The Preparation Of Chitosan-based Adsorbent And Its Adsorption Performance For Ionic Dyes

Chitosan(CS)is the second largest,environmentally-friendly,easy biodegradation and nontoxicity biopolymer in nature after cellulose.Since there is a large number of hydroxyl and amino groups in its molecular structure which makes it easy to interact with dye molecules.CS is widely used as an adsorbent in dye removal from aqueous solution.However,the powdery CS was difficult to be separated from the solution after adsorption,moreover,CS exhibited poor adsorption capacity toward cationic dye due to positively charged surface.In this paper,CS was selected as a potential adsorbent material due to its abundant hydroxyl and amino groups.To improve its separation performance,magnetic nanoparticle component Fe3O4 was introduced or composite beads materials were fabricated.In order to enhance its adsorption capacities toward cationic or anionic dyes,anionic functional group-COOH or cationic amine group-NH2 was introduced to increase the adsorption active sites.The modified adsorbents were applied to the synthetic single or binary cationic or anionic dye system to evaluate its adsorption performance and explore its possible adsorption mechanism.The main research contents and results are as follows:(1)With the combined introduction of magnetic nanoparticle Fe3O4 and cationic component ethylenediamine,ethylenediamine modified magnetic CS composite(MCS-NH2)adsorbent was synthesized facilely by one-pot method.The structural analysis of the composite were obtained from FT-IR,XRD,TGA,VSM,SEM,TEM,Zeta potential and BET.Its adsorption capacities and mechanism toward anionic dye Orange ?(OR ?)were studied in a batch system.The results showed that the highest ORII removal of 94.3%was obtained at the optimum conditions:pH 7.07,initial ORII concentration 100 mg L-1,adsorbent dose 3 g L-1,room temperature(298 K)at 30 min.Meanwhile,MCS-NH2 composite exhibited excellent adsorption capacities toward anionic dye,which should have potential applications in effluent treatment in printing and dyeing industry.(2)The bead adsorbent CS/Gel-xGN was derived from chitosan and gelatin,filled with graphene for improving its thermal stability and swelling stability in aqueous solution.The as-prepared composite bead CS/Gel-xGN was characterized by FT-IR,XRD,TGA,FESEM and Zeta potential.Its adsorption behavior of toward ORII was evaluated,where the effect of the contact time,pH,the initial ORII concentration on ORII removal were systematically studied.Moreover,the swelling behavior and recyclability of CS/Gel-xGN were also studied.The adsorbent showed the highest ORII removal of 84.3%at the optimum conditions.In addition,the effects of the co-existed inorganic salt and surfactants(CTAB,SDS,Triton X-100)on its adsorption performance toward ORII were also investigated.Subsequently,the adsorption kinetics and isothermal studies were performed and analyzed in order to achieve a thorough comprehension of dyes adsorption mechanism.The results revealed that electrostatic interactions and hydrogen bond were mainly involved in the dye adsorption process.(3)With the combined introduction of the monochloroacetic acid(MCA)component with a higher carboxyl content into chitosan structure,a pH-sensitive N,O-carboxymethyl chitosan(CCSx)adsorbent with tunable adsorption and separation capacity was successfully prepared and characterized by FT-IR,XRD,SEM,EDX,Zeta potential and BET measurement.Its adsorption capacities toward anionic dye methyl orange(MO)and cationic dye methylene blue(MB)were studied and the possible adsorption mechanism was also proposed.The results showed that carboxymethylation of CS with MCA occurred mainly at C6-OH and C2-NH2 positions.At the optimal pHs(pH>5 for MB and pH<3 for MO),the highest removal of 94.5%and 90.6%for MB and MO,respectively,were observed for CCS1.The adsorption data fitted better with Langmuir isotherm model(R2>0.99)and the maximum adsorption capacities of 92.51 and 64.56 mg g-1 were obtained for MB and MO,respectively.Moreover,MB or MO could be separated efficiently at pH>5 or pH<3 in the MB/MO binary system,indicating its selective adsorption and separation property.