Synthesis of N-doped and non-doped partially oxidised graphene membranes supported over ceramic materials

Graphene has a great potential to substitute other amorphous carbon materials and has been widely used in many water and wastewater treatments such as purification or photocatalytic processes. Graphene powder with different degrees of oxidation was synthesised and subsequently used to prepare supported membranes. Ceramic porous materials were chosen as membrane support due to the robustness and long life required in a likely application. Ultrathin membranes (7–9 µm) were successfully prepared through vacuum filtration of highly oxidised graphene or reduced graphene oxide solutions (1 mg ml⁻¹). The influence of depositing different amounts of membrane precursor was extensively studied (0.003–0.037 mg cm⁻²); above 0.037 mg cm⁻², drying-related shrinkage problems are detected. Moreover, the ceramic support pore size (SPS) (0.008–0.08 µm) shows little impact in terms of the overall membrane flux resistance, and the deposited graphene layer usually governs the membrane permeation. Finally, long-term filtration experiments were also performed for weeks without substantial variation of the membrane structure or permeation (≤2 %), which is demanded in most conventional water treatments. Overall, the addition of partially oxidised graphene to conventional ceramic membranes greatly decreases their electrical resistivity (~2.8 × 10⁻⁵ Ω m), opening up the possibility of being employed for many environmental purposes.