Controlled degrees of oxidation of nanoporous graphene filters for water purification using an aqueous arc discharge

Graphene-based nanofiltration membranes with different degrees of oxidation were produced using a novel aqueous arc discharge process for water purification applications. By adjusting the current level during the arc discharge the degree of oxidation was controlled from 28.1% at 1 A (Gr1A) to 53.9% at 4 A (Gr4A). Over 70% of the resulting graphene sheets had less than 10 layers. The effect of the degree of graphene oxidation on water purification was evaluated by monitoring pressure-driven water flux and the self-diffusion of ions across the membrane. The water flux through the graphene membranes was proportionally increased with pressure, which showed the highest water flux (362.3 L h⁻¹ bar⁻¹ m⁻²) at 31.09 kPa. Membrane thickness affected the self-diffusion rates of ions. Compared to a commercial polyamide membrane, the transported concentration of Na⁺ decreased by 67.7% (0.58 mM h⁻¹) and 64.5% (0.55 mM h⁻¹) for the Gr1A and Gr4A manufacturing processes, respectively where the membrane was 1120 nm thick. The ability to control the chemical and physical properties of the graphene membranes enhances their water purification performance and demonstrates their potential for use in practical water purification applications.