Efficient removal of different basic dyes using graphene

Adsorptive removal of two basic dyes, methylene blue (MB) and malachite green (MG) using thermally reduced graphene (TRG) is reported. TRG was synthesized by thermal exfoliation and reduction of graphite oxide, and characterized by X-ray diffraction, transmission electron spectroscopy, and surface area measurements. The factors affecting the adsorption process such as initial dye concentration, initial solution pH, temperature, and Dye/TRG ratio were investigated. The Dye/ TRG ratio was found to be the most important factor controlling the adsorption of MB and MG on graphene surface. Highest adsorption capacity was observed at dye/TRG ratio of 1, irrespective of the initial dye concentration. The maximum measured adsorption capacity of 687 mg/g-TRG for MB and 212 mg/g-TRG for MG, and removal efficiency of 99.62% for MB and 98.74% for MG were obtained. Both dyes followed the Langmuir isotherm indicating the monolayer adsorption on the graphene surface. Thermodynamic analysis indicated the adsorption of MB is an exothermic process whereas adsorption of MG is an endothermic process. In addition, an equilibrium model to model the experimental adsorption data was developed which successfully described the experimental adsorption results and predicted maximum theoretical capacity of 730 mg/g-TRG for MB and 380 mg/g-TRG for MG, consistent with previously reported results for MB adsorption on graphene and its derivatives.