Removal of a Cationic Dye from Aqueous Solution Using Graphene Oxide Nanosheets: Investigation of Adsorption Parameters

Abstract

In this study, graphene oxide (GO) nanosheets have been used for the adsorption of methyl green, a cationic dye from aqueous solution. GO nanosheets consist of single layered graphite structure decorated with a number of oxygen containing functionalities such as carboxyl, epoxy, ketone, and hydroxyl groups which impart a negative charge density to it in aqueous solution at a wide range of pH. Thus, GO nanosheets can be predicted as a good adsorbent material for the adsorption of cationic species. The adsorption of the methyl green onto the GO nanosheets has been carried out at different experimental conditions such as adsorption kinetics, concentration of adsorbate, pH, and temperature. The kinetics of the adsorption data were analyzed using four kinetic models such as the pseudofirst-order model, pseudosecond-order model, intraparticle diffusion, and the Boyd model to understand the adsorption behavior of methyl green onto the GO nanosheets and the mechanism of adsorption. The kinetics of adsorption result shows that the adsorption maximum was reached at 60 min and follows the linear form of pseudosecond-order kinetics. The adsorption isotherm of adsorption of the methyl green onto the GO nanosheets has been investigated in the pH range of 4 to 9 at 25 °C. The equilibrium data were fitted well to the Langmuir model. Various thermodynamic parameters such as the Gibbs free energy (ΔG°), enthalpy (ΔH°), and entropy (ΔS°) change were also evaluated. The negative value of ΔG indicates spontaneity of the adsorption process of the methyl green–GO system. The interaction of methyl green onto the GO nanosheets has been investigated by diffuse reflectance infrared Fourier transform (DRIFT) spectroscopy.