Coated material (Graphene oxide coated sand) as a new approach in wastewater treatment field: Equilibrium and thermodynamic studies

Abstract

The present work describes a coating process that was carried out on the surface of graphene oxide powder. Coated material (GO−Sand composite) was prepared by soaking screened and washed sand particles (100 µm) with 3% graphene oxide aqueous solution. The coating process was done in two stages, first at a temperature of 105 ◦C for three hours then at 150 ◦C for two hours. FTIR spectroscopy was used to investigate the surface of graphite and graphene oxide. Adsorption of methylene blue and methyl orange dyes onto the prepared graphene oxide-coated sand was done experimentally using batch apparatus with controlled conditions of temperature and stirring. The effects of temperature and initial dye concentration for the adsorption process were examined. The analysis of adsorption equilibrium isotherms shows that the experimental data follows the Freundlich isotherm model with a coefficient of variance (R2) equal to (0.99). This indicates that the adsorption of both dyes onto the GO−sand was done on the heterogeneous surface with a multilayer of dye molecules. Furthermore, basic thermodynamic parameters for the adsorption of both dyes on GO−sand were calculated using the most well-known relationships. The results indicate that the process is spontaneous and exothermic as the values of Gibbs free energy changes lie between-37.078 and-24.231 kJ/mole and the values of enthalpy changes lie between-0.669 and-0.348 kJ/mole for methylene blue and methyl orange dyes. Finally, the activation energy for the adsorption process was determined using the Arrhenius equation and found to be equal to 28.643 kJ/mol and 20.224 kJ/mol for methylene blue and methyl orange adsorption, respectively. This proves the physical nature of dye adsorption on the surface of the adsorbent.