Preparation Of ZnAl-LDHs/GO Nanocomposites And Its Application In Removal Of Chromium Ion From Aqueous Solutions

With the accelerated process of industrialization,the massive and unreasonable emission of industrial waste water causes enormous harm to the environment.The pollution of heavy metals such as chromium has serious impact on the surrounding flora and fauna as well as human life and health.In view of this problem,this study prepared ZnAl layered double hydroxides and graphene oxide(ZnAl-LDHs/GO)nanocomposites through layer by layer self-assembly and a one-pot hydrothermal methods.The materials were characterized,and the mechanisms of adsorption were explored,in addition,the effects of ZnAl-LDHs/GO nanocomposites prepared by two methods on the removal of Cr(?)ions in aqueous solution were investigated.Graphene oxide(GO)was synthesized using a modified Hummers method,and ZnAl-LDHs was prepared by urea method.The results of XRD?FT-IR and TEM showed that the wrinkled GO and hexagonal ZnAl-LDHs were well prepared,and the effects of different conditions on adsorption capacity of ZnAl-LDHs were studied.The results showed that the maximum adsorption capacity was 34.27 mg/g when Zn/Al molar ratio was 2:1,synthesis temperature of 105?,crystallization temperature of 95? and ageing time of 24 hours.LDHs/GO-LBL nanocomposite was prepared via layer by layer self-assembly technique.The microstructure of LDHs/GO-LBL was the GO and ZnAl-LDHs stacked in alternating sequence which was characterized by FTIR,TEM,XRD and other techniques.The LDHs/GO-LBL nanocomposites were applied in the removal of Cr(VI)in water and parameters such as the exfoliated time of ZnAl-LDHs,initial Cr(VI)concentration,and pH for Cr(VI)removal were investigated.The results showed that the maximum removal rate of Cr(VI)on LDHs/GO-LBL nanocomposites was 94.13%.In addition,the adsorption process followed pseudo-second-order kinetic model and Freundlich isotherm.LDHs/GO-OPM nanocomposite was fabricated through a one-pot hydrothermal method.Characterizations such as FTIR,TEM,XRD,Raman and other techniques showed that in the obtained LDHs/GO-OPM nanocomposite two kinds of oppositely charged nanosheets which were stacked face-to-face in alternating sequence.The LDHs/GO-OPM nanocomposites were applied in the removal of Cr(?)in aqueous solution and parameters such as the mass fraction of GO,initial Cr(?)concentration,temperature and pH for Cr(?)removal were investigated.The results indicated that a maximum adsorption capacity of 48.56 mg/g was achieved on LDHs/GO-OPM contains 6.0%of GO,pH 3.0,Cr(?)solution with initial concentration of 50 mg/L,and room temperature with 1.0 g/L dosage.In addition,the influence of coexisting substances on Cr(?)removal was studied.Cr(?)removal by LDHs/GO-OPM less influenced by most coexisting substances,only particular anions could suppress Cr(?)removal.And the adsorption process followed pseudo-second-order kinetic model and Freundlich isotherm.As suggested by FT-IR and XPS analysis,a possible adsorption mechanism was that the adsorbents and Cr(?)ions occurred surface complexation or chemical sorption and synergistic contribution from each components in LDHs/GO-OPM nanocomposites enhanced Cr(?)adsorption capacity.