A novel S-scheme 3D ZnIn2S4/WO3 heterostructure for improved hydrogen production under visible light irradiation

In-plane epitaxial growth of ZnIn2S4 nanosheets on the surface of hexagonal phase WO3 nanorods was achieved by a facile solvothermal method. The unique 3D heterostructure not only enlarged the specific surface area, but also red-shifted the absorption edge from 381 to 476 nm to improve the light harvesting ability, which largely enhanced the photocatalytic hydrogen evolution. The H2 production rate of the best performing ZnIn2S4/WO3 photocatalyst (ZIS-2.5/W, the material with a molar rate of ZnIn2S4 (ZIS) to WO3 (W) of 2.5) was 300 μmol·g−1·h−1, around 417 times and 2 times higher than the rates of pristine WO3 and ZnIn2S4, respectively. The apparent quantum efficiency for ZIS-2.5/W composite was up to 2.81% at 400 nm. Based on the difference in Fermi levels between WO3 and ZnIn2S4, and the distribution of the redox active sites on WO3/ZnIn2S4 heterostructure, a S-scheme electron transfer mechanism was proposed to illustrate the improved photocatalytic activity of WO3/ZnIn2S4 heterojunction, which not only stimulated the spatial separation of the photogenerated charge carriers, but also maintained the strong reduction/oxidation ability of the photocatalyst.