Photo-catalytic oxidation of gaseous toluene by Z-scheme Ag3PO4-g-C3N4 composites under visible light: Removal performance and mechanisms

Abstract Volatile organic compounds (VOCs) which exist widely in indoor air, are confirmed to be harmful to human health. In this study, gaseous toluene, the representative VOCs, was degraded by photo-catalytic oxidation (PCO) under visible light. The Ag3PO4-g-C3N4 composites with different weight ratios of Ag3PO4/g-C3N4 were synthesized and used as the photo-catalysts. The results indicated that the Ag3PO4-g-C3N4 composites with the weight ratio of 2.6% exhibited the most superior photo-catalytic activity, and the removal efficiency of toluene was 87.52% within 100 min irradiation, which was higher than that of bare g-C3N4 and Ag3PO4. The pseudo-one-order model was applied to analyzing the reaction process, and the apparent reaction rate constant of 2.6%-APO-g-C3N4 was 0.005 min-1. After 3 cycles, the removal efficiency was still higher than 80.72%. According to the results of PLS and ESR, the combination of Ag3PO4 and g-C3N4 could improve photo-induced carrier separation as well as OH and O2− radicals were both detected. Furthermore, the Z-scheme mechanism of Ag3PO4-g-C3N4 photo-catalysts was proposed. Therefore, the superior photo-catalytic activity of composites was significantly increased by the Z-scheme. In addition, the small proportion of Ag3PO4 in composites may be beneficial for a wide range of applications, given the cost of noble metal Ag.