Preparation Of Chitosan Modified Adsorbent And Its Application For Heavy Metal Ions

With the development of industrialization,heavy metal ions pollution has become an environmental problem that can not be ignored.Heavy metal ions wastewaters often exist in acidic form and originate mainly from various industrial and agricultural activities.Except for a few essential trace elements for human body,most heavy metals,such as lead,mercury,cadmium,arsenic,chromium and so on,will cause harm to human body even if the concentration is very low.Heavy metals are not biodegradable and are easy to accumulate in the biological chain and spread through the food chain.The existing methods for treating heavy metal ions of wastewaters are mainly divided into physical-chemical methods,chemical methods and biological methods.Among them,adsorption is one of physical-chemical method.Because of its high treatment efficiency,simple operation and low cost,it has become one of the preferred methods for the treatment of heavy metal ions.The key of adsorption method is the selection of adsorbent.A good adsorbent should have the characteristics of high adsorption capacity,fast adsorption rate,easy desorption and regeneration and so on.Chitosan is a polysaccharide polymer obtained by deacetylation of chitin,and chitin is an important biopolymer produced by crustaceans.Chitosan is the second most abundant biopolymer after cellulose,which is cheap,biodegradable and biocompatible.Chitosan has amino and hydroxyl groups in its structural units,which can be used as adsorption sites for chelation with heavy metal ions.Therefore,chitosan has a broad application prospect in the treatment of heavy metal wastewater.However,chitosan is soluble in acidic solution.Hence,chitosan must be modified before it is used for the removal of heavy metal ions in acidic wastewaters.In this paper,three new materials were prepared by three different methods using chitosan as raw material.Their structures and morphologies were characterized by different methods and their adsorption properties for heavy metal ions were studied.Main research results are given as follows:1.The preparation of polymer compositing-modified chitosan material and its application for adsorption of Hg²⁺Firstly,chitosan（CS）was dissolved with itaconic acid monomer（IA）.Then,A new chitosan modified material（PPCS）was prepared by compositing with polyvinylpyrrolidone（PVP）in chitosan-itaconic acid solution using potassium persulfate as initiator.The structure and morphology of this material were characterized by FT-IR,TGA,XRD and SEM.The characterization results showed that this material was mainly consisted of micron particles.This morphology would be beneficial to improve its adsorption capacity.The research results for adsorption of some typical heavy metal ions on this material indicated that this material had higher uptake for Hg²⁺.Hence,main factors of Hg²⁺adsorption on this material were studied.The results showed that the optimum pH of the adsorption was 6 and the adsorption equilibrium time was about 180 min.The kinetic research showed that the adsorption was accorded with the pseudo second order kinetics.The isotherm research showed that the adsorption conformed to the Langmuir model,and the theoretical maximum adsorption capacity was 1111 mg/g.The existence of other ions would reduce the adsorption capacity.Thermodynamic studies showed that the adsorption was an exothermic and spontaneous process with increase of disorder.The adsorbent could be desorbed and regenerated.2.Preparation of graphene oxide modified chitosan and its application for selective adsorption of Hg²⁺Graphene oxide（GO）was first synthesized from graphite powder by modified Hummers method.Then,amine functionalized graphene oxide（GO-NH₂）was prepared by the reaction of graphene oxide withγ-aminopropyl triethoxysilane（APTES）.Next,chitosan（CS）was oxidized to form aldehyde groups by sodium periodate and a schiff base-modified chitosan material（GOCS）was prepared by the reaction of oxydic chitoan with GO-NH₂.The material was characterized by FT-IR,TGA,XRD and SEM methods and the results indicated that the material was successful prepared.The research results for adsorption of some typical heavy metal ions on this material indicated that this material had higher uptake for Hg²⁺.Therefore,main factors for Hg²⁺adsorption onto this material was studied.The optimum pH of Hg²⁺adsorption was 6 and the adsorption equilibrium time was about 70 min.The kinetic research showed that the adsorption followed the pseudo second order kinetics.The isotherm research showed that the adsorption followed the Langmuir model,and the theoretical maximum adsorption capacity was 461.5 mg/g.The research results on the adsorption under Hg²⁺and another coexisting heavy metal ion indicated that GOCS had selectivity for adsorption of Hg²⁺.The increase of adsorbent dosage was beneficial to improve the removal rate for Hg²⁺.The existence of other ions would reduce the adsorption capacity of GOCS.Thermodynamic study indicated that the adsorption was a spontaneous and exothermic process with increased disorder.The adsorbent could be desorbed and regenerated.3.Preparation of poly-p-aminodiphenylamine modified chitosan and its application for adsorption of Pb²⁺One pot method was used in the preparation.A new chitosan material（DPACS）was prepared by polymerization of p-aminodiphenylamine using ammonium persulfate as initiator and crosslinking between chitosan and poly p-aminodiphenylamine with glutaraldehyde.The structure of this material was characterized by FT-IR,TGA,XRD and SEM and the results indicated the successful synthesis of DPACS.The research results for adsorption of some typical heavy metal ions on DPACS indicated that this material had higher uptake for Pb²⁺.Therefore,the adsorption performance of DPACS for Pb²⁺soultion was studied.The optimum pH of Pb²⁺asorption solution was 5 and the adsorption equilibrium time was about 180 min.The kinetic research showed that the adsorption followed the pseudo second order kinetics.The isotherm research showed that the adsorption followed the Langmuir and Temkin model,and the theoretical maximum adsorption capacity was 409.9 mg/g.Thermodynamic studies showed that the adsorption was an endothermic and spontaneous process with increased disorder.For20 mg/L Pb²⁺solution,the removal rate of Pb²⁺was 83.33%.The adsorbent could be desorbed and regenerated.By the above modification,the capacity of three modified chitosan materials for the adsorption of some typical heavy metal ions were higher than that before modification.EDTA could be used for desorption and regeneration.Therefore,they were expected to be used for the removal of relevant heavy metal ions from wastewater.