MOFs-derived TiO2 composite ZnIn2S4 to construct Z-scheme heterojunction for efficient photocatalytic hydrogen evolution under visible light

The ultra-high specific surface area of metal-organic frameworks (MOFs) with a large number of mesopores makes them good platforms for photocatalytic reactions. The materials derived from MOFs can usually retain the original framework structure and have more reaction sites. TiO2 is a practical and stable photocatalyst, but its wide bandgap (3.2 eV) results in low utilization of solar energy. ZnIn2S4 (ZIS) has a suitable bandgap (2.4 eV) and well visible light absorption, which could be a good photocatalytic material, but its chemical stability is poor. In this paper, a simple route was used to composite porous MOF-derived TiO2 with ZIS to prepare a core-shell-like Z-scheme heterojunction composite photocatalyst to produce hydrogen via photocatalysis. Porous TiO2 provided a larger specific surface area and fuller close contact with ZIS. The direct Z-scheme heterojunction greatly improved the separation and migration of carriers, and ZIS/TiO2 presented the superior hydrogen evolution rate under visible light (lambda>400 nm) which was 2.1515 mmol/g/h, which is twice that of ZIS and 119.5 times that of MOF-derived TiO2. Various methods such as in-situ XPS and theoretical calculation were used to deeply explore the heterojunction types of the photocatalyst and its photocatalytic mechanism. This study presents the enormous research potential of MOF-derived materials for photocatalysis and the superiority of Z-scheme heterojunction composite materials.