin Films Prepared by Langmuir-Blodgett Technique Paolo Bertoncello

1

51

101 131

151

177 201

PREFACE The Langmuir-Blodgett (LB)technique for the preparation of ultrathin films of various organic, metallorganic, and polymeric compounds play an increasingly important role as a means or organizing molecular materials at the microscopic level. The LB technique has many potential applications in molecular electronics, nonlinear optics and conducting thin films. This book presents current research from across the globe in the study of Langmuir Monolayers, including the study of thermotropic liquid crystals and binary mixtures of dichroic azo dye/liquid crystal in Langmuir and Langmuir-Blodgett films; proteo-lipidic nanostructures generated via the Langmuir-Blodgett film method; Langmuir Monolayers in biosensors; as well as adsorptive characteristics of bovine serum albumin onto cationic Langmuir Monolayers of sulfonated poly-grafted cellulose. Chapter 1 - In this article, various adsorption isotherm models, kinetic models, adsorption thermodynamics and the technical viability of carbons made from different biomaterials and different types of naturally occurring clays for heavy metals removal by adsorption from contaminated water has been reviewed. Natural clays and carbons prepared from waste plant products can be employed for heavy metals removal from aqueous solutions and disposed of with little cost. Modification of these materials can also improve their adsorption capacity. In this review, an extensive literature survey from the past decade on the heavy metals removal characteristics of clays and carbons has been compiled to provide a summary. It is evident from this literature survey that carbons made from biomaterials and clays have demonstrated outstanding removal capabilities for certain metal ions. Some of the highest adsorption capacities reported are: for Cd(II), 180 mg/g by bean husk (Phaseolus vulgaris) carbon; for Cr(VI), 120.48 mg/g by date palm seed wastes carbon; for Pb(II), 279.92 mg/g by carbon made from Euphorbia rigida; for Hg(II), 151.5 mg/g by ZnCl2 activated walnut shells carbon; for Cr(III), 117.5 mg/g by Smectite clay with a small proportion of kaolinite; for Cd(II), 74.07 mg/g by petra clay; for Cu(II), 105.38 mg/g by modified Unye clay; for Pb(II), 104.28 mg/g by natural palygorskite clay; for Cu(II), 909 mg/g by Saudi bentonite. It is important to note that the adsorption capacities of the adsorbents presented in this paper vary, depending on the experimental conditions, characteristics of the individual adsorbent, the extent of chemical modifications, and the concentration of adsorbate. Chapter 2 - In this review articles the results of the study of thermotropic liquid crystals and of binary mixtures of dichroic azo dye/liquid crystal in Langmuir and Langmuir-Blodgett films are presented. The liquid crystals of rod-like shape from various homologous series and nine azo dyes with different molecular structure as well as different values and directions of

viii

Jennifer A. Sherwin

the dipole moment were chosen. It was found that the liquid crystals with the terminal isothiocyanato (–NCS) group are not able to form a compressible monolayer at the water surface. Very short and very long alkyl or alkoxy chains attached to the rigid molecular core also hinder the creation of the stable film. Azo dyes cannot form the Langmuir film themselves; therefore, the liquid crystals 4-n-octyl-4'-cyanobiphenyl (8CB) and trans-4-noctyl(4‟-cyanophenyl)-hexane (8PCH) were used as supporting matrices. The Langmuir films were characterized by the surface pressure-area and surface potential-area isotherms and by Brewster angle microscopy (BAM). The analysis of the isotherms and BAM images of liquid crystals indicated that the organization of the mesogenic molecules at the air-water interface is dependent on their structure and to some extent reflects their ability to form an appropriate mesophase in the bulk. For the binary azo dye/8CB mixtures the miscibility of two components as well as the organization and the packing of molecules at the water surface were determined. The absorption spectra by using natural and linearly polarized light were recorded for both Langmuir and Langmuir-Blodgett films. Information about spectral properties of ultra-thin layers and ability of dye and liquid crystal molecules to form selfaggregates was obtained. The polarized absorption spectra allowed one to determine the alignment of molecules on the quartz surface. Chapter 3 - Recently, much of the emphasis in biotechnology has been on producing nanosystems and nanodevices for a vast range of medical applications, including nanoelectronic biosensors, drug delivery systems, and diagnostic and imaging techniques, to name a few. This chapter reviews the potentially useful creation of proteo-lipidic nanostructures generated via the Langmuir-Blodgett (LB) film method, and their direct characterization by atomic force microscopy (AFM). Following the introductory sections, a brief overview on LB film fabrication on surfaces suitable for AFM will be presented, LB films containing proteins, lipids, and biocompatible amphiphilic molecules will be described, and how they have been studied using various AFM imaging modes. We aim to highlight recent developments that illustrate the unique capability of AFM in elucidating nanometer scale organization and the physicochemical properties of artificially engineered biological membranes through the Langmuir-Blodgett method; as it could potentially open a new pathway toward the development of self-organized nanostructures of technological significance. Chapter 4 - In recent years, the Langmuir-Blodgett (LB) technique for the preparation of ultrathin films of various organic, metallorganic, and polymeric compounds plays an increasingly important role as a means of organizing molecular materials at the microscopic level. The LB technique has many potential applications in molecular electronics, nonlinear optics and conducting thin films. The most important advantage of this method is that the characteristic of the film can be varied by changing various LB parameters, namely, surface pressure of lifting, temperature, barrier speed, dipping speed, molar composition, etc. So it is important to study different molecules having various chromophores with interesting photophysical and electrical properties, confined in the restricted geometry of the LB films to fabricate various molecular electronic devices and also to realize the basic physicochemical processes involved at the mono and multilayer films [1]. Chapter 5 - Investigation on adsorption behaviour of Bovine Serum Albumin (BSA) on polymeric adsorbent materials is critical for many analytical and biomedical applications. In the present study a novel adsorbent poly(glycidylmethacrylate)-grafted-cellulose having sulfonate functional groups (PGMA-g-Cell-SO3H) was prepared by graft copolymerization of

Preface

ix

glycidylmethacrylate (GMA) onto cellulose in the presence of ethyleneglycoldimethacrylate as crosslinker using α,ά-azobisisobutryronitrile as initiator followed by the introduction of sulfonic acid groups through ring opening reaction of the epoxide groups of the grafted GMA with sodium sulfite–isopropanol–water mixture. The original and the modified materials were characterized by means of FTIR, SEM, XRD and BET analysis. Adsorption characteristics of BSA onto PGMA-g-Cell-SO3H were investigated under different optimized conditions of pH, contact time, initial BSA concentration, adsorbent dose and temperature. The maximum value of BSA adsorption was found to be 49.95 and 72.07 mg/g for an initial concentration of 100 and 150 mg/L, respectively at pH 4.5. Kinetic studies showed that the equilibrium conditions were achieved within 3 h. The kinetic data obtained at different concentrations and temperatures were analyzed using a pseudo-first-order and pseudo-second-order equation. The adsorption process followed pseudo-second-order kinetics. The experimental kinetic data were correlated by the external mass transfer and intraparticle mass transfer diffusion models. The intraparticle mass transfer diffusion model gave a better fit to the experimental data. Experimentally obtained isotherms were evaluated with reference to Langmuir, Freundlich and Sips equations. The isotherm data were best modelled by the Langmuir isotherm equation and the maximum monolayer adsorption capacity was found to be 124.85 mg/g at 30 °C. Thermodynamic study revealed an endothermic adsorption process. The negative ΔG° values indicate feasible and spontaneous adsorption of BSA onto PGMA-g-Cell-SO3H. The positive and small value of enthalpy change ΔHo (9.50 kJ/mol) indicates the endothermic nature of adsorption primarily through weak physical forces between adsorbent and adsorbate. The positive and small value of entropy change, ΔSo (185.52 J/mol/K) indicates that the order less nature of adsorption system increases with adsorption of BSA onto adsorbent surface. Also at all temperatures ΔHo 6 and 1.0 g/50 mL, respectively. The kinetic data supported pseudo-second-order model and intra-particle model. The activated carbons with 20% ZnCl2 solution was the best sample of the produced activated carbons from olive stone with the specific surface area of 790.25 m2/g. The results showed that the produced activated carbon from olive stone was an alternative low-cost adsorbent for removing Cd(II). Activated carbon prepared from hazelnut husks with zinc chloride activation at 973 K in nitrogen atmosphere was studied for adsorption of Cu(II) and Pb(II) by Imamoglu and Tekir (2008). BET surface area of the activated carbon was found as 1092 m2/g. The activated carbon exhibited good adsorption potential for copper and lead ions. The maximum

18

John U. Kennedy Oubagaranadin and Z.V.P. Murthy

adsorption capacity of the adsorbent for Cu(II) and Pb(II) ions was calculated from the Langmuir isotherm and found to be 6.645 and 13.05 mg/g, respectively. The applicability of sulphurised activated carbon (SAC) as adsorbent for the effective removal of Co(II) from aqueous solutions was investigated by Krishnan and Anirudhan (2008). Bagasse pith, a sugarcane industry waste, was used for the synthesis of SAC. Maximum adsorption was observed in the pH range of 4.5–8.5. With an initial concentration of 50 and 100 mg/L of the adsorbate at pH 6.0, the percentage adsorptions were found to be 90.3 and 81.0%, respectively. SAC showed a high adsorption capacity for Co(II) removal when compared with laboratory and commercial grade activated carbons. The adsorption process obeyed Langmuir isotherm model. In a study by Demiral et al. (2008), activated carbon was prepared from olive bagasse by physical activation using steam. BET surface area of the activated carbon was determined as 718 m2/g. The maximum Cr(VI) adsorption yield was obtained at the initial pH of 2. The adsorption kinetics followed pseudo-second-order rate expression. Equilibrium results were analyzed by the Langmuir, Freundlich, Dubinin-Redushkevich, Temkin and Frumkin equations. Langmuir equation was found to fit the equilibrium data for Cr(VI) adsorption. Gerçel and Gerçel (2007) studied the adsorption of Pb(II) onto activated carbon prepared from renewable plant material, Euphorbia rigida. Adsorption data of Pb(II) onto activated carbon from E. rigida obeyed the Langmuir isotherm model. Maximum adsorption capacity of Pb(II) onto adsorbent was 279.72 mg/g at 40 °C. It was indicated that the adsorption of Pb(II) onto activated carbon from E. rigida could be described by the pseudo-second-order kinetic model and also followed the simple external-diffusion model for the initial 10 min and then by intra-particle diffusion model up to 50 min. A carbon rich adsorbent prepared from the reaction of sugar beet pulp with sulphuric acid and gas formed during carbonization process have been studied for Cr(VI) removal from aqueous solutions by Altundogan et al. (2007). The SO2 rich gas was shown to be an excellent Cr(VI) reductant. The equilibrium and kinetic studies were conducted by using the carbonaceous adsorbent derived from sugar beet pulp. Lower pH favored Cr(VI) adsorption, hence substantial Cr(VI) reduction was observed. Langmuir model best fitted the equilibrium isotherm data. The maximum adsorption capacity of chromium calculated from Langmuir isotherm was about 24 mg/g at 25 °C. The adsorption of Cr(VI) was endothermic and followed the pseudo-second-order rate kinetics. The sulphuric acid-carbonization was found to be economical particularly for chromium removal because the gas generated during carbonization exhibited good Cr(VI) reduction properties. In a study by Wilson et al. (2006) peanut shells were converted to activated carbons for use in adsorption of select metal ions; namely Cd(II), Cu(II), Pb(II), Ni(II) and Zn(II). Milled peanut shells were pyrolyzed in an inert atmosphere of nitrogen gas, and then activated with steam at different activation times. Following pyrolysis and activation, the carbons underwent air oxidation. The prepared carbons were evaluated for adsorption efficiency and these parameters were compared to the same parameters obtained from three commercial carbons, namely, DARCO 12 × 20, NORIT C GRAN and MINOTAUR. One of the peanut shell-based carbons had metal ion adsorption efficiency greater than two of the three commercial carbons but somewhat less than but close to MINOTAUR. This study demonstrated that the peanut shells can serve as a source for activated carbons with metal ion-removing potential and may serve as a replacement for coal-based commercial carbons in applications that warrant their use.

Carbons and Clays for Heavy Metals Removal …

19

The performance of a commercially available palm shell based activated carbon to remove Pb(II) from aqueous solutions by adsorption was evaluated by Issabayeva et al. (2006). The adsorption experiments were carried out at pH 3.0 and 5.0. Palm shell activated carbon showed high adsorption capacity for Pb(II), especially at pH 5 with an ultimate uptake of 95.2 mg/g. This high uptake showed palm shell activated carbon as a promising adsorbent. Removal and recovery of chromium were carried out by using low-cost activated carbon made from sugar industry waste (Fahim et al., 2006). Three types of activated carbons, viz., C1 (the waste generated from sugar industry) and the others C2, C3 (commercial granular activated carbons) were used. The effect of pH, particle size and type of adsorbent on the adsorption isotherm of Cr(III) were studied in batch system. The sorption data fitted well with Langmuir adsorption model. The efficiencies of activated carbons for the removal of Cr(III) were found to be 98.86, 98.6 and 93 % for C1, C2 and C3, respectively. The order of selectivity was C1 > C2 > C3 for removal of Cr(III) from tannery wastewater. Carbon “C1” of the highest surface area (520.66 m2/g) had the highest adsorptive capacity for the removal of Cr(III). The results revealed that the trivalent chromium was significantly adsorbed on activated carbon collected from sugar industry waste. Kannan and Rengasamy (2005) studied the removal of Cd(II) from aqueous solutions by adsorption on commercial activated carbon (CAC) and chemically prepared activated carbons (CPACs) from raw materials such as straw, saw dust and datesnut. The percentage removal increased with decrease in initial concentration and particle size of CPACs and an increase in contact time, dose and initial pH of the solution. The kinetics of adsorption was found to be first order with intra-particle diffusion as one of the rate determining steps. Results of the studies on adsorption of Cd(II) ions from simulated wastewater were compared with that of CAC and Tulsion CXO-9(H), a commercial ion exchange resin / cationic resin (CR). Straw carbon showed the maximum adsorption capacity towards Cd(II). Granular activated carbon (GAC) was treated chemically with potassium bromate for surface modification and its adsorption capacity was investigated with nickel ions by Satapathy and Natarajan (2006). There was an increase in the adsorption capacity of the modified carbon by 90–95% in comparison with the raw granular activated carbon towards nickel ions. Potassium bromate oxidation treatment was employed for a period of about 30 min initially followed by 60 min and the oxidized carbons were adsorbed with nickel ions. Metal adsorption characteristics of as received and modified activated carbons were measured in batch experiments. Equilibrium data fitted well with Langmuir model which indicated monolayer adsorption. Effects of pH of initial solution, time of oxidation and mode of treatment on the adsorption process were studied. Experimental results showed that metal uptake increased with an increase in pH and oxidation time. An efficient adsorption process was reported for the decontamination of Cr(III) from tannery effluents by Mohan et al. (2006). A low cost activated carbon (ATFAC) was prepared from coconut shell fibers and utilized for Cr(III) removal from water/wastewater. A commercially available activated carbon fabric cloth (ACF) was also studied for comparative evaluation. The Langmuir model best fitted the equilibrium isotherm data. The maximum adsorption capacities of ATFAC and ACF at 25 °C were 12.2 and 39.56 mg/g, respectively. Cr(III) adsorption increased with an increase in temperature (at 10 °C, ATFAC: 10.97 mg/g, ACF: 36.05 mg/g; at 40 °C, ATFAC: 16.10 mg/g, ACF: 40.29 mg/g). The adsorption of Cr(III) followed the pseudo-second-order rate kinetics. The sorption capacities of ATFAC

20


and ACF were comparable to many other adsorbents / carbons / biosorbents utilized for the removal of trivalent chromium from water/wastewater. Activated carbon prepared from Ceiba pentandra hulls, an agricultural solid waste byproduct, for the removal of copper and cadmium from aqueous solutions was studied by Rao et al. (2006). The adsorbent exhibited good sorption potential for copper and cadmium at pH 6.0. The C=O and S=O functional groups present on the carbon surface were the adsorption sites to remove metal ions from solution. The maximum adsorption capacity of Cu(II) and Cd(II) was calculated from Langmuir isotherm and found to be 20.8 and 19.5 mg/g, respectively. Desorption studies were carried out using dilute HCl and the effect of HCl concentration on desorption was also studied. Maximum desorption of 90% for Cu(II) and 88% for Cd(II) occurred with 0.2 M HCl. Apricot stones were carbonized and activated after treatment with sulphuric acid (1:1) at 200 °C for 24 h by Kobya et al. (2005). The ability of the activated carbon to remove Ni(II), Co(II), Cd(II), Cu(II), Pb(II), Cr(III) and Cr(VI) ions from aqueous solutions by adsorption was investigated. Batch adsorption experiments were conducted to observe the effect of pH (1–6) on the activated carbon. The adsorption of these metals was found to be dependent on solution pH. Highest adsorption occurred at pH 1-2 for Cr(VI) and pH 3-6 for the rest of the metal ions, respectively. Adsorption capacities for the metal ions were obtained in the order of Cr(VI) > Cd(II) > Co(II) > Cr(III) > Ni(II) > Cu(II) > Pb(II) for the activated carbon prepared from apricot stone. Adsorption capacity of Cr(VI) onto Hevea brasilinesis (rubber wood) sawdust activated carbon was investigated in a batch system by considering the effects of various parameters like contact time, initial concentration, pH and temperature by Karthikeyan et al., 2005. Cr(VI) removal was found to be maximum at pH 2.0. Increase in adsorption capacity with increase in temperature indicated that the adsorption reaction was endothermic. Pseudosecond-order model was found to explain the kinetics of Cr(VI) adsorption most effectively. Intraparticle diffusion studies at different temperatures show that the mechanism of adsorption is mainly dependent on diffusion. Langmuir isotherm showed better fit than Freundlich and Temkin isotherms in the temperature range studied. The results showed that the rubber wood sawdust activated carbon can be efficiently used for the treatment of wastewaters containing chromium as a low cost alternative. Removal of Pb(II) from aqueous solutions by adsorption onto coconut-shell carbon was investigated by Sekar et al. (2004). Adsorption of Pb(II) was strongly affected by pH. The coconut-shell carbon (CC) exhibited the highest lead adsorption capacity at pH 4.5. The equilibrium data fitted well to the Langmuir model. At pH 4.5, the maximum lead adsorption capacity of CC estimated with the Langmuir model was 26.50 mg/g. The thermodynamics of Pb(II) on CC indicated spontaneous and endothermic nature of the adsorption. Quantitative desorption of Pb(II) from CC was found to be 75% which facilitated the adsorption of metal by ion exchange. In a study, the technical feasibility of coconut shell charcoal (CSC) and commercial activated carbon (CAC) for Cr(VI) removal was investigated in batch studies using synthetic electroplating wastewater (Babel and Kurniawan, 2004). Both the granular adsorbents were made up of coconut shells (Cocos nucifera L.). Surface modifications of CSC and CAC with chitosan and/or oxidizing agents, such as sulfuric acid and nitric acid, respectively, were also conducted to improve removal performance. The adsorbents chemically modified with an oxidizing agent demonstrated better Cr(VI) removal capabilities than as-received adsorbents


21

in terms of adsorption rate. Both CSC and CAC, which were oxidized with nitric acid, had higher Cr(VI) adsorption capacities (CSC: 10.88, CAC: 15.47 mg/g) than those oxidized with sulfuric acid (CSC: 4.05, CAC: 8.94 mg/g) and non-treated CSC coated with chitosan (CSCCC: 3.65 mg/g), respectively, suggesting that surface modification of a carbon adsorbent with a strong oxidizing agent generated more adsorption sites on their solid surface for metal adsorption. Hasar (2003) prepared activated carbon from almond husk by activating without (MACI) and with (MAC-II) H2SO4 at different temperatures. The ability of the activated carbon to remove Ni(II) from aqueous solutions by adsorption has been investigated under several conditions such as pH, carbonization temperature of husk, initial concentration of metal ions, contact time, and adsorbent concentration. Optimal conditions were pH 5.0, the carbonization temperature of 700 °C, 50 min of contact time and adsorbent concentration of 5 g/L. The results indicated that the effective uptake of Ni(II) ions was obtained by activating the carbon, prepared from almond husk at 700 °C, through the addition of H2SO4. The removal of Ni(II) was found to be 97.8% at initial concentration of 25 mg/L and the adsorbent concentration of 5 g/L. When the adsorbent concentration was increased up to 40 g/L, the adsorption capacity decreased from 4.89 to 0.616 mg/g for MAC-II. In the isotherm studies, the experimental adsorption data fitted reasonably well to Langmuir isotherm for both MAC-I and MAC-II. The use of low-cost activated carbon derived from bagasse was investigated by Mohan and Singh, (2002) for the removal of Cd(II) and Zn(II). The uptake of Cd(II) was found to be slightly greater than that of Zn(II) and the adsorption capacity increased with increase in temperature. The adsorption equilibrium data were better fitted by the Freundlich isotherm as compared to Langmuir in both the single- and multi-component systems. The adsorption occurred through a film diffusion mechanism at low as well as at higher concentrations. Activated carbon (AC) prepared from waste Parthenium was used to eliminate Ni(II) from aqueous solution by adsorption (Kadirvelu et al., 2002). The adsorption capacity calculated from the Langmuir isotherm was 54.35 mg Ni(II)/g of AC at initial pH of 5.0 and 20°C, for the particle size 250-500 μm. Increase in pH from 2 to 10 increased percent removal of the metal ions. The regeneration of Ni(II)-saturated carbon by HCl indicated an adsorption mechanism by ion-exchange between metal ions and H+ ions on the AC surfaces. Quantitative recovery of Ni(II) was possible with HCl. Activated carbon prepared from coconut tree sawdust was used as an adsorbent for the removal of Cr(VI) from aqueous solution by Selvi et al. (2001). Adsorption capacity was calculated from the Langmuir isotherm and was 3.46 mg/g at an initial pH of 3.0 for the particle size 125-250 μm. The adsorption of Cr(VI) was pH dependent and maximum removal was observed in the acidic pH range. A summary of carbons made from different starting materials and their adsorption capacities for different heavy metal ions is given in Table 3.1.

3.2. Clays Clays are one of the prospective low cost alternatives to activated carbons as adsorbents for the heavy metals removal. The clays sorption capabilities come from their high surface area (up to 800 m2/g) and exchange capacities (Cadena et al., 1990). The negative charge on the structure of clay minerals gives clay the capability to attract metal ions. There are three

22


basic species of clay, viz., smectites (such as montmorillonite), kaolinite, and micas; out of which montmorillonite has the highest cation exchange capacity. Therefore, a number of studies have been conducted using clays to show their effectiveness for removing metal ions. Table 3.1. Activated carbon adsorbents for heavy metals from solutions Source material for activated carbon Bamboo Shorea robusta

Waste activated carbon (WAC)

Adsorption capacity,Reference qm (mg/g) 12.08 Wang et al., 2010 PAC: 4.0 Oubagaranadin and CACs : ≈ 7.0 Murthy, 2009a Cd(II) CAC: 90.09 Tajar et al., 2009 PAC: 104.17 SCAC: 126.58 SPAC: 142.86 Pb(II), Zn(II), 21.8, 21.2, 19.5, 15.7 Rao et al., 2009 Cu(II), Cd(II) Pb(II) 99 Li and Wang, 2009 Cu(II) 58.27 Demirbas et al., 2009 Pb(II) 43.85 Acharya et al., 2009 Hg(II) A: 151.5; B:100.9 Zabihi et al., 2009 Cr(VI) 35.2 Nemr, 2009 Pb(II) MBRC: 10.66 Lalhruaitluanga et al., MBAC: 53.76 2009 Cr(VI) WAC1: 7.48 Ghosh, 2009 WAC2: 10.93

Zea Mays

Cr(VI)

Date palm seed wastes Date-pit

Cr(VI) Al(III)

PAC: 34 CAC1: 23.24 CAC2: 27.1 CAC3: 33.4 120.48 0.305

Parthenium Bean husk (Phaseolus vulgaris) Euphorbia rigida Sugar beet pulp Palm shell Coconut shell fibers Ceiba pentandra hulls Coconut-shell Coconut shell

Ni(II) Cd(II)

17.24 180

Pb(II) Cr(VI) Pb(II) Cr(III) Cu(II), Cd(II) Pb(II) Cr(VI)

279.72 24 95.2 12.2 20.8, 19.5 26.5 10.88

Parthenium Coconut tree sawdust

Ni(II) Cr(VI)

54.35 3.46

Nut shells

Phaseolus aureus hulls Spartina alterniflora Hazelnut shell Tamarind wood Walnut shells Pomegranate husk Melocanna baccifera

Adsorbate metal ion Cd(II) Pb(II)

Oubagaranadin and Murthy, 2009b

Nemr et al., 2008 Al-Muhtaseb et al., 2008 Lata et al., 2008 Chávez-Guerrero et al., 2008 Gerçel and Gerçel, 2007 Altundogan et al., 2007 Issabayeva et al., 2006 Mohan et al., 2006 Rao et al., 2006 Sekar et al., 2004 Babel and Kurniawan, 2004 Kadirvelu et al., 2002 Selvi et al., 2001

Vieira et al. (2010) studied the adsorption of nickel on calcined Bofe bentonite clay. The influence of parameters such as pH, amount of adsorbent, adsorbate concentration and temperature was investigated. The kinetics data were better represented by the second-order model. The Bofe clay removed nickel with a maximum adsorption capacity of 1.91 mg/g of clay (20°C, pH 5.3) and that the thermodynamic data indicated that the adsorption reaction was spontaneous and exothermic. The Langmuir model provided the best fit for sorption isotherms.


23

Ghorbel-Abid et al. (2009) characterized local clay from Jebel Chakir (Tunisia, North Africa). The clay was basically a smectite with a small proportion of kaolinite. The adsorption properties of the natural clay and the Na-purified clay in a chromium rich aqueous solution was studied by batch technique. The amount of adsorbed chromium ions was determined for the adsorption systems as a function of contact time, pH, adsorbent, and metal ion concentration. The results showed that the uptake of Cr (III) at pH 4, by the purified clay was very rapid. The quantity removed from the solution reached a maximum value at 15 min after mixing, and 1 h for the natural clay, although the latter removes greater quantities of Cr(III) ions compared to the Na-purified clay. The amounts adsorbed by the natural clay were about 117.5 mg of Cr(III)/g of clay and 61.4 mg/g with the Na-purified clay. Moreover, the results showed that the adsorption behavior of both the clays depended highly on the pH. Adsorption increased with the pH of the suspension in the range of 3-5.3. The pH was limited to values equal or less than 5.3 because of the precipitation of the hydroxide chromium at higher pH. The equilibrium data well fitted to the linearized Freundlich isotherm for the natural clay and Langmuir model for the Na-purified clay. Three types of Saudi Arabian clays, viz., Tabuk, Baha, and Khaiber; were tested for their abilities to adsorb Pb(II) from wastewater by Al-Jlil and Alsewailem (2009). The clays were treated with hydrochloric acid to activate adsorption sites within clay particles. Untreated Tabuk clay had the largest adsorption capacity for Pb(II), about 30 mg/g, in comparison with those of Baha and Khaiber clays. Least adsorption was observed with Khaiber clay, about 10 mg/g, which was attributed to the prior existence of lead within the clay. Adsorption of the acid-activated clays was not enhanced compared to those of untreated clays. The Langmuir model described the experimental data for all untreated clays, while the Freundlich model described the experimental data of untreated Khaiber clay and treated Baha clay. The results showed that the Tabuk clay could be utilized as a cost-effective and efficient adsorbent for removing heavy metals from wastewater in Saudi Arabia. Modified kaolinite clay with 25% (w/w) aluminium sulphate and unmodified kaolin were investigated as adsorbents to remove Pb(II) from aqueous solution by Jiang et al., 2009. The results showed that the amount of Pb(II) adsorbed onto modified kaolin (20 mg/g) was more than 4.5 times than that adsorbed onto unmodified kaolin (4.2 mg/g) under optimized conditions. It was observed that the data from both the adsorbents fitted well to the Langmuir isotherm. The kinetic adsorption of modified and unmodified kaolinite clay fitted well to the pseudo-second-order kinetic model. Experiments with real wastewater showed that higher amount of Pb(II) (the concentration reduced from 178 to 27.5 mg/L) and other metal ions were removed by modified kaolinite clay as compared with unmodified adsorbent (the concentration reduced from 178 to 168 mg/L). In a work by Wang et al. (2009), removal of Pb(II) from aqueous solution by adsorption onto Na-bentonite was reported under ambient conditions as a function of shaking time, pH, ionic strength, Na-bentonite content and temperature using batch technique. The kinetic adsorption was well described by the pseudo-second-order rate equation. The adsorption of Pb(II) on Na-bentonite was strongly dependent on pH. The Langmuir model fitted the adsorption isotherm very well. The thermodynamic parameters suggested that the adsorption of Pb(II) was endothermic and spontaneous. At low pH, the adsorption of Pb(II) was dominated by outer-sphere surface complexation and ion exchange with Na+/H+ on Nabentonite surfaces, whereas inner-sphere surface complexation was the main adsorption mechanism at high pH.

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A hectorite (H) clay sample was modified with 2-mercaptobenzimidazole using homogeneous and heterogeneous routes by Guerra et al. (2009). Both modification methodologies resulted in similar products, named HHOM and HHET, respectively. The effect of two variables (contact time and metal concentration) was studied using batch technique at room temperature and pH 2.0. After achieving the best conditions for Cr(VI) adsorption, isotherms of this adsorbate on using the chosen adsorbents were obtained, which were fitted to non-linear Sips isotherm model. The maximum number of moles adsorbed was determined to be 11.63, 12.85 and 14.01 mmol/g for H, HHOM and HHET, respectively, reflecting the maximum adsorption order of HHET > HHOM > H. Batch sorption experiments were conducted with cadmium and lead ions at low equilibrium concentrations in 0.01 M of NaNO3 onto Petra clay in single component systems by Baker (2009). The equilibrium isotherms were determined at pH 6 under constant ionic strength and at different temperature. From the Langmuir isotherm, the equilibrium adsorption capacity for Cd(II) was found to be 74.074 to 144.927 mg/g and that for Pb(II) was 83.333 to 263.158 mg/g. The results showed that Petra clay, which was mainly composed of 20% of kaolinite and 55% of calcium montmorillomite, exhibited higher selectivity for Pb(II), whereas its selectivity for Cd(II) was often lower at all concentrations studied. From the R2 values for different isotherm models it was found that the sorption was good for the two metal ions and good correlation confirmed the formation of a monolayer of Cd(II) and Pb(II) on the surface of the clay. Isotherms analysis showed that the binding for these metal ions with Petra clay minerals was physisorption and the process was endothermic. Oubagaranadin and Murthy (2009c) studied the removal of Pb(II) from aqueous solution by adsorption on a montmorillonite-illite type of clay (MIC) collected from the Gulbarga district of Karnataka, India. Batch adsorption equilibrium data were determined with different initial Pb(II) concentrations (100, 150, and 200 ppm) at pH 4 and 37 °C, and the data were tested with isotherm models. The three-parameter Freundlich-Langmuir model gave the best fit to the equilibrium data. However, as the initial Pb(II) concentration was increased (150 and 200 ppm), then multi-layer adsorption was observed. The maximum monolayer adsorption capacity of the clay was determined to be ~ 52 mg/g. Kinetic studies indicated that the rate of adsorption of Pb(II) on the clay followed a second-order rate mechanism, with decreasing rate constant values of 0.1097, 0.0571, and 0.0022 g/(mg min) as the initial Pb(II) concentration was increased in the order of 100, 150, and 200 ppm, respectively. The value of the Freundlich constant (n) in the range of 2.5-4.6 indicated that MIC was a good adsorbent of divalent lead. At a higher initial Pb(II) concentration (200 ppm), the adsorption process was determined to be film-diffusion controlled, with a rate of 0.051 min-1. The mean values of the thermodynamic parameters showed that the adsorption process was endothermic, thermodynamically favorable, and spontaneous. The proposed two-stage adsorber system has reduced the clay dose by 8.5%, as compared to that of a single-stage adsorption system. In another work by Oubagaranadin and Murthy (2010), the natural montmorillonite-illite clay was activated with sulfuric acid and used for lead(II) removal. Raw clay disintegrated on acid activation and showed a particle size distribution. The montmorillonite and illite phases in the raw clay disappeared on acid activation and the activated clay, showed with sodiumaluminum-silicate and beidellite phases apart from quartz (low) phase. When tested for adsorption of Pb(II) in aqueous solutions, the acid-activated clay showed about 50% increased adsorption than raw clay. Sips adsorption isotherm and pseudo-second-order kinetic models were found to be best for the batch adsorption data. Kinetic studies showed the


25

existence of film diffusion and intraparticle diffusion. A two-stage batch adsorber was designed for the removal of Pb(II) from aqueous solutions. There was about 63% increase in the monolayer adsorption capacity of the clay adsorbent due to acid activation. From the twostage batch adsorption system proposed using the experimental data, it was observed that the two-stage system reduced the adsorbent dose by about 14 and 30% of raw and activated clay, respectively, when compared with that of single-stage adsorption system. Adsorption of Cu(II) ions on a zeolite, clay and diatomite from Serbia was studied by Ńljivić et al. (2009), at different pH. The amounts of Cu(II) removed from the solution increased with increasing initial pH, reaching nearly 100% at pH > 7, due to precipitation of Cu(OH)2. Relatively constant final pH values and less significant increase of Cu(II) uptake was observed in the initial pH range 4–6, which have pointed out the role of buffering properties of investigated adsorbent materials. The maximum adsorption capacities decreased in the order of zeolite (0.128 mmol/g) > clay (0.096 mmol/g) > diatomite (0.047 mmol/g). The Langmuir isotherm gave the best fit. Ion exchange of exchangeable cations and protons were identified as main adsorption mechanisms. Removal of Cr(III) and Cr(VI) from aqueous solutions by white, yellow and red sands from the United Arab Emirates, as low cost abundant adsorbents, was investigated by Khamis et al. (2009). The effect of contact time, pH, temperature, metal concentration and sand dosage were studied. The optimal pH for adsorption was 5.0 for Cr(III) and 2.0 for Cr(VI). The optimal adsorption time for both ions was 3 h. Even at the optimal pH, adsorption of Cr(VI) on all sand forms was very low (removal ≤10%) and could not be fitted to any of the common isotherms. While at pH 5.0, Cr(VI) was not at all adsorbed and Cr(III) was totally removed. Adsorption of Cr(III) by the three sand forms obeyed Lagergren first-order kinetics. For Cr(III), the Langmuir isotherm gave best fit for adsorption. At 25 °C, the maximum mass of Cr(III) removed per gram of sand was 62.5, 9.80 and 2.38 (mg/g) for white, yellow and red sands, respectively. ΔH° was 14.5, 51.2 and 45.8 kJ/mol and ΔS° was 24.0, 136 and 111 J /K/mol for adsorption on white, yellow and red sands, respectively. Unuabonah et al. (2008a) studied the adsorption behavior of a polyvinyl alcohol modified (PVA-modified) kaolinite clay. Modification of kaolinite clay with PVA increased its adsorption capacity for 300 mg/L Pb(II) and Cd(II) by a factor of about 6, i.e., from 4.5 mg/g to 36.23 mg/g and from 4.38 mg/g to 29.85 mg/g, respectively, at 298 K. Binary mixtures of Pb(II) and Cd(II) decreased the adsorption capacity of unmodified kaolinite clay for Pb(II) by 26.3% and for Cd(II) by 0.07%, respectively. For PVA-modified kaolinite clay, the reductions were up to 50.9% and 58.5% for Pb(II) and Cd(II), respectively. The adsorption data of Pb(II) and Cd(II) onto both unmodified and PVA-modified kaolinite clay adsorbents were found to fit the pseudo-second-order kinetic model, indicating that adsorption on both the surfaces was mainly by chemisorption. Kaolinite clay obtained from Ubulu-Ukwu in Nigeria was modified with sodium tetraborate (NTB) to obtain NTB-modified kaolinite clay by Unuabonah et al. (2008b). Modification with sodium tetraborate reagent increased the adsorption capacity of kaolinite clay from 16.16 mg/g to 42.92 mg/g for Pb(II) and 10.75 mg/g to 44.05 mg/g for Cd(II) at 298 K. Increasing temperature was found to increase the adsorption of both the metals onto both the adsorbents suggesting endothermic adsorption. The simultaneous presence of electrolyte in aqueous solution with Pb(II) and Cd(II) was found to decrease the adsorption capacity of NTB-modified adsorbent for Pb(II) and Cd(II). The thermodynamic calculations for the modified kaolinite clay sample indicated an endothermic nature of adsorption and an

26


increase in entropy as a result of adsorption of Pb(II) and Cd(II). The small positive values of free energy change indicated that the adsorption of Pb(II) and Cd(II) onto the modified adsorbent may require some small amount of energy to make it more feasible. Modeling equilibrium adsorption data suggested that NTB-modified adsorbent sample had homogeneous adsorption sites and fitted well with Langmuir model. NTB-modified kaolinite clay sample showed good potentials as a low-cost adsorbent for the adsorption of Pb(II) and Cd(II) from aqueous solutions. Adsorption of Cu(II) by raw bentonite (RB) and acid-activated bentonite (AAB) samples was investigated by Eren and Afsin (2008) as a function of initial Cu(II) concentration, solution pH, ionic strength, temperature, the competitive and complexation effects of ligands (Cl−, SO42−, PO43−). Langmuir monolayer adsorption capacity of the RB (42.41 mg/g) was found to be greater than that of the AAB (32.17 mg/g). The spontaneity of the adsorption process was established by decrease in ΔG which varied from −0.34 to −0.71 kJ/mol (RB), −1.13 to −1.49 kJ/mol (AAB) in the temperature range of 303-313 K. Infrared (IR) spectra of the bentonite samples showed that the positions and shapes of the fundamental vibrations of the OH and Si-O groups were influenced by the adsorbed Cu(II) cations. Differential thermal analysis (DTA) results showed that adsorbed Cu(II) cations have a great effect on the thermal behavior of the bentonite samples. The X-ray diffraction (XRD) spectra indicated that the Cu(II) adsorption onto the bentonite samples led to changes in unit cell dimensions and symmetry of the parent bentonites. Eren (2008) reported the adsorption of Cu(II) from aqueous solution on modified Unye bentonite. Adsorption of Cu(II) by manganese oxide modified bentonite (MMB) sample was investigated as a function of the initial Cu(II) concentration, solution pH, ionic strength, temperature and inorganic ligands (Cl−, SO42−, HPO42−). The adsorption properties of raw bentonite were further improved by modification with manganese oxide. Langmuir monolayer adsorption capacity of the MMB (105.38 mg/g) was found to be greater than that of the raw bentonite (42.41 mg/g). The spontaneity of the adsorption process was established by decrease in ΔG which varied from −4.68 to −5.10 kJ/mol in temperature range of 303– 313 K. The high performance exhibited by MMB was attributed to the increased surface area and higher negative surface charge acquired after modification. The adsorption of Pb(II) onto Tunisian smectite-rich clay in aqueous solution was studied in a batch system by Chaari et al. (2008). In this study, four samples of clay (AYD, AYDh, AYDs, AYDc) were used. The AYD was raw clay. AYDh and AYDs correspond to AYD activated by 2.5 mol/L hydrochloric acid and 2.5 mol/L sulphuric acid, respectively. AYDc corresponds to AYD calcined at different temperatures (100, 200, 300, 400, 500 and 600 °C). Preliminary adsorption tests showed that sulphuric acid and hydrochloric acid activation of raw AYD clay enhanced its adsorption capacity for Pb(II). However, the uptake of Pb(II) by AYDs was very high compared to that of AYDh. This fact was attributed to the greater solubility of clay minerals in sulphuric acid compared to hydrochloric acid. Thermo activation of AYD clay reduced the Pb(II) uptake as soon as calcination temperature reaches 200 °C. Kinetic experiments showed that the sorption of lead ions on AYDs was very fast and the equilibrium was practically reached after only 20 min. The results also revealed that the adsorption of lead increased with increase in the solution pH from 1 to 4.5 and then decreased slightly between pH 4.5 and 6, and rapidly at pH 6.5 due to the precipitation of Pb(II) ions. The equilibrium data were analyzed using Langmuir isotherm model. The maximum adsorption capacity increased from 25 to 25.44 mg/g with increasing temperature from 25 to


27

40 °C. It was observed that sulphuric acid activated clay was more efficient than physically activated clay. Adsorption of Cr(VI) onto spent activated clay (SAC), a waste produced from an edible oil refinery company, was investigated for its beneficial use in wastewater treatment by Weng et al. (2008). After pressure steam treatment, SAC was used as an adsorbent. The adsorption kinetic data were analyzed and fitted well with pseudo-first-order equation and the rate of removal was found to speed up with decreasing pH and increasing temperature. The maximum adsorption capacities for Cr(VI) were ranged from 0.743 to 1.422 mg/g for temperature between 4 and 40 °C under a condition of pH 2.0. The studies conducted show the process of Cr(VI) removal to be spontaneous at high temperature and endothermic in nature. Kaolinite and montmorillonite were used as adsorbents for Fe(III), Co(II) and Ni(II) in aqueous medium by Bhattacharyya and Gupta (2008). The effect of different variables, namely, concentration of metal ions, amount of clay adsorbents, pH, time and temperature of interaction was investigated. Adsorption increased with pH till precipitation of insoluble hydroxides became dominant. The processes conformed to second-order kinetics. Montmorillonite had a much higher adsorption capacity for the metal ions with the Langmuir monolayer capacity of 28.4 to 28.9 mg/g compared to that of 10.4 to 11.2 mg/g for kaolinite. All the interactions were exothermic except those between Co(II) and kaolinite. The adsorption processes were accompanied by an appreciable decrease in Gibbs energy. Both kaolinite and montmorillonite were observed to be suitable for treating water contaminated with Fe(III), Co(II) and Ni(II). Argun (2008) described the removal of Ni(II) ions from aqueous solutions using clinoptilolite. The effect of clinoptilolite level, contact time, and pH were determined. Different isotherms were also obtained using concentrations of Ni(II) ions ranging from 0.1 to 100 mg/L. The ion-exchange process followed second-order kinetics and the Langmuir isotherm. The work revealed that the ion-exchange process was spontaneous and exothermic under natural conditions. The maximum removal efficiency obtained was 93.6% at pH 7 and with a 45 min contact time (for 25 mg/L initial concentration and a 15 g/L solid-to-liquid ratio). The use of bentonite for the removal of Pb(II) from aqueous solutions for different contact times, pH of suspension, and initial concentration of lead and particle sizes of absorbent was investigated by Zhu et al. (2008). Batch adsorption kinetic experiments revealed that the adsorption of Pb(II) onto bentonite involved fast and slow processes. The adsorption mechanisms in the lead/bentonite system followed pseudo-second-order kinetics with a significant contribution of film-diffusion. The Langmuir model represented the adsorption process. The maximum adsorption capacity of Pb(II) onto natural bentonite was 78.82 mg/g. Çoruh (2008) investigated the effects of conditioning with NaCl and HCl solutions on the removal of Zn(II) from aqueous solutions using natural clinoptilolite collected from ManisaGördes region of Turkey. The clinoptilolite sample was used in four different forms, which consisted of one unconditioned (NC) and three conditioned (CC1, CC2 and CC3). The results clearly showed that the conditioning improved both the exchange capacity and the removal efficiency. It was found that the highest removal efficiency was obtained with CC2 sample. Adsorption isotherm of Zn(II) was best modeled by the Langmuir equation. The maximum adsorption capacities for Zn(II) shown by NC, CC1, CC2 and CC3 samples were 21.2, 20.8,

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22.2 and 17.9 mg/g, respectively. Results indicate a significant potential for the natural and conditioned clinoptilolites as an adsorbent/ion-exchange material for heavy metal removal. Trivalent chromium was removed from synthetic wastewater using low-cost diatomite in batch and continuous systems by Gürü et al. (2008). In batch system, four different sizes and five different amounts of adsorbent were used. Langmuir adsorption capacities were found to be 28.1, 26.5 and 21.8 mg Cr(III)/g diatomite at 15, 30 and 45 °C, respectively. Adsorption process was exothermic in nature. The kinetic data showed that the pseudo-second-order equation was more appropriate, which indicated that the intra-particle diffusion is the ratelimiting factor. Laboratory grade Fuller‟s earth (FE) was used as an adsorbent in a work by Oubagaranadin et al. (2007) to remove mercury from aqueous solutions. For the purpose of comparison, simultaneous experiments using laboratory grade activated carbon (AC) was also done. Isotherms such as Freundlich, Langmuir, Dubinin–Radushkevich, Temkin, HarkinsJura, Halsey and Henderson were tested to the equilibrium data. Kinetic studies based on Lagergren first-order, pseudo-second-order rate expressions and intra-particle diffusion studies were done. The batch experiments were conducted at room temperature (30ºC) and at the normal pH (6.7) of the solution. It was observed that Hg(II) removal rate was better for FE than AC, and the adsorption capacity of AC (69.44 mg/g) was found to be much better than FE (1.15 mg/g). Hybrid fractional error function analysis showed that the best-fit for the adsorption equilibrium data were represented by Freundlich isotherm. Kinetic and filmdiffusion studies showed that the adsorption of mercury on FE and AC was both intra-particle diffusion and film-diffusion controlled. In a study by Abu-El-Sha‟r and Haddad (2007), lead adsorption onto soil samples from Irbid, which were subjected to high temperatures, was investigated. These samples were collected from ground surface and heated to temperatures of 25, 70, 100, 200, 225, 250, 275, 300, 400, and 550°C. Based on these temperatures the soil was divided into ten different groups. Each group was first characterized by conducting a set of experiments to estimate the liquid limit (LL), plastic limit (PL), and plasticity index, the organic carbon content, and a set of batch experiments to study lead adsorption. Results indicated that the LL, PL, total organic carbon were slightly affected by high temperatures less than 200°C, showed an abrupt change between temperature from 200 and 300°C, and then slight change above 300°C. Adsorption of lead onto heated samples, however, was not significantly changed. This may be explained by the fact that adsorption of heavy metals mainly occurs onto the soil mineral parts which are slightly affected by the temperature range used in this study. The adsorption of Pb(II) onto Turkish (Bandirma region) kaolinite clay was examined in aqueous solution with respect to the pH, adsorbent dosage, contact time, and temperature by Sari et al. (2007). The linear Langmuir and Freundlich models were applied to describe equilibrium isotherms and both models fitted well. The monolayer adsorption capacity was found as 31.75 mg/g at pH 5 and 20 °C. Dubinin–Radushkevich isotherm model was also applied to the equilibrium data. The mean free energy of adsorption (13.78 kJ/mol) indicated that the adsorption of Pb(II) onto kaolinite clay may be carried out via chemical ion-exchange mechanism. The adsorption of Pb(II) onto kaolinite clay was feasible, spontaneous and exothermic in nature. Furthermore, the experimental data fitted well with the pseudo-secondorder kinetics. Removal of copper and zinc from aqueous solutions was investigated by Veli and Alyüz, (2007) using Cankiri bentonite natural clay. The effects of pH, clay amount, heavy metal


29

concentration and agitation time on adsorption efficiency were studied. Langmuir, Freundlich and Dubinin–Radushkevich isotherms were applied in order to determine the efficiency of natural clay used as an adsorbent. Results showed that all isotherms were linear. It was observed that adsorption data of Cu(II) and Zn(II) were well-fitted by the second-order reaction kinetics. In addition, calculated and experimental heavy metal amounts adsorbed by the unit clay mass were too close to each other. It was concluded that natural clay could be used as an effective adsorbent for removing Cu(II) and Zn(II) from aqueous solutions. A work by Santos and Masini (2007) presented an evaluation of vermiculite as a low cost adsorbent for treatment of wastewater from a coatings industry containing Cd(II), Pb(II) and Cu(II). Adsorption data were fitted by Freundlich isotherms, as well as by partition constants at pH 4, 5 and 6. It was observed that the non-expanded vermiculite presented the following affinity orders by the studied ions: pH 4: Cu(II) < Cd(II) < Pb(II); pH 5: Cu(II) ≈ Cd(II) < Pb(II); pH 6: Cd(II) < Cu(II) < Pb(II). For Pb(II) and Cd(II), the adsorption percentages determined in real wastewaters were around 20% lower than the removal percentage previewed by the Freundlich parameters, a fact that may be explained by competition of the studied cations among themselves, and with Fe(III) species, which were present in the water at concentration levels similar to Cd(II), Cu(II) and Pb(II). Additionally, the high content of organic compounds in the wastewater might have decreased the adsorption of Cu(II) and Pb(II) because of possible formation of soluble complexes between the heavy metal cations and the organic compounds. On the other hand, adsorption of Cd(II) from the real wastewater was about 20% higher than that previewed by the Freundlich parameters, denoting the complexity of interactions that ions are liable in matrices of wastewaters. A series of activated palygorskite clays by HCl with different concentrations were prepared and applied as adsorbents for removal of Cu(II) from aqueous solutions by Chen et al. (2007). The results showed that adsorption capacity of activated palygorskites increased with increasing the HCl concentration and the maximum adsorption capacity with 32.24 mg/g for Cu(II) was obtained at 12 mol/L of HCl concentration. Kinetic studies indicated that the adsorption mechanisms in the Cu(II)/acid-activated palygorskite system followed the pseudosecond-order kinetic model with a relatively small contribution of film-diffusion. Equilibrium data fitted well with the Freundlich isotherm model compared to the Langmuir isotherm model, indicating that adsorption taking place on heterogeneous surfaces of the acid-activated palygorskite. The use of natural palygorskite clay for the removal of Pb(II) from aqueous solutions for different contact times, pH of suspension, adsorbent amounts and particle sizes of palygorskite clay were investigated by Chen and Wang (2007). Batch adsorption kinetic experiments revealed that the adsorption of Pb(II) onto palygorskite clay involved fast and slow processes. It was found that the adsorption mechanisms in the lead/palygorskite system followed pseudo-second-order kinetics with a significant contribution from film-diffusion. The Langmuir model represented the adsorption process better than the Freundlich model. The maximum adsorption capacity of Pb(II) onto natural palygorskite was found to be 104.28 mg/g. Adsorption of Pb(II) ions from aqueous solution onto clinoptilolite was investigated by Günay et al. (2007) to evaluate the effects of contact time, initial concentration and pretreatment of clinoptilolite on the removal of Pb(II). Maximum experimental adsorption capacity was found to be 80.933 and 122.400 mg/g for raw and pretreated clinoptilolite,

30


respectively, for the initial concentration of 400 mg/L. Results of the kinetic studies showed that the best fitted kinetic models were obtained to be in the order: the pseudo-first-order, the pseudo-second-order and Elovich equations. The negative value of change in Gibbs free energy (ΔG°) indicates that the adsorption of Pb(II) on clinoptilolite was spontaneous. Bhattacharyya and Gupta (2007) investigated the influence of acid activation of montmorillonite on adsorption of Cd(II), Co(II), Cu(II), Ni(II), and Pb(II) from aqueous medium and comparison of the adsorption capacities with those on parent montmorillonite. The clay-metal interactions were studied under different conditions of pH, concentration of metal ions, amount of clay, interaction time, and temperature. The interactions were dependent on pH and the uptake was controlled by the amount of clay and the initial concentration of the metal ions. The adsorption capacity of acid-activated montmorillonite increased for all the metal ions. The interactions were adsorptive in nature and relatively fast and the rate processes were more akin to the second-order kinetics. The Langmuir monolayer capacity of the acid-activated montmorillonite was more than that of the parent montmorillonite (Cd(II): 32.7 and 33.2 mg/g; Co(II): 28.6 and 29.7 mg/g; Cu(II): 31.8 and 32.3 mg/g; Pb(II): 33.0 and 34.0 mg/g; and Ni(II): 28.4 and 29.5 mg/g for montmorillonite and acid-activated montmorillonite, respectively). The thermodynamics of the rate processes showed that the adsorption of Co(II), Pb(II), and Ni(II) to be exothermic, accompanied by decreases in entropy and Gibbs free energy, while the adsorption of Cd(II) and Cu(II) was endothermic, with an increase in entropy and an appreciable decrease in Gibbs free energy. The results established the potential use of montmorillonite and its acid-activated form as adsorbents for Cd(II), Co(II), Cu(II), Ni(II), and Pb(II) ions from aqueous media. Application of riverbed sand for the adsorptive separation of Cd(II) from aqueous solutions has been investigated by Sharma et al. (2007). Metal removal increased from 26.8 to 56.4% by decreasing the initial concentration of cadmium from 7.5 × 10−5 to 1.0 × 10−5 M at pH 6.5, 25 °C temperature, agitation speed of 100 rpm, 100 μm particle size and 1.0 × 10−2 NaClO4 ionic strength. Process of separation is governed by first-order rate kinetics. Values of thermodynamic parameters ΔGo, ΔHo and ΔSo were also calculated and were recorded as −0.81 kcal/mol, −9.31 kcal/mol and −28.10 kcal/mol, respectively, at 25°C. The solution pH has been found to affect the removal of cadmium significantly and maximum removal (58.4%) has been found at pH 8.5. In a work by Shawabkeh et al. (2007), natural bentonite was treated by hydrochloric, nitric, and phosphoric acids followed by washing with sodium hydroxide in order to enhance its adsorption capacity. The sample which was treated with hydrochloric acid, followed by further treatment with NaOH, showed the highest cation exchange capacity with a value of 51.20 meq/100 g. Adsorption isotherms for both cobalt and zinc were fitted using Langmuir, Freundlich, and Redlich-Peterson and showed an adsorption capacity of 138.1 mg Co(II) and 202.6 mg Zn(II) per gram of treated adsorbent sample. The adsorption characteristics of palygorskite with respect to cadmium were studied with the aim of assessing its use in water purification systems by Álvarez-Ayuso and GarcíaSánchez (2007). The adsorption of Cd on palygorskite appeared as a fast process, with equilibrium being attained within the first half-an-hour of interaction. This process was described by the Langmuir model and gave a maximum Cd sorption of 4.54 mg/g. This sorption capacity value was greatly affected by both pH and ionic strength. High competing electrolyte concentrations have decreased the amount of Cd sorbed (close to 60%), suggesting a great contribution of replacement of exchange cations in this metal removal by palygorskite.


31

The increase of mineral dose provoked a Cd removal raise; removal values in the range of 8545% were attained for Cd initial concentrations of 10–150 mg/L (0.089–1.34 mmol/L) when the palygorskite dose of 20 g/L was employed. Column studies were also performed in order to estimate the potential of palygorskite to be used in continuous flow purification systems, showing the effectiveness of this mineral to purify, down to the legal limit of waste, moderate volumes of Cd-containing solutions with a similar concentration (50 mg/L or 0.445 mmol/L) to those mostly found in the upper range of concentrations usually present in industrial wastewaters. In a study by Kubilay et al. (2007), the removal of Cu(II), Zn(II) and Co(II) ions from aqueous solutions using adsorption onto natural bentonite was investigated as a function of initial metal concentration, pH and temperature. For all the metal cations studied, the maximum adsorption was observed at 20°C. The batch method was employed using initial metal concentrations ranging from 15 to 70 mg/L at pH 3.0, 5.0, 7.0 and 9.0. It was found that in every concentration range, adsorption data of bentonitic clay - heavy metal cations, matched to Langmuir, Freundlich and Dubinin-Kaganer-Radushkevich (DKR) isotherms. Bentonite used was sensitive to pH changes and the amounts of heavy metal cations adsorbed increased as pH was increased in adsorbent-adsorbate system. According to the adsorption equilibrium studies, the selectivity order was found to be: Zn(II)>Cu(II)>Co(II). These results showed that bentonitic clay holds great potential to remove the relevant heavy metal cations from wastewater. The sorption of Cr(III) from aqueous solutions on kaolinite was studied by a batch technique by Turan et al. (2007). The adsorbed amount of chromium ions on kaolinite increased with increasing pH and temperature and decreased with increasing ionic strength. The sorption of Cr(III) on kaolinite was found to be endothermic. Sorption data have been interpreted in terms of Freundlich and Langmuir equations. The experimental data were correlated reasonably well by the Langmuir adsorption isotherm. The enthalpy change for chromium adsorption was estimated to be 7.0 kJ/mol. In a work by Manohar et al. (2006), a natural bentonite clay collected from Ashapura Clay Mines, Gujarat State, India, was utilized as a precursor to produce aluminum-pillared bentonite clay (Al-PILC) for the removal of Co(II) ions from aqueous solutions. Adsorption experiments were conducted under various conditions, i.e., pH, contact time, initial concentration, ionic strength, adsorbent dose and temperature. The most effective pH range for the removal of Co(II) ions was found to be 6.0–8.0. The maximum adsorption of 99.8% and 87.0% took place at pH 6.0 from an initial concentration of 10.0 and 25.0 mg/L, respectively. Kinetic studies showed that an equilibrium time of 24 h was needed for the adsorption of Co(II) ions on Al-PILC and the experimental data were correlated by the external mass transfer diffusion model for the first-stage of adsorption and the intraparticle mass transfer diffusion model for the second-stage of adsorption. The intraparticle mass transfer diffusion model gave a better fit to the experimental data. The equilibrium isotherm data were analyzed using the Langmuir, Freundlich and Scatchard isotherm equations and the adsorption process was expressed by Freundlich isotherm. The adsorption behavior of vermiculite was studied with respect to cadmium, copper, lead, manganese, nickel, and zinc as a function of pH and in the presence of different ligands by Malandrino et al. (2006). The continuous column method was used in order to evaluate the feasibility to use the clay in wastewater purification systems. The total capacity of vermiculite was found to increase in the following order: Mn > Ni > Zn > Cd > Cu > Pb. The adsorption

32


of metal ions on vermiculite decreased with decreasing pH and increasing ionic strength. The metal uptake on the clay was hindered by the presence of strong complexing agents in solution and it decreased with increasing of the complexation of the ligands with exception of cysteine and tiron. It was concluded that the vermiculite has good potentialities for costeffective treatments of metal-contaminated wastewaters. Natural Jordanian adsorbent (consisting of quartz and aluminosilicates and secondary minerals, i.e., calcite and dolomite) was shown to be effective for removing Zn(II), Pb(II) and Co(II) from aqueous solution as reported by Al-Degs et al. (2006). The major mineral constituents of the sorbent were calcite and quartz. Dolomite was present as minor mineral and palygorskite was present as trace mineral. The sorbent had microporous structure with a modest surface area of 14.4 m2/g. The adsorption capacities of the metals were: 2.86, 0.32, 0.076 mmol cation/g for Zn(II), Pb(II) and Co(II) at pH 6.5, 4.5 and 7.0, respectively. Adsorption data of metals were described by Langmuir and Freundlich models over the entire concentration range. It was found that the mechanism of metal adsorption was mainly due to the precipitation of metal carbonate complexes. The overall adsorption capacity has decreased after acid treatment, as this decreases the extent of precipitation on calcite and dolomite. Kinetic data were accurately fitted to pseudo-first-order and external diffusion models, which indicated that adsorption of Zn(II) occurred on the exterior surface of the adsorbent and the contribution of internal diffusion mechanism was insignificant. Gupta and Bhattacharyya (2006) investigated the adsorptive interactions of Ni(II) ions with kaolinite, montmorillonite, and their poly(oxo-zirconium) and tetrabutylammonium (TBM) derivatives in aqueous medium. The adsorption strongly depended on pH of the medium with enhanced adsorption as the pH turns from acidic to alkaline side till precipitation started. The process was fast initially and maximum adsorption was observed within 180 min of agitation. The kinetics of the interactions showed better agreement with second-order kinetics. The adsorption data gave Langmuir monolayer capacity of 2.75 to 21.14 mg/g for the clay adsorbents. The adsorption process was exothermic accompanied by decrease in entropy and Gibbs free energy. The results showed that montmorillonite had the largest adsorption capacity followed by ZrO-montmorillonite, TBA-montmorillonite, kaolinite, ZrO-kaolinite and TBA-kaolinite. Introduction of ZrO- and TBA- groups into the clays reduced their adsorption capacity by blocking the available adsorption sites. Bhattacharyya and Gupta (2006) investigated the removal of Fe(III) ions from an aqueous solution using kaolinite, montmorillonite and their acid activated forms. The specific surface areas of kaolinite, acid activated kaolinite, montmorillonite and acid activated montmorillonite were 3.8, 15.6, 19.8 and 52.3 m2/g, respectively, whereas the cation exchange capacity (CEC) was measured as 11.3, 12.2, 153.0, and 341.0 meq/100g for the four clay adsorbents, respectively. Adsorption increased with pH till Fe(III) became insoluble at pH > 4.0. The second-order kinetics (k2 = 4.7×10− 2 to 7.4×10− 2 g/mg/min) gave a better description of the kinetic data. The Langmuir monolayer capacity of the clay adsorbents was from 11.2 to 30.0 mg/g. The adsorption was exothermic with ΔHo in the range of −27.6 to −42.2 kJ/mol accompanied by decrease in entropy (ΔSo = −86.6 to −131.8 J/mol/K) and decrease in Gibbs free energy. The results showed that the kaolinite, montmorillonite and their acid activated forms could be used as adsorbents for separation of Fe(III) from aqueous solution. Acid activation enhanced the adsorption capacity as compared to the untreated clay minerals.


33

A study was carried out by Sprynskyy et al. (2006) on the adsorption of heavy metals (Ni(II), Cu(II), Pb(II), and Cd(II)) from single- and multi-component aqueous solutions by raw and pretreated clinoptilolite. The adsorption had ion-exchange nature and consisted of three stages, i.e., the adsorption on the surface of microcrystals, the inversion stage, and the moderate adsorption in the interior of the microcrystals. The finer clinoptilolite fractions adsorbed higher amounts of the metals due to relative enrichment by the zeolite proper and higher cleavage. The slight difference between adsorption capacity of the clinoptilolite toward lead, copper, and cadmium from single- and multi-component solutions testified to individual adsorption centers of the zeolite for each metal. The decrease of nickel adsorption from multicomponent solutions was probably caused by the closeness of its adsorption forms to the other metals and by competition. The maximum sorption capacity towards Cd(II) was determined as 4.22 mg/g at an initial concentration of 80 mg/L and towards Pb(II), Cu(II), and Ni(II) as 27.7, 25.76, and 13.03 mg/g, respectively, at 800 mg/L of initial concentration. The adsorption results fitted well to the Langmuir model. Vermiculite, a 2:1 clay mineral, was applied as adsorbent for removal of cadmium, zinc, manganese, and chromium from aqueous solutions by Fonseca et al. (2006). All isotherms observed were L-type of the Gilles classification, except zinc (S-type). The adsorbent showed good adsorption potential for these cations. The experimental data were analyzed by the Langmuir isotherm model showing reasonable adjustment. The quantity of adsorbed cations was 0.50, 0.52, 0.60, and 0.48 mmol/ g of Cd(II), Mn(II), Zn(II), and Cr(II), respectively. Manohar et al. (2005) investigated the possibility of using a natural bentonite clay as a precursor to produce aluminum-pillared clay (Al-PILC) for the removal of vanadium(IV) from aqueous solutions. Batch experiments were carried out as a function of solution pH, contact time, vanadium(IV) concentration, adsorbent dose, ionic strength, and temperature. The maximum adsorption capacity was observed in the pH range of 4.5−6.0. The maximum adsorption of 99.8 and 88.5% took place at pH 5.0 from an initial concentration of 5 and 10 mg/L, respectively. It was shown that the adsorption of vanadium(IV) could be fitted to the intra-particle mass-transfer model. The temperature dependence indicated the endothermic nature of adsorption. The percentage removal of vanadium(IV) decreased with increasing ionic strength. The Freundlich isotherm was found to well represent the measured adsorption data. Kaolin (bright white lumps) from Ubulu-Ukwu in Nigeria was modified with 200 μg/mL of phosphate and sulphate anions to give phosphate- and sulfate-modified adsorbents, respectively and the adsorption of four metal ions (Pb(II), Cd(II), Zn(II), and Cu(II)) was studied as a function of metal ions concentration by Adebowale et al. (2005). The metal ions showed stronger affinity for the phosphate-modified adsorbent with Pb(II), Cu(II), Zn(II), and Cd(II) giving an average of 93.28%, 80.94%, 68.99%, and 61.44% uptake capacity, respectively. The order of preference for the various adsorbents shown by the metal ions was as follows: Pb(II) > Cu(II) > Zn(II) > Cd(II). Desorption studies showed that the phosphatemodified adsorbent had the highest affinity for the metal ions, followed by the sulfatemodified clay, while the unmodified clay had the least affinity. The experimental data were fitted by both the Langmuir and Freundlich models. In a study, Srivastava et al. (2005) investigated the adsorption of Cd(II), Cu(II), Pb(II), and Zn(II) onto kaolinite in single- and multi-element systems as a function of pH and concentration, in a background solution of 0.01 M NaNO3. The pH was varied from 3.5 to 10.0 with total metal concentration of 133.3 μM in the single-element system and 33.3 μM

34


each of Cd(II), Cu(II), Pb(II), and Zn(II) in the multi-element system. The value of pH50 (the pH at which 50% adsorption occurs) was found to follow the sequence Cu < Zn < Pb < Cd in single-element systems, but Pb < Cu < Zn < Cd in the multi-element system. Adsorption isotherms at pH 6.0 in the multi-element systems showed that there was competition among various metals for adsorption sites on kaolinite. The adsorption and potentiometric titrations data for various kaolinite-metal systems were modeled using an extended constantcapacitance surface complexation model that assumed an ion-exchange process below pH 7.0 and the formation of inner-sphere surface complexes at higher pH. Inner-sphere complexation was more dominant for the Cu(II) and Pb(II) systems. The adsorption of the heavy metals (Cd(II), Cu(II), Mn(II), Pb(II), and Zn(II)) from aqueous solutions by a natural Moroccan stevensite was studied by Benhammou et al. (2005a). The surface area of stevensite was 134 m2/g and the cation exchange capacity (CEC) was 76.5 meq/100 g. Adsorption tests of Cd(II), Cu(II), Mn(II), Pb(II), and Zn(II) in batch reactors were carried out at ambient temperature and at constant pH. The increasing order of the adsorption rates followed the sequence: Mn(II) > Pb(II) > Zn(II) > Cu(II) > Cd(II). The maximal adsorption capacities at pH 4.0 determined from the D–R and Langmuir models vary in the following order: Cu(II) > Mn(II) > Cd(II) > Zn(II) > Pb(II). The equilibrium data fitted well with the three-parameter Redlich–Peterson model. The values of mean energy of adsorption show mainly an ion-exchange mechanism. The objective of a study by Benhammou et al. (2005b) was to investigate the adsorption of the heavy metals Hg(II) and Cr(VI), from aqueous solutions, onto Moroccan stevensite. In order to improve the adsorption capacity of stevensite for Cr(VI), a preparation of stevensite was carried out. It consisted of saturating the stevensite in ferrous iron Fe(II) and reducing the total Fe by Na2S2O4. Then, the adsorption experiments were studied in batch reactors at 25 °C. The influence of the pH solution on the Cr(VI) and Hg(II) adsorption was studied in the pH range of 1.5-7.0. The optimum pH for the Cr(VI) adsorption was in the pH range of 2.0-5.0, and for Hg(II) above 4.0. The adsorption kinetics was tested by a pseudo-secondorder model. The adsorption rate of Hg(II) was 54.35 mmol/kg-min and that of Cr(VI) was 7.21 mmol/kg-min. The adsorption isotherms were described by the Dubinin-Radushkevich model. The maximal adsorption capacity for Cr(VI) increased from 13.7 (raw stevensite) to 48.86 mmol/kg (modified stevensite) and for Hg(II) it decreased from 205.8 to 166.9 mmol/kg. A study was carried out by Sarioglu et al. (2005) to examine the removal of copper from an aqueous solution by phosphate rock (PR). The optimum conditions for adsorption were evaluated by changing various parameters, viz., effects of pH, adsorbent concentration, initial metal concentration and contact time. The study showed that copper removal from an aqueous solution increased with increasing pH and adsorbent concentration (up to 5 g/L) and decreased with increasing initial copper concentration, and the equilibrium (contact) time was 40 min. The adsorption capacity of PR was determined as 0.17 mmol/g by fitting the experimental results to Langmuir isotherm. The potential of using activated phosphate as a new adsorbent for the removal of Pb from aqueous solutions was investigated by Mouflih et al. (2005). The kinetics of lead adsorption and the adsorption process were compared for natural phosphate (NP) and activated phosphate (AP). The results indicate that equilibrium was established in about 1 h for NP and 3 h for AP. The effect of the pH was examined in the range of 2–6 and the maximum removal obtained was between 2 and 3 for NP and between 3 and 4 for AP. The maximum adsorption


35

capacities at 25 °C were 155.04 and 115.34 mg/g for AP and NP, respectively. The thermodynamic parameter showed that adsorption of lead on NP and AP was an endothermic process. These results showed that AP was a good adsorbent for heavy metals from aqueous solutions and could be used as a purifier for water and wastewater. Kinetic and equilibrium adsorption experiments on removal of Zn(II) from aqueous solutions by scoria (a vesicular pyroclastic rock with basaltic composition) from Jeju Island, Korea, in order to examine its potential use as an efficient sorbent, was conducted by Kwon et al. (2005). The batch-type kinetic sorption tests under variable conditions indicated that the percentage of Zn(II) removal by scoria increased with decreasing initial Zn(II) concentration, particle size, and sorbate/sorbent ratio. However, the adsorption capacity decreased with the decrease of initial Zn(II) concentration and sorbate/sorbent ratio. Equilibrium adsorption tests showed that Jeju scoria had a larger capacity and affinity for Zn(II) sorption than commercial powdered activated carbon (PAC), at initial Zn(II) concentrations of more than 10 mM, the adsorption capacity of Jeju scoria was about 1.5 times higher than that of PAC. The acquired adsorption data better fitted to the Langmuir isotherm. The adsorption behavior was mainly controlled by cation exchange and typically displayed characteristics of „cation sorption‟. The Zn(II) removal capacity decreased when solution pH decreased because of the competition with hydrogen ions for adsorption sites, while the Zn(II) removal capacity increased under higher pH conditions, which was likely due to hydroxide precipitation. At an initial Zn(II) concentration of 5.0 mM, the removal increased from 70% to 96% with the increase of initial pH from 3.0 to 7.0. The kinetics of sorption of Cu(II) on a Saudi clay mineral (bentonite) was investigated by Al-Qunaibit et al. (2005) at 20ºC using different weights of the clay (0.5, 1.0, 1.5, and 2 g). Each weight represented a certain sample size. The order of the process appeared to be 1 with respect to Cu(II), and 1½ with respect to the clay surface area. The adsorption rate was found to depend on internal diffusion, which produced certain decrease in the specific rate of sorption as a function of time. Adsorption characteristics were described using two-site Langmuir isotherm. The desorption experiments proved that Cu(II) ions were chemisorbed on the bentonite surface. The maximum adsorption obtained was 909 mg Cu(II)/g clay. Calcined phosphate (CP) was evaluated as a new adsorbent for removal of heavy metals from aqueous solution by Aklil et al. (2004). Removal of Pb(II), Cu(II), and Zn(II) on the CP was investigated in batch experiments. The influence of pH was studied and the adsorption capacities obtained at pH 5 were 85.6, 29.8, and 20.6 mg/g for Pb(II), Cu(II) and Zn(II), respectively. The adsorption between phosphate rock (PR) and metals (Pb, Cu, and Zn) was studied by Cao et al. (2004). Phosphate rock had the highest affinity for Pb, followed by Cu and Zn, with sorption capacities of 138, 114, and 83.2 mmol/kg PR, respectively. In the Pb–Cu–Zn ternary system, competitive metal sorption occurred with adsorption capacity reduction of 15.2%, 48.3%, and 75.6% for Pb, Cu, and Zn, respectively, compared to the mono-metal systems. A fractional factorial design showed the interfering effects in the order of Pb > Cu > Zn. The capacity of sepiolite for the removal of lead ions from aqueous solution was investigated under different experimental conditions by Bektaş et al. (2004). The Langmuir and Freundlich equations were applied to fit the data. The constants and correlation coefficients of these isotherm models at different conditions, such as pH, temperature and particle size were calculated and compared. The equilibrium process was well described by the Langmuir isotherm model and the maximum sorption capacity was found to be 93.4 mg/g

36


for the optimal experimental conditions. The best correlation coefficients were obtained using the pseudo-second-order kinetic model. Removal of heavy metals Mn(II), Co(II), Ni(II), and Cu(II) from aqueous solutions was studied using a raw kaolinite by Yavuz et al. (2003). The adsorption of these metals on kaolinite conformed to linear form of Langmuir adsorption equation. Langmuir adsorption capacity for each metal was found as 0.446 mg/g (Mn), 0.919 mg/g (Co), 1.669 mg/g (Ni), 10.787 mg/g (Cu) at 25°C. The thermodynamic parameters showed that the adsorption of these heavy metals on kaolinite were an endothermic process. Dho and Lee (2003) conducted a combined adsorption-sequential extraction analysis by which five phases (i.e., exchangeable, carbonate, Mn-Oxide, organic, and Fe-Oxide phases) of adsorbed heavy metals were analyzed, to investigate temperature effects on single and competitive adsorptions of Zn(II) and Cu(II) onto natural clays. In the case of single adsorption of Zn, the exchangeable phase adsorption decreased from 65 to 40%, but the carbonate phase adsorption increased from 30 to 40%, with an increase in temperature from 15 to 55°C. However, in its competitive adsorption with Cu, Zn was mostly present in the exchangeable phase (over 90%), and with an increase in temperature, the exchangeable phase adsorption decreased only 10%. In the case of Cu, over 50% among the total amount of adsorption was present in the carbonate phase in both cases of single and competitive adsorptions. The carbonate phase adsorption of Cu increased from 56 to 61% and from 60 to 66% in single and competitive adsorptions, respectively, with a temperature increase. These results showed that in the case of Zn, the major mechanism of retention in natural clay soils could be exchangeable phase adsorption, especially in the case of competitive adsorption with Cu. However, in the case of Cu, the major mechanism could be carbonate phase adsorption. It was observed that the adsorption of Zn and Cu onto natural clays was endothermic, which indicated that the adsorption equilibrium constants and capacities increase with a temperature increase, with the exception of exchangeable phase adsorption. The adsorption behavior of sepiolite was studied with respect to cadmium and zinc in order to consider its application to remediate soils polluted with these metals by ÁlvarezAyuso and García-Sánchez (2003a). The Langmuir model was found to describe the sorption processes well, offering maximum sorption capacities of 17.1 and 8.13 mg/g for cadmium and zinc, respectively, at pH 6. The sorption capacities were pH dependent, undergoing a decrease with H+ concentration increase. The column studies also showed a high reduction in the leaching of cadmium and zinc (69 and 52%, respectively) when a sepiolite dose of 4% was applied. The adsorption behavior of palygorskite was studied with respect to lead, copper, zinc and cadmium in order to consider its application to remediate soils polluted with these metals by Álvarez-Ayuso and García-Sánchez (2003b). The Langmuir model was found to describe the adsorption processes well offering maximum sorption values of 37.2 mg/g for lead, 17.4 mg/g for copper, 7.11 mg/g for zinc and 5.83 mg/g for cadmium at pH 5–6. The column studies also showed a high reduction in the metal leaching (50% for lead, 59% for copper, 52% for zinc and 66% for cadmium) when a palygorskite dose of 4% was applied. The adsorption characteristics of heavy metals such as Cd(II), Cr(III), Cu(II), Ni(II), Pb(II), and Zn(II) ions by kaolin (kaolinite) and ballclay (illite) from Thailand were studied by Chantawong et al. (2003). It was found that, except Ni, metal adsorption increased with increased pH of the solutions and their adsorption followed both Langmuir and Freundlich isotherms. Adsorption of metals in the mixture solutions by kaolin was: Cr > Zn > Cu ≈ Cd ≈


37

Ni > Pb, and for ballclay was: Cr > Zn > Cu > Cd ≈ Pb > Ni. The adsorption of metals was endothermic, with the exception of Cd, Pb and Zn for kaolin, Cu and Zn for ballclay. The presence of Cr(III) induced the greatest reduction of metal adsorption onto kaolin, as did the presence of Cu(II) for ballclay. A bentonite and an expanded perlite (Morocco) were used for the removal of trivalent chromium from aqueous solutions by Chakir et al. (2002). The kinetic study showed that the uptake of Cr(III) by bentonite was very rapid as compared to expanded perlite. For both the adsorbents the adsorption capacity increased with increasing pH of the suspensions. Results showed that bentonite was more effective in removing trivalent chromium (96%) from aqueous solution than expanded perlite (40%). Surface complexation played an important role in the sorption of Cr(III) species on expanded perlite. In the case of bentonite, cationexchange was the predominate mechanism for adsorption of trivalent chromium ions. A thiol-functionalized layered magnesium phyllosilicate material (Mg-MTMS) was investigated as a high-capacity adsorbent for heavy metal ions by Lagadic et al. (2001). Structural characterization by powder X-ray diffraction, infrared spectroscopy, NMR spectroscopy and elemental analyses confirmed the smectite-type structure. Mg-MTMS was found to be highly effective for the adsorption of Hg(II), Pb(II), and Cd(II) ions, exhibiting extraordinary metal ion uptake capacities of 603, 365, and 210 mg of metal/g of adsorbent, respectively. The high effectiveness of Mg-MTMS for the capture of metal ions is attributed to both high concentration of complexing thiol groups (6.4 mmol of SH/g of Mg-MTMS) and expansion capability of the framework, which facilitates the accessibility of the binding sites. De-oiled spent bleaching clay was activated either by acid treatment followed by heat activation or by heat activation alone at temperatures between 200 and 800°C by Seng et al. (2001). The surface area of the heat-activated clay attained a maximal value of ≈120 m2/g at temperatures between 400 and 500°C, while the acid-heat-treated clay attained maximal surface area of ≈140 m2/g. The adsorption capacities of Cr(VI) for both series studied increased as the activation temperature increased until 300°C and decreased again at higher temperatures. At lower pH, more than 95% of the Cr(VI) was absorbed in a solution with initial concentration of 1 mg/L per gram of adsorbent activated at 300°C. The adsorption patterns followed Freudlich isotherm. The amount of Ni(II) adsorbed increased with the pH of the solution for all samples studied. The maximal adsorption capacities of the adsorbents in solution containing initial Ni(II) concentration of 5 mg/L per 0.5 g of adsorbent and at pH 6 were found to be 44 and 42%, respectively, for the acid-treated sample activated at 500°C and for the nonacid-treated sample activated at 700°C. The use of an adsorbent produced by the chemical treatment of locally available clay for the removal of some metals from waste water was investigated by Vengris et al. (2001). The modification of the natural clay was performed by treatment with hydrochloric acid and subsequent neutralization of the resultant solution by sodium hydroxide. The adsorption amounts of iron, aluminium and magnesium compounds were increased with the modified sorbent. Acidic treatment led to the decomposition of the montmorillonite structure. Adsorption studies were carried out by both batch and column methods. The uptake capacity of the modified clay for nickel, copper and zinc significantly increased. Batch and column sorption methods enabled the removal of nickel, copper and zinc ions till the permissible sewerage discharge concentration. The sorption process was reflected by Langmuir-type isotherm.

38

John U. Kennedy Oubagaranadin and Z.V.P. Murthy Table 3.2. Clay adsorbents for heavy metals from solutions Type of clay

Adsorbate metal ion Ni(II)

Calcined Bofe bentonite clay Smectite with a small Cr(III) proportion of kaolinite (From Jebel Chakir, Tunisia, North Africa). Tabuk and Khaiber (From Pb(II) Saudi Arabia) Kaolin Pb(II) Petra clay Cd(II), Pb(II) Montmorillonite – Illite clay Pb(II) White, yellow and red sands Cr(III) from the United Arab Emirates Raw and acid-activated Cu(II) bentonite Modified Unye bentonite Cu(II) Tunisian smectite-rich clay Pb(II) Spent activated clay Cr(VI) Kaolinite and Fe(III), Co(II), montmorillonite Ni(II) Bentonite Pb(II) Natural clinoptilolite Zn(II) Diatomite Cr(III) Laboratory grade Fuller‟s Hg(II) earth Turkish kaolinite Pb(II) Activated palygorskite Cu(II) Natural palygorskite Pb(II) Clinoptilolite Pb(II) Montmorillonite Cd(II), Co(II), Cu(II), Ni(II), Pb(II) Palygorskite Cd(II) Natural and activated phosphate Saudi bentonite Calcined phosphate Sepiolite Raw kaolinite Sepiolite Palygorskite

Adsorption capacity, Reference qm (mg/g) 1.91 Vieira et al., 2010 117.5

Ghorbel-Abid et al., 2009

30, 10 4.2 74.07, 83.33 Raw: 52 Acid activated: 78 62.5, 9.8, 2.38

Al-Jlil and Alsewailem, 2009 Jiang et al., 2009 Baker, 2009 Oubagaranadin and Murthy, 2009c and 2010 Khamis et al., 2009

42.41, 32.17

Eren and Afsin, 2008

105.38 25 1.422 10.4 to 11.2 28.4 to 28.9 78.82 21.2 26.5 1.15

Eren, 2008 Chaari et al., 2008 Weng et al., 2008 Bhattacharyya and Gupta, 2008 Zhu et al., 2008 Çoruh, 2008 Gürü et al., 2008 Oubagaranadin et al., 2007

31.75 32.24 104.28 80.93 32.7, 28.6, 31.8, 28.4, 33.0

Sari et al., 2007 Chen et al., 2007 Chen and Wang, 2007 Günay et al., 2007 Bhattacharyya and Gupta, 2007

4.54

Pb(II)

115.34, 155.04

Álvarez-Ayuso and GarcíaSánchez, 2007 Mouflih et al., 2005

Cu(II) Pb(II), Cu(II), Zn(II) Pb(II) Mn(II), Co(II), Ni(II), Cu(II) Cd(II), Zn(II)

909 85.6, 29.8, 20.6

Al-Qunaibit et al., 2005 Aklil et al., 2004

93.4 0.446, 0.919, 1.669, 10.787 17.1, 8.13

Bektaş et al., 2004 Yavuz et al., 2003

Pb(II), Cu(II), Zn(II), Cd(II)

Álvarez-Ayuso and GarcíaSánchez, 2003ª 37.2, 17.4, 7.11, 5.83Álvarez-Ayuso and GarcíaSánchez, 2003b

Rashed (2001) reported suitable conditions for the use of naturally occurring minerals (talc, chalcopyrite and barite) as adsorbents for the removal of lead ions. The adsorption of lead ions from solutions containing different initial lead concentrations (50, 100, 200, 400, 600, 800 and 1000 mg/L Pb as lead nitrate) using different size fractions ( πc, which is like the yield point of a solid film.

INTERROGATION TECHNIQUES FOR THE STUDY LAYERS Protein monolayer films can be characterized by almost all known biophysical techniques – circular dichroism, Brewster angle microscopy, atomic force microscopy, scanningtunneling microscopy, infrared and electron-paramagnetic-resonance spectroscopy, X-ray diffraction, absorption spectra, nanogravimetry and other. It is in no way intended here to provide a full description of the methods of characterizing thin films, since that would comprise an entire book, not just a short review. Many of the techniques described briefly below are reviewed moreover in more detail elsewhere [32-34].

Monolayers at Air-Water Interface During compression a monolayer at the air-water interface, the surface tension of water is reduced. This “pressure” can be measured by various means, such as piece of filter paper and mostly by platinum Wilhelmy plate dipped into the subphase and attached to a balance. Since

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Jadwiga Sołoducho and Joanna Cabaj

the concentration and volume of solution spread and the area of the monolayer are known, it is possible to plot surface area per unit against surface pressure. This plot is known as isotherm. When deposition of monolayer onto solid surface occurs, a feedback circuit may be used to keep the surface pressure content. Since area of the substrate is known, it is possible to obtain a deposition ratio, i.e. area of monolayer deposited per area of substrate. A ratio of 1 is indicative of good transfer of the monolayer.

Brewster Angle Microscopy (BAM) Brewster angle microscopy (BAM) is a well established method for visualization the morphology of ultra-thin surface films over aqueous subphase. BAM images show contrast within a film from differences in reflectivity to polarized light incident at Brewster‟s angle for the clean air-water interface. Without a surface film the reflection is zero (black field), but when the thin film forms the reflective index is different from that of the subphase (white field). This technique permits to observe separation of the monolayer of domains and surrounding film after interaction between different surface active molecules. The value of the Brewster angle depends upon the material at the surface, and so it is possible to visualize the domain structure of the monolayer, as the presence of the monolayer changes the Brewster angle [35]. The morphology of phospholipids monolayers over water subphase are well known, but one interesting morphologic feature regarding these lipid layer is the formation of well defined, bean-shaped domains that appear when the film undergoes the liquid-expanded-toliquid-condensed transition (Fig. 4). At the beginning of the compression, the film is completely homogenous, and on decreasing of surface area, small spots appear. Such spots change to bean shaped domains. After the end of the phase transition, these domains coalesce and the film becomes homogenous on the liquid-condensed phase until they collapse [36].

Figure 4. BAM images of L-α-dipalmitoylphosphatidylcholine at the air-water interface [37]

Langmuir Monolayers in Biosensors

139

Addition of hydrophilic unit (i.e. cytochrome b6f complex) in the subphase to spread phospholipid monolayer leads to considerable changes of surface morphology and homogeneity of mixed film. As a result of surface interaction between the protein and the lipid molecules are formed aggregates and large surrounding areas. The obtained result suggests stronger surface interactions between the protein complex b6f and lipid molecules in mixed monolayer and formation of more packed structure at the surface. In case of phospholipids – frutalin (α-D-galactose lectin) film formation it was observed that galactocerebroside stabilizes the formation of liquid-condensed domains in the phospholipids film, which could be formed at lower values of surface pressure [37]. Frutalin showed two main effects over the morphology of the mixed films: first, it favors the appearing of clusters even for the noncompressed film, that is also a reason for the more expanded isotherm at high areas (Fig. 5). Second, the lectin promoted the blending of the lipids, since the duality of domains existent in the absence of the protein vanished in presence of it. Probably, it is due to the expulsionm of frutalin at high states of packing, predicted by the surface pressure-area isotherm.

Figure 5. Surface pressure vs area isotherms phospholipids, Langmuir monolayers formed over subphases of pure PBS buffer (○, □), and PBS buffer with 0.1μg/mL frutalin dissolved (●, ■) [36]

Mass-Sensitive Techniques The mass of a thin film can be monitored using a quartz crystal microbalance (QCM). It is useful for monitoring the rate of deposition in thin film deposition systems under vacuum. In liquid, it is highly effective at determining the affinity of molecules (i.e. proteins, in particular) to surfaces functionalized with recognition sites. Larger entities such as viruses or polymers are investigated, as well. QCM has also been used to investigate interactions


140

between biomolecules. This if often especially suitable for sensing applications since it can monitor mass changes taking place whilst the sample is immersed in a solution. Binding or desorption of species will cause the mass of the film to be changed, and this can be monitored in real time. Reviews on this subject include [38] and [39]. The change in resonance frequency is recorded after each deposition step and correlated to the deposited mass (Δm, ng) and layer thickness (Δt, nm) by the Sauerbrey equation [40]. -Δf = [2f02 /A√ρq μq]Δm

(1)

Where f0 (Hz) is the resonance frequency, A is the area of the electrode, ρq is the quartz density, and μq is its shear modulus. The Sauerbrey equation was developed by G. Sauerbrey in 1959 as a method for correlating changes in the oscillation frequency of a piezoelectric crystal with the mass deposited on it. He simultaneously developed a method for measuring the characteristic frequency and its changes by using the crystal as the frequency determining component of an oscillator circuit. His method continues to be used as the primary tool in quartz crystal microbalance experiments for conversion of frequency to mass and is valid in nearly all applications. Because the film is treated as an extension of thickness, Sauerbrey‟s equation only applies to systems in which the following three conditions are met: the deposited mass must be rigid, the deposited mass must be distributed evenly and the frequency change Δf / f < 0.02.

Spectroscopy and Microscopy Many of the spectroscopic techniques used to characterize “bulk” samples can also be used to characterize deposited thin films. UV–vis spectroscopy can be performed on samples deposited on suitable transparent or reflective substrates and can give quantitative measurements of the amount of material present. FTIR spectroscopy can also be used and can give information about any reactions that may have taken place within the film. The problems of sensitivity can be overcome by depositing the thin film on an ATR crystal or on a gold-coated substrate and using reflection/adsorption FTIR spectroscopy. Xray photoelectron spectroscopy (XPS) can give the elemental composition of the film and also some depth profiling-related information, giving an idea of the physical location of various moieties within the film. Low-angle X-ray diffraction can give Bragg peaks which give a measurement of order and repeat spacing within the film [23]. Ellipsometry can be used to measure film thickness and refractive index [41]. Atomic force microscopy (AFM), scanning tunneling microscopy (STM) and scanning electron microscopy (SEM) can be used to visualize the thin film and can give information about the regularity of the film, any phase separation or aggregation and may be able to visualize any binding events that have occurred [33]. To further explore the nature of chain organization within each thin film is utilized by UV/vis absorption and PL spectroscopy. It has been known that a specific interchain stacking

141


of conjugated polymers results in the formation of new electronic species called aggregates [42, 43-48].

Atomic Force Microscopy (AFM) Atomic force microscopy (AFM) or scanning force microscopy (SFM) is a very highresolution type of scanning probe microscopy, with demonstrated resolution on the order of fractions of a nanometer, more than 1000 times better than the optical diffraction limit (Fig. 6) Because the atomic force microscope relies on the forces between the tip and sample, knowing these forces is important for proper imaging. The force is not measured directly, but calculated by measuring the deflection of the lever, and knowing the stiffness of the cantilever. Hook‟s law gives F = -kz

(2)

where F is the force, k is the stiffness of the lever, and z is the distance the lever is bent. Because of AFM‟s versatility, it has been applied to a large number of research topics.

bent.

where F is the force, k is the stiffness of the lever, and z is the distance the lever is Laser Photodiode

Cantilever Sample

Scanner

Figure 6. General principle of AFM

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Direct interaction between the scanning stylus and the biological sample is required, there is a potential risk of sample deformation. Therefore, samples well known from electron microscopic and x-ray analyses have been studied with the AFM to demonstrate the precision of topography recorded with the AFM. The structure of the heptametrical GroES complex was seen at a resolution of 1 nm with the AFM before the x-ray structure was available to confirm the topography data [49]. Furthermore, comparative electron microscopy and AFM analyses of DNA–protein complexes and DNA triplexes have been reported as well [50]. Although reliable instruments allowing routine operation have been available for several years, progress has been made recently by improving the sample-preparation methods and by finding buffer conditions that optimize the tip–sample interaction. The AFM is now a powerful tool and can reveal the surface structure of protein assemblies in their native environment at submolecular resolution. As demonstrated with the few examples here, it is not just the resolution that makes these topography attractive but also the ability to monitor conformational changes of biological assemblies directly and under native conditions.

EFFECTS OF SOLVENT Protein-based catalysts are less stable than many traditional chemical catalysts, particularly in water-miscible organic solvents. These commonly used solvents disrupt the tertiary structure of the enzyme, so inactivated it. Nevertheless, it is well known that proteins are stable in some organic solvents and even multicomponent enzymes have been shown to retain catalytic activity, albeit at significantly lower levels than in water [51]. Proteins in hydrophobic solvents are thought to retain their native structure as a result of kinetic trapping, which results from stronger hydrogen bonding between the protein atoms and a more rigid structure in the absence of water. In hydrophobic water-immiscible solvents, any water that might be present will tend to stay at the protein surface because of the solvophobic and hydrophilic nature of the protein surface [52]. In fact, the addition of even a minute amount of water (1% v/v) is sufficient to drastically increase catalytic activity in these unnatural solvents; this observation is linked to the role that water plays in the structure and dynamics of the protein [53]. Conversely, polar solvents that can easily strip water from the surface of the protein and compete strongly for hydrogen bonds between protein atoms (e.g. dimethyl sulfoxide [DMSO], dimethylformamide [DMF], formamide) usually denature the structure to a largely unfolded state [54]. Alcohols have some hydrophilic component, but are only moderate competitors for amide hydrogen bonds. They tend to disrupt tertiary structure and leave secondary structure interactions largely undisturbed. Indeed, methanol has gained some attention as a denaturant that increases the concentration of possible folding intermediates and has therefore been used in protein folding studies [55]. In this light, it is noteworthy that, although there is no doubt that there exists a minimum structural requirement for catalytic activity, the idea that all proteins must be intact relative to the native state for catalysis to occur is not completely general, as partially unfolded subtilisin Carlsburg was recently found to be catalytically active in organic solvents [56].


143

Most of organic solvent-tolerant enzymes are lipolytic and proteolytic enzymes. Although impurities often influence the stability of enzymes in the presence of organic solvents, some were investigated without enzyme purification. High thermal stability of enzymes is considered to be positively correlated with stability in the presence of organic solvents [57]. Thermophiles and hyperthermophiles are host for many useful thermophilic enzymes, i.e. an esterase from Pyrobaculum calidifontis was stable in water-miscible solvents including methanol, ethanol, 2-propanol, acetonitrile and DMF [58]. However, the enzyme activity was markedly reduced in these solvents.

IMAGING SURFACE STRUCTURE During the last decade, the unique ability of AFM to image specimens at subnanometer resolution and in aqueous solution has been intensively exploited to investigate the structure of cell surface layers made of two-dimensional protein crystals. Traditionally, X-ray crystallography has been the premier technique for atomic resolution of protein crystals, while electron crystallography examines the specimen in a more native-like environment at nearatomic resolution. More recently, the oblique lattice of the S-layer of Bacillus stearothermophilus was visualized to a lateral resolution of about 1.5 nm [59], and nanometer lateral resolution was achieved for the S-layers of B. coagulans and B. sphaericus strains recrystallized on silanized silicon substrates [60]. Interestingly, an elegant preparation method has been developed to investigate S-layers from Bacillus species in conditions relevant to their native state [61]. The proteins are recrystallized on a lipid monolayer in a Langmuir-Blodgett trough, and the composite lipid/S-layer structure is then deposited on a flat substrate. Under these conditions, S-layers attach to the lipid film with their inner face, which corresponds to the orientation found in the living organism (Table 1). The morphology of the deposited multilayered structures is characterized at nanometer level by AFM that is a tool with different possibilities and limits. Multilayered structures are possible to form because the technique gives the possibility to form multilayered architectures controlled at molecular level. Atomic force microscopy (AFM) can image biological samples under aqueous conditions with high resolution in three dimensions without the use of any probes. AFM has been successfully used to image isolated phase separated bilayers and peptide–lipid domains in supported bilayers. Also monolayers containing glycosphingolipids and cholesterol have been imaged [66] as well as phenoloxidases or glucose oxidase mixed (with linoleic acid, phospholipids) LB/LS films [3]. The phenoloxidases (laccase, tyrosinase) and glucose oxidase hetero layers were visualized by contact mode AFM (Figs. 7ab and 8ab). The enzyme molecules were fairly well deposited onto solid substrate. Immobilized phenoloxidases as well as glucose oxidase were observed as an aggregated pattern in solid-like state with keeping their characteristic random cloud-like or island structure. The heterogeneous films roughness was found relatively high (especially in case of tyrosinase film) for an LB film, which indeed shows that the enzymes were transferred. The roughness of linoleic acid - laccase film was measured as 7.17 nm (similar results was found for film of lipase [67]), when the roughness value of tyrosinase film was found as 19 nm. To compare, the roughness of glucose oxidase LB film has been


144

measured as 0.38 nm [68] or 1.9 for LS films. These obtained values were attributed to the immobilization process of comparatively large molecule aggregates of enzymes (laccase, tyrosinase, glucose oxidase) incorporated to LB/LS films. This leads to conclude that there is sometime formation of an agglomerate of enzymes rather than an organized monolayer at the air/water interface. The AFM results showed that the effect could be also associated with changes in the enzyme conformations A monolayer rearrangement, such as two- dimensional formation or hindered molecular orientation, might take place during the phase transition behaviour resulted in the molecular aggregates on the protein layer. Table 1. Imaging the ultrastructure of different surface layers Organism

Sample

Bacillus sphaericus S-layer

Bacillus sphaericus S-layer

Bacillus stearothermophilus

S-layer

Deinococcus radiodurans

S-layer

Halobacterium halobium

Purple membrane

Escherichia coli

a

Immobilization Observationsa Reference procedure Covalent linkage Square lattice; r 12 nm 62 to glass/mica (agreement with electron microscopy) Recrystallization Square lattice; r = 1-2 nm 61 on supported (novel S-layer/lipid lipid bilayers bilayer structures) Recrystallization Oblique lattice; r 1.5 59 on various siliconnm (study of surfaces recrystallization process) Adsorption on Conformational change 63 mica of central pores

Adsorption on Hexagonal symmetry; r = 64 mica, silanized 1.1 nm glass, and supported lipid bilayers Aquaporin Z Assembly on Tetramers; p42(1)2 and 65 mica in the p4 symmetry, r < 1 nm presence of lipids (proteolytic cleavage force-induced conformational changes)

r values are lateral resolution determined directly from the images or after image processing

Figure 7. AFM topography images of a) linoleic acid – laccase LB film, b) linoleic acid – tyrosinase LB film [3]


145

Figure 8. AFM images of a) phospholipids – tyrosinase LS film, b) phospholipids –glucose oxidase LS film

LB FILMS, INCORPORATION WITHIN BIOSENSORS After the initial work on bioactive molecules in monolayers, it was inevitable that workers would attempt to transfer these films onto solid substrates since a major problem with the use of LB films is their extreme fragility, requiring deposition onto a suitable substrate for support and to allow measurements to be made on the film. One of the earliest papers [69] reports deposition of phospholipids or cholesterol onto an ionically conductive polyacrylamide hydrogel, giving a structure capable of an electrochemical response. The sensing of i.e. glucose is of paramount interest and much work has been done on developing biosensors based on glucose oxidase which can be adsorbed into a polymeric matrix or cast as a thick film and cross-linked with glutaraldehyde. Problems with these sensors include stability and slow response times. Table 2 shows the behaviour of some of these conventional sensors and compares them with some of the sensors manufactured using the techniques described. Often species of biological interest are water-soluble which means they cannot be directly deposited by the LB method, however, should they be charged molecules, they can be dissolved in the subphase. If a layer of an oppositely charged amphiphile is then spread on the water surface and formed into an LB film, the biomolecule will then be incorporated into the LB film. Penicillinase could be co-deposited [70] with stearic acid onto an ISFET to give a penicillin sensor. Glucose oxidase was also studied [71,72] by using different lipids to adsorb the enzyme from solution and showing that a glucose sensor could best be made by codepositing glucose oxidase with octadecyltrimethylammonium chloride. Okahata et al. [73] mixed glucose oxidase with a cationic lipid and deposited a bilayer on a platinum electrode and showed it to respond to glucose with a response time of 5 s, much faster than other techniques (Table 2). FTIR studies [74] were performed on fatty acid/glucose oxidase and phospholipids/glucose oxidase monolayer deposited onto ATR crystals, the fatty acid was shown to incorporate more of the enzyme. Chymotrypsin and urease as well as fenoloxidases were also studied [75, 3]. Glutathione-S-transferase is another enzyme which can be spread at the interface and compressed and deposited as an LB film [76]. The resultant film was shown to maintain its biological activity towards pesticides such as atrazine, even after being heated to 423 K,

146


whereas in solution all activity is lost at 353 K. The same group also successfully deposited enzymes such as urease onto silanised glass surfaces [77] and studied the films using QCM and potentiometric measurements. Phenolooxidase (laccase, tyrosinase) enzymes could be immobilized via glutaraldehyde coupling onto amine-terminated thiol monolayers [78] and then used to detect catechol. A combination of fungal laccase and a cystamine monolayer gave optimal results, giving a linear amperometric response between concentrations of 0.001 and 0.4 mM. An interesting variant on the use of gold–thiol monolayers has been rather than attaching the thiol to gold electrode, instead to use small colloidal gold particles as the substrate. Table 2. Comparison of selected protein sensors immobilized in thin films Immobilization method

Sample Response thickness time 2 layers 0.12 min

Glucose oxidase LB deposition with lipids Glucose oxidase LB deposition with 1 layer polythiophene Catalase immobilized in LB film of 1 layer phospholipids Alcohol dehydrogenase in LB film of 1 layer phospholipids Laccase LB deposition with N-heptyl- 5 layers bis(thiophene)carbazole and tricosenoic acid cross-linked with glutaraldehyde Horseradish peroxidase LB deposition 1 layer with phsospholipids Laccase LB deposition with N-nonyl- 5 layers bis(thiophene)diphenylamine and stearic acid cross-linked with glutaraldehyde Tyrosinase LB deposition with N5 layers nonyl-bis(thiophene)diphenylamine and stearic acid cross-linked with glutaraldehyde Laccase LB deposition with 5 layers benzothiadiazole-based copolymer

2 min

Stability Reference 3 month 73 40 days 79

not reported >3 month not reported >3 month 1.5 min >3 month

80

not reported > 2 weeks 1.5 min >3 month

83

2 min

>3 month

84

1 min

>3 month

3

81 82

84

CONSLUSION The LB technique has a myriad of uses, but generally takes on one of two roles. First the LB trough can be used to deposit one or more monolayers of specific amphiphiles onto solid substrates. They are in turn used for different areas of science ranging from optics to rheology. Secondly, the LB technique can be used itself in an experimental device to test interfacial properties such as the surface tension of various fluids, as well as the surface pressure of a given system. The system can also be used as an observation mechanism to


147

watch how drugs interact with lipids, or to see how lipids arrange themselves as the number to area ratios are varied. The use of thin films, especially self-assembly ones provide a simple method for the fictionalization of electrode surfaces using nanogram amounts of material. Langmuir-Blodgett technique can give either highly ordered films, giving a high level of control of the environment and often resemble the environment found inside biomembranes, thereby helping to stabilize proteins. Biosensors produced using these various types of films can display high sensitivities, be easily interrogated using electronic, optical or mass-sensitive techniques, can often be regenerated and display good stability. The potential for usable devices based on these types of films devices in the medical diagnostic and environmental monitoring applications is immense. Accordingly, for nearly 50 years we have witnessed tremendous progress in the development of electrochemical biosensors. Elegant research on new sensing concepts, coupled with numerous technological innovations, has thus opened the door to widespread applications of electrochemical biosensors. Major fundamental and technological advances have been made for enhancing the capabilities and improving the reliability of chemical measuring devices. As this field enters its fifth decade of intense research, we expect significant efforts that couple the fundamental sciences with technological advances.

LITERATURE [1] [2] [3] [4] [5] [6] [7] [8] [9] [10] [11] [12] [13] [14] [15]

S. Biswas, D. Bhattacharjee, R. K. Nath, S. A. Hussain, J. Coll. Inter. Science., 2007, 311, 361-367 J. Cabaj, J. Sołoducho, A. Nowakowska, A. Chyla, Electroanalysis, 2006, 18(8), 801806 J. Cabaj, J. Sołoducho, A. Nowakowska-Oleksy, Sens. Actuat. B, 2010, 143, 508-515 G. L. Gaines, Insoluble monolayers at liquid-gas interfaces, Interscience, New York, 1966. K. S. Birdi, Self-assembly monolayer structures of lipids and macromolecules at interfaces, Kluwer Academic Press, Dordrecht, 1999 L. Dziri, K. Puppala, R. M. Leblanc, J. Colloid Interface Sci., 1997, 194, 37-43 G. K. Chudinova, O. N. Pokrovskaya, A. P. Savitskii, Russ. Chem. Bull., 1995, 44, 1958-1962 Langmuir, J. Am. Chem. Soc., 1915, 37, 1139-1141 Langmuir, V. J. Schaefer, J. Am. Chem. Soc., 1938, 60, 1351-1360 L. Netzer, J. Sagiv, J. Am. Chem. Soc., 1983, 105, 674-676 C. Nicolini, Ann. New York Acad. Sci., 1996, 799, 297-311 G. L. Gaines, Insoluble monolayers at the liquid-gas interfaces, Interscience, New York, 1966 Riccio, M. Lanzi, C. Antolini, C. De Nitti, C. Tavani, C. Nicolini, Langmuir, 1996, 12, 1545-1549 V. Erokhin, P. Facci, C. Nicolini, Biosens. Bioelectron., 1995, 10, 25-34 P. Girart-Ergot, S. Godoy, L. J. Blum, Adv. Colloid Interface Sci, 2005, 116, 205-225

148


[16] L. Caseli, M. E. D. Zaniquelli, R. P. M. Furriel, F. A. Leone, Colloid Surf. BBiointefaces, 2002, 25, 119-128 [17] F. J. Pavinatto, L. Caseli, A. Pavinatto, D. S. Dos Santos, T. M. Nobre, M. E. D. Zaniquelli, H. S. Silva, P. B. Miranda, O. N. de Oliveira, Langmuir, 2007, 23, 76667671 [18] L. Caseli, T. M. Nobre, D. A. K. Silva, W. Loh, M. E. D. Zaniquelli, Colloid Surf. BBiointerfaces, 2001, 22, 309-321 [19] J. A. Castillo, A. Pinazo, J. Carilla, M. R. Infante, M. A. Alsina, I. Haro, P. Clapes, Langmuir, 2004, 20, 3379-3387 [20] L. Caseli, F. N. Crespilho, T. M. Nobre, M. E. D. Zaniquelli, V. Zucoletto, O. N. Oliveira, Jr., J. Colloid Interface Sci., 2008, 319, 100-108 [21] P. H. B. Aoki, P. Alessio, M. L. Rodriguez-Mendez, J. A. De Saja Saez, C. J. L. Constantino, Langmuir, 2009, 25, 13062-13070 [22] J. A. Castillo, A. Pinazo, J. Carilla, M. R. Infante, M. A. Alsina, I. Haro, P. Clapes, Langmuir, 2004, 20, 3379-3387 [23] Langmuir, J. Am. Chem. Soc., 1917, 39, 1848-1906 [24] R. D. Smith, J. C. Berg, J. Colloid Interface Sci., 1980, 74, 273-286 [25] J. Miñones Jr., S. Pais, J. Miñones, O. Conde, P. Dynarowicz-Łątka, Biophysical Chemistry, 2009, 140, 69-77 [26] P. Dynarowicz-Łątka, K. Hąc, Colloids Surf. B, 2004, 37, 21-25 [27] T. H. Chou, C. H. Chang, Langmuir, 2000, 16, 3383-3390 [28] B. M. Discher, W. R. Schief, V. Vogel, S. B. Hall, Biophys. J., 1999, 77, 2851-2861 [29] U. Paddeu, S. Erokhin, C. Nicolini, Thin Solid Films, 1996, 254, 252-256 [30] F. Vilallonga, Biochim. Biophys. Acta, 1968, 163, 290-300 [31] Angelova, D. Vollhardt, R. Ionov, J. Phys. Chem., 1996, 100, 10710-10720 [32] R. H. Tredgold, Order in thin molecular films, Cambridge University Press, Cambridge, 1994 [33] Ulman, An introduction to ultrathin organic films: from Langmuir–Blodgett to selfassembly, Academic Press, San Diego, 1991; A. Ulman,. Thin films: self-assembled monolayers of thiols (thin films), Academic Press, San Diego, 1998 [34] F. Davis, S, P. J. Higson, Biosens. Bioelec., 2005, 21, 1-20 [35] R. Traiphol, N. Charoenthai, T. Srikhirin, D. Perahia, Synth. Met., 2010, 160, 13181324 [36] T. M. Nobre, F. J. Pavinatto, M. R. Cominetti, H. S. Selistre de-Araujo, M. E. D. Zaniquelli, L. M. Beltramini, BBA-Biomembranes, 2010, 1798, 1547-1555 [37] Q. He, J. Li, Biochemical and Biophysical Research Communications, 2003, 300, 541545 [38] K. A. Marx, Biomacromolecules, 2003, 4, 1099-1120 [39] C. K. O‟Sullivan, G. G. Guilbault, Biosens. Bioelec., 1999, 14, 663-670 [40] R. Maget-Dana, Biochim. Biophys. Acta Biomembr., 1999, 1462, 109-140 [41] H. G. Tompkins, W. A. McGahan,. Spectroscopic ellipsometry and reflectometry: a user’s guide, Wiley-Interscience, 1999 [42] C.-K. Shin, H. Lee, Synth. Met., 2004, 149, 177-181 [43] B. J. Schwartz, Annu. Rev. Phys. Chem., 2003, 54, 141-172 [44] T.-Q. Nguyen, I. B. Martini, J. Liu, B. J. Schwartz, J. Phys. Chem. B, 2000, 104, 237255


149

[45] R. Traiphol, N. Charoenthai, Synth. Met., 2008, 158, 135-142 [46] R. Traiphol, N. Charoenthai, T. Srikhirin, T. Kerdcharoen, T. Osotchan, T. Maturos, Polymer, 2007, 48, 813-826. [47] R. Traiphol, N. Charoenthai, P. Manorat, T. Pattanatornchai, T. Srikhirin, T. Kerdcharoen, T. Osotchan, Synth. Met., 2009, 159, 1224-1233. [48] S. Tretiak, A. Saxena, R. L. Martin, A. R. Bishop, J. Phys. Chem. B, 2000, 104, 70297037 [49] J. Mou, J. Yang, Z. Zhao, FEBS Lett., 1996, 381, 161–164 [50] D.I. Cherny A. Fourcade, F. Svinarchuk, P. E. Nielsen, C. Malvy, E. Delfin, Biophys. J., 1998, 74, 1015–1023 [51] S. F. Oppenheim, J. M. Studts, B. G. Fox, J. S. Dordick, Appl Biochem Biotechnol., 2001, 90,187-197 [52] M. T. Ru, J. S. Dordick, J. A. Reimer, D. S. Clark, Biotechnol. Bioeng., 1999, 63, 233241 [53] M. Klibanov, Trends Biotechnol., 2000, 18, 85-86 [54] T. Knubovets, J. J. Osterhout, A. M. Klibanov, Biotechnol. Bioeng., 1999, 63, 242-248 [55] K. R. Babu, A. Moradian, D. J. Douglas, J. Am. Soc. Mass Spectrom, 2001, 12, 317-328 [56] Y. Guo, D. S. Clark, Biochim. Biophys. Acta, 2001, 1546, 406-411 [57] G.A. Sellek, J.B. Chaudhuri, Enzyme Microb. Technol., 1999, 25, 471–482 [58] Y. Hotta, S. Ezaki, H. Atomi, T. Imanaka, Appl. Environ. Microbiol., 2002, 68, 3925– 3931 [59] D. Pum, U. B. Sleytr, Supramol. Sci., 1995, 2, 193-197 [60] D. Pum, U. B. Sleytr,. Molecular nanotechnology and biomimetics with S-layers, p. 175-209. In U. B. Sleytr et al. (ed.), Crystalline bacterial cell surface proteins. R. G. Landes, Austin, Tex, 1996 [61] B. Wetzer, D. Pum, U. B. Sleytr, J. Struct. Biol. 1997, 119, 123-128 [62] F. Ohnesorge, W. M. Heckl, W. Häberle, D. Pum, M. Sára, H. Schindler, K. Schilcher, A. Kiener, D. P. E. Smith, U. B. Sleytr, and G. Binnig, Ultramicroscopy, 1992, 42-44, 1236-1242 [63] D. J. Müller, W. Baumeister, and A. Engel., J. Bacteriol., 1996, 178, 3025-3030 [64] H. J. Butt, K. H. Downing, and P. K. Hansma, Biophys. J. ,1990, 58, 1473-1480 [65] S. Scheuring, P. Ringler, M. Borgnia, H. Stahlberg, D. J. Müller, P. Agre, and A. Engel., Z. EMBO J. 1999, 18, 4981-4987 [66] C. Yuan and L.J. Johnston. Biophys. J., 2000, 79, 2768–2781 [67] M. Baron, A. F. Lubambo, V. M. G. Lima, P. C. de Camargo, D. A. Mitchell, N. Krieger, Microsc. Microanal., 2005, 11, 74-77 [68] R. Singhal, A. Chaubey, T. Srikhirin, S. Aphiwantrakul, S. S. Pandey, B. D. Malhotra, Cur. Appl. Phys., 2003, 3, 275-279 [69] Arya, U. J. Krull, M. Thompson, H. E. Wong, Anal. Chim. Acta, 1985, 173, 331-336 [70] J. Anzai, J. Hashimoto, T. Osa, T. Matsuo,.Anal. Sci., 1988, 4, 247-250 [71] M. Sriyudthsak, H. Yamagishi, T. Morizumi, Thin Solid Films, 1988, 160, 463-470 [72] H. Tsuzuki, T. Watanabe, Y. Okawa, S. Yoshida, S. Yano, K. Koumoto, M. Komiyana, Y. Nibei, Chem. Lett., 1988, 8, 1265-1268 [73] Y. Okahata, T. Tsuruta, K. Ijiro, K. Ariga, Langmuir, 1988, 4, 1373-1375 [74] D. G. Zhu, M. C. Petty, H. Ancelin, J. Yarwood, Thin Solid Films, 1989, 176, 151-156 [75] J. Anzai, S. Lee, T. Osa, Makromol. Chem. Rapid Commun., 1989,10, 167-170

150


[76] F. Antolini, S. Paddeu, C. Nicolini, Langmuir, 1995, 11, 2719-2725 [77] S. Paddeu, A. Fanigliulo, M. Lanzi, T. Dubrovsky, C. Nicolini, Sens. Actuat. B, 1995, 24, 876-882 [78] G. Gupte, V. Rajendran, P. Atanossov, Electroanalysis, 2002, 15, 1577-1583 [79] R. Singhal, W. Takashima, K. Kaneto, S. B. Samanta, S. Annapoorni, B. D. Malhotra, Sens. Actuat. B, 2002, 86, 42-48 [80] T. Goto, R. F. Lopez, O.N. Oliveira, L. Caseli, Langmuir, 2010, 26, 11135-11-139 [81] L.Caseli, A. C. Perinotto, T. Viitala, V. Zucolotto, O. N. Oliveira, Langmuir, 2009, 25, 3057-3061 [82] J. Cabaj, K. Idzik, J. Sołoducho, A. Chyla, J. Bryjak, J. Doskocz, Thin Solid Films, 2008, 516, 1171-1174 [83] T.F. Schmidt, L. Caseli, T. Viitala, O. N. Oliveira, BBA-Biomembranes, 2008, 1778, 2291-2297 [84] J. Cabaj, J. Soloducho, A. Chyla, J. Bryjak, K. Zynek, Sens. Actuat. B, 2009, 136, 425431

In: Langmuir Monolayers … Editors: Jennifer A. Sherwin

ISBN: 978-1-61122-461-0 ©2011 Nova Science Publishers, Inc.

Chapter 5

ADSORPTIVE CHARACTERISTICS OF BOVINE SERUM ALBUMIN ONTO CATIONIC LANGMUIR MONOLAYERS OF SULFONATED POLY (GLYCIDYLMETHACRYLATE)GRAFTED CELLULOSE: MASS TRANSFER ANALYSIS, ISOTHERM MODELING AND THERMODYNAMICS T. S. Anirudhan and P. Senan Department of Chemistry, University of Kerala, Trivandrum, India

ABSTRACT Investigation on adsorption behaviour of Bovine Serum Albumin (BSA) on polymeric adsorbent materials is critical for many analytical and biomedical applications. In the present study a novel adsorbent poly(glycidylmethacrylate)-grafted-cellulose having sulfonate functional groups (PGMA-g-Cell-SO3H) was prepared by graft copolymerization of glycidylmethacrylate (GMA) onto cellulose in the presence of ethyleneglycoldimethacrylate as crosslinker using α,ά-azobisisobutryronitrile as initiator followed by the introduction of sulfonic acid groups through ring opening reaction of the epoxide groups of the grafted GMA with sodium sulfite–isopropanol–water mixture. The original and the modified materials were characterized by means of FTIR, SEM, XRD and BET analysis. Adsorption characteristics of BSA onto PGMA-g-Cell-SO3H were investigated under different optimized conditions of pH, contact time, initial BSA concentration, adsorbent dose and temperature. The maximum value of BSA adsorption was found to be 49.95 and 72.07 mg/g for an initial concentration of 100 and 150 mg/L, respectively at pH 4.5. Kinetic studies showed that the equilibrium conditions were achieved within 3 h. The kinetic data obtained at different concentrations and temperatures were analyzed using a pseudo-first-order and pseudo-second-order  Corresponding author, Tel : +914712308682, E-mail address : [email protected] (T. S. Anirudhan)

152

T. S. Anirudhan and P. Senan equation. The adsorption process followed pseudo-second-order kinetics. The experimental kinetic data were correlated by the external mass transfer and intraparticle mass transfer diffusion models. The intraparticle mass transfer diffusion model gave a better fit to the experimental data. Experimentally obtained isotherms were evaluated with reference to Langmuir, Freundlich and Sips equations. The isotherm data were best modelled by the Langmuir isotherm equation and the maximum monolayer adsorption capacity was found to be 124.85 mg/g at 30 °C. Thermodynamic study revealed an endothermic adsorption process. The negative ΔG° values indicate feasible and spontaneous adsorption of BSA onto PGMA-g-Cell-SO3H. The positive and small value of enthalpy change ΔHo (9.50 kJ/mol) indicates the endothermic nature of adsorption primarily through weak physical forces between adsorbent and adsorbate. The positive and small value of entropy change, ΔSo (185.52 J/mol/K) indicates that the order less nature of adsorption system increases with adsorption of BSA onto adsorbent surface. Also at all temperatures ΔHo Sips > Freundlich. The results obtained with the Langmuir isotherm show that an increase in temperature within the range studied increased the maximum adsorption capacity and increased the value of the Langmuir constant. This indicates that the adsorption capacity and the affinity between the active sites and BSA increase with increasing temperature. The value of b, relating to the binding energy, also increases as the temperature increases, suggesting the contribution of stronger binding sites at higher temperature conditions. As temperature increases, the weaker binding sites are occupied first and that the binding strength increases with increasing degree of site occupation [35]. The Langmuir adsorption model assumes that the molecules are adsorbed at a fixed number of well-defined sites, each of which can only hold a single molecule. All adsorption sites have the same affinity for adsorbate, and there are no lateral interactions between molecules adsorbed to adjacent sites [24]. The Langmuir isotherm model has most widely been used as the simple adsorption model for various adsorbent–protein systems [36], even though the adsorption mechanism of proteins may not strictly obey the assumptions of the Langmuir model [37]. As seen from the figure an increase in the BSA concentration in the adsorption medium led to an increase in the amount of adsorbed BSA on the PGMA-g-CellSO3H but this relation leveled off at around 350 mg/L BSA in the adsorption medium. This could be explained by saturation of interacting group of PGMA-g-Cell-SO3H with the adsorbed BSA molecules, as a result of which maximum adsorption capacity is reached. The adsorption capacity (qmax) corresponding to all the three models exhibited significant increase with rise in temperature, which is an indication of the endothermic nature of the process. As deduced from data in Table 2, the maximum adsorption capacity of BSA at 30 °C on PGMAg-Cell-SO3H is 124.85 mg/g. Table 2. Isotherm parameters for the adsorption of BSA onto PGMA-g-Cell-SO3H Langmuir o Temp Q o

( C ) (mg/g)

10 20 30 40

126.01 132.57 141.67 155.37

b R (L/mg)

χ

0.23 0.998 0.32 0.999 0.50 0.998 0.71 0.997

0.2 0.3 0.4 0.3

2

2

Freundlich KF 1/n R2

72.7 78.6 83.4 92.6

0.097 0.095 0.099 0.105

χ

2

0.776 8.5 0.832 7.2 0.899 6.9 0.905 5.5

qmax bs (mg/g) 127.6 130.5 139.7 140.5

0.219 0.269 0.356 0.654

Sips 1/ns

R2

χ2

0.789 0.882 0.901 0.978

0.921 0.934 0.944 0.951

1.5 2.5 3.5 4.7

The Langmuir parameters given in Table 2 can be used to predict the affinity between the sorbate and sorbent using dimensionless separation factor (RL):

RL 

1 1  b C0

(14)

Adsorptive Characteristics of Bovine Serum Albumin …

169

where b is the Langmuir isotherm constant relating to binding energy and Co is the initial solute concentration. The values of RL at 30 ºC were determined and were formed to be 0.0057, 0.0038, 0.0028, 0.0023, 0.0019, 0.0016, 0.0014, 0.0012 and 0.0016 at an initial BSA concentration of 100, 150, 200, 250, 300, 350, 400, 450, 500 and 550 mg/L, respectively. The RL values for the present experimental data fell between 0 and 1, which is indicative of favorable adsorption of BSA onto PGMA-g-Cell-SO3H. These results indicate that the adsorption of BSA is more favourable at higher initial BSA concentration than lower ones. Earlier workers have already been demonstrated that the Langmuir isotherm model gives adequate results for the adsoption of BSA onto different adsorbents. According to Langmuir model, the maximum adsorption capacity obtained for BSA was reported to be 39.49, 48.9 and 68.7 mg/g for adsorption onto modified chitosan [38], polypyrrole-based adsorbents doped with chloride [24] and macroporous poly(glycidylmethacrylate–triallyl-isocyanurate– divinylbenzene) matrix [39], respectively. Inorder to determine the theoretical number of stages for the adsorption of BSA from aqueous solution, operational lines are drawn with a slope of −V/m (where V is the volume of BSA solution and m is the mass of PGMA-g-Cell-SO3H). The operational lines join Co,qo to Ce,qe at equilibrium and effect of changing of Co with constant mass generates a series of operating lines as shown in Fig. 9. The operating lines having a slope V/m=−0.5 were drawn through two BSA initial concentrations, 200 and 300 mg/L. The values of qe obtained from the operating lines (96.2 and 118.1 mg/g) and from the Langmuir isotherm equation (95.4 and 117.3 mg/g) exhibit reasonable correlation for initial concentrations, 200 and 300 mg/L. Also it was found that in both cases, ~ 100% BSA adsorption can be achieved in two stages. 140 30 °C

120

Sorbent dose : 2 g/ L Initial pH :4.5 Agitation time :3 h

qe(mg/g)

100 80 60 40 20 0 0

50

100

150

200

250

300

350

Ce (mg/L)

Figure 9. The operational lines along with the theoretical number of stages for the adsorption of BSA onto PGMA-g-Cell-SO3H

3.7. Thermodynamic Studies In order to explain the effect of temperature on the adsorption thermodynamic parameters, standard free energy (ΔG°), standard enthalpy (ΔH°), and standard entropy (ΔS°) were determined. To calculate the value of the parameters, the following equations were used:

170

T. S. Anirudhan and P. Senan G0=-RTln b

ln b 

0

S H  R RT

(15) 0

(16)

where R is the ideal gas constant 8.314 (J/mol/K) and T is temperature (K). The values of ln b were found to be 18.25, 18.43, 18.55 and 18.64 at 10, 20, 30 and 40 °C, respectively. Plotting of ln b vs 1/T (van‟t Hoff plot) gives a straight line with a slope and intercept equal to ΔH°/RT and ΔS°/R, respectively. The ΔG° values for BSA adsorbed on PGMA-g-Cell-SO3H were calculated for each temperature and were found to be -42.94, -44.91, -46.73, -48.51 kcal/mol for 10, 20, 30 and 40 °C, respectively. The Gibbs free energy indicates the spontaneity of the adsorption process, where higher negative values reflect a more energetically favorable adsorption process. The negative ΔG° values obtained for each temperature in this study confirm the feasibility of the adsorbent and spontaneity of adsorption of BSA onto PGMA-g-Cell-SO3H. Also the increase in the negative ΔGo with temperature suggests that the adsorption is more favorable at high temperatures. Therefore, high temperatures favor the adsorption of BSA onto PGMA-g-Cell-SO3H. The ΔSo value for the adsorption of BSA to PGMA-g-Cell-SO3H was found to be 185.52 J/mol/K. Positive value of ΔSo indicates an increase in the total disorder of the system during adsorption [40]. The calculated ΔHo value of the system for the interaction for BSA with PGMA-g-Cell-SO3H was 9.50 kJ/mol indicates that BSA adsorption is endothermic in nature, which is supported by the increase in the adsorption onto PGMA-g-Cell-SO3H with a rise in temperature, as shown in Fig. 7. Isothermal data at four different temperatures were used to estimate the isosteric heat of adsorption process (ΔHx) and is calculated using Clausius–Clapeyron equation [41]

d ln Ce  H x  dt RT 2

(17)

The plots of ln Ce versus 1/T (Figure not shown) for different amounts of BSA adsorption were found to be linear and the values of ΔHx were measured from the slopes of the plots. The values of ΔHx were found to remain almost constant (~ 26.45 kJ/mol) with increase in surface loading from 60.00 to 105.00 mg/g. This indicates that the surface of PGMA-g-Cell-SO3H is energetically more or less homogeneous and the lateral interactions between adsorbed BSA ions do not exist.

3.3. Design of Single Stage Batch Reactor Scheme 2 represents the schematic diagram of the single stage batch adsorption system designed from the adsorption isotherm data. The solution containing Co (mg/L) of BSA in V(L) of water is reduced to C1 (mg/L) after the adsorption process. During the adsorption process W (g) of PGMA-g-Cell-SO3H is added, and the BSA concentration on PGMA-gCell-SO3H increases from qo (initially) to qe. The mass balance equation of BSA adsorption from the aqueous solution to that loaded on the adsorbent is:


C1 C0 V  qt  qo W

171 (18)

When fresh adsorbent is used, q0 = 0 and if the system is allowed to reach equilibrium, then Eq. (18) can be expressed as:

C1  C o  W  V qe

(19)

Substituting for qe from Eq. (11) and rearranging gives:

C  Co [1  bCe ] W  1 V Qo bC e

(20)

C  Co [1  1.73Ce ] W  1 V 212.24 C e

(21)

This equation can be used to calculate the mass of PGMA-g-Cell-SO3H required to achieve certain percentage removal by treating a definite volume of BSA initial concentration Co. Fig. 10 represents the experimental and theoretical masses of PGMA-g-Cell-SO3H against different volumes for different percentages of removal of BSA and mass of PGMA-g-CellSO3H against different concentrations and different volumes for the removal of BSA (>99.0%) from aqueous solutions. The amounts of adsorbent calculated using the model Eq. (11) match those observed experimentally for different volumes of effluent and concentrations. W g PGMA-g-Cell-S O 3H

qo mg of BS A in W g of PGMA-g-Cell-S O 3H

V L of aqueous solution Co mg of BS A in 1 L of aqueous solution

V L of aqueous solution C t mg of BS A in 1 L of aqueous solution

qe mg of BS A in W g of PGMA-g-Cell-S O 3H

W g PGMA-g-Cell-S O 3H

Scheme 2. Diagram of a single-stage batch reactor

172

T. S. Anirudhan and P. Senan Experimental

3

Calculated

99.6%

Mass of adsorbent (g)

Mass of adsorbent (g)

20

95.60% 88.80% 10

82.70%

A

Experimental

2.5

Calculated

125 mL 100 mL

2

75 mL 50 mL

1.5 1 0.5

B

0

0 0

5

10

15

0

50

Volume of effluent (L)

100

150

200

250

Co (mg/L)

Figure 10. (A) Mass of PGMA-g-Cell-SO3H against different volumes for different percentages of adsorption of BSA and (B) mass of PGMA-g-Cell-SO3H against different concentrations and different volumes for adsorption of BSA from aqueous solutions.

Adsorption/Desorption, %

150

Initial concentration :100 mg/L pH : 4.5 Equilibrium time : 3 h

Adsorption Desorption

100

50

0 1

2

3

4

No of cycles Figure 11. Adsorption-desorption cycles of BSA

3.9. Desorption Experiments The use of an adsorbent in the adsorption of proteins depends not only on the adsorption capacity, but also on how well the exhausted adsorbent can be regenerated and used again. To test repeatedly using the adsorbent and to recover the adsorbed BSA, the recovery and regeneration tests were conducted with different types of desorbing agents (NaCl, CH3COOH, KSCN, sodium acetate buffer and sodium lauryl sulfate) through batch adsorption technique. The percentage desorption of BSA from spent adsorbent was found to be 60.1, 93.1, 79.5, 80.1, and 81.2% for 0.1 M concentration of NaCl, CH3COOH, KSCN, sodium acetate buffer and sodium lauryl sulfate, respectively. CH3COOH was found to be more effective desorbing agent and hence desorption of BSA from PGMA-g-Cell-SO3H was carried out with different concentrations of CH3COOH. The % desorpion was found to be


173

55.4, 69.9, 77.5, 93.1 and 98.2% for 0.025, 0.05, .075, 0.1 and 0.2 M CH3COOH, respectively. The adsorption/desorption cycles were repeated for 4 cycles using the same amount of adsorbent. The results of regeneration study of BSA by CH3COOH solution are shown in Fig. 11. The results indicate that the adsorbent can be effectively reused upon treatment with 0.2 M CH3COOH solution, which may be attributed to the displacement of BSA bound to the adsorbent with H+ ions. After four cycles the adsorption capacity of PGMA-g-Cell-SO3H decreased from 49.1 mg/g (99.9%) to 44.7 mg/g (95.1%), while the recovery of BSA decreased from 98.2 % in the first cycle to 94.1 % in the fourth cycle. These results show that PGMA-g-Cell-SO3H can be repeatedly used in protein adsorption/desorption without much noticeable losses in its initial adsorption capacity.

CONCLUSION The present investigation showed that the PGMA-g-Cell-SO3H prepared from cellulose was an effective adsorbent for the adsorption of BSA from aqueous solutions. The adsorption behaviour of BSA onto PGMA-g-Cell-SO3H was investigated under various reaction conditions. The pH of the medium has an important effect on the adsorption equilibrium of BSA, and maximum adsorption occurs at pH 4.5. Kinetic studies showed that the equilibrium conditions were achieved within 3 h. The kinetic data were described using pseudo first-order and pseudo second-order equations and pseudo second-order equation was found to explain the kinetics most effectively. It was also found that the intraparticle mass transfer diffusion played an important role in the adsorption. The isotherm data were best modeled by the Langmuir isotherm equation and the maximum monolayer adsorption capacity was found to be 124.85 mg/g at 30 °C. Thermodynamic parameters were calculated and the results show that the adsorption process is spontaneous and endothermic in nature. The isosteric heat of adsorption process (ΔHx) was investigatd using Clausius–Clapeyron equation and the values remained almost constant, suggesting that the surface of PGMA-g-Cell-SO3H is energetically more or less homogeneous. More than 98.0% of the adsorbed BSA was desorbed using 0.2 M CH3COOH as the elution agent. Repeated BSA adsorption/elution processes showed that PGMA-g-Cell-SO3H can be used for the separation of BSA in aqueous solutions. Thus PGMA-g-Cell-SO3H seems to provide an adequate approach to adsorb BSA from aqueous solutions.

ACKNOWLEDGMENTS The authors are thankful to the Department of Chemistry, University of Kerala, Thiruvananthapuram, India, for providing the laboratory facilities.

REFERENCES [1]

Ball, V.; Schaaf, P.; Voegel, J.C. Malmsten, M. (Ed.), Biopolymers at interfaces. In: Surfactant Science Series, Marcel Dekker, New York, 1998; Vol. 75. pp. 453–484

174 [2] [3] [4] [5] [6] [7] [8] [9] [10] [11] [12] [13] [14] [15] [16] [17] [18] [19] [20] [21] [22] [23] [24] [25] [26] [27] [28] [29] [30] [31] [32] [33] [34] [35] [36] [37]

T. S. Anirudhan and P. Senan Andrade, J. D. Protein Adsorption, Plenum, New York, 1985; Vol. 2. pp. 1–80. Hu, J.; Songjun, L.; Bailing, L. Biochem. Eng. J. 2005, 23, pp. 259–263 Suen, S. Y.; Lin, S. Y.; Chiu, H. C. Ind. Eng. Chem. Res. J. 2000, 39, 478-487. Hao, W.; Wang, J.; Li, J. J. Chromatographia. 2004, 60, pp. 449–454. Zhou, D.; Zhang, L.; Zhou, J.; Guo, S. Water Res. 2004, 38, pp. 2643-2650. Tanyolaç, D.; Sönmezışık, H.; Özdural, A.R. Biochem. Eng. J. 2005, 22, pp. 221-228 Liu, C.; Bai, R. J.Memb. Sci. 2005, 267, pp. 68-77 Purohit, G.; Sakthivel, T.; Florence, A.T. J. Pharmaceutics. 2003, 254, pp. 37-41. Zhao, Z.P.; Wang, Z.; Wang, S.C. J. Memb. Sci. 2003, 217, pp. 151-158. Kim, M.; Saito, K.; Furusaki, S.; Sugo, T. J. Membr. Sci. 1993, 85, pp. 21–28. Yu, Y.H.; Sun, Y. J. Chromatrogr. A 1999, 855, pp. 129–136. Kim, M.; Saito, K.; Sugo, T.; Okamoto, J. J. Membrane Sci. 1991, 56, pp. 289–302. Hebeish, A. ; Guthrie, J.T. Polymers - Properties and Applications. Springer-Verlag, Berlin Heidelberg, New York. 1981, 4 Sidney, S. Quantitative Organic Analysis, 3rd ed., John Wiley and Sons, New York, 1967; pp. 124-127 Schwarz, A.; Driscoll, C. T.; Bhanet, A. K. J. Colloid. Interface Sci. 1984, 97(1), pp. 55-61. Shubha, K. P.; Raji, C.; Anirudhan, T. S. Water Res. 2001, 35(1), pp. 300-310. Alberti, A.; Bertini, S.; Gastaldi, G.; Iannaccone, N.; Macciantelli, D.; Torri, G.; Vismara, E. Europ. Polym. J. 2005, 41, pp. 1787–1797 Silverstein, R. M. ; Bassler, G. C.; Terrence, C. M. Spectroscopic identification of organic compounds. John Wiley and Sons, Inc. New York. 1991. Wang, F.; Yang, Z.; Zhou, Y.; Weng, S.; Zhang, L.; Wu, J. J. Molec. Struc. 2006, 794, pp. 1–11 Anirudhan, T. S. ; Jalajamony, S. ; Suchithra, P. S. Colloids and Surf. A: Physicochem. Eng. Aspects. 2009, 335, pp. 107–113 Joon, T. O.; Kim, J. H. Enzyme Microb. Technol. 2000, 27, pp. 356–361. Haynes, C. A.; Norde, W. Colloids Surf. B. 1994, 2, pp. 517-566. Zhang, X.; Bai, R.; Tong, Y. W. Sep. Purif. Tech. 2006, 52, pp. 161–169 Hu, J.; Li, S.; Liu, B. Biochem. Eng. J. 2005, 23, pp. 259–263 Lagergren, S.; Svenska, B. K. Zur theorie der sogenannten adsorption geloester stoffe, Veternskapsakad Handlingar 1898, 24 (4), pp. 1–39. Ho, Y. S.; Mckay, G. Process Biochem. 1999, 34, pp. 451–465. Ruthven, D. M. Principles of Adsorption and Adsorption Processes, Wiley, New York, 1984. McKay, G.; Otterburn, M. S.; Sweeny, A. G. Water Res. 1981, 15, pp. 327-331. Urano, K.; Tachikawa, H. Ind. Eng. Chem. Res. 1991, 30, pp. 1897-1899. Michelson, L. D.; Gideon, P. G.; Pace, E. G.; Kutal, L. H. Bulletin No.74 Office of Water Research and Technology. U.S. Department of Industry. 1975. Langmuir, I. J. Am. Chem. Soc. 1918, 40, pp. 1361-1403. Freundlich, H. M. F. J. Phys. Chem. 1906, 57, pp. 385-470. Sips, R. J. Chem. Phys. 1948, 16, pp. 490-495. Ruzic, I. Marine Chem. 1996, 53, pp. 1-15. Fernandez, M. A.; Carta, G. J. Chromatogr. A. 1996, 746, pp. 169-183. Haynes, C. A.; Norde, W. Colloids Surf. B. 1994, 2, pp. 517-566.

Adsorptive Characteristics of Bovine Serum Albumin … [38] [39] [40] [41]

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Fu, G.; Zhao, J.; Yu, H.; Liu, L.; He, B. React. Func. Polym. 2007, 67, pp. 442–450 Yu, Y.; Sun, Y. J. Chromatogr. A. 1999, 855, pp. 129–136 Finette, G. M. S.; Mao, Q.M.; Hearn, M. T. W. J. Chromatogr. A. 1997, 763, pp. 71-90. Young, D. M.; Crowell, A. D. Physical Adsorption of Gases. Butterworth, London: 1962

In: Langmuir Monolayers … Editors: Jennifer A. Sherwin

ISBN: 978-1-61122-461-0 ©2011 Nova Science Publishers, Inc.

Chapter 6

ELECTROCHEMISTRY OF POLYMERIC THIN FILMS PREPARED BY LANGMUIR-BLODGETT TECHNIQUE *

Paolo Bertoncello Department of Chemistry, The University of Warwick, United Kingdom

ABSTRACT The utilization of the Langmuir-Blodgett (LB) technology for the fabrication of engineered supramolecular thin films has received an exceptional development in these last years due to possibility of different applications in materials science ranging from nanotechnology to biosensors. The materials fabricated by LB technology provide an accurate control of the order at the molecular level. The main objective of this chapter is to give an overview of the electrochemical properties of a particular class of polymeric thin films such as conducting polymers and ionomer polymers and describe the potentialities of some recent electrochemical technique for nanotechnological applications mainly scanning electrochemical technique (SECM) and SECM combined to Langmuir trough.

LANGMUIR-BLODGETT TECHNIQUE This technique originates his name from the pioneeristic works of I. Langmuir and K. Blodgett that, in 1917 and in 1935, respectively, studied the properties of organic surfactants (fatty acids) spread from solution onto the air-water interface of a trough [1, 2]. In particular, *

A version of this chapter also appears in Progress in Electrochemistry Research, edited by Magdalena Nuñez, published by Nova Science Publishers, Inc. It was submitted for appropriate modifications in an effort to encourage wider dissemination of research.

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they found that fatty acids having long chains can form a molecular monolayer at the airwater interface, resulting in an overall orientation of the molecules perpendicular to the water surface. By using a barriers system, it is possible to control the area available per molecule. The 2-dimensional pressure exerted on the barriers by the molecules can be measured allowing the pressure-area relationship. By monolayer compression, it is possible to pack the film and transfer it onto a solid substrate. There are different techniques to transfer monolayer: for films having low viscosity, the most used is the Langmuir-Blodgett technique, in which the substrate is simply dipped and raised vertically while maintaining constant the surface pressure (figure 1 A-D). This procedure can be repeated several times resulting in the formation of a multilayers structure. In the standard Langmuir-Blodgett transfer process, it will be built up centrosymmetrical or Y-type films. Other two kind of multilayers structure can be possible: the first one called Z-type, if the film is transferred at the upstroke and X-type if the monolayer is transferred at the downstroke [3, 4].

Figure 1. Schematic of the Langmuir-Blodgett technique: deposition of amphiphilic molecule on the water subphase with a solid substrate (A), monolayer compression (B), monolayer transfer to both side of substrate (C), a multilayers structure is built up by repeating monolayer transfer (D), LangmuirSchaefer method (horizontal lifting) (E); different types of multilayers structures (X,Y and Z). From Ref. [7], Reproduced by permission of the PCCP Owner Societies, Copyright (1999)

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Usually, the vertical dipping technique is the most successful for liquid-like monolayers such as phospholipids or fatty acids having long chains. Instead, if the film is more viscous and there is formation of aggregates or crystallites, the vertical transfer can be difficult: in this case is more preferable a horizontal dipping of the substrate thus leading to a monolayer transfer. This approach is called Langmuir-Schaefer method [5]. This approach were then transferred in the 60‟ by Kuhn et al to exploit the LB formation of dye containing surfactants and in these last decades in the field of molecular electronics [6]. Currently, in the organic electronics, the focus of the research is to emphasize the need to control the micro and nanoscale structure of molecular architectures [7]. Recently, it has been demonstrate the possibility to fabricate LB films of ionomeric polymers [8-11]. Among perfluorinated ionomers, Nafion® (cations exchanger) is still object of study due to the different possible application, ranging from fuel cells to chemically modified electrodes [9-21]. Nafion® (Trademark of DuPont de Nemours Co.) (Figure 2) is constituted by a long fluorocarbon chains intercalated with oxygen groups and terminating with a sulfonated group. The sulfonated group is responsible of the partial solubility in water and confers to the polymer good cations exchange properties. Nafion® is expected to attain a micellar conformation with the polar sulfonated groups located on the surface of the micelles and the hydrophobic fluorocarbon chains in the inner part [22]. These properties of cations exchange has been utilized to fabricate chemically modified electrodes by incorporation of different molecules having cationic character for the determination of heavy metals in the water and also to preconcentrate biological molecules such as proteins and cytochromes [9-11]. Figure 3 shows the pressure-area isotherms of Nafion obtained in subphases containing different electrolytes.

Figure 2. formula of Nafion

The addition of strong electrolytes in the subphase is a key factor for the obtaining of a stable and reproducible isotherm. In particular, the degree of condensation of the LB film depends on the specific interactions between Nafion and the cations dissolved in the subphase. The degree of condensation follows the sequence Na+>H+>Li+, in agreement to the ion exchange selectivity coefficients [23]. This fact suggests that the factor, which favours the ion exchange incorporation, also helps the aggregation of the interfacial films at the air water interface. Another important factor influencing the interfacial film at the air-water interface is the cationic charge utilized in the subphase as demonstrated recently in the case of the incorporation of TiO2 into Nafion LB films [24]. The electrochemical properties of Nafion LS

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fims have been investigation employing methylviologen as cationic electroactive specie: Figure 4 reports the voltammograms of 40 Nafion LS films after loading in 10-5 M MV2+;

Figure 3. Pressure–area (–A) isotherm curves of Nafion at different subphases: (1) H2O, (2) 0.1 M NaCl, (3) 0.1 M NaCl + HCl (pH 2), (4) HCl (pH 2), (5) 0.1 M LiClO4, (6) 0.1 M Ca(NO3)2 ; barrier speed: 1.67 mm s-1. From Ref. [8], Reproduced by permission of the PCCP Owner Societies, Copyright (2002)

Figure 4. CVs of 40 Nafion LS films at different scan rates after loading in 10-5 M MV2+, supporting electrolyte 10-2 M NaNO3. From Ref. [8], Reproduced by permission of the PCCP Owner Societies, Copyright (2002)


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The analysis of the voltammograms indicate a linear dependence of the peak current on the square root of the scan rate, v, between 40 mV s-1 and 200 mV s-1. At scan rate lower than 40 mV -1 and in particular between 5 and 20 mV -1 the peak current depends directly on the scan rate. In this last case the peak separation, ΔEp is 30 mV, meanwhile in the first case the peak separation is about 60 mV. These data evidence the occurrence of a one-electron reversible reduction and a process diffusion controlled at v>40 mV s-1. The following equation correlates the thickness of the diffusion layer to the scan rate: δ= (RTDapp/Fv)1/2

4,0

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scan rate (mV/s)

Figure 5. CVs recorded at 10 layers LB Nafion-cyt c in 0.01 M phosphate buffer (pH 7.0), at different scan rates: 2, 5, 10, 20, 50, 100 mV s-1 (a); Dependence of the anodic peak current on the scan rate (b). Reprinted from Ref. [11], Copyright (2004) with permission from Elsevier.

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Where δ is the diffusion layer thickness, Dapp is the apparent diffusion coefficient, v the scan rate, R and T the gas constant and the temperature, respectively [18]. When the diffusion layer is smaller than the film thickness (at high scan rate), a semiinfinite diffusion condition takes place. In contrast, a surface (or thin-layer like) process is observed at lower scan rate. It is interesting to note that, in the case of very thin films (10 Nafion LS films) a surface process is observed even at higher scan rate as high as 200 mV s-1. Other results point to a proportionality between the amount of MV2+ (calculated by integrating the peak area of the first reduction peak (figure not shown) with the number of layers deposited and then with the amount of Nafion deposited employing LB procedure. In addition, Nafion LS films evidence permselectivity properties, repelling anions (such as [Fe(CN)6]3-, as expected. LB films of perfluorinated ionomer can be used also for the incorporation of biological molecules such as cytochrome c [11]. Figure 5 shows the voltammograms at different scan rate related to 10 Nafion/cytochrome c LB films. It observes a reduction peak between 14 and 19 mV (at scan rate of 5 and 100 mV, respectively) and an oxidation peak at about -10 mV vs Ag/AgCl. The quasi-reversible process is due to the oxidation of the heme group of the cytochrome c accordingly to the following reaction: [cyt c- Fe(III)] + e-  [cyt c-Fe(II)]

(2)

The calculated E1/2 (-0.12 mV) is practically constant respect to the scan rate. Interestingly, this value is more negative than the E1/2 of the cytochrome c, related to other similar systems [25-29] but is very similar to the value reported by Sagara et al., in the case of reduction of cytochrome c adsorbed on gold substrates [30]. A linear relation is observed between the reduction peak current and the scan rate, indicating a thin-layer like controlled process. This approach to incorporate biological molecules is interesting because in this way it is possible to increase the electrons exchange with the electrode surface otherwise impossible by using a solution casting approach [31]. These positive results can now open new possibilities and strategies in electroanalysis. A similar situation is observed in the case of Tosflex®, an anionic perfluorinated ionomer, trademark of Tosoh Co. (Japan) (see Figure 6): As in the case of Nafion®, the addition of strong electrolytes to the subphase changes drastically the shape of the isotherms.

Figure 6. Formula of Tosflex IE-SA 48

In general, the isotherms obtained for Tosflex® seem to have a trend quite similar to those observed in the case of Nafion. This agrees with the similarity in the perfluorinated backbone skeleton present both in Tosflex® and Nafion® structures (see Figure 2 and Figure 6). On the other hand, in contrast, the fact that Tosflex® is an anion exchanger while Nafion®


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is a cation exchanger reflects in the evidence that, for Tosflex®, the successful compression of the interfacial film depends on the nature of the anions added to the subphase. In the case of the isotherms reported in Figure 7, the condensation degree of the interfacial film changes following the sequence Fe(CN)63- > SO42- > COO- > NO3- > Cl- > CH3COO-. Interestingly, this sequence parallels the sequence of the ion-exchange selectivity of anion exchangers [25] so suggesting that the same factor (namely charge/radius ratio) rules both LB films condensation and ion exchange selectivity of Tosflex®.

Figure 7. Pressure–area (–A) isotherms of Tosflex® in different electrolytes as shown in figure. Reprinted from Ref. [10], Copyright (2004) with permission from Elsevier.

Figure 8. CV of 10 Tosflex® LB films deposited in subphase containing 10-4 M [Fe(CN)6]3- after transfer in 10-2 M NaCl; scan rates: 5, 10, 20, 50 mV s-1. Reprinted from Ref. [10], Copyright (2004) with permission from Elsevier.

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The preconcentration and ion-exchange characteristics of Tosflex® LB films were investigated by using an anionic electroactive specie having electrochemical reversibility such as [Fe(CN)6]3-. The reduction peak at 250 mV is due to the one-electron reduction of [Fe(CN)6]3- (Figure not shown) incorporated in the film. In this case the peak current linearly scales with the square root of the scan rate, indicating a diffusion controlled process. Interestingly, the incorporation of the electroactive specie can be performed directly into the film by dissolution of the anion in the subphase. The related voltammogram recorded after transferring in a solution containing only the supporting electrolyte is reported in Figure 8. The shape of the voltammograms and the linear dependence of the peak current on v (for v= 100 mV s-1) indicates a thin-layer like behavior at relatively high scan. This fact can be ascribed to the higher condensation degree of the Tosflex® LB films when Fe(CN)63- is dissolved in the subphase. To note, that the voltammetric signal of Tosflex® LB films remains almost constant after several hours of dipping in supporting electrolyte. This fact is interesting for future application in electrocatalysis. An interesting application of the Langmuir-Blodgett technique has been recently proposed by Moretto et al. for another ionomeric polymer, namely Kodak AQ55 incorporating cytochrome c [4]. The pressure-area isotherms of AQ55 (see formula in Figure 9) in different electrolytes are shown in Figure 10.

Figure 9. formula of AQ 55

Even if the AQ55 isotherms are characterized by a different marked phase transitions than those of Nafion® and Tosflex®, their shapes shows some similarities with the trends observed previously. Curve a shows the isotherm of pure cytochrome c in subphase containing phosphate 0.1 M at pH 7. The isotherm is characterized by a broad trend with a collapse pressure of about 20 mN m-1. This behavior is very similar to the trend of LB films of cytochrome p450 reported in literature [32]. Curve b shows the isotherm of AQ55: the behavior is quite different respect to those observed for Nafion® and Tosflex® isotherms. Even if the trend is steeper than the cytochrome c isotherm, the maximum surface pressure is 25 mN m-1, quite lower than the values recorded for Nafion® and Tosflex® isotherms. Also in this case, the addition of strong electrolytes is a necessary requirement to obtain stable monolayers at the air-water interface. The electrolytes added in the subphase may increase the solubility of the polymer and, at the same time, decrease the electrical repulsions due to the neutralization of the negative charge of the sulfonic groups. The isotherm of the mixed cytochrome c/A55 is reported in curve c; it evidences the typical behavior of mixture of two different compounds having limited miscibility [33]: two different collapse pressures are observed even if an interfacial film is formed between cytochrome c and AQ55. The lower trend observed for the AQ55 isotherms that those of Nafion® and Tosflex® is in agreement with the water solubility of AQ55 [3].


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b Surface pressure / mN m-1

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a 10

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0 200

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400

500

600

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Figure 10. Pressure–area (–A) isotherm of cytochrome c (a), AQ55 (b) and cytochrome c/AQ55 (c). Reprinted from Ref. [11], Copyright (2004) with permission from Elsevier.

Figure 11. Pressure–area (–A) and surface potential isotherms of different PS-PMMA ionomers. Reprinted from Ref. [34], Copyright (2004) with permission from American Chemical Society.

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Recently, copolymer LB films of ionomers were utilized for the detection of dopamine [34]. In Particular, they use poly(styrene-co-methyl mathacrylate) (PS-PMMMA) ionomers with different grades of sulfonation. The results evidence the formation of stable Langmuir monolayer in the range between 6-8% of sulfonation. In Figure 11, the pressure-area isotherms and the surface potential curves are reported.

Figure 12. CVs of dopamine in 0.1 M HCl: bare ITO (a), 31 PS-PMMA 3% LB films and ascorbic acid (AA), (b), 31 PS-PMMA 3% LB films I the presence of AA. Reprinted from Ref. [34], Copyright (2004) with permission from American Chemical Society.

The calculated area per molecule for the copolymers in the condensed phase was found to increase when the degree of sulfonation decrease. The values calculated were found to be 18, 21 and 29 Å2/r.u. for PS-PMMA at 8, 6 and 3%, respectively. Higher percentage of sulfonation evidences material loss to the increase of the water solubility. This fact is


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reflected also in the surface potential behavior curve with the shift of the curve related to PSPMMA 8%. If there is solubility of material, the presence of the ions should decrease the solubility of the ionomer and then to increase the area per molecule accordingly to Osawa [35]. In reality, the presence of the salt in the subphase screens the electrostatic repulsion between the negative charges of the sulfonated groups, leading to a more coiled structure. These results are in agreement with previous report of Bertoncello et al. regarding Nafion LS films [8]. LB films of this copolymer were prepared and tested for the voltammetric determination of dopamine, an important molecule associated with Parkinson‟s disease [36]. These films prevent the interference of the anions similarly to the Nafion LS films [8]. For this reason the PS-PMMA ITO electrode was tested also in the presence of ascorbic acid, the main interference in this kind of application. In the bare ITO, it observes an oxidation and reduction peak at 0.68 V and -0.33 V, respectively. The peaks are related to the oxidation and then reduction of dopamine to dopaminequinone and viceversa and the participation of two electrons [37]. The addition of dopamine in the PS-PMMA electrode causes the appearance of the peaks at 0.31 V and -0.38 V. The oxidation peak is shifted to lower potential (about 0.3 V) evidencing that PS-PPMA acts as electrocatalytic agent for dopamine oxidation. No peaks are observed when 31 PSPMMA LB films were immersed in AA solution. When dopamine is added, it observes a shift of the peak potential due to the interaction of dopamine with ascorbic acid but maintaining the permselectivity respect ot the ascorbic acid. Recently, Ferreira et al. [38] fabricated LB films of polyaniline/ruthenium complexes as modified electrodes for dopamine detection. The way proposed allows avoiding the interference of the ascorbic acid. Dopamine is an important molecule of the mammalian nervous central system. Loss of dopamine inside neurons may result also in Parkinson‟s desease. They use a mixture of PANI and a ruthenium complex, namely mer-[RuCl3(dppb)(py)], were dppb= PPh2 (CH2) 4PPh2 and py= pyridine. In this case, the ruthenium complex acts as modifier electrodes and is used to detect dopamine.

Figure 13. CVs of 21 LB of PANI and PANI/Ruby 10%, scan rate: 0.05 V s -1, supporting electrolyte: 1 M. Reprinted from Ref. [38], Copyright (2004) with permission from Elsevier.

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The redox peak of PANI corresponds to the interconversion between the oxidation states leucoemeraldine to emeraldine. LB films of PANI/Ruby 10% evidences a drop of the peak current due to the decrease of the electroactivity operated by Rubpy. These peaks are attributed to the PANI because, in this range of potential (-0.6 V-0.4 V), rubpy is not electroactive [39]. The peak at about 0.1 V is attributed to quinone-like species [40]. The redox peaks at 0.23 and 0.00 V are associated to the oxidation/reduction of dopamine to dopaminequinone with the gain/loss of two electrons. The fact that the peak appears at lower potential than the bare ITO suggest that PANI and PANI/Rupy 10% are electrocatalysis agents for the oxidation of dopamine. Figure 14 (b) evidences that there is no variation of the peak position with the change of the scan rate. A plot of the peak current with the square root of the scan rate indicates that the electrochemical process is diffusion controlled. Instead, the peak current related to the PANI system at -0.22 V and -0.38 V changes linearly with the scan rate, indicating a thin layer or surface process, characteristic of adsorbed species at the electrode surface [41].

Figure 14. CVs of 21 LB PANI/Ruby 10% electrode; scan rate 0.04 V s-1, supporting electrolyte 1 M HCl, without dopamine (dotted line) and in presence of 4.8 10-4 M dopamine (dashed line) (a); CV as (a) at different scan rates (b);relation between anodic peak current and square root of the scan rate (c). Reprinted from Ref. [38], Copyright (2004) with permission from Elsevier.

The PANI/Rupy system was then employed to detect dopamine. The calibration curve (figure not shown) evidences a linearity in the range between 10-5 M to 10-3 M and a detection


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limit equal to 4 10-5 M. Further investigations demonstrated that the electrocatalytic effect is observed also in the PANI system: even if the addition of Rupy does not improve the electrocatalytic effect of PANI, the addition of Rupy give some advantages such as transferability and stability of PANI films [38, 39]. The system was tested also to understand the effect of the interferents such as inorganic anions (Cl-, Br-,), and many others [27]. The data evidence the possibility to detect dopamine with a concentration of ascorbic acid equal to three times the concentration of dopamine. This system is comparable to other different system reported in literature [36, 42-43] Another interesting way to immobilize cytochrome c by using LB technique has been recently proposed by Oh et al. [44]. Photosensitive polyimide films on gold substrated were fabricated by using Langmuir-Blodgett technique and then, micro-array pattern were obtained by lithographic technique. Cytochrome c was then immobilized by using decanethiol and mercaptoundecanoic acid. The procedure utilized is summarized in Figure 15.

Figure 15. Immobilization procedure of cytochrome c on polyimide patterned gold substrates. Reprinted from ref. [25], Copyright (2003), with permission from Elsevier

Figure 16 shows the voltammogram of cytochrome on 5 and 10 polyimide LB films patterned on gold substrate. The typical redox peaks of cytochrome c are clearly visible. Interestingly, a higher current is observed with 5 layers polyimide LB films than 10 layers. An interesting application involving the use of the LB technology to fabricate nanoorganized systems constituted by phospholipids incorporating redox molecules has been proposed by Mecheri et al. [45]. They fabricate LB films of a mixed system tetramethylbenzidine (TMB)/dipalmitoylphosphatidic (DPPA) acid. Langmuir monolayers were prepared by spreading TMB e DPPA (dipalmitoylphosphatidic acid): TMB in fact does not form stable LB films, consequently it is necessary to use a system such as DPPA, able to allow stable monolayers at the air-water interface. The isotherm of pure DPPA (figure not shown) evidences a value of the area per molecule of 0.45 nm2. This value is lower than the value obtained in the mixed DPPA-TMB

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system (about 1.10 nm2). This fact is due to the instability of the TMB LB film with consequent destabilization of the interfacial film at the air/water interface. Then, two possible approaches can be used to fabricate LB films: the first one by spreading TMB-DPPA mixture and transfer of the LB films onto gold electrodes, the second one by transfer the DPPA LB films on the gold electrodes followed by immersion of the DPPA gold modified electrodes in TMB solution. The electrochemical data demonstrated a strong dependence from the immobilization procedure. If the first approach allows a stable immobilization of the mediator inside the film but hindering the mobility, the second approach allowed to a higher mobility with consequent better electrochemical performances regarding the electrocatalytic oxidation of NADH. The voltammogram of TMB in solution (figure not shown) evidence two oxidation and reduction peaks, demonstrating that the oxidation of TMB involves two electrons: the first oxidation process generates a semiquinone-imine cation free radical that rapidly convert to a cationic systems [46]. In contrast, the TMB LB films (Figure 12b), shows only one oxidation and reduction peak. Taking into account that in the first step of the oxidation process there is a formation of a charge transfer complex between the reduced form and the oxidized form of TMB, this means that the first step of oxidation does not occur in the LB films. The oxidation process takes place directly at the electrode by formation of the double oxidized species: in fact, the immobilization of TMB prevents the dimer formation.

Figure 16. CVs of cytochrome immolized on patterned gold substrate. Reprinted from ref. [44], Copyright (2003), with permission from Elsevier

This system was then tested for the electrocatalytic study of TMB for NADH. The results evidence that the oxidation peak current of TMB increase in the presence of NADH, meanwhile the reduction peak current decrease, indicating a fast and efficient electrocatalytic effect. In 1999, Ram et al. demonstrated the possibility to fabricated conducting polymers Langmuir-Schaefer films [47]. They fabricate thin films of polyaniline derivatives chemically synthesized such as polyaniline (PANI), poly(o-toluidine) (POT), poly(o-anisidine) (POAS) and poly(o-ethoxyaniline) (PEOA). The doping of the LB monolayer by addition of acid in the subphase is a necessary step for the obtaining thin films highly ordered. Figure 18 reports the pressure-area isotherms in aqueous subphase at pH 1 for PANI, POT, POAS and PEOA.


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The different shapes of the curves can be ascribed to the substituent in PANI backbones. The molecular area was estimated by using the repeat unit of each PANI derivatives. The values found were 26, 45, 55, 62 Å2/r.u for PANI, POT, POAS and PEOA, respectively and the cross-area was estimated 20 Å2 [48, 49]. The shapes of the isotherms change considerably, in particular when in subphase HCl at pH 1 is added. The doping with acids contributes to the stability of the system at the air-water interface by increase of the structure order. The area per molecule estimation is 20, 25, 21, 45 Å2/r.u for PANI, POT, POAS and PEOA. These variations can be ascribed to the change from emeraldine base to emeraldine salt at pH 1 [48, 49]. The differences observed for PEOA system are due to the ethoxy group pf PEOA. This substituent can promote different rearrangement at the air-water interface. The electrochemistry of such thin films was then investigated by using cyclic voltammetry. The related voltammograms are reported in Figure 19.

Figure 17. CVs of 3 TMB/DPPA LB films (dotted and solid line indicate the two different ways of TMB immobilization). Reprinted from ref. [45], Copyright (2004), with permission from Elsevier

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Figure 18. Pressure-area isotherms of PANI, POT, POAS and PEOA in deionized water (a) and in deionized water at pH 1 (b). Reprinted from ref. [47], Copyright (2004), with permission from Elsevier

The CVs show the redox characteristics of the individual polyaniline. The decrease of the redox potential respect to PANI can be explained in term of different substituent in the PANI derivatives. The shift to more positive potentials of the peak at about 200 mV is associated to the non polar conformations induced by the different substituents of the PANI derivatives. This fact causes the decrease of the conjugation along the polymer backbone and, at the same time, a decrease of the number of polarons/bipolarons states. The changes in the oxidation potentials can be ascribed to the higher electronic density states, which facilitate the protonation and oxidation of the amine groups. Different oxidation states can be detected: from leucoemeraldine to emeraldine, from emeraldine to pernigraniline and protonation from undoped base to doped salt form. LB films of PEOA were also used for the detection of heavy metals by using differential pulse voltammetry [50]. Figure 20 shows the voltammogram evidencing the presence of the peaks due to the different metals. A calibration plot obtained for Pb2+ (not shown, [31]) evidence a linear relation between current and lead concentration, confirming the possibility to use conducting polymers LB films as electrochemical sensors.


193

Figure 19. CVs of 30 PANI derivatives LB films deposited on glass/ITO electrodesin 1 M HCl, scan rate 50 mV s-1: PANI (a), POT (b), POAS (c) and PEOA (d). Reprinted from ref. [47], Copyright (2004), with permission from Elsevier

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Figure 20. Differential pulse voltammetry (DPV) of 50 PEOA LS films containing different metallic cations. Reprinted from ref. [50], Copyright (2001), with permission from Wiley-VCH

Ultrathin films of copolymers LB films based on PANI have been studied by Ram et al. polyaniline and poly(o-anisidine) copolymer was synthesized thin films were fabricated by using LS technique [51]. Figure 21 shows the pressure-area isotherms of PANI/POAS copolymer at different molar compositions in subphase at pH 1. As above mentioned, the doping is an important factor to improve the order of the film at the air-water interface and then the stability of the monolayer [52]. PANI evidences an higher collapse pressure due to the solvent effect (in this case NMP). The effect of the copolymerization is evidenced in curves 3-5: the calculated area per molecule was found 48, 32, 30 Å2/r.u. Based on these results it appears evident that the area per molecule values decrease with the increase of the ratio of poly(o-anisidine) in the copolymer. This fact can be explained in terms of better orientation of the fraction containing higher percentage of POAS respect to the fraction containing PANI.

Figure 21. Pressure-area isotherms of PANI, POAS and copolymers (PANI/POAS) at different molar composition as indicated in figure. Reprinted from ref. [51], Copyright (2001), with permission from Elsevier


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Figure 22 reports the voltammograms related to PANI and copolymer PANI/POAS at different molar ratio compositions. A decrease of the redox potentials is observed. This fact is due to the substituents effect of the PANI system. In addition, there is a shift to less positive potential values for the oxidation peaks: this fact can be described in term of decrease of the number of charges states (polarons/bipolarons) due to the increase of the percentage of POAS in the system. The diffusion coefficients for the different copolymer systems were calculated by using the Bufler-Volmer equation [41]: the calculated values decrease from about 10-6 cm2 s-1 for PANI to about 5 10-8 cm2 s-1 for PANI/POAS (25:75). The diffusion coefficient decreases with the increase of the percentage of POAS in the system.

Figure 22. CVs of different polyaniline based systems: PANI (curve 1), PANI/POAS (75:25) copolymer (curve 2) , PANI/POAS (50:50) (curve 3), PANI/POAS (25:75) (curve 4). Reprinted from ref. [51], Copyright (2001), with permission from Elsevier

Figure 23. Pressure-area isotherm of Ru complex in subphase containing 10-5 M Prussian blue. Reprinted with permission from Ref. [53], Copyright (2000) American Chemical Society

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Recently, hybrid materials LB films such as Prussian blue and a surfactant derivative of the ruthenium tris(bipyridine) complex have been fabricated [53]. Figure 23 shows the pressure-area isotherm of Ru(bpy)[bpy(C17)2]22+. The isotherm does not present any plateau, suggesting that no phase transition occurs during the compression of the molecules. It observes a collapse pressure of about 40 mN m-1: this result is in agreement with previous report previously published [54]. Interestingly, the Prussian blue dissolved in the subphase does not modify the compression isotherm: this usually does not happen when positively charged molecules are dissolved in the subphase. Infrared spectra evidence the incorporation of Prussian blue inside the LB film, instead, X-ray diffraction evidence that some parts of the hybrid composite have lamellar structure [53].

Figure 24. Cvs of 8 LB Ru complex incorporating Prussian blue LB films at different scan rates. Reprinted with permission from Ref. [53], Copyright (2000) American Chemical Society

The Cvs show the typical reversible peaks corresponding to oxidation of Ru2+ to Ru3+ at about 1.1 V, the reduction of Prussian blue to Everitt‟s salt (0.2 V) and the oxidation of Everitt‟s salt to Prussian yellow (0.9 V). All these peaks increase with the number of layers (figure not shown), evidencing a homogeneous transfer. As observed in similar lamellar systems, the peak separation and the half-peak width increase with the LB films thickness [55]. This result can be explained in terms of partial hindrance of the diffusion of the charged species by the increasing of the long chain of the surfactant. Both a linear dependence of the peak current with the scan rate and with the square root of the scan rate are observed. These apparent opposite results must be correlated with the large diffusion effect due to the long chain of the surfactant layer [56]. A novel combination Langmuir-Blodgett tecnique with scanning electrochemical microscopy (SECM) has been recently proposed by Unwin et al. [57]. In this case the lateral conductivity of a LB film of polyaniline (PANI) is measured by using SECM. This application is really new and very important due to the importance of the electrically conducting polymers such as PANI in micro and nanoelectronics for applications as light emitting diodes, photovoltaic cells [58, 59]. In this way it has been possible to measure the electrical conductivity “in situ” avoiding the segregation effects that may happen after the PANI monolayer is transferred to a solid support. It has been possible to detect the electrical


197

transition from insulator to conductor of a PANI monolayer. With this approach, a biased microelectrode generates a flux of electroactive species, which may undergo a redox reaction at the interface (PANI monolayer), the extent of which depends on the surface conductivity. The schematic of SECM configuration is reported in Figure 25

Figure 25. Scanning electrochemical microscopy (SECM) configuration for measurements of the conductivity of a LB PANI monolayer. Reprinted with permission from Ref. [57], Copyright (2003) American Chemical Society

The conductivity of the PANI monolayer is investigated by using SECM in feedback mode in aqueous subphase contained 0.1 mM ferrocene monocarboxylic acid and HCl, to ensure that PANI monolayer is in the protonated (doped) emeraldine state. At low surface pressure it observes a decrease of the steady-state current when the distance between the microelectrode and the monolayer decrease. Instead, at high surface pressure it observes an increase of the steady-state current.

Figure 26. diagram of the charge transfer process occurring in the SECM feedback experiment. ΔE refers to the potential difference at the PANI monolayer induced by the variation of the redox specie concentration in soluiton. Reprinted with permission from Ref. [57], Copyright (2003) American Chemical Society

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The current at the microelectrode is affected by two processes: the hindrance of the ferrocene diffusion while approaching the interface and the regeneration of the electroactive species at the interface. The fact that the feedback current changes from negative to positive as a function of surface pressure is therefore due to an insulator to conductor transition that is caused by compressing the film. In the SECM measurements, the lateral charge propagation in the monolayer is driven by the potential difference, established by variations in the concentration of the redox couple (Nernst relation) in the gap between the tip and the monolayer. The diffusion problem is treated by numerical simulation [57]. In Figure 26 is reported the diagram evidencing the charge transport process occurring in the SECM feedback experiment. The tip current Itip is the sum of two contributions: the component (known) due to hindered diffusion of ferrocene monocarboxylic acid Ihind and the current through the PANI monolayer, Imonolayer, which is deduced. Linear relation is obtained (data not shown) between ΔE and Imonolayer, for each of the approach curves. For each surface pressure is then calculated the conductivity of the film taking into account the cylindrical geometry of the electrode and the thickness of the PANI LB films, determined by AFM and XPS. The results evidence an increase of the conductivity with the increase of the surface pressure, consequently, to obtain efficient lateral propagation the PANI LB film has to be highly compact. A remarkable increase in the conductivity is evidenced, beyond a threshold pressure of about 20 mN m-1, demonstrating that ultrathin 2D conducting polymer films must be highly compact to promote efficient lateral charge propagation.

REFERENCES [1] [2] [3] [4] [5] [6] [7] [8] [9] [10] [11] [12] [13] [14] [15] [16] [17] [18]

Langmuir, I., J. Am. Chem. Soc. 1917, 39, 1848 Blodgett, K.B, J. Am. Chem. Soc. 1935, 57, 1007 Ulman, A., In “An Introduction to Ultra-thin Organic Films, From Langmuir-Blodgett to Self-assembly”, Academic Press, London, 1991 Langmuir-Blodgett film, Plenum Press, New York, 1990 Langmuir, I., Schaefer, V.J., J. Am. Chem. Soc. 1938, 60, 1351 Kuhn, H., Thin Solid Films 1983, 99, 1 Bjørholm, T.; Hassenkam, T.; Reitzel, N., J. Mater. Chem. 1999, 9, 1975 Bertoncello, P.; Ram, M.K.; Notargiacomo, A.; Ugo, P.; Nicolini, C., Phys.Chem.Chem.Phys. 2002, 4, 4036 Bertoncello, P.; Ugo, P.; J. Braz. Chem. Soc. 2003, 14, 517 Ugo, P.; Bertoncello, P.; Vezza‟ F., Electrochim. Acta 2004, 49, 3785 Moretto, L.M.; Bertoncello, P.; Vezza‟ F.; Ugo, P., Bioelectrochemistry 2005, 66, 29 Yeo, R.S., J. Electrochem. Soc. 1983, 533 Tazi, B.; Savadogo, O., Electrochim. Acta 2000, 45, 4329 Baradie, B.; Dodelet, J.P.; Guay, D., J. Electroanal. Chem. 2000, 489, 101 White, H.S.; Leddy, J.; Bard, A.J., J. Am. Chem. Soc. 1982, 104, 4811 Martin, C.R.; Rubinstein, I.; Bard, A.J., J. Am. Chem. Soc. 1982, 104, 4817 Buttry, D.A.; Saveant, J.M.; Anson, F.C.; J. Phys. Chem. 1984, 88, 3086 Buttry, D.A.; Anson, F.C., J. Am. Chem. Soc. 1984, 104, 4824


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[19] Huang, Q.; Lu, Z.; Rusling, J., Langmuir 1996, 12, 5472 [20] Galeska, I.; Chattopadhyay, D.; Moussy, F.; Papadimitrakopoulos, F., Biomacromolecules 2000, 1, 202 [21] Fresnadillo, D.G.; Marazuela, M.D.; Moreno-Bondi, M.C.; Orellana, G., Langmuir 1999, 15, 6451 [22] Yeo R.S.; Yeager H.L., 1985, in “Modern Aspects of Electrochemistry”, eds. Conway, B.E.; White R.E.; Bockris, J. O‟M., Plenum Press, New York, 1985, vol. 16, ch. 6 [23] Steck A.; Yeager, H.L., Anal.Chem. 1980, 52, 273 [24] Bertoncello, P.; Notargiacomo, A.; Nicolini, C., Langmuir 2005, 21, 172 [25] Majda, M., in “Molecular design of electrode surface”, Ed. Murray, R.W., Wiley, New York, 1992, ch.4 [26] Ugo, P.; Zangrando, V.; Moretto, L.M., Brunetti, B., Biosens.&Bioelectron. 2002, 17, 479 [27] Lojou, E.; Luciano, P.; Nitsche, S.; Bianco, P., Electrochim. Acta 1999, 44, 3341 [28] Eddowes, M.J.; Hill, H.A.O., J. Am. Chem. Soc. 1979, 101, 4461 [29] Ugo, P.; Pepe, N.; Moretto, L.M.; Battagliarin, M., J. Electroanal. Chem. 2003, 560, 51 [30] Sagara, T.; Murakami, H.; Igarasho, S.; Sato, H.; Niki, K., Langmuir 1991, 7, 3190 [31] Hahn C.E.W.; Hill, H.A.O.; Ritchie, M.D.; Sear, J.W., J. Chem. Soc. Chem. Comm. 1990, 125 [32] Nicolini, C.; Erokhin, V.; Ghisellini, P.; Paternolli, C.; Ram, M.K.; Sivozhelezov, V., Langmuir 2001, 17, 3719 [33] M.Petty, in “Langmuir-Blodgett films – an introduction”, Cambridge University Press, 1996, Cambridge [34] Carvalho, A.J.F.; Ferreira, M.; Balogh, D.T.; Oliveira O.N.Jr.; Faria, R.m., J. Phys. Chem. B 2004, 108, 7033 [35] Osawa, F., in “Polyelectrolytes”, M. Dekker, New York, 1971, Ch. 7 [36] Lin, X.-Q.; Zhang, L.; Anal. Lett. 2001, 34, 1685 [37] Zhao, H.; Zhang, Y.; Yuan, Z.; Anal. Chim. Acta 2001, 441, 117 [38] Ferreira, M.; Dinelli, L.R.; Wohnrath, K.; Batista, A.A.; Oliveira O.N.Jr., Thin Solid Films 2004, 446, 301 [39] Ferreira, M.; Wohnrath, K.; Torresi, R.M.; Costantino, C.J.L.; Aroca, R.F.; Oliveira Jr, O.N.; Giacometti, R.A., Langmuir 2002, 18, 540 [40] Mello, S.V.; Mattoso, L.H.C.; Faria, R.M.; Oliveira Jr., O.N., Synth. Met., 1995 71, 2039 [41] Bard, A.J.; Faulkner, L., in “Electrochemical Methods: Fundamental and Applications”, 2nd edition, J. Wiley, 2001 [42] Ju, H.X.; Ni, J.G.; Gong, Y.; Chen, H.Y.; Leech, D.; Anal. Lett. 1999, 32, 2951 [43] Ciszewski, A.; Milczarek, G.; Anal. Chem. 1999, 71, 1055 [44] Oh, S.Y.; Park, Y.-K.; Ko, C.-B.; Choi, J.-W., Biosens.&Bioelectron. 2003, 19, 103 [45] Mecheri, B.; Piras, L.; Caminati, G., Bioelectrochemistry 2004, in press [46] Josephy, P.D.; Eling, T.; Mason, R.P., J. Biol. Chem. 1982, 257, 3669 [47] Ram, M.K.; Adami, M.; Sartore, M.; Salerno, M.; Paddeu, S.; Nicolini, C., Synth. Met.1999, 100, 249 [48] Ram, M.K.; Sundaresan, N.S.; Malhotra, B.D.; J. Phys. Chem. 1993, 97, 11580 [49] Ram, M.K.; Gowri, R.; Malhotra, B.D.; J. Appl. Polym. Sci. 1997, 13, 141 [50] Ram, M.K.; Bertoncello, P., Nicolini, C., Electroanalysis 2001, 13, 574

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[51] Ram, M.K; Sarkar, N.; Ding, H.; Nicolini, C., Synth. Met. 2001, 123, 197 [52] Ram, M.K.; Carrara, S.; Paddeu, S.; Maccioni, E.; Nicolini, C.; Langmuir 1997, 13, 2760 [53] Torres, G.R.; Dupart, E.; Mingotaud, C.; Ravaine, S., J. Phys. Chem. B 2000, 104, 9487 [54] Valenty, S.J.; Behnken, D.E.; Gaines, G.L., Inorg. Chem. 1979, 18, 2160 [55] Saliba, R.; Agricole, B.; Mingotaud, C.; Ravaine, S., J. Phys. Chem. B 1999, 103, 9712 [56] Aoki, K.; Tokuda, K.; Matsuda, H.; J. Electroanal. Chem. 1984, 160, 33 [57] Zhang, J.; Barker, A.L.; Mandler, D.; Unwin, P.R., J. Am. Chem. Soc. 2003, 125, 9312

INDEX A absorption, viii, 51, 56, 57, 69, 70, 71, 85, 86, 87, 88, 89, 92, 93, 94, 95, 96, 97, 98, 99, 114, 137, 140, 158 absorption spectra, viii, 51, 57, 69, 70, 71, 85, 86, 88, 89, 93, 94, 95, 96, 97, 98, 99, 137 absorption spectroscopy, 114 accessibility, 37 accuracy, 17, 54 acetonitrile, 143 acetylcholinesterase, 114, 133 acid, ix, 8, 14, 15, 16, 17, 18, 20, 23, 24, 26, 29, 30, 32, 37, 38, 39, 41, 42, 43, 44, 46, 48, 102, 103, 108, 111, 122, 125, 126, 127, 137, 143, 144, 145, 146, 151, 153, 155, 156, 159, 188, 190, 191, 198 activated carbon, 12, 13, 14, 15, 16, 17, 18, 19, 20, 21, 22, 28, 35, 39, 41, 42, 43, 44, 45, 46, 47, 48, 49 activation energy, 166 active site, 166, 168 actuality, 2 adhesion, 113, 114, 115, 121 adhesion force, 114, 115 adjustment, 33 adsorption, vii, viii, 1, 2, 3, 4, 5, 6, 7, 8, 10, 11, 12, 13, 14, 15, 16, 17, 18, 19, 20, 21, 22, 23, 24, 25, 26, 27, 28, 29, 30, 31, 32, 33, 34, 35, 36, 37, 38, 39, 40, 41, 42, 43, 44, 45, 46, 47, 48, 49, 103, 112, 117, 133, 134, 140, 151, 152, 154, 156, 157, 159,땠160, 161, 162, 163, 164, 165, 166, 167, 168, 169, 170, 172, 173, 174 adsorption isotherms, 13, 16, 34, 166 advantages, 119, 189 AFM, viii, 101, 102, 103, 108, 109, 114, 115, 116, 117, 118, 119, 120, 122, 123, 128, 129, 140, 141, 142, 143, 144, 145, 199 aggregates, 179

aggregation, 52, 140, 179 agriculture, 42 AIBN, 153 aluminium, 2, 23, 37 amines, 133 amino acids, 135, 152 ammonium, 16 amorphous silicon, 130 anodization, 103 antibiotic, 117, 118 antibody, 113, 120, 127 antigen, 120 aqueous solutions, vii, ix, 1, 2, 13, 14, 15, 16, 17, 18, 19, 20, 21, 24, 25, 26, 27, 28, 29, 30, 31, 33, 34, 35, 36, 37, 39, 41, 42, 43, 44, 45, 46, 47, 48, 49, 152, 153, 161, 171, 172, 173 architecture, 52, 102 ascorbic acid, 187, 188, 190 atmospheric pressure, 112 atomic force, viii, 101, 102, 114, 121, 122, 123, 124, 128, 129, 130, 137, 141 atomic force microscope, 122, 123, 129, 130, 141 atoms, 142 attachment, 131, 152, 161

B bandwidth, 69, 70, 85, 86, 87 barriers, 177 bending, 15, 158 benzene, 57 binding energies, 5 binding energy, 5, 167, 168, 169 biological activity, 113, 145 biomass, 15, 43, 45 biomaterials, vii, 1 biomedical applications, viii, 151 biosensors, vii, viii, ix, 101, 102, 125, 126, 145, 147, 177

202

Index

biotechnology, viii, 101 bleaching, 37, 48 bonds, 2, 113, 142 boundary conditions, 9, 10

C cadmium, 20, 24, 30, 31, 33, 36, 39, 41, 42, 43, 44, 45, 46, 47, 48, 49 calcination temperature, 26, 39 calcium, 2, 24 calibration, 189, 193, 196 capillary, 115 carbohydrate, 122 carbon, vii, 1, 2, 12, 13, 14, 15, 16, 17, 18, 19, 20, 21, 22, 28, 43, 44, 45, 46, 49 carbonization, 18, 21, 41 carcinogen, 45 casting, 183 catalysis, 142 catalyst, 48 catalytic activity, 142 cation, 2, 22, 30, 32, 34, 35, 37, 39, 157, 183, 191 cattle, 14, 49 CEC, 32, 34, 39 cell membranes, 120 cell surface, 143, 149 cellulose, vii, viii, 151, 152, 153, 156, 160, 173 CH3COOH, ix, 152, 172, 173 chemical bonds, 2 chemical structures, 133 chemisorption, 10, 12, 25, 46 China, 130 chloroform, 54, 69, 70, 72, 84, 87, 88, 103 cholesterol, 108, 110, 124, 143, 145 chromium, 13, 15, 16, 18, 19, 20, 23, 28, 31, 33, 37, 42, 43, 44, 45, 46, 47, 48 chymotrypsin, 127 class, ix, 177 clay minerals, 2, 21, 24, 26, 32 clean air, 138 cleaning, 54 cleavage, 33, 144 clusters, 139 coal, 18 coatings, 29 cobalt, 30, 45, 46, 49 color, iv compensation, 78 competition, 8, 29, 33, 34, 35 competitors, 142 complexity, 29, 152 complications, 113 composite, 197

composition, viii, 35, 72, 75, 76, 99, 101, 112, 131, 135, 140, 154, 196 compost, 14, 49 compounds, vii, viii, 29, 37, 52, 53, 54, 56, 57, 59, 66, 97, 112, 125, 131, 152, 185 compressibility, 105, 112 compression, 56, 57, 58, 59, 61, 63, 66, 67, 72, 74, 79, 81, 82, 83, 84, 85, 98, 99, 103, 104, 105, 106, 135, 136, 137, 138, 177, 178, 183, 197 condensation, 12, 179, 183, 184 conditioning, 27 conductivity, 198, 199 conductor, 198, 199 configuration, 198 conjugation, 193, 196 contact time, ix, 15, 16, 19, 20, 21, 23, 24, 25, 27, 28, 29, 31, 33, 34, 151, 156, 162 cooling, 54, 155 copolymerization, 195 copolymers, 186, 195, 196 copper, 14, 17, 20, 28, 31, 33, 34, 36, 37, 39, 42, 43, 44, 47, 48, 49 correlation, 8, 14, 24, 35, 39, 69, 78, 162, 164, 166, 169 correlation coefficient, 8, 35, 162, 164, 166 cost, vii, 1, 2, 12, 13, 14, 17, 19, 20, 21, 23, 25, 26, 28, 29, 32, 39, 44, 46, 49, 152 cost effectiveness, 39 covering, 108, 118 crystalline, 160 crystallinity, 160 crystallites, 179 crystals, vii, 51, 52, 53, 54, 57, 59, 60, 61, 66, 69, 71, 78, 95, 98, 143, 145 cycles, 107, 172, 173 cytochrome, 135, 139, 181, 182, 184, 185, 190, 191 cytochrome p450, 185

D damages, iv decomposition, 37, 94 defects, 108 deformation, 73, 115, 142 dehydration, 15 denaturation, 120, 133 density, 193, 196 deposition, 54, 56, 71, 87, 106, 107, 108, 111, 113, 114, 123, 131, 133, 136, 138, 139, 140, 145, 146, 178 depression, 118 derivatives, 32, 39, 110, 112, 130, 191, 193, 194, 195 desorption, ix, 10, 20, 35, 39, 140, 152, 156, 172

203

Index detection, 102, 112, 120, 125, 186, 188, 189, 193, 196 deviation, 75, 167 dielectric constant, 55, 62 diffraction, 141, 160, 197 diffusion, ix, 9, 11, 13, 14, 16, 18, 19, 20, 21, 24, 25, 27, 28, 29, 31, 32, 35, 40, 44, 46, 128, 152, 162, 163, 164, 165, 166, 173, 181, 184, 189, 196, 198, 199 diffusion process, 46 dimethylformamide, 142 dipole moments, 78, 79, 80, 91, 92, 93 direct observation, 65 discs, 159 disorder, 170 displacement, 173 distilled water, 153, 154 distortion, 115 DMF, 142, 143 DNA, 45, 120, 129, 142 DNA damage, 45 domain structure, 102, 138 dopamine, 186, 187, 188, 189 doping, 191, 192, 195 dosage, 16, 17, 25, 28, 161 double bonds, 111 drug delivery, viii, 101, 102, 117, 129 drug interaction, 117, 118 drugs, 117, 135, 147, 152 duality, 139 dyes, vii, 42, 51, 52, 53, 54, 55, 72, 75, 76, 77, 78, 79, 84, 85, 86, 87, 88, 93, 94, 95, 96, 98, 99

E effluent, 3, 39, 171 effluents, 2, 19 electric charge, 161 electrical conductivity, 198 electrical properties, viii, 124, 131 electrocatalysis, 184, 189 electrochemistry, 192 electrode, 182, 187, 188, 189, 191, 199, 200 electrodes, 125, 132, 179, 188, 190 electrolyte, 25, 30, 105, 180, 184, 188, 189 electrolytes, 179, 183, 184, 185 electron, 124, 131, 137, 142, 143, 144, 156, 160, 181, 184 electron microscopy, 142, 144 electrons, 182, 188, 189, 191 electroplating, 20 endothermic, ix, 14, 18, 20, 23, 24, 25, 27, 30, 31, 33, 35, 36, 37, 152, 166, 168, 170, 173 engineering, 11, 39, 48, 125, 133

England, 54 entropy, ix, 11, 12, 26, 30, 32, 41, 152, 169 environmental conditions, 112 enzymatic activity, 125 enzyme immobilization, 127 enzymes, 101, 102, 112, 113, 125, 127, 133, 134, 142, 143, 146 epoxy groups, 153, 154, 155, 156, 158 equilibrium, ix, 2, 3, 5, 7, 8, 9, 11, 12, 13, 14, 15, 16, 17, 18, 19, 20, 21, 23, 24, 26, 28, 30, 31, 34, 35, 36, 39, 40, 42, 43, 44, 45, 47, 49, 57, 65, 137, 151, 162, 165, 166, 167, 169, 171, 173 erosion, 117 ester, 158 ethanol, 86, 87, 88, 125, 133, 143, 153 evaporation, 135 excitation, 90, 91 exciton, 89, 90, 91, 92 exertion, 104 experimental condition, vii, 1, 15, 35, 133, 137 extinction, 85 extraction, 36

F fabrication, viii, ix, 54, 101, 132, 133, 135, 177 fatty acids, 52, 103, 110, 133, 135, 137, 152, 177, 178 feedback, 133, 138, 198, 199 fiber, 56 fiber bundles, 56 fibers, 19, 22 film formation, 58, 102, 139 film thickness, 140, 181 films, vii, viii, ix, 51, 52, 53, 54, 56, 57, 58, 59, 60, 61, 62, 65, 69, 70, 71, 72, 73, 74, 75, 77, 78, 79, 86, 87, 88, 89, 90, 93, 94, 95, 96, 97, 98, 99, 101, 102, 103, 106, 108, 110, 112, 113, 114, 116, 117, 119, 120, 122, 123, 124, 125, 126, 127, 129, 130, 131, 132, 134, 135, 136, 137, 138, 139, 143, 145, 146, 147, 148, 177, 178, 179, 180, 181, 183, 184, 185, 186, 187, 188, 189, 190, 191, 192, 193, 194, 195, 196, 197, 198, 199, 200 Finland, 54 fixed rate, 106 fluid, 2, 112, 115, 128 fluorescence, 66, 102, 108, 114, 128 folding intermediates, 142 formamide, 142 formula, 92, 179, 184 fragility, 145 fragments, 113, 127 free energy, 4, 11, 12, 26, 28, 30, 32, 40, 104, 126, 169, 170

204

Index

friction, 114, 116 FTIR, ix, 15, 17, 114, 140, 145, 151, 156, 157, 158 FTIR spectroscopy, 140, 156 fuel, 179 functionalization, 112 fusion, 103, 117, 128 future, 184

G gel, 136 Gibbs energy, 27, 41 glow discharge, 125 glucose, 125, 126, 127, 143, 145 glucose oxidase, 125, 127, 143, 145 glutathione, 45 glycerol, 108, 116 gold, 182, 190, 191 GPC, 47 grades, 16, 186 grazing, 102, 128

H Hamiltonian, 89, 90 heavy metals, vii, 1, 2, 12, 14, 21, 22, 23, 28, 33, 34, 35, 36, 38, 39, 42, 46, 48, 179, 193, 196 height, 115, 116, 118 heme, 181 hemicellulose, 158 heterogeneity, 117, 167 hexane, viii, 51, 53, 58 histidine, 113 HIV, 122 homogeneity, 71, 95, 139 host, 74, 143 hybrid, 6, 125, 197 hydrogen, 2, 35, 142, 152, 158 hydrogen bonds, 142 hydrophilicity, 110 hydrophobic properties, 110 hydrophobicity, 110 hydroxide, 23, 35 hydroxyl, 158 hysteresis, 57, 59, 135

I ideal, 6, 75, 103, 115, 135, 170 image, 56, 108, 115, 116, 120, 143, 144, 160 images, viii, 16, 51, 56, 65, 66, 67, 68, 79, 81, 82, 83, 84, 85, 98, 102, 109, 114, 115, 116, 117, 118, 119, 122, 124, 126, 129, 138, 144, 145, 160 imitation, 102 immersion, 106, 107, 108, 113, 190

immobilization, 41, 125, 126, 135, 144, 191, 192 immobilized enzymes, 132 immunodeficiency, 117 immunoglobulin, 102, 121, 125, 126 immunoglobulins, 113 impregnation, 13, 16 impurities, 143 incidence, 56, 57, 70, 71, 95, 96, 102, 128 incubation time, 117, 118 India, 1, 24, 31, 151, 153, 173 infrared spectroscopy, 37 insulin, 135 integration, 9, 12 intercepts, 164 interface, viii, 51, 52, 56, 57, 59, 62, 63, 69, 72, 78, 79, 81, 82, 83, 84, 85, 97, 98, 101, 103, 104, 105, 106, 108, 110, 112, 113, 114, 121, 123, 128, 132, 133, 134, 135, 137, 138, 144, 145, 177, 179, 185, 190, 192, 195, 198, 199 interference, 8, 66, 68, 80, 187, 188 intermolecular interactions, 52, 76, 135 inversion, 33 ion adsorption, 18, 43, 45, 49 ion-exchange, 2, 21, 27, 28, 33, 34, 183, 184 ionic strength, 15, 23, 24, 26, 30, 31, 32, 33 ions, vii, ix, 1, 2, 8, 11, 12, 13, 14, 17, 18, 19, 20, 21, 23, 24, 25, 26, 27, 29, 30, 31, 32, 33, 35, 36, 37, 38, 39, 41, 42, 43, 44, 45, 47, 48, 49, 152, 170, 173, 186 iron, 2, 34, 37 isotherms, viii, ix, 2, 3, 16, 20, 24, 25, 27, 28, 29, 30, 31, 33, 34, 36, 48, 51, 58, 59, 60, 61, 62, 67, 72, 73, 74, 75, 77, 79, 81, 82, 83, 84, 85, 98, 99, 105, 112, 139, 152, 166, 179, 183, 184, 185, 186, 191, 192, 193, 195

J Japan, 156, 183

K KBr, 159 kinetic constants, 162 kinetic equations, 8 kinetic model, vii, 1, 8, 10, 13, 14, 18, 23, 24, 25, 29, 30, 36, 40, 41, 44, 163, 164 kinetic parameters, 164, 166 kinetic studies, 8, 18, 30, 41 kinetics, ix, 2, 8, 10, 11, 13, 14, 15, 18, 19, 20, 22, 25, 27, 28, 29, 30, 32, 34, 35, 39, 42, 43, 44, 46, 47, 49, 102, 121, 152, 164, 173 kinks, 105 Korea, 35

205

Index

L labeling, 102 leaching, 36 lecithin, 124 lens, 66, 69, 98 life sciences, 117 lifetime, 101, 125 light, 198 light beam, 56, 57 light emitting diode, 198 light emitting diodes, 198 linear dependence, 181, 184, 198 linearity, 189 lipids, viii, 101, 110, 113, 117, 133, 139, 144, 145, 146, 147 liposomes, 114, 128 liquid crystals, vii, 51, 52, 53, 54, 58, 59, 61, 62, 66, 69, 70, 71, 72, 74, 75, 77, 78, 84, 88, 95, 96, 98, 99 liquid interfaces, 123 liquid phase, 57, 65, 109 liquid-air interface, 134 liquids, 3, 45, 130 lithography, 103 luciferase, 127 Luo, 122

M macromolecules, 113, 130, 133, 147 magnesium, 2, 37 majority, 131 manganese, 26, 31, 33, 43, 49 manipulation, 102 manufacture, 14 manure, 14, 49 Marx, 148 materials science, ix, 177 matrix, 72, 99, 113, 135, 145, 169 maximum sorption, 33, 35, 36 media, 30, 62 membranes, viii, 101, 103, 110, 112, 114, 119, 121, 124, 125, 126, 127, 128, 129, 135 mercury, 28, 42, 46, 47, 49 metals, vii, 1, 2, 20, 25, 32, 33, 34, 35, 36, 37, 39, 152, 179, 193, 196 methanol, 133, 142, 143 micelles, 179 microporous materials, 43 microscope, 56, 66, 98, 130, 156

microscopy, viii, 51, 65, 101, 102, 108, 114, 117, 118, 121, 122, 124, 126, 128, 129, 130, 137, 138, 140, 141, 143, 198 miniaturization, 52 mixing, 23, 75 mobility, 191 model system, 102, 114, 117, 119 modeling, 16 modelling, 45 modification, 14, 24, 26, 37, 39, 47, 118, 125, 157, 159 modulus, 114, 136, 140 moisture, 44 molecular orientation, 97, 119, 144 molecular oxygen, 45 molecular sensors, 123 molecular structure, vii, 51, 53, 54, 59, 69, 72, 75, 93, 94, 98, 99, 102, 126 molecules, viii, 2, 5, 7, 11, 51, 52, 53, 54, 57, 59, 61, 63, 68, 69, 70, 71, 72, 74, 75, 78, 79, 80, 84, 88, 89, 90, 91, 92, 93, 94, 95, 96, 97, 98, 99, 101, 103, 104, 105, 106, 110, 112, 113, 114, 115, 117, 131, 132, 133, 134, 135, 138, 139, 143, 145, 160, 161, 166, 168, 177, 179, 181, 182, 190, 197 monitoring, 139, 147 monoclonal antibody, 102, 113 monolayer, viii, ix, 4, 6, 7, 14, 15, 17, 19, 24, 25, 26, 27, 28, 30, 32, 51, 54, 55, 56, 57, 58, 61, 62, 63, 65, 66, 69, 72, 74, 75, 78, 79, 81, 82, 83, 84, 85, 87, 95, 97, 98, 99, 101, 102, 103, 104, 105, 106, 107, 108, 109, 110, 112, 113, 121, 123, 127, 132, 133, 134, 135, 136, 137, 138, 139, 143, 144, 145, 146, 147, 152, 166, 173, 177, 178, 179, 186, 191, 195, 198, 199 monolayers, 178, 185, 190 monomers, 69, 90, 93, 94, 95, 97, 99, 114 Morocco, 37 morphology, 56, 65, 102, 118, 120, 138, 139, 143, 160 multi-component systems, 21 multilayer films, viii, 123, 131, 135 multilayered structure, 143 myoglobin, 135

N NaCl, 27, 109, 172, 180, 184 NADH, 191 nanodevices, viii, 101 nanoelectronics, 198 nanogravimetry, 137 nanolithography, 122 nanometer, viii, 101, 102, 103, 114, 115, 117, 119, 141, 143

206

Index

nanometer scale, viii, 101, 102, 103, 114, 117 nanostructures, vii, viii, 52, 101, 102, 103, 113, 116, 122 nanosystems, viii, 101 nanotechnology, ix, 149, 177 NCS, viii, 51, 57, 98 neurons, 188 next generation, 120 nickel, 19, 22, 31, 33, 37, 42, 44, 45, 47, 48, 49 Nigeria, 25, 33 nitrate, 38 nitrogen, 17, 18 nitrogen gas, 18 NMR, 37 noise, 56 nonlinear optics, vii, viii, 53, 131 North Africa, 23, 38 nucleation, 137

O oil, 27 olive oil, 14 optical microscopy, 102, 108, 116, 124, 130 optical properties, 52 organic compounds, 29, 174 organic solvents, 133, 142, 143 organism, 143 organizing, vii, viii, 131 orientation, 177, 195 oscillation, 140 osmotic pressure, 152 oxidation, 18, 19, 181, 188, 189, 191, 193, 196, 198 oxygen, 2, 179

P parallel, 56, 70, 71, 92, 95, 96, 114 particle mass, 33 particle size distribution, 24 partition, 29, 102 penicillin, 145 pepsin, 113, 132 peptides, 101, 117, 129 percolation, 117 performance, 12, 14, 16, 19, 20, 26, 46, 112 permission, iv, 109, 115, 116, 118, 119, 178, 180, 182, 183, 184, 185, 186, 187, 188, 189, 190, 191, 192, 193, 194, 195, 196, 197, 198, 199 permit, 2 permittivity, 55 pesticides, 145 phase behavior, 102, 105, 121 phase transitions, 105, 123, 127, 185

phosphatidylcholine, 112, 130 phosphatidylethanolamine, 112, 115, 129 phospholipids, 102, 103, 110, 112, 114, 117, 124, 128, 133, 135, 136, 137, 138, 139, 143, 145, 146, 178, 190 photobleaching, 102, 114 photonics, 52 photovoltaic cells, 198 physical chemistry, 48 physicochemical properties, viii, 101, 103, 106 physics, 52 pith, 18, 45, 46 plasma membrane, 121 plasticity, 28 platinum, 45, 137, 145 PMMA, 186, 187, 188 Poland, 51, 54, 100, 131 polar groups, 78 polarization, 114 polyacrylamide, 145 polyimide, 190 polyimide film, 190 polymer, 125, 136, 152, 179, 184, 185, 193, 196, 199 polymer films, 199 polymerization, 152, 153 polymers, ix, 130, 131, 139, 141, 177, 179, 191, 193, 196, 198 polypeptide, 135 polyvinyl alcohol, 25, 48, 153 porosity, 16, 164 potassium, 2, 13, 16, 19 precipitation, 23, 25, 26, 27, 32, 35 probe, 114, 115, 120, 130, 141 promoter, 108 propagation, 199 proportionality, 181 protein engineering, 133 protein folding, 142 protein structure, 120, 135 protein-protein interactions, 102 proteins, viii, 101, 102, 103, 112, 113, 114, 117, 126, 132, 133, 135, 139, 142, 143, 147, 149, 152, 161, 168, 172, 179 proteolytic enzyme, 143 protons, 25 prototype, 125 pulp, 18, 22, 41, 47 pure water, 56, 105 purification, 30, 31, 54, 143, 153 PVA, 25, 153 pyrolysis, 18

Index

Q quartz, viii, 24, 32, 51, 53, 56, 60, 71, 72, 87, 95, 96, 98, 139, 140 quinone, 188

R radiation, 56 radius, 183 raw materials, 19 reaction rate, 8 reactions, 44, 140 reagents, 153 real time, 102, 119, 130, 140 reality, 186 recognition, 102, 112, 113, 132, 135, 139 recommendations, iv recrystallization, 144 red shift, 92 reduction, 181, 182, 184, 188, 189, 191, 198 reflectivity, 65, 138 refractive index, 140 regeneration, 21, 156, 172, 199 regression, 162 regression analysis, 162 relative size, 116 relaxation, 137, 152 reliability, 147 remediation, 43 replacement, 18, 30 residues, 135 resistance, 57, 135, 164 resolution, 56, 102, 103, 108, 112, 114, 115, 116, 118, 119, 120, 122, 126, 129, 130, 141, 142, 143, 144 response time, 112, 145 reusability, 156 rheology, 146 rice husk, 15 rings, 66, 68, 80, 158 room temperature, 13, 16, 24, 28, 104 roughness, 143 Royal Society, 123 rubber, 20 ruthenium, 188, 197

S saturation, 3, 168 Saudi Arabia, 23, 38, 41 sawdust, 13, 20, 21, 22, 45 scanning electron microscopy, 140 scarcity, 39

207

scattering, 114, 128, 160 Schrödinger equation, 90, 91 seed, vii, 1, 16, 22, 46 segregation, 114, 198 selectivity, 19, 24, 31, 179, 183 self-assembly, 132, 133, 147, 148 self-organization, 119 SEM micrographs, 159 sensing, 112, 113, 131, 140, 145, 147 sensitivity, 112, 140 sensitization, 127 sensors, 112, 125, 145, 146, 193, 196 Serbia, 25, 48 serine, 116 serum, vii, 121, 133, 152 serum albumin, vii, 121, 133, 152 shape, vii, 51, 66, 85, 93, 95, 108, 166, 183, 184 shear, 140 signals, 158 silica, 2 silicon, 2, 106, 123, 143, 144 simulation, 199 Singapore, 48 SiO2, 125, 126 skeleton, 183 sodium, ix, 2, 16, 24, 25, 30, 37, 48, 151, 153, 154, 172 sodium hydroxide, 30, 37 solid phase, 106 solid surfaces, 8 solid waste, 20, 46 solubility, 17, 26, 54, 110, 131, 133, 179, 185, 186 solubility in water, 179 solution, 177, 183, 184, 188, 191 solvent, 195 solvents, 131, 142, 143 sorption experiments, 24 sorption isotherms, 22 sorption kinetics, 156 sorption method, 37 sorption process, 36, 37, 44, 156 species, 2, 14, 22, 29, 37, 96, 105, 133, 135, 140, 141, 143, 145, 161, 188, 189, 191, 198, 199 specific surface, 17, 32, 164 spectrophotometer, 56, 57, 156 spectroscopy, 37, 54, 114, 137, 140 speed of response, 131 spontaneity, 26, 170 stabilization, 113 steroids, 133, 152 sterols, 103, 135 streams, 15 stretching, 15, 158

208

Index

stroke, 56, 106 strong interaction, 89 styrene, 186 substitution, 123 sugar beet, 18, 41, 47 sugar industry, 19 sugarcane, 18 sulfuric acid, 13, 15, 16, 20, 24 Sun, 174, 175 surface area, 14, 15, 16, 17, 18, 19, 21, 26, 32, 34, 35, 37, 39, 48, 103, 110, 132, 138, 157, 160 surface energy, 166 surface layer, 134, 144 surface modification, 19, 21, 160 surface structure, 115, 142 surface tension, 54, 104, 105, 132, 135, 137, 146 surfactant, 16, 46, 197, 198 surfactants, 177, 179 survey, vii, 1, 39 suspensions, 37 sustainability, 39 symmetry, 26, 115, 144 synthesis, 18, 153 synthetic polymers, 135

T tactics, 113 talc, 38 temperature dependence, 33 tension, 54, 104, 105 testing, 2, 112 texture, 102 Thailand, 36 thermal analysis, 26 thermal stability, 143 thermodynamic calculations, 25 thermodynamic parameters, 12, 23, 24, 30, 36, 169 thermodynamics, vii, 1, 11, 20, 30, 42, 44, 46, 48 thin film, ix, 177, 181, 191, 192, 195 thin films, vii, viii, ix, 103, 119, 122, 131, 133, 137, 140, 146, 147, 148, 177, 181, 191, 192, 195 third dimension, 66, 104 topology, 130 total internal reflection, 114, 128 toxicity, 39 transducer, 112 transition temperature, 136 transport, 11, 47, 152, 199 tunneling, 137, 140 Turkey, 27, 43

U ultrastructure, 144 unconditioned, 27 uniform, 4, 5, 44, 57, 65 United Arab Emirates, 25, 38 United Kingdom, 177 urea, 125, 127

V vacuum, 139, 153 valence, 2 vanadium, 33 vapor, 106 variations, 192, 199 vector, 71, 92 versatility, 119, 141 vesicle, 103, 114, 128 vibration, 15, 158 viruses, 139 viscoelastic properties, 114 viscosity, 178 visualization, 120, 129, 138

W waste, vii, 1, 13, 14, 15, 16, 18, 19, 21, 27, 31, 37, 42, 43, 44, 46, 48 wastewater, 2, 8, 12, 15, 17, 19, 20, 23, 27, 28, 29, 31, 35, 39, 41, 42, 43, 46, 47, 48 water, 177, 178, 179, 185, 186, 190, 192, 193, 195 water resources, 2 wavelengths, 69, 92, 93, 96 weight gain, 156 wood, 13, 14, 17, 20, 22, 41, 46, 48 workers, 145, 165, 169

X XPS, 140, 199 X-ray, 26, 37, 102, 128, 137, 140, 143, 156, 160, 197 X-ray analysis, 160 X-ray diffraction, 26, 37, 102, 137, 140, 156, 197 X-ray photoelectron spectroscopy (XPS), 140 XRD, ix, 43, 151, 158, 160

Z zeolites, 42 zinc, 14, 17, 28, 30, 31, 33, 36, 37, 39, 41, 42, 43, 46, 47, 48 zirconium, 32

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