Insights into the photocatalytic ozonation over Ag2O-ZnO@g-C3N4 composite: Cooperative structure, degradation performance, and synergistic mechanisms

Abstract

In this work, Ag2O and ZnO modified g-C3N4 (Ag2O-ZnO@CNx) catalysts were fabricated by a simple precipitation-reflux method and employed for visible-light-driven photocatalytic ozonation process towards oxalic acid (OA) degradation. A series of characterizations such as XRD, TEM, XPS, UV–vis DRS, PL, Mott-Schottky were conducted to investigate the impact of loading Ag2O-ZnO on the microstructure and catalytic properties of catalysts. It was noteworthy that the mesoporous and backbone structure did not perceptibly change after doping Ag2O-ZnO to g-C3N4. Moreover, the separation of photogenerated e−−h+ pairs, the mobility of e− transfer, and the photocatalytic ozonation performance were improved with the increase in doping amount of g-C3N4. Amongst, the Ag2O-ZnO@CN0.4 achieved 83.43% of OA removal efficiency and the highest k value (0.0311 min−1), showing an excellent synergistic effect (synergy index η = 10.37) in this coupling system. Moreover, the Ag2O-ZnO@CN0.4 exhibited satisfactory reusability for multiple consecutive cycles (≥5). Through the radical scavenger experiments and ESR spectra, the reactive species including h+, e−, O2•−, 1O2 and •OH were verified to play an important role in PhOx system. Accordingly, an empirical kinetic model was established to predict OA concentration with the given operational parameters. The synergistic mechanism of OA degradation in the PhOx system was also proposed. Overall, the results presented a new insight into the application of PhOx process in water treatment.