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 (H2) 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 H2 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 H2 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 H2 production, owing to the accelerated transport of photo-excited electrons between the semiconductors. Under the optimum conditions, H2 production by 10 % of graphene into CuO and ZnO reached a maximum value of 48.6 mmol/g.h when Na2S/Na2SO3 was used as a sacrificial agent. The charge transfer carriers were monitored to explain the photocatalytic H2 production mechanism based on the optical property characterizations and S-scheme heterojunction system. An excellent reusability was achieved after five consecutive cycles of H2 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 H2 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.