Preparation Of Expanded Graphite And Its Adsorption Performance For Malachite Green

The discharge of dye wastewater has become increasingly serious,and its treatment has attracted widespread attention.In recent years,expanded graphite(EG)has shown good removal performance in the treatment of dye polluted water.The EG has a unique pore structure and physicochemical properties,which make it have good removal ability for most dye molecules.Due to the different of preparation processes,the physicochemical properties of EG are significantly different.Existing studies have different opinions on the mechanism of EG removal of dyes in water.Therefore,it is of great significance for deeply studying of the adsorption mechanism of malachite green(MG)dye on EG to improve the removal performance and apply in practice.In this paper,the natural flake graphite(NFG)was used as raw material to prepare EG by oxidation intercalation and high temperature expansion two-step methods.The physicochemical properties of EG were characterized by various methods.The adsorption isotherms,kinetics and thermodynamic behavior of MG on EG were studied comprehensively,and the mechanism of EG removal of MG was analyzed in depth.Theoretical guidance is provided for the preparation of specific adsorbents for the removal of different contaminants.The main findings of this paper are as follows:(1)The EG preparation process was optimized by orthogonal test(OT),and the optimal process parameters are:C(g):K2Cr2O7(g):HNO3(mL):HClO4(mL):CH3COOH(mL)=5 g:1.3 g:3 mL:2mL:11 mL,reaction temperature 50?,reaction time 50 min,expansion temperature 1000?,drying temperature 80?,drying time 40 min,expansion volume(EV)375 mL/g.The order of influence of various factors on EV is:reaction temperature>expansion temperature>reaction time>potassium dichromate dosage>nitric acid dosage>glacial acetic acid dosage>perchloric acid dosage.(2)EG was characterized by SEM,XPS,XRD,pore structure test and FT-IR.The characterization of results showed that no new functional groups were introduced during the preparation of EG;under the optimal process parameters for the preparation of EG,and the specific surface area of EG was 124.00 m~2/g,the proportion of the number of mesopores is 72.21%.(3)The kinetic data were analyzed by three adsorption kinetics models.The results show that the quasi-secondary kinetic model more fits the EG removal process.Compared with the Freundlich model,the Langmuir model showed a better fit to the experimental data,indicating that the adsorption process is a monolayer adsorption process,and the adsorption isotherm of EG to MG is type I.According to the thermodynamic calculation,the entropy change?S>0,the adsorption free energy?G<0,and the adsorption heat?H range from 5~15 kJ/mol.It indicates that the adsorption process is a spontaneous physical adsorption process.(4)Study the different expansion temperatures of preparing EG to removal of MG.The results showed that the adsorption amount of MG was basically linear with the specific surface area of EG.The characterization results of XPS and FT-IR and the fitting results of the Langmuir model on the experimental data prove that the process of EG removal of MG is surface adsorption,the larger adsorption amount is mainly attributed to the?bond structure of the expanded graphite surface,the interaction with MG by?-?action;And the hydrogen bonding of MG as the cationic dye to the surface of EG.