Direct Z-Scheme TiO2/NiS Core-Shell Hybrid Nanofibers with Enhanced Photocatalytic H-2-Production Activity

Photocatalytic water splitting to generate hydrogen (H-2) is a sustainable approach for solving the current energy crisis. A novel TiO2/NiS core-shell nanohybrid was fabricated where few-layer NiS nanoplates were deposited on TiO2 skeletons via electrospinning and hydrothermal methods. The NiS nanoplates with a thickness of ca. 28 nm stood vertically and uniformly upon the TiO2 nanofibers, guaranteeing intimate contact for charge transfer. XPS analysis and DFT calculation imply that the electrons in NiS would transfer to TiO2 upon hybridization, which creates a built-in electric field at the interfaces and thus facilitates the separation of useful electron and hole upon photoexcitation. In-situ XPS analysis directly proved that the photoexcited electrons in TiO2 migrated to NiS under UV-visible light irradiation, suggesting that a direct Z-scheme heterojunction was formed in the NiS/TiO2 hybrid. This direct Z-scheme mechanism greatly promotes the separation of useful electron-hole pairs and fosters efficient H-2 production. The hybrid nanofibers unveiled a high H-2-production rate of 655 mu mol h(-1) g(-1), which was 14.6-fold of pristine TiO2 nanofibers. Isotope ((D2O)-D-4) tracer test confirmed that H-2 was produced from water, rather than from any H-containing contaminants. This work provides an alternative approach to rationally design and synthesize TiO2-based photocatalysts with direct Z-scheme pathways toward high-efficiency photogeneration of H-2.