The Preparation Of Chitosan-metal Based Composites And Its Application For The Removal Of Dyes And Chromium (?) In Waste Water

Chitosan-metal composite has drawn a great deal of attention due to enhanced adsorption capacity for toxic heavy metal ions and various dyes.The enhanced adsorption capacity depends directly on the type of metal chelated with chitosan.Various factors such as pH,type of metal and solution matrix are the key aspects that determine how the metal will be bonded with amine and hydroxyl groups of the polymer.In this work,different kinds of chitosan-metal complex have been prepared and these important factors were studied.Firstly,this study investigates the factors effecting the adsorption ability of chitosan-metal complex,including various kinds of metal centers such as Fe???,Cu???,Mg???,Ni???and Mn???,different metal salts and crosslinking degree.The results show that chitosan-Fe???complex prepared by sulfate salts exhibited the best removal rates?100%?with various dyes in very short time duration?10 min?,and its maximum adsorption capacity achieved 349.2 mg/g.The anion of the metal salt which was used in preparation played an important role to enhance the adsorption ability of chitosan metal complex.SO₄^2-ions not only had the effect of crosslinking through coulombic interaction with amine group of chitosan polymer,but also could facilitate the chelation of metal ions with chitosan polymer during the synthesis process.Additionally,the pH sensitivity and the sensitivity of ionic environment for chitosan-metal complex were analyzed.We hope that these factors effecting the adsorption of the chitosan-metal complex can help not only in optimizing its use but also in designing new chitosan-metal based complexes.Secondly,despite the high adsorption ability,efficient catalytic activity of chitosan-metal complex has been developed through the chelation of chitosan polymer with bimetals Cu???and Fe???.The removal of C.I.Reactive Black 5?RB 5?by chitosan-Cu-Fe complex/H₂O₂ system was studied in the pH range from 4.0 to 12.The maximal dye removal rate was achieved at an optimal concentration of Cu and Fe in the chitosan-Cu-Fe matrix,demonstrating the combination of sorptive enrichment and catalytic degradation.The results indicated that TOC removal and discoloration of dye achieved 89.9%and96.5%in a short reaction time.The pH sensitivity of chitosan complex,the effect of the coexisting ions and the adsorption of other anionic dyes were also studied.X-ray photoelectron spectroscopy?XPS?,Fourier transform infrared spectroscopy?FTIR?,scanning electron microscopy?SEM?and energy-dispersive X-ray spectroscopy?EDX?were analyzed to study the structure of chitosan bi-metal complex and the possible mechanism was proposed.Additionally,the Fenton reaction which has the advantages of short reaction time,economic and nontoxic,and easy to run and control was used to improve the adsorption ability of chitosan for Cr???adsorption.After the Fenton modification,chitosan could efficiently adsorb Cr???through a sandwich model under a wide pH range.The adsorption of Cr???onto Fenton modified chitosan agreed well to the Freundlich adsorption model and its adsorption capacity was found to be 140.5 mg/g.During the Fenton reaction,H₂O₂and HO·radicals with high oxidative activity broke the hydrogen bonds in chitosan structure and Fe³⁺ions chelated with chitosan.The distance between chitosan polymer chains became large and more adsorption sites were released.At last,HCrO₄^-could enter the gap between chitosan polymer and be adsorbed on new adsorption sites.The sandwich adsorption model made the Fenton modified chitosan have a greater concentration of active sites for Cr???adsorption.