Preparation And Characterization Of Cross-Linked Narrow Molecular Weight Distribution And Low Polymerization Degree Chitosan Pyruvic Acid Derivatives For The Removal Of Lead, Copper And Cadmium

Chitosan derivatives have gained significant interest as effective adsorbent for the removal of heavy metals due to the high number of amino and hydroxyl groups, non-toxicity, low cost and available in large quantities. Nevertheless, the applications of chitosan suffer severe drawbacks since it is insoluble in neutral or alkaline pH because of its very stable crystalline structure arising from strong hydrogen bonds. Hence, it is necessary to degrade chitosan into narrow molecular weight distribution and low polymerization degree chitosan (NLCS11, n is degree of polymerization degree) in order to increase their solubility in neutral pH aqueous solutions. Chemical modifications of NLCS11with carboxylic groups, such as pyruvic acid (PA), are to increase the selectivity and capacities for metal ions. Narrow molecular weight distribution and low polymerization degree chitosan carboxymethyl derivatives have numerous reactive functional groups such as the amino group, carboxyl group and hydroxyl group. This enables it to show chelation with various metal ions. For adsorption purposes, narrow molecular weight distribution and low polymerization degree chitosan carboxymethyl derivatives which dissolve in acidic solution and water, were crosslinked with glutaraldehyde (GLA) to enhance the mechanical strength and chemical resistance.The first objective of this study was to prepare and characterize cross-linked NLCS11chitosan pyruvic acid derivatives. Chitosan was degraded into two kinds of narrow molecular weight distribution and low polymerization degree chitosan (NLCS8and NLCS11), modified with pyruvic acid (PA), and then cross-linked with glutaraldehyde (GLA) to obtain cross-linked narrow molecular weight distribution and low polymerization degree chitosan pyruvic acid derivatives (NLCS8PA-GLA and NLCS11PA-GLA). The prepared NLCS8PA-GLA and NLCS11PA-GLA were characterized with Size Exclusion Chromatography (SEC), Fourier Transform Infrared Spectroscopy (FTIR), Scanning Electron Microscopy (SEM), Thermogravimetic/Differential Scanning Calorimetry (TG/DSC), X-Ray Diffraction (XRD) and Brunauer-Emmet-Teller (BET) methods. From all the characterization methods, the prepared sorbents exhibited excellent physical and chemical characteristics for heavy metal removal.The second objective of this study was to examine the removal of lead from aqueous solution onto cross-linked narrow molecular weight distribution and low polymerization degree chitosan pyruvic acid derivatives (NLCS8PA-GLA and NLCS11PA-GLA). The adsorption capacity of the prepared NLCS11PA-GLA (n=8,11) were examined by employing batch mode system and23factorial design method. Three (3) factors and two (2) levels of adsorbent dose (A)(0.05and0.1g), adsorbent type (B)(NLCS8PA-GLA and NLCS11PA-GLA) and concentration of lead solution (C)(1and3mg/L) were considered. From the statistical analysis, all the main parameters (A, B, and C) and some interactions of the main parameters (AC and ABC) had influence on the adsorption process at5%significance level. The adsorption process was greatly influenced by the adsorbent type (B). The adsorption equilibrium results correlated well with the Freundlich isotherm model. The adsorption kinetic data also correlated well with the pseudo second order. The thermodynamic studies also revealed that the nature of lead adsorption was spontaneous, and endothermic. Isothermal Titration Calorimetry (ITC) technique confirmed the spontaneous nature of lead sorption onto narrow molecular weight distribution and low polymerization degree chitosan pyruvic acid derivative. The findings suggested that these two derivatives were good for lead removal. The third objective of this study was to explore the sorption of copper (Ⅱ) ions onto cross-linked narrow molecular weight distribution and low polymerization degree chitosan pyruvic acid derivative (NLCS11PA-GLA). A24full factorial design analysis was performed to determine the variables affecting Cu (II) removal efficiency. Two levels of pH of the solution (A)(4and5), temperature (B)(40℃and50℃), dose of sorbent (C)(0.1and0.3g), and concentration of the solution (D)(1and3mg/L) were considered. From the statistical analysis, dose of sorbent (C) and Cu (Ⅱ) concentration (D) influenced removal efficiency at5%significance level. Also, some interactions such as ABCD, ACD, ABC, and AC affected the removal process. Compared to the other models, Freundlich isotherm model was the best isotherm model. The kinetic study results followed the pseudo second-order model. The thermodynamic studies also revealed that the nature of copper sorption was spontaneous and endothermic. From the desorption studies, the sorbent can be used efficiently for a number of sorption/desorption cycles.The fourth objective of this study was to evaluate the sorption of cadmium (Ⅱ) ions onto glutaraldehyde cross-linked narrow molecular weight distribution and low polymerization degree chitosan pyruvic acid derivative (NLCS8PA-GLA). A23factorial design analysis was done to determine the variables affecting Cd (Ⅱ) removal efficiency method. Three (3) factors and two (2) levels of solution pH (6.0or10.0), temperature (45℃or70℃) and Cd (Ⅱ) concentration (1or3mg/L) were examined. The sorption equilibrium results correlated well with the Freundlich isotherm model. The sorption kinetic data also correlated well with the pseudo first order. The thermodynamic studies also revealed that the nature of cadmium sorption was spontaneous and endothermic. The findings suggested that the sorbent was good for cadmium sorption. Among other things, the novelty in this study is the preparation and characterization of NLCS8PA-GLA and NLCS11PA-GLA for the removal of Pb (Ⅱ), Cu (Ⅱ) and Cd (Ⅱ) using batch mode system and full factorial design. Also, the use of Isothermal Titration Calorimetry (ITC) to determine the interaction between metal ion and narrow molecular weight distribution and low polymerization degree chitosan pyruvic acid derivative is a good contribution.