Visible light-assisted S-scheme p- and n-type semiconductors anchored onto graphene for increased photocatalytic H2 production via water splitting

This work reports on photocatalytic hydrogen (H 2 ) production via water splitting by synthesizing CuO and ZnO semiconductors anchored onto graphene by varying the mass ratios of CuO and ZnO into the graphene matrix. The high H 2 production performance for binary nanocomposite (CuO/ZnO) compared to its components confirms the synergistic effect between ZnO and CuO nanoparticles. Introducing 10 wt% graphene into CuO and ZnO displayed the highest H 2 production reaching to 37.2 mmol/g.h, which was 3.29 times higher than pristine binary nanocomposite (CuO/ZnO). The graphene played a critical role in enhancing the photocatalytic activity of CuO and ZnO towards H 2 production, owing to the accelerated transport of photo-excited electrons between the semiconductors. Under the optimum conditions, H 2 production by 10 % of graphene into CuO and ZnO reached a maximum value of 48.6 mmol/g.h when Na 2 S/Na 2 SO 3 was used as a sacrificial agent. The charge transfer carriers were monitored to explain the photocatalytic H 2 production mechanism based on the optical property characterizations and S-scheme heterojunction system. An excellent reusability was achieved after five consecutive cycles of H 2 production reaction. The outcome of this research introduces a reusable and effective catalyst with a facile and easy configuration for energy production applications and confirms that the decoration of semiconductors on graphene could be a promising strategy for highly-efficient photocatalytic H 2 production. Furthermore, by offering a clean alternative to fossil fuels and reducing greenhouse gas emissions - especially when produced from renewable sources - hydrogen can significantly contribute to achieving sustainable development goal 7 (SDG 7), thus advancing toward a more sustainable, equitable future.