Preparation Of Chitosan-based Adsorbents And Its Application For The Removal Of Heavy Metal Ions From Aqueous Solutions

Due to nondegradable and cumulative effects in living organisms,heavy metal ions can cause the permanent contamination to the ecosystem,environment and human health.Many methods,such as chemical precipitation,ion exchange,membrane separation,electrolysis,solvent extraction and adsorption,have been developed for removal of heavy metal ions from waste water.Among them,adsorption is one of the most remarkable and economical methods because of its simplicity of design,ease of operation and high efficiency.Chitosan?CS?is a natural polysaccharide with many inherent characteristics,such as nontoxicity,natural abundance,biocompatibility and biodegradability.Owing to the reactivity of amine groups and hydroxyl groups,CS and its derivatives have been applied as adsorbents for removing heavy metal ions.Glow discharge electrolysis plasma?GDEP?is a kind of non-equilibrium plasma,which can generate a large number of energetic species such as H·,HO·,O·,HO₂·and H₂O₂ in aqueous solutions.These active species would initiate the grafted polymerization reaction.This article synthesizes three kinds CS-based adsorbent by GDEP technique,and then studies the adsorption properties for heavy metal ions.The main contents are summarized as follow:Chapter 1.In order to improve its solubility and widen its application,there is necessary in chemical modification of chitosan.This chapter reviews the various methods such as chemical,radiation,glow discharge electrolysis plasma to prepare modification chitosan-based adsorbents.The several grafted groups such as carboxyl,amino,sulfydryl,thiourea,ether linkage have been introduced.The effects of pH and contact time,kinetics,isotherm,selectivity and reusability are discussed.Chapter 2.A novel CS/PEG/PAA adsorbent was prepared by GDEP technique and then applied for the selective adsorption of Pb²⁺.A copolymerization mechanism initiated by GDEP was proposed.The structure,thermal stability,and morphology of CS/PEG/PAA adsorbent were characterized by FT-IR,TG/DTG and SEM.The effects of the solution pH and contact time on the single-component adsorption were examined by batch experiments.Competitive adsorptions of Pb²⁺and Cd²⁺were carried out under equal mass concentration and equal molar concentration.In addition,regeneration and reusability of adsorbent was also investigated in detail.The results show that the maximum adsorption capacities for Pb²⁺and Cd²⁺are 431.7 and 265.0 mg g^-1,respectively.The kinetic behaviors of the adsorption and the fourth desorption for single component and the competitive adsorption for Pb²⁺follow the pseudo-second-order model.The CS/PEG/PAA adsorbent has good adsorption selectivity for Pb²⁺with the coexistence of Cd²⁺.The adsorbent displays excellent regeneration and reusability in the EDTA-4Na solution.Chapter 3.The CS/P?AMPS-co-AA?adsorbent was prepared in aqueous solution by a simple one-step procedure using GDEP technique.The reusability of adsorbent in HNO₃,EDTA-2Na and EDTA-4Na was investigated in detail.The competitive adsorption of the metal ions at the initial stage was compared with their equal mass concentration and equal molar concentration.In addition,the adsorption mechanism of the adsorbent for adsorption of Pb²⁺was also analyzed by XPS.The results show that the optimum pH of adsorption was 4.8,and time of adsorption equilibrium was about 60 min.Adsorption kinetics fitted well to the pseudo second-order model.The equilibrium adsorption capacities of Pb²⁺,Cd²⁺,Co²⁺,Cu²⁺and Ni²⁺at pH 4.8 were 673.3,358.3,176.7,235.0 and 171.7 mg g^-1,respectively.The adsorbent displays an excellent reusability using 0.015 mol L^-1 EDTA-4Na solution as the eluent.Moreover,the adsorbent shows good adsorption selectivity for Pb²⁺.The molar adsorption capacity at the initial stage with equal molar concentration was more reliable than the mass adsorption capacity during the study of selective adsorption.According to the XPS results,the adsorption of Pb²⁺by the CS/P?AMPS-co-AA?absorbent could be attributed to the coordination between N atom and Pb²⁺and ion-exchange between Na⁺and Pb²⁺.Chapter 4.A green and simple GDEP technique was used to synthesize the CS/ATP/P?AA-co-AMPS?microporous polymer.The results show that the optimum pH for the adsorption of Pb²⁺,Cd²⁺,Co²⁺,and Cu²⁺is 4.8,and time of adsorption equilibrium is 60 min.Adsorption kinetics fits well to the pseudo second-order model.The maximum adsorption capacities for Pb²⁺,Cd²⁺,Cu²⁺and Co²⁺ions are 500.0,301.7,180.0 and 151.7 mg g^–1,respectively.The microporous polymer has higher adsorption selectivity toward Pb²⁺with the coexistence of Cd²⁺,Co²⁺,and Cu²⁺.The CS/ATP/P?AA-co-AMPS?possesses promising regeneration and reusability using 2.0 g L^–1 EDTA-4Na solution as eluent.CS/ATP/P?AA-co-AMPS?can be used as a very promising absorbent for the separation,purification and selective recovery of Pb²⁺in aqueous solution containing Cd²⁺,Co²⁺,and Cu²⁺ions.