Removal and recycling of ppm levels of methylene blue from an aqueous solution with graphene oxide

Dye-containing wastewater is one of the major issues in water contamination, and its treatment remains a serious problem due to the low concentrations of dyes in polluted natural water and high cost for purification. Herein, we report the application of graphene oxides (GO) in the decontamination of ppm levels of methylene blue (MB) in an aqueous solution. During the dye removal process, GO adsorbs MB molecules via strong interactions including pi-pi stacking and electrostatic attraction, and facilitates the precipitation of GO/MB complexes, which can be readily removed from the solution. The adsorption progress follows the Langmuir isotherm model and the pseudo-second-order kinetic model. The thermodynamic parameters indicate that the adsorption progress is a spontaneous progress. By using our strategy, a dye removal rate as high as 95% has been achieved with a final dye concentration of only 0.25 ppm. In addition, 82% of the dye can be recycled through ethanol extraction from the collected GO/MB complexes. All the results demonstrate that GO nanosheets can effectively remove and recover ppm levels of cationic dye pollutants, represented by MB, showing the promising application of GO in ultra-low concentration dye containing wastewater treatment.