Synergistically catalytic oxidation of toluene over Mn modified g-C₃N₄/ZSM-4 under vacuum UV irradiation

The process of vacuum ultraviolet (VUV)-assisted photocatalytic oxidation (PCO) has attracted great interest for volatile organic compounds (VOCs) degradation owing to its strong oxidation capability. However, the O₃ by-product from VUV irradiation causes secondary pollution and needs to be overcome. In this study, a multi-functional photocatalyst of Mn/g-C₃N₄/ZSM-4 was thus developed by a one-pot hydrothermal method, and then combined with VUV irradiation to eliminate O₃ byproduct as well as enhance toluene degradation via ozone-assisted catalytic oxidation (OZCO). Under VUV irradiation alone, 64% of toluene degradation was occurred but 51 ppm of O₃ was residual. In contrast, toluene degradation was enhanced to 96% over the Mn/g-C₃N₄/ZSM-4 while residual O₃ was decreased to 4 ppm. The enhanced performance was attributed to the synergistic PCO and OZCO, as the Mn modification can efficiently enhance the photocatalytic activity of g-C₃N₄ and trigger the catalytic ozonation simultaneously. The results of electron spin resonance (ESR) confirmed the generation of reactive species such as OH and O₂^- by VUV irradiation and then greatly enhanced after Mn/g-C₃N₄/ZSM-4 was added. Moreover, the possible mechanism of toluene degradation was also revealed through monitoring of reaction intermediate. Obviously, the process of Mn/g-C₃N₄/ZSM-4 cooperated well with VUV is promising for VOCs degradation.