Preparation Of Novel Modified And Crosslinked Chitosan And Its Adsorption Of The Copper Subgroup Metal Ions

Copper, silver, gold are three of the IB group elements in the periodic table, also known as copper subgroup metal elements. The natural polymer chitosan and its chemical modification derivatives can be applied as an available adsorbent for copper subgroup metal ions in waste water, which is of great significance in metallurgy, chemical industry and environment field, etc.In this thesis, the novel modified and crosslinked chitosan resins were prepared by different methods. The structure and morphology of the resin were characterized by scanning electronic microscope (SEM), X-ray diffraction (XRD) and fourier transform infrared spectroscopy (FTIR) methods, and the adsorption properties of the resins for copper subgroup metal ions were focused studied. The main research contents and results were as follows:1. Under microwave irradiation, polyaminated and crosslinked chitosan beads (PCCB) were prepared using copper ion as template. The synthesis mechanism of PCCB resin was studied by SEM, FTIR and XRD, respectively and the synthesis conditions were optimized as well. The results showed that the PCCB resin was with high resistance to acid and alkali, high water absorption swelling properties and high crystallinity; more amino groups existed on PCCB resin contrasting with the crosslinked chitosan. The best synthesis conditions were:3mL of ethanol,5mL of epichlorohydrin, 11mL of tetraethylenepentamine, and 3 min of polyaminated time under microwave irradiation.The PCCB resin was used to adsorb Cu(Ⅱ), Ag(Ⅰ) and Au(Ⅲ), and the influence of the adsorption conditions(pH value, temperature,intitial concentration, contact time, etc) on adsorption capacity, the adsorption kinetics, the adsorption isothermal properties and the adsorption thermodynamic parameters were investigated, respectively. The maximum adsorption capacities of Cu(Ⅱ), Ag(Ⅰ) and Au(Ⅲ) ions on PCCB were observed at pH values of 5,4 and 2, respectively. The kinetics results indicated that the adsorption behaviors of Cu(Ⅱ), Ag(Ⅰ) and Au(Ⅲ) onto PCCB resin obeyed pseudo-second order kinetic model and intraparticle diffusion model, and the adsorption process were controlled by intraparticle diffusion and liquid membrane diffusion. The calculated values of Eacu and Ag were 7.773 and 10.92 kJ·mol-1, respectively. Adsorption equilibrium data of PCCB resin for Cu (Ⅱ) and Ag (Ⅰ) agreed very well with the Langmuir model, otherwise the adsorption of Au (Ⅲ) on PCCB obeyed Langmuir equation and Freundlich equation. The adsorption of PCCB resin for Cu (Ⅱ) and Ag (Ⅰ) was endothermic chemical adsorption, and the adsorption of Au (Ⅲ) was exothermic physical adsorption. Selective adsorption experiments showed that the adsorption ability of PCCB resin for metal ions was Cu(Ⅱ)>Ag(Ⅰ)>Au(Ⅲ).2. Using dibutyl phthalate as additive, novel crosslinked chitosan pompoms (CCP) with short-fibers surface were prepared, and CCP was used to adsorbing Cu(Ⅱ) ions. The results showed that dibutyl phthalate coulf make CCP with fiber-like surface structure through softening the particles of crosslinked chitosan. The CCP resin was with higher specific surface area (39.14 m·g-1) and higher crystallinity than pure crosslinked chitosan, and the chemical structure of CCP was the same with CCB. Thermal stability of CCP was worse than chitosan. The adsorption process for Cu(Ⅱ) could achieved equilibrium in 8 h, and the adsorption capacity was 12.55 mg·g-1.3. Using CS2 as modifying agent, xanthated crosslinked chitosan(XCCS) resin was prepared under microwave irradiation, which was used to adsorb Ag(Ⅰ) and Au(Ⅲ) from aqueous solution. The optimization experiment results showed that high adsorption capacity was obtained with 3min of xanthated time and 2mL of CS2, respectively. Rough surfaced XCCS was with the sulfhydryl and hydroxyl groups which can adsorb metals ions effectively. The maximum adsorption capacity for Ag(Ⅰ) was observed at pH 4 and 50℃, and the maximum adsorption capacity of Au(Ⅲ) ions on XCCS was observed at pH 1 and 20℃. The kinetic experimental data corresponded well to the pseudo-second order kinetic model. Langmuir and Freundlich adsorption models were applied to describe the isotherms and isotherm constants. Equilibrium data agreed very well with the Langmuir model. Thermodynamic parameters of adsorption process were calculated. The adsorption process of Ag(Ⅰ) on XCCS was spontaneous and endothermic, and the adsorption process depended on coordination. The adsorption process of Au(Ⅲ) on XCCS was spontaneous and exothermic, and the adsorption was mainly effected by electrostatic interaction. At room temperature in thiourea-H2SO4 solution, the desorption ratio of XCCS-Au was 97.89% in 100min, which was 95.15% of XCCS-Ag in 6 h, respectively.4. The formaldehyde pre-crosslinked and epichlorohydrin crosslinked chitosan microspheres, which were used for adsorbing Cu(Ⅱ) from aqueous solution, were prepared by emulsion crosslinking method under microwave irradiation. The crosslinked chitosan microspheres were characterized by FT-IR, SEM and particle size analyzer. The crosslinked chitosan microspheres were spherical in shape, and the amino of chitosan could be protected by schiff base. The average particle size, the weight loss, and the water adsorption ratio of microspheres were 65.95 μm,1.62%, and 253%, respectively. The best preparation conditions(600r·min-1 of stirring rate,1.5mL of formaldehyde,3mL of epichlorohydrin,8min of acid treatment time and 40mL of hydrochloric acid) were obtained by single-factor experiments. The crosslinking chitosan microspheres adsorbed Cu(Ⅱ) easily under the conditions of pH 5.0 at 50℃ in solution of initial concentration(10mg·mL-1). The adsorption process reached equilibrium in 480 min. The pseudo-second order kinetic model can describe well the adsorption rate of crosslinked chitosan microsphere for Cu (Ⅱ), and the value of Ea was 6.455 kJ·mol-1. Langmuir isotherm adsorption model was more suitable to describe the adsorption process. The adsorption process of Ag(Ⅰ) on XCCS was spontaneous and endothermic chemical process.