Preparation And Adsorption Of Cr(?) And Hg(?) On Magnetic Graphene Oxide Composite Adsorbents

Graphene oxide?GO?has abundant oxygen-containing functional groups both on the basal planes and at the edges of GO sheets,such as hydroxyl,epoxy and carboxyl groups.It has large surface area which serves as superb platform for loading contaminants in the process of wastewater treatment.However,GO as a nano adsorbent has some shortages,such as high dispersibility in aqueous solution makes it difficult to separate from treated water,which limits its application in environmental protection.In this study,magnetic graphene?CFGO?and magnetic chitosan/graphene oxide?MCGO?,prepared by hydrothermal method,were used to remove Cr???and Hg???from wastewater by batch experiments.1.The experiments on adsorption of Cr Cr???and Hg???by CFGO mainly draw the following conclusions:A graphene oxide-based adsorbent?CFGO?was prepared by magnetic graphene oxide by hydrothermal method.And the optimum preparation conditions,designed by orthogonal test,are as follows:1 g cobaltironoxide,70 mg GO react at 85 ? for 12 hours.Diffuse reflectance infrared Fourier transform spectroscopy,X-ray diffraction?XRD?and X-ray photoelectron spectroscopy?XPS?analyses were used to characterize CFGO,which indicated that GO was successfully grafted on cobaltironoxide,the crystal structure of cobaltironoxide didn't change during hydrothermal reaction and CFGO had plentiful oxygen-containing functional groups on its surface.Effects of dosage,initial pH value,reaction time and temperature on adsorption of Cr???and Hg???in aqueous solutions,using CFGO composite,were investigated in batch experiments.The removal of Cr???and Hg???in aqueous solutions by CFGO preferred acidic and neutral/acidic conditions,respectively.Adsorption performance of Cr???and Hg???from aqueous solution increased with increasing reaction time and temperature.While the presence of coexisting/coexistence cations and iron strength inhibited the adsorption of Cr???and Hg???.The pseudo-second-order model agreed with the experimental value better than that of the pseudo-first-order model and elovich model of both adsorption processes.Langmuir model and Freundlich model were more precise in evaluating adsorption of Cr???and Hg???onto CFGO respectively.Thermodynamic parameters indicated that the sorption processes were exothermic and spontaneous.The maximum adsorption capacities of Cr???and Hg???by CFGO were 19.17 mg/g and 15.07 mg/g respectively.The adsoption of Cr???and Hg???may mainly be electrostatic attraction according to the results of diffuse reflectance and XPS spectra before and after adsorption.2.The experiments on adsorption of Cr???by MCGO mainly draw the following conclusions:Diffuse reflectance infrared Fourier transform spectroscopy,X-ray diffraction and X-ray photoelectron spectroscopy analyses were used to characterize MCGO.The existed elements of C,O and extra element of N indicated that GO and chitosan?CS?were successfully grafted on cobaltironoxide.Adsorption performance of Cr???benefited from low pH value,increasing reaction time and temperature in batch experiments.Electrostatic repulsion between coexisting cations and-COOH₂⁺,-OH₂⁺,competition between coexistence cations and HCrO₄^-,Cr₂O₇^2-inhibited adsorption of Cr???.Adsorption of Cr???decreased with increasing iron strength owing to the droop of electrostatic attraction.The elovich model fitted the adsorption kinetics of Cr???better than that of the pseudo-first-order model and pseudo-second-order model.Langmuir model was more precise in evaluating adsorption of Cr???.Thermodynamic parameters indicated that the sorption processes were exothermic and spontaneous with a maximum adsorption capacity of 114.38 mg/g which was much higher than that of CFGO.Adsorption of Cr???by MCGO may be electrostatic attraction between-COOH₂⁺,-OH₂⁺and Cr???,and complexation between-NH₂ and Cr???mainly according to Diffuse reflectance infrared Fourier transform spectroscopy and X-ray photoelectron spectroscopy analyses.