High performance of reduced graphene oxide and g-C₃N₄ co-doped CuFe₂O₄ for peroxymonosulfate activation under visible light: Degradation process of sulfamethazine via a singlet oxygen dominated pathway

Peroxymonosulfate (PMS) activation by heterogeneous metal -based catalysts has been extensively applied for the degradation of organic pollutants in water. However, the catalysts suffer from the low oxidant utilization efficiency, pH limitations and severe matrix interference. Here, a reduced graphene oxide and g-C3N4 co -doped copper ferrite (rGO-CNCF) was synthesized and its performance for PMS activation under visible light was evaluated for removal of sulfamethazine. In the condition of rGO-CNCF (0.2 g/L) and PMS (0.1 g/L), the vis/rGO-CNCF/PMS system could degrade 99.9 % of sulfamethazine (SMT, 10 mg/L) within 30 min at pH 7.0, and the system also showed high degrading abilty of SMT over a wide pH range (0-14), along with a good adaptability to common coexisting ions in water solution. The introduction of rGO not only enhanced the stability of rGO-CNCF but also changed the binding sites between PMS and rGO-CNCF which reduced the adsorption energy. Singlet oxygen (O-1(2)) was unveiled to be the major reactive oxygen species (ROS), which was produced by the transformation between negatively charged PMS (HSO5-) and water,along with the self -degradation of PMS. SMT was decomposed through four degradation pathways in this system, and quantitative structure-activity relationship (QSAR) predictions indicated a significant decrease in its toxicity. Results of this study indicated that the material can efficiently activate persulfate for the removal of organic pollutants from water under visible light conditions and it provided a novel catalytic system for removal of organic contaminants in water.