Kinetics and Adsorption Behavior of the Methyl Blue at the Graphene Oxide/Reduced Graphene Oxide Nanosheet-Water Interface: A Comparative Study

摘要

The adsorption behavior of the methyl blue dye molecule, a mutagenic agent onto the graphene oxide (GO) and reduced graphene oxide (rGO) nanosheets, has been investigated at different pH values, adsorption times, temperatures, and also in the presence of different ions like Na~+, Ca~(2+), Mg~(2+), and SO4~(2-). A green solution chemistry approach has been adopted for the synthesis of rGO where ascorbic acid is used as a reducing agent under ultrasonication. A kinetic investigation has revealed that adsorption of methyl blue at the GO/rGO nanosheets-water interface follows linear pseudo second-order kinetics. The endothermic and spontaneous nature of the adsorption process was ascertained by the thermodynamic parameters such as Gibbs free energy change (ΔG°), enthalpy change (ΔH°), and entropy changes (ΔS°). The adsorption density of methyl blue at the GO nanosheet-water interface increases with increasing pH of the medium, while it decreases at the rGO nanosheet-water interface. Such results indicates that methyl blue interacts with GO nanosheets mainly by its positively charged =(N~+H-) group, while with rGO nanosheets interact by its negatively charged SO3~- groups. The influence of presence of different monovalent and divalent ions like Na~+, Ca~(2+), Mg~(2+), and SO4~(2-) on the adsorption density of the methyl blue onto the GO and rGO nanosheets was also investigated. The mechanism of the adsorption process was finally investigated by diffuse reflectance infrared Fourier transform (DRIFT) spectra of GO and rGO nanosheets before and after adsorption of methyl blue dye molecule.