g–C3N4 induced acceleration of Fe3+/Fe2+ cycles for enhancing metronidazole degradation in Fe3+/peroxymonosulfate process under visible light

In this study, a Fe 3+ /g-C 3 N 4 hybrid catalyst system was proposed to activate peroxymonosulfate (PMS) for the metronidazole (MNZ) photocatalytic degradation . The two catalysts, Fe 3+ and g-C 3 N 4 , exhibited an obvious synergistic effect in the photocatalytic degradation process. When 1 mM PMS, 0.04 mM Fe 3+ and 0.05 g L −1 g-C 3 N 4 were applied, the rate constant of the Fe 3+ /g-C 3 N 4 /PMS/LED process at 0.07288 min −1 is around 3.6 to 6.8 times faster than that of Fe 3+ /PMS/LED and g-C 3 N 4 /PMS/LED processes at 0.0198 and 0.01076 min −1 , respectively. Under visible light, electron transfer from photo-activated g-C 3 N 4 to Fe 3+ , resulting in the continuous regeneration of Fe 2+ in the system, which ensures non-stopping production of radicals for MNZ degradation. UV–visible spectra were used to confirm the regeneration of Fe 2+ . In addition, EPR tests were used to identify the reactive oxygen species involved in the reaction system. Typically, the effects of various operation parameters, including the catalyst dosage, PMS dosage, initial concentration of MNZ and initial pH were examined. This work provided a new idea of promoting pollutant degradation by accelerating Fe 3+ /Fe 2+ redox through semiconductor, which could help to use the catalyst more effectively for wastewater treatment and/or chemical industries.