Preparation And Adsorption Property Of Amino-functionalized Carbon-based Magnetic Nanocomposites For Ag~+ In Aqueous Solution

Magnetic nanocomposites with high effiency, energy saving, easy separation properties and no secondary pollution were extensively applied to be adsorbents for removal of heavy metal ions pollutant from aqueous solution and have been focused a lot of interests by researchers.In this study, natural flake graphite was used to synthesize expanded graphite（EG） and graphene oxide（GO） by oxidation-interaction, high temperature expansion and modified Hummer’s method, respectively. Subsequently, amino-functionalized carbon-based magnetic nanocomposites including ethylenediamine modified magnetic expanded graphite（NH₂-MEG） nanocomposites and magnetic graphene oxide（NH₂-MGO） nanocomposites were prepared by one-pot solvothermal method using EG and GO as carbon bases, FeCl₃·6H₂O as precursor, ethylenediamine as modifier and reductant, ethanediol as surfactant and reductant, sodium acetate as stabilizer. The as-synthesized carbon based magnetic nanocomposites were characterized by means of SEM, TEM, XRD, FTIR, VSM, XPS, Zeta and UV-Vis, as well as the adsorption properties for Ag⁺ from aqueous solution were investigated by batch experiments under different conditions of pH value, initial concentration, dosage, contact time and temperature. Adsorption thermodynamics were studied by calculating enthalpy change（ΔH）, entropy change（ΔS） and Gibbs free energy change（ΔG） of adsorption pocesss according to Van’t Hoff equation. Pseudo-first kinetic model and pseudo-second kinetic model were used to study adsorption kinetics. Langmuir and Freundlich models were also utilized to investigate isothermal adsorption process.The research results showed that the NH₂-MEG nanocomposites and NH₂-MGO nanocomposites were successfully prepared, the saturation magnetization of which met the requirement of retrieving adsorbents from aqueous solution after adsorption. Acid aqueous environment was more suitable for the synthesized amino-functionalized carbon-based magnetic nanocomposites to adsorb Ag⁺ from aquous solution and the removal efficiency was over 95% in low concentration. As well as, the adsorption rate of NH₂-MGO nanocomposites for Ag⁺ was obviously fast than that of NH₂-MEG nanocomposites at the same conditions. The adsorption of carbon-based magnetic nanocomposites for Ag⁺ in aquous solution was a spontaneous endothermic process with an increasing disorder. The better agreement with pseudo-second kinetic model showed that chemical adsorption was in dominance during adsorption process. Equilibrium research showed that Langmuir model was followed by experimental data, which fur ther illustrated that the adsorption process occurred on monolayers with uniform surface.