Hierarchical S-scheme heterojunctions of ZnIn2S4-decorated TiO2 for enhancing photocatalytic H2 evolution

Photocatalytic water splitting to produce H2 using semiconductor photocatalysts is a reliable approach to alleviating energy shortages and environmental pollution. However, the inadequate light-harvesting ability, rapid photogenerated carrier recombination, and inferior redox capacity of the individual photocatalysts restrict their photocatalytic activity. To address these limitations, a hierarchical S-scheme heterojunction of ZnIn2S4-nanosheet-decorated flower-like TiO2 microspheres for enhancing photocatalytic H2 evolution, purposely constructed through in situ chemical bath deposition, has been reported. The as-synthesized TiO2/ZnIn2S4 heterojunctions exhibited ZnIn2S4-content-dependent photocatalytic activity for solar-driven H2 evolution. As a result, the optimized TiO2/ZnIn2S4 heterojunction exhibited a superior photocatalytic H2 evolution rate of 6.85 mmol g–1 h–1, approximately 171.2- and 3.9-fold with respect to that obtained on pure TiO2 and ZnIn2S4, respectively, mainly attributed to the unique hierarchical structure, extended light-harvesting ability, enhanced redox capacity, and improved separation and transfer efficiencies of the photogenerated carriers induced by the S-scheme heterojunctions. Simultaneously, a detailed analysis of the S-scheme electron transfer pathway in the TiO2/ZnIn2S4 heterojunction was performed using in situ irradiated X-ray photoelectron spectroscopy and electron paramagnetic resonance spectroscopy. This study provides insights into the design of highly active heterojunction photocatalysts for sustainable solar-to-fuel energy conversion.