STUDY OF CHITOSAN-BASED BIOPOLYMER ADSORBENTS AND THEIR APPLICATIONS IN HEAVY METAL REMOVAL LI NAN NATIONAL UNIVERSITY OF SINGAPORE 2006 STUDY OF CHITOSAN-BASED BIOPOLYMER ADSORBENTS AND THEIR APPLICATIONS IN HEAVY METAL REMOVAL LI NAN (B.Eng. WUHAN UNIV) A THESIS SUBMITTED FOR THE DEGREE OF DOCTOR OF PHILOSOPHY DEPARTMENT OF CHEMICAL AND BIOMOLECULAR ENGINEERING NATIONAL UNIVERSITY OF SINGAPORE 2006 ACKNOWLEDGEMENT First of all, I would like to express my cordial gratitude to my supervisor, A/P Bai Renbi for his heartfelt guidance, invaluable suggestions, and profound discussion throughout this work, for sharing with me his enthusiasm and active research interests, which are the constant source for inspiration accompanying me throughout this project. The valued knowledge I learned from him on how to research work and how to enjoy it paves my way for this study and for my life-long study. I would like to thank all my colleagues for their help and encouragement, especially to Mr. Lim Aikleng, Ms. Liu Chunxiu, Mr. Liu Changkun, Mr. Wee Kin Ho and Mr. Han Wei. In addition, I also appreciate the assistance and cooperation from lab officers and technicians of Department of Chemical and Biomolecular Engineering. Finally, I would like to give my most special thanks to my parents, Mr. Li Xiusheng and Ms. Wu Meiju, my sister, Miss Li Hao and my husband, Dr. Cai Qinjia for their continuous love, support, and encouragement. I TABLE OF CONTENTS ACKNOWLEDGEMENT I TABLE OF CONTENTS II SUMMARY VI LIST OF TABLES IX LIST OF FIGURES X LIST OF SCHEMES XIV LIST OF SYMBOLS XV NOMENCLATURE XVII CHAPTER INTRODUCTION 1. 1.1 Overview 2. 1.2 Objectives and scopes of the study 7. CHAPTER LITERATURE REVIEW 10. 2.1 Heavy metal pollution 2.1.1 General 2.1.2 Copper, Lead and Mercury 2.1.2.1 Copper (Cu) 2.1.2.2 Lead (Pb) 2.1.2.3 Mercury (Hg) 11. 11. 13. 13. 15. 16. 2.2 Methods for heavy metal removal 19. 2.3 Bioadsorption 2.3.1 Seaweed 2.3.2 Alginate 2.3.3 Dead biomass and rice hulls 2.3.4 Chitin and chitosan 2.3.4.1 Physical and chemical properties of chitosan 2.3.4.2 Application of chitosan in water treatment 24. 25. 25. 26. 27. 28. 30. CHAPTER STUDY OF CHITOSAN-CELLULOSE HYDROGEL BEADS FOR COPPER ADSORPTION: BEHAVIORS AND MECHANISMS 41. II 3.1 Introduction 42. 3.2 Materials and methods 3.2.1 Materials and chemicals 3.2.2 Preparation of chitosan-cellulose hydrogel beads 3.2.3 Swelling, hydration rate, dissolution and mechanical property test 3.2.4 Zeta potential measurement 3.2.5 Adsorption experiments 3.2.5.1 Copper adsorption at different solution pH 3.2.5.2 Adsorption equilibrium study 3.2.5.3 Kinetic adsorption experiments 3.2.6 Surface morphology observation with SEM 3.2.7 Fourier tranform infrared (FTIR) spectroscopy 3.2.8 X-ray photoelectron spectroscopy (XPS) 45. 45. 45. 47. 49. 50. 50. 51. 52. 53. 53. 54. 3.3 Results and discussion 3.3.1 Surface morphology 3.3.2 Swelling, hydration, solubility and mechanical properties 3.3.3 Zeta potentials 3.3.4 Characterization of chitosan-cellulose beads 3.3.5 Effect of pH on copper adsorption 3.3.6 Adsorption isotherms 3.3.7 Adsorption kinetics 3.3.8 Adsorption mechanisms 55. 55. 59. 64. 65. 70. 73. 78. 81. 3.4 Conclusion 88. CHAPTER A NOVEL AMINE-SHIELDED SURFACE CROSSLINKING OF CHITOSAN HYDROGEL BEADS FOR ENHANCED METAL ADSORPTION PERFORMANCE 89. 4.1 Introduction 90. 4.2 Materials and methods 4.2.1 Materials and chemicals 4.2.2 Preparation and crosslinking chitosan hydrogel beads 4.2.3 SEM observation 4.2.4 Zeta potential measurement 4.2.5 Adsorption experiments 4.2.6 FTIR analysis 4.2.7 XPS study 93. 93. 93. 95. 95. 95. 97. 98. 4.3 Results and discussion 4.3.1 Surface treatments and crosslinking mechanisms 4.3.2 Zeta potentials 4.3.3 Adsorption performance 4.3.4 Adsorption mechanisms 99. 99. 111. 112. 117. 4.4 Conclusions 122. III CHAPTER ENHANCED AND SELECTIVE ADSORPTION OF MERCURY IONS ON CROSSLINKED CHITOSAN BEADS GRAFTED WITH POLYACRYLAMIDE VIA SURFACE-INITIATED ATOM TRANSFER RADICAL POLYMERIZATION 123. 5.1 Introduction 124. 5.2 Materials and methods 5.2.1 Materials 5.2.2 Preparation of chitosan beads 5.2.3 Polymerization of acrylamide on chitosan beads through ATRP method 5.2.4 Metal adsorption experiments 5.2.5 Desorption experiments 5.2.6 Surface analyses 127. 127. 127. 127. 129. 131. 131. 5.3 Results and discussion 5.3.1 Surface modification reactions 5.3.2 Mercury adsorption kinetics 5.3.3 Equilibrium adsorption of mercury ions 5.3.4 Effect of pH on selective or competitive adsorption of mercury and lead 5.3.5 Mechanism of selective adsorption 5.3.6 Desorption of adsorbed metal Ions on chitosan-g-polyacrylamide beads 132. 132. 147. 149. 151. 155. 162. 5.4 Conclusion 164. CHAPTER HIGHLY EFFECTIVE REMOVAL OF LEAD IONS WITH CROSSLINKED CHITOSAN BEADS GRAFTED WITH POLYACRYLIC ACID CHAINS 165. 6.1 Introduction 166. 6.2 Materials and methods 6.2.1 Materials 6.2.2 Preparation of PAAc-grafted chitosan beads 6.2.3 Lead adsorption experiments 6.2.4 Desorption experiments 6.2.5 FESEM observation 6.2.6 Zeta potential measurement 6.2.7 FTIR analyses 169. 169. 169. 170. 171. 172. 172. 172. 6.3 Results and discussion 6.3.1 Grafting of PAAc on DCHB beads 6.3.2 Zeta potentials 6.3.3 Adsorption performance at different solution pH values 6.3.4 Adsorption isotherms 6.3.5 Adsorption kinetics 6.3.6 Desorption study 6.3.7 Adsorption mechanism of lead ions on DCHB-PAAc beads 173. 173. 179. 180. 181. 186. 188. 190. 6.4 Conclusions 195. IV CHAPTER CONCLUSIONS AND RECOMMENDATIONS 196. 7.1 Conclusion 197. 7.2 Recommendations and future work 200. REFERENCE 203. LIST OF PUBLICATIONS 218. V SUMMARY Biopolymers have attracted great research interests in their use as adsorbents in recent years. Chitosan, a derivative of chitin, a natural biopolymer existing in various crustacean biomasses and being widely available from seafood industry waste, has been extensively studied as an adsorbent for the removal of heavy metal ions and natural organic matters from aqueous solutions, largely attributed to the non-toxicity of, and the presence of the free amine and hydroxyl groups in chitosan. The purpose of this study was to develop novel chitosan-based biopolymer granular adsorbents for enhanced removal of heavy metal ions. The research included synthesis and characterizations of mechanically strong chitosan-cellulose hydrogel beads through polymer blending, improvement of chitosan hydrogel beads for acid resistance by novel amine group protected crosslinking and functionalizations of chitosan beads through surface grafting for selective and enhanced adsorption of heavy metal ions. In the first part of the study, chitosan was blended with cellulose to make chitosan-cellulose hydrogel beads and the hydrogel beads were crosslinked with ethylene glycol diglycidyl ether (EGDE). It was found that the addition of cellulose into chitosan made the hydrogel beads materially denser (hence mechanically stronger) and crosslinking improved the chemical stability of the chitosan-cellulose beads in solutions with pH values down to 1. Batch adsorption experiments for copper ion removal showed that both chitosan-cellulose and crosslinked chitosan-cellulose hydrogel beads had reasonably high adsorption capacities for copper ions, although the crosslinked chitosan-cellulose beads exhibited lower adsorption capacities than the VI non-crosslinked beads, attributed to the consumption of the amine groups of chitosan in the crosslinking process. Then, a new amine-shielded crosslinking method of the chitosan beads with ethylene glycol diglycidyl ether (EGDE) was attempted in order to improve the metal adsorption performance of the crosslinked chitosan beads. Most of the amine groups in chitosan were converted to –N=CH2 groups through formaldehyde treatment and hence they were not involved in the crosslinking reaction with EGDE. A final treatment of the beads with a HCl solution after the crosslinking reaction effectively released the shielded nitrogen atoms in the –N=CH2 groups into the form of the primary amine. Copper ion adsorption experiments confirmed that chitosan beads crosslinked with the new method had significantly greater adsorption capacities than the beads crosslinked with the traditional method. Another effort has been made toward the selectivity of the adsorbent in the removal of heavy metal ions from aqueous solutions. Chitosan beads were modified through surface grafting and polymerization of acrylamide, via a surface-initiated atom transfer radical polymerization (ATRP) method, to achieve enhanced and selective removal of mercury ions. The chitosan-g-polyacrylamide beads were found to have significantly greater adsorption capacity and faster adsorption kinetics for mercury ions than chitosan beads. In co-adsorption experiments with both mercury and lead ions, the chitosan-g-polyacrylamide beads showed excellent selectivity for mercury ion adsorption over lead ions, in contrast to chitosan beads which did not show clear selectivity for either of the two metal species. Mechanism study suggested that the selectivity in mercury ion adsorption with chitosan-g-polyacrylamide beads can be VII attributed to the ability of mercury ion to form covalent bonds with the amide groups of the beads. A final attempt was made to increase or enhance the adsorption capacity of crosslinked chitosan beads for their effective applications in acidic solution. Chitosan beads were crosslinked by the conventional method and then grafted with polyacrylic acid (PAAc) via a simple and environmental friendly two-step surface modification method. Zeta potential analysis showed that the modified beads had negative zeta potential at pH greater than 4, which favored the adsorption of cation metal ions at a wider pH range (pH > 4), as compared to chitosan (DCHB) beads at only pH > 6.7. Adsorption experiments showed that the modified chitosan-polyacrylic acid (DCHB-PAAc) beads had much greater adsorption capacity for lead ions than the DCHB beads at all the pH values studied. 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Res., 44, pp. 6692-6700. 2005. Li, N, R.B. Bai and C.K. Liu. Enhanced and Selective Adsorption of Mercury Ions on Chitosan Beads Grafted with Polyacrylamide via Surface-initiated Atom Transfer Radical Polymerization, Langmuir, 21, pp. 11780-11787. 2005. Li, N and R.B. Bai. Highly Effective Removal of Lead Ions with Chitosan Beads Grafted with Polyacrylic Acid Chains, Ind. Eng. Chem. Res., 45, pp. 7897-7904. 2006. Li, N and R.B.Bai. Development of Chitosan-based Granular Adsorbents for Enhanced and Selective Adsorption Performance in Heavy Metal Removal, Wat. Sci. Technol., 54, pp. 103-113. 2006. Conference Papers Li, N, R.B. Bai, and C. Tien. Novel Modification of Chitosan Hydrogel Beads for Improved Properties as an Adsorbent, presented at: [263] - Novel Developments in Adsorption, AIChE Annual Meeting 2004, Austin, Texas, United States, 7-12 November 2004. Li, N and R.B. Bai. Novel Chitosan-Cellulose Hydrogel Adsorbents for Lead Adsorption, presented at: [253] - Trace Impurity Removal by Adsorption, AIChE Annual Meeting 2004, Austin, Texas, United States, 7-12 November 2004. Liu, C.X., R.B. Bai and N. Li. Sodium Tripolyphosphate (TPP) Crosslinked Chitosan Membranes and Application in Humic Acid Removal, presented at: [394] - Novel Membranes and Membrane Processes for Recovery/Recycle, AIChE Annual Meeting 2004, Austin, Texas, United States, 7-12 November 2004. Bai, R.B. and N. Li. Polyacrylamide-grafted chitosan beads for enhanced and selective adsorption of mercury ions, presented at: 80th ACS Colloid & Surface Science Symposium, Boulder, Colorado, United States, 18-21 June 2006. Bai, R.B. and N. Li. Polyacrylic acid grafted chitosan beads for highly effective 218 adsorption of lead ions, presented at: 2nd International Conference on Environmental Science and Technology, Huston, Texas, United States, 19-22 August 2006. Li, N. and R.B. Bai. Development of Chitosan-Based Granular Adsorbents for Enhanced and Selective Adsorption Performance in Heavy Metal Removal, presented at: 5th IWA World Water Congress, Beijing, China, 10-14 Sept. 2006. 219 [...]... (reaction time of 48h, monomer concentration of 7.5M) Figure 5.5 C 1s XPS spectra of (a) 2% chitosan beads, (b) surface-initiated chitosan beads, (c) chitosan-g-polyacrylamide beads (reaction time of 24h, monomer concentration of 7.5M), and (d) chitosan-g-polyacrylamide beads (reaction time of 48h, monomer concentration of 7.5M) Figure 5.6 Adsorption kinetics of mercury ions on chitosan-g-polyacrylamide and. .. solutions of different pH values Figure 6.5 Effect of solution pH values on the performance of lead ion adsorption on the DCHB and DCHB-PAAc beads Figure 6.6 Adsorption isotherms of lead ions on (a) DCHB-PAAc beads and (b) DCHB beads Figure 6.7 Kinetic adsorption results of lead ions on the DCHB-PAAc beads Figure 6.8 Desorption kinetics of lead ions from the DCHB-PAAc beads in different solutions Figure... chitosan-g-polyacrylamide beads (II) (monomer concentration of 7.5M, reaction time of 48h) Figure 5.3 FTIR spectra of (a) chitosan-g-polyacrylamide beads (monomer concentration of 3M, reaction time of 48 h) and (b) chitosan-g-polyacrylamide beads (monomer concentration of 7.5M, reaction time of 48 h) Figure 5.4 Typical wide scan XPS spectra of (a) chitosan beads, (b) surface-initiated chitosan beads, and (c) chitosan-g-polyacrylamide... Final/equilibrium concentration Ct0 (=C0) (mg/L) Initial concentration Cti (mg/L) Metal ions concentration at time ti Hr Hydration rate k2 (g/mg·min) Rate constant of the pseudo-second-order kinetic model kd Intrinsic kinetic rate constant for diffusion-controlled adsorption Kd (mL/g) Distribution coefficient ks (mg/L) Constant of Langmuir model m (M)(g) Dry weight of adsorbents n Constant depicting the adsorption... different ATRP times Table 5.6 Adsorption and desorption (recovery) behaviors of Hg2+ and Pb2+ on chitosan-g-polyacrylamide beads Table 6.1 Calculated Pb adsorption equilbrium constants Table 6.2 Adsorption and desorption behaviors of Pb on DCHB-PAAc beads Pb2+ on IX LIST OF FIGURES Figure 2.1 Structures of cellulose, chitin and chitosan Figure 3.1 The set-up of the granulation system Figure 3.2 Chitosan-cellulose... ion concentration = 15 mg/L) Figure 4.7 Effect of initial solution pH values on copper adsorption capacities on the NRCHBs, DCHBs, and CHBs (initial copper ion concentration in the solution = 15 mg/L; contact time=24h) Figure 4.8 Adsorption isotherm results of copper ions on NRCHBs and DCHBs (initial pH=4; contact time=24h, V=10 ml, initial concentration ranging from 10 to 200 mg/L) Figure 4.9 Typical... protection of environmental quality and public health Various chemical and physical methods have been used to remove heavy metal ions in the last few decades These methods include chemical precipitation, solvent extraction, ion exchange, evaporation, reverse osmosis, electrolysis and adsorption Among these methods, chemical precipitation, solvent extraction, ion exchange and adsorption are more commonly... Figure 3.11 Effect of initial solution pH values on copper adsorption capacities on the chitosan-cellulose and the crosslinked chitosan-cellulose beads (initial copper ion concentration in the solution: 30 mg/L) Figure 3.12 Adsorption capacities of copper ions on the chitosan-cellulose and the crosslinked chitosan-cellulose beads at various initial copper concentrations (initial solution pH = 6) Figure... selectivity to different types of heavy metal ions There has been increasing interest in highly selective adsorption of heavy metals because this can prevent second pollution of heavy metals and allow recovery and reuse of the different types of heavy metals that are usually the common and often expensive industrial raw materials Although many studies have reported surface modification of chitosan to... adsorption results of copper ions on the two types of hydrogel beads (initial solution pH = 6, initial copper ion concentration = 15 mg/L) Figure 3.15 The fitting of diffusion-controlled kinetic model, Eq (3.10), to the dynamic adsorption amounts of copper ions for the experimental results in Figure 3.14 Figure 3.16 FTIR spectra for the two types of hydrogel beads before and after copper adsorption: (a) Chitosan-cellulose . time of 24h, monomer concentration of 7.5M), and (d) chitosan-g-polyacrylamide beads (reaction time of 48h, monomer concentration of 7.5M). Figure 5.6 Adsorption kinetics of mercury ions on. beads (II) (monomer concentration of 7.5M, reaction time of 48h). Figure 5.3 FTIR spectra of (a) chitosan-g-polyacrylamide beads (monomer concentration of 3M, reaction time of 48 h) and (b) chitosan-g-polyacrylamide. Zeta potentials of DCHB and DCHB-PAAc beads in solutions of different pH values. Figure 6.5 Effect of solution pH values on the performance of lead ion adsorption on the DCHB and DCHB-PAAc