Modification Of Chitosan And Investigation Of Its Adsorption Behavior For Heavy Metal Ions And Dyes

A large number of wastewater containing heavy metals and dyes have been produced because of the rapid development of modern industry. The wastewater is non-degradable and easy to be concentrated in living bodies through food chain. It constitutes a great threat to environment and human life. Biosorption, as a new method, is a potential method for the removal of heavy metal ions and dyes due to the simple operation and high treatment efficiency. Among all kinds of adsorbents, chitosan attracted a wide spread attention, because of the abundant resources, high adsorption capacity, high adsorption and selective adsorption, etc. In this paper, we carried out the graft modification of chitosan and study of its adsorption behavior to metal ions and cationic dyes based on the full literature survey. The main work about the biosorption for metal ions and cationic dyes are summarized as follows:1. Chitosan microspheres was synthesized using glutaraldehyde as the crosslinker, paraffin as the dispersant and Span-80 as the emulsifier. The study focused on the effect of the dosage of crosslinker to the appearance of chitosan microsphere. The modified chitosan was characterized using SEM and FTIR analysis. The alteration of the microspheres' thermal characteristic was measured by differential scanning calorimetry and thermal balance. The adsorption behavior of crosslinked chitosan to Cd2+, Pb2+, Cu2+, Ag+, Co2+ and Zn2+ was studied and the adsorption mechanism was discussed. The results indicate that the adsorption of crosslinked chitosan to the metal ions depend on the coordination of -NH2 or -OH with metal ions. The adsorption capacity of crosslinked chitosan decreased in different degrees for the active groups of -NH2 were occupied, but it still can adsorb metal ions solution with low concentration.2. Pyromellitic dianhydride (PMDA) grafted chitosan microspheres were prepared, and characterized by Scanning electric microscope (SEM), Fourier transform infrared spectroscopy (FTIR) and X-ray photoelectron spectroscopy (XPS). The changes in particle diameter of the microspheres before and after modification were also investigated by BET autosorb instrument, and the decreased surface area indicated that the particle diameter of the microspheres increased after the modification. The adsorption behavior of the modified microspheres to Cd2+, Pb2+, Cu2+, Ag+, Co2+ and Zn2+ was studied. The adsorption curves were fitted with the Langmuir, Freundlich and Temkin equations. The results showed that The Langmuir isotherm fitted best in the aforesaid equations. The negative values of standard free energy changes (△G°) of each metal ion showed that the adsorption reactions were spontaneous. The loaded biosorbent was regenerated by using 0.2 mol·L-1 EDTA or 5% thiourea-0.5 mol·L-1 HCl and could be used repeatedly at three times with little loss of uptake capacity. Good results were obtained when the modified microsphere was used to treat the real wastewater.3. In the paper, crosslinked carboxymethyl chitosan was prepared by a simple method. The presence of chloroacetic acid on the surface of chitosan was verified by FTIR and XPS. The adsorption curves were fitted well with Langmuir equation and the result indicated that the adsorption reaction of metal ions was adsorbed on the modified microspheres as monolayer. The kinetics for Pb2+, Cd2+ and Co2+ adsorption followed the pseudo-second-order kinetics, and the treatment efficiency improved greatly because of the higher initial absorbing rate. Compared with other adsorbents, the modified microspheres have the higher adsorption capacity and good regeneration ability, so it can be used repeatedly.4. A modified chitosan microspheres were prepared by grafting poly (amic acid), which was obtained via reaction of PMDA and L-arginine, onto the surface of chitosan. The modified chitosan was characterized using FTIR. The effect of pH, adsorption time, concentration of metal ions, coexisted ionic strength and temperature to the adsorption of methylene blue and neutral red were studied. Thermodynamic constants of methylene blue and neutral red adsorption under different temperature were discussed. The results showed that methylene blue adsorption was exothermic reaction, while the neutral red adsorption was endothermic reaction. The result of the treat of real wastewater showed the good practical application value of modified chitosan.5. In this study, the graft copolymerization of methacrylic acid onto chitosan was carried out in aqueous medium using potassium persulfate (PPS) as initiator. The obtained poly (methacrylic acid) modified chitosan was characterized by SEM, FTIR and XPS. Under the selected optimum conditions, the maximum adsorbing capacity of modified chitosan to four kinds of cationic dyes, methylene blue, neutral red, malachite green and crystal violet, were 1000.00,1062.15,471.70 and 1401.16 mg·g-1, respectively, which are higher than that of the unmodified chitosan. The loaded biosorbent was regenerated well by using acid titanium bioxide hydrosol with nanoparticles size. The adsorbent and the hydrosol could be easily separated by centrifugation. The adsorbent and the hydrosol could be reused with little loss of the ability, and it showed good potential to use in practical.