Photocatalytic ozonation of oxalic acid by g-C3N4/graphene composites under simulated solar irradiation

• g-C3N4–rGO nanocomposite was synthesized by grinding and calcination process.
• Introduction of rGO promotes the separation of photo-generated charges.
• Photocatalytic ozonation of OA by g-C3N4–rGO is more efficient than g-C3N4.
• g-C3N4–rGO shows excellent stability for photocatalytic ozonation of OA.

Graphitic carbon nitride (g-C3N4)–reduced graphene oxide (rGO) nanocomposites were synthesized successfully by grinding a mixture of melamine and graphene oxide (GO) with different weight ratios, followed by calcination at 550 °C under flowing nitrogen atmosphere. Photoluminescence (PL) analysis was performed to investigate the efficiency of charge separation in g-C3N4–rGO composite. The result showed that the intensity of emission peak for g-C3N4–rGO composite is much lower than pure g-C3N4. The activity of g-C3N4–rGO composite in photocatalysis and photocatalytic ozonation process was evaluated by degradation of oxalic acid (OA) under simulated solar light irradiation. The results demonstrated that the degradation rate of OA with g-C3N4–rGO composite was significantly improved compared with pure g-C3N4 in both process. This enhancement was due to the hetero-junction built between rGO and g-C3N4. Furthermore, during photocatalytic ozonation process, g-C3N4–rGO composite could trigger a synergistic effect between photocatalysis and ozonation. This study indicated that the metal-free g-C3N4–rGO nanocomposite showed high solar-light activity in photocatalytic ozonation process, which makes them promising materials for further applications in wastewater treatment.