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

In this study, a Fe3+/g-C3N4 hybrid catalyst system was proposed to activate peroxymonosulfate (PMS) for the metronidazole (MNZ) photocatalytic degradation. The two catalysts, Fe3+ and g-C3N4, exhibited an obvious synergistic effect in the photocatalytic degradation process. When 1 mM PMS, 0.04 mM Fe3+ and 0.05 g L-1 g-C3N4 were applied, the rate constant of the Fe3+/g-C3N4/PMS/LED process at 0.07288 min(-1) is around 3.6 to 6.8 times faster than that of Fe3+/PMS/LED and g-C3N4/PMS/LED processes at 0.0198 and 0.01076 min(-1), respectively. Under visible light, electron transfer from photo-activated g-C3N4 to Fe3+, resulting in the continuous regeneration of Fe2+ in the system, which ensures non-stopping production of radicals for MNZ degradation. UV-visible spectra were used to confirm the regeneration of Fe2+. 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 Fe3+/Fe2+ redox through semiconductor, which could help to use the catalyst more effectively for wastewater treatment and/or chemical industries.

Automated summary

In this study, a Fe3+/g-C3N4 hybrid catalyst system showed a synergistic effect in the photocatalytic degradation of metronidazole (MNZ) by activating peroxymonosulfate (PMS). The continuous regeneration of Fe2+ through electron transfer from photo-activated g-C3N4 to Fe3+ ensures the non-stopping production of radicals for MNZ degradation under visible light. The study also examined the effects of various operation parameters on the degradation process.