Peroxymonosulfate activation on FeCo2S4 modified g-C3N4 (FeCo2S4-CN): Mechanism of singlet oxygen evolution for nonradical efficient degradation of sulfamethoxazole

FeCo2S4-CN particles were used as an innovative heterogeneous catalyst to degrade sulfamethoxazole (SMX) via peroxymonosulfate (PMS) activation. The combination of 20 mg/L FeCo2S4-CN and 0.15 mM PMS exhibited an extraordinarily high catalytic activity towards SMX degradation (91.9%, 0.151 min(-1)). Reactive oxygen species (ROS) generated in the FeCo2S4-CN/PMS process were identified by radical scavenging tests and electron spin response (EPR) analysis. Singlet oxygen (O-1(2)) dominated noradical pathway was verified to be the major route contributed to the degradation of SMX, which was generated by direct self-decomposition of PMS, the recombination of superoxide ions, and the interaction between g-C3N4 and PMS. Additionally, multiple characterization techniques were applied to clarify the physicochemical properties of the catalyst, which revealed that the FeCo2S4-CN contained S2-, S-n(2-), S-0, SO32-, and SO42-. Thus, we systematically explored the role of sulfur species. Based on these results, the plausible catalytic mechanisms and the degradation pathways of SMX were proposed. These findings shed some insight on the application of metal sulfides for the oxidative elimination of micropollutants by peroxyrnonosulfate activation.