g-C3N4/ZnWO4 nanocomposites as efficient and stable S-scheme photocatalysts for hydrogen evolution

The use of photocatalysis to decompose water and produce hydrogen (H2) is a promising green energy technology with numerous potential applications. In this study, the design of g-C3N4/ZnWO4 (CN/ZWO) accompanied by an “S-scheme” heterojunction mechanism is reported for the first time, along with a thorough investigation of their photocatalytic H2 evolution activity and mechanism. It was found that the CN/ZWO nanocomposites effectively address the inherent issues of band gap defects, instability, and poor H2-evolving photocatalytic performance of pure CN. The CN/ZWO-0.15 in particular exhibited particularly high photocatalytic activity (1.195 mmol g−1 h−1), being 17.57 and 7.71 times more effective than pure CN and ZWO, respectively. In addition, the CN/ZWO-0.15 displayed good stability over a period of 12 h (four cycles) while maintaining its high activity. The presence of the nanocomposites was confirmed using TEM and in situ irradiated XPS (ISI-XPS), and the mechanism at the heterojunction was determined to be the S-scheme via ISI-XPS, EPR and theoretical calculations. The S-scheme mechanism involves the effective utilization of the valence-conduction band gap width of the system and the efficient photoinduced charge separation, and is believed to be responsible for the superior H2 release ability of the nanocomposites. This work presents a novel approach involving an S-scheme heterojunction to overcome the intrinsic defects of CN-based photocatalysts.