Environmentally friendly route for graphene oxide production via electrochemical synthesis focused on the adsorptive removal of dyes from water.

This work shows a promising, environmentally friendly and greener alternative for the production and application of electrochemically produced Graphene Oxide (GO) for the adsorptive removal of Methylene Blue (MB) dye in an aqueous medium. During the adsorption tests, GO produced via electrochemical route reached the equilibrium in only 10 min of contact, exhibiting a percentage removal of MB over 97%. It could also be observed that the experimental data better fitted to the pseudo-second order kinetic model. By analysing the isotherms, it was verified the maximum adsorptive capacity was 500 mg g-1 (303.15 K) and that in overall, adsorptive capacity decreases with the increase in temperature. Experimental equilibrium data were better fitted to the Freundlich isotherms in all temperatures studied (303.15, 318.15 and 333.15 K). The thermodynamic analysis confirmed the exothermic nature of the process, and that MB adsorption onto GO occurs spontaneously. ΔH◦ and ΔG◦ values suggested that physisorption occurred, which is mainly due to π-π interactions and electrostatic interactions between MB and oxygen functional groups on the GO surface. Cost-effectiveness analysis showed there is a lower cost involved in the production of electrochemical GO, as compared to the Hummers method; and in the reusability study, even after 5 cycles GO removed ≥ 90% MB. Thus, the electrochemically produced GO seems to be an efficient, cost-effective and environmentally friendly alternative for colour removal from water, as it uses less hazardous and expensive reagents when compared to those applied in the traditional GO synthesis, without losing, however, the efficiency in colour removal from water.