Synthesis Of Chitosan-based Adsorbents And Its Adsorption Behavior For Heavy Metal Ions

Water pollution has become a major environmental problem, especially for the heavy metal ions pollution in aquatic ecosystems. Adsorption is an environmental friendly method with the advantages of high efficiency. Therefore, adsorption has received great attention for dealing with the heavy metal ions over the past ten years.Hydrogels are cross-linked, three-dimensional hydrophilic polymers, which swell but not dissolve in water. Because hydrogels contain one or more electron-donor atoms such as N, S, O and P that can form coordinate bonds with the most of heavy- metal ions. So they can be used as a adsorbent for removel of heavy- metal ions from wasterwater. C hitosan is one of the most abundant natural biopolymers and has payed considerable attention as a functional, biodegradable and special biocompatible biopolymer. This article focused on the synthesis of chitosan-based hydrogel by glow discharge electrolysis plasma（GDEP）, and studied the adsorption properties for metal ions. We expect this method can play a certain role in the practical application of industrial waste water purification. The main contents are summarized as follow:Chapter 1. The source and endanger of heavy metal ions pollution were reviewed. The existing state and treatment method of water pollution is summarized. At the same time, the concept, synthetic methods, application of hydrogel and research progress of chitosan-based hydrogel were decribed in detail.Chapter 2. In aqueous solution, using N, N’-methylene-bis-acrylamide as a cross- linker, a chitosan/ attapulgite /poly acrylic acid（CS/ATP/PAA） polymer adsorbent was synthesized by the glow-discharge electrolysis plasma（GDEP）, and then employed to study the adsorption properties for five heavy metal ions. The structure of the hydrogel was charactered by Fourier transform infrared spectroscopy（FT-IR）, X-raydiffraction analysis（XRD）, X-ray photoelectron spectroscopy（XPS）, and scanning electron microscopy（SEM）. The thermostability was measured by the thermogravimetric analysis（TG/DTG）. Meanwhile, the optimal adsorption conditions of CS/ATP/PAA hydrogel for removing of heavy metal ions were studied, such as pH and adsorption time. The selectivity and reusability of five mixed solution were discussed. The results showed that the best adsorption pH is 4.8, adsorption equilibrium is reached for 3 h, and the maximum equilibrium adsorption capacities of hydrogel are 471.7, 263.3, 295.0, 138.3 and 145.0 mg·g-1, respectively. The adsorption behaviors could be described by pseudo-second-order kinetic model. The CS/ATP/PAA hydrogel exhibited excel ent selectivity and reusability.Chapter 3. C hitosan/poly（acrylic amide-co-acrylic acid）（CS/P（AM-co-AA）） hydrogel was prepared by the glow-discharge electrolysis plasma（GDEP） as an initiator in aqueous solution, and used as heavy metal ions adsorption agents. Structure and morphology were charactered by FT-IR spectra, X-raydiffraction analysis（XRD）, scanning electron microscopy（SEM） and X-ray photoelectron spectroscopy（XPS）. The thermostability was researched by the thermogravimetric analysis（TG/DTG）. In addition, the optimal adsorption conditions of CS/P（AM-co-AA） hydrogel for heavy metals, such as pH, adsorption time and initial concentration were investgated, and the selectivity in three mixed solution was disscussed. The result showed that the equilibrium adsorption time is 3 h, and the optimal pH is 6, the saturation adsorption capacities are 954.0, 229.3 and 453.7 mg·g-1 for Pb²⁺, Cu²⁺ and Cd²⁺ in a single solution. The adsorption process existed ion-exchange and is described by the pseudo-second-order kinetic model and Langmuir isotherm model.Chapter 4. A chitosan/P（2-acrylamido-2-methyl-1-propanesulfonic acid-co-acrylic amide）（CS/P（AMPS-co-AM）） hydrogel was prepared in aqueous solution by glow-discharge electrolysis plasma（GDEP） as an initiator and N,N’-methylene-bis-acrylamide as a cross-linker. The thermal stability of CS/P（AMPS-co-AM） hydrogel was studied by thermal gravimetric analysis（TG-DTA）. The structure and morphology of CS/P（AMPS-co-AM） before and after adsorption were characterized by Fourier transform infrared spectroscopy（FT-IR） and scanning electron microscopy（SEM）. The influences of various pH and adsorpt ion time on the adsorption capacity were investigated in detail. In addition, the adsorption-desorption and selectivity properties of hydrogel for Pb²⁺ were studied as well. The results showed that the equilibrium adsorption time is 3 h and the optimal pH is 4, the maximum equilibrium adsorption capacities for Pb²⁺ is 260.8mg·g-1. The chemical complexation plays an important role for heavy- metal ion adsorption onto hydrogel. The adsorption process can be described by the pseudo-second-order kinetic. The hydrogel has reusability and selectivity for the adsorption of Pb²⁺.