Preparation Of Amino-grafted Chitosan Composites For Their Adsorption Of Cu(Ⅱ) And Cr(Ⅵ)

Adsorption is one of the widely used methods of heavy metal treatment.At present,the capacity and adsorption rate of used adsorbents is still far from satisfaction.In this research,chitosan was used as main adsorption material to prepare two sub-micron size materials PS/Fe₃O₄/CS-PEI and Hollow Fe₃O₄/SiO₂/CS-TETA by adding different base materials and functional groups.We study the performance of the removal of heavy metals and discuss the related mechanism,which provides a certain theoretical basis and method guidance for the development and application of chitosan adsorbents.Firstly,we synthesized the carboxyl-functionalized polystyrene particles using the emulsifier-free emulsion polymerization,and then Fe₃O₄ nanoparticles were prepared onto the surface of polystyrene using the in situ co-precipitation method.Next,the magnetic polystyrene particles were coated with chitosan thin-film.Finally,PEI was grafted on the surface of the PS/Fe₃O₄/CS.Then TEM,SEM,XRD,FT-IR and VSM were adopted to characterize the structure of the material.When the synthesized PS/Fe₃O₄/CS-PEI microspheres were used as an absorbent for the absorption of Cu（II）ions,batch and column adsorption of Cu（II）was performed by the composite material as a function of solution pH,concentration and time.the adsorption isotherms and adsorption kinetics well fitted the Langmuir model and the pseudo-second-order model,respectively.The maximum adsorption capacity was about 204.6 mg g^-1.The adsorption was considerably fast,reaching the equilibrium within 15 min.In addition,the adsorbed Cu（II）ions could be effectively desorbed using 0.1 mol L^-1 HCl solution,and the regeneration study proved that the adsorption capacity of composite microspheres could up to 85%of first adsorption after six cycles.On this basis,to further increase the specific surface area of the composite microspheres.The previous synthesized PS/Fe₃O₄ was coated uniformly with a layer of silica,and then the PS/Fe₃O₄/SiO₂ was calcined at 500℃to remove the polystyrene.Next,the surface of hollow Fe₃O₄/SiO₂ was coated with chitosan thin-film.Finally,TETA was grated on the hollow Fe₃O₄/SiO₂/CS.Then SEM,XRD,FT-IR and BET were adopted to characterize the structure of the material.Batch and column adsorption of Cr（VI）was performed by the composite material as a function of solution pH,concentration,time,and adsorbent dose.The adsorption isotherms and adsorption kinetics well fitted the Langmuir model and the pseudo-second-order model,respectively.The maximum adsorption capacity of Cr（VI）was about 254.6 mg g^-1 and the reaching the equilibrium within 15 min.In addition,the adsorbed Cr（VI）ions could be effectively desorbed using 0.1 mol L^-1NaOH solution,and the regeneration study proved that the adsorption capacity of composite microspheres could up to 90%of first adsorption after five cycles.