Ag-Doped ZnIn₂S₄ Nanosheets on Hollow Co₉S₈ Polyhedral Nanocages as Photocatalysts for Enhanced Hydrogen Production and Pollutant Reduction

The effective combination of two metallic sulfides to form a heterojunction and regulate semiconductor structure can significantly improve the response of photocatalysts under visible light. In this study, we have successfully grown Ag-doped ZnIn₂S₄ nanosheets randomly on carefully designed hollow Co₉S₈ polyhedral nanocages to construct the Co₉S₈/Ag:ZnIn₂S₄ heterojunction. The optimized 1.0 wt % Co₉S₈/Ag:ZnIn₂S₄ heterostructure shows excellent activity with the H₂ generation rate of 1947.7 μmol g^–1 h^–1, which is 1.58 times greater than the Ag:ZnIn₂S₄ (1232.0 μmol g^–1 h^–1). However, pure Co₉S₈ has a narrow band gap but almost no response in visible light due to the fast photogenerated carrier recombination rate. The degradation trend of methyl orange (MO) in all as-prepared samples is the same as that of hydrogen production. The compound with the Co₉S₈ mass fraction of 1.0 wt % has the fastest degradation rate and can completely degrade MO within 16 min. In addition, the Co₉S₈/Ag:ZnIn₂S₄ heterostructure has also shown long-term stability after 20 photocatalytic hydrogen evolution and MO degradation cycle experiments, respectively. This work highlights the significance of improving the photocatalytic performance by modulating the morphology of metallic semiconductors and constructing heterostructures.