Singlet Oxygen Formation Mechanism for the H₂O₂-Based Fenton-like Reaction Catalyzed by the Carbon Nitride...

The singlet oxygen (¹O₂) oxidation process activated by metal-free catalysts has recently attracted considerable attention for organic pollutant degradation; however, the ¹O₂ formation remains controversial. Simultaneously, the catalytic activity of the metal-free catalyst limits the practical application. In this study, carbon nitride (HCCN) containing an intramolecular homojunction, a kind of metal-free catalyst, exhibits excellent activity compared to g-C₃N₄ (CN) and crystalline carbon nitride (HCN) for tetracycline hydrochloride degradation through the H₂O₂-based Fenton-like reaction. The rate constant for HCCN increased about 16.1 and 8.9 times than that of CN and HCN, respectively. The activity of HCCN was enhanced, and the dominant reactive oxygen species (ROS) changed from hydroxyl radicals (^•OH) to ¹O₂ with an increase in pH from 4.5 to 11.5. A novel formation pathway of ¹O₂ was revealed. This result is different from the normal reference, in which ^•OH is always the primary ROS in the H₂O₂-based Fenton-like reaction. This study may provide a possible strategy for the investigation on the nonradical oxidation process in the Fenton-like reaction.