Preparation Of Modified Chitosan For The Adsorption Of Heavy Metal Ions And Dyes In The Water

Contaminant of heavy metal ions and dyes in water has led to a lot of environmental problems.In recent years,how to treat wastewater with highly efficiency,simplicity and safety is becoming a hot spot of water treatment research.Chitosan is one of a natural alkaline polysaccharides,which is a widely recognized natural adsorbent.In this thesis,chitosan were prepared by alkaline N-deacetylation of squid pens ?-chitin.Three kinds of modified chitosan were synthesized by a variety of modification methods,and their adsorption behavior for heavy metal ions and dyes were further investigated.Experimental methods and results are shown as follows:1.Three kinds of novel modified chitosan adsorbents were synthesized by cross-linking and compound modification,which are thiosemicarbazide modified chitosan?TSFCS?,diethylenetriamine and epichlorohydrin modified chitosan microspheres?DECS?,2-chloroethylamine hydrochloride modified magnetic and ion-imprinted chitosan microspheres?AECS,ion-imprinted interpenetrating polymer network abbreviated to II-IPN,non-imprinted interpenetrating polymer network abbreviated to NI-IPN?.These modified chitosan were characterized by FTIR,SEM,XRD,TGA and VSM.2.TSFCS was used as adsorbent for adsorption of Cu?II?in water,and the results showed that the maximum Cu?II?ions adsorption capacity of three different degrees of substitution samples were 53.8,86.2,134.0 mg·g-1 at pH 3.6 and 25 ?.Adsorption isotherms was analyzed,which indicated the adsorption process followed Langmuir model;Dynamics studies showed that the external surface uptake and equilibrium uptake have equal importance in the adsorption system,and the adsorption process involved multiple models.DECS was used as adsorbent for adsorption of congo red?CR?and acid green 50?AG50?,and the results showed that the adsorption kinetics of two kinds of dyes followed the pseudo-second-order model and the maximal adsorption capacities calculated by Langmuir equations at p H 3.0 and 25 ?were 428.7 mg·g-1 and 691.8 mg·g-1 respectively;Freundlich model was analyzed,which indicated the favourable adsorption and endothermic reaction happened for the dyes onto the microspheres.AECS was used as adsorbent for adsorption of Cd?II?in water,and the results showed that the adsorption process conforms to the pseudo-second-order model and Langmuir model.The maximal adsorption capacities of II-IPN and NI-IPN calculated by Langmuir equations at p H 6.0 and 25 ? were 25.7 mg·g-1 and 6.4 mg·g-1 respectively.Competitive adsorptions of Cd²⁺/Cu²⁺,Cd²⁺/Cr²⁺ and Cd²⁺/Pb²⁺ pairs were investigated from their binary solutions to examine the selectivity of II-IPN,and found II-IPN showed a good selectivity for Cd?II?.3.Regeneration of TSFCS,DECS and AECS have been studied and used 0.01 M Na₂EDTA?0.1 M Na OH and 0.1 M HNO3 as eluent,respectively.The results showed that TSFCS and DECS were released successfully and the adsorption capacity could retain above 80% and 92% even after 5 adsorption-desorption cycles,but AECS?II-IPN?decrease to 74% after 6 adsorption-desorption cycles.