Enhancing built-in electric field via ZnIn₂S₄ nanosheet decorated with ZnS quantum dots photocatalyst for highly...

Two dimensional (2D) photocatalytic materials are desirable to achieve synergistic charge transfer and segregation. Here, we have developed 2D ZnIn₂S₄ nanosheet (3-4 nm) that generates more active sites for excellent photocatalytic activity. Further, we have fabricated ZnS quantum dots (QDs) and ZnS nanoparticles (NPs) embedded with ZnIn₂S₄ nanosheet in the form of ZnS QDs/ZnIn₂S₄ and ZnS NPs/ZnIn₂S₄ heterostructures prepared via one step hydrothermal method. The optimal ZnS QDs/ZnIn₂S₄ presents the hydrogen evolution rate (HER) of 4.5 mmol g^-1 h^-1 which was approximately 5 and 34 times higher than that of their counterparts as well as about 3 times more efficient than ZnS NPs/ZnIn₂S₄ heterostructure. The apparent quantum efficiency (AQE) of 21.2% was observed at 350 nm. The work functions determined through Ultraviolet photoelectron spectroscopy (UPS) elaborate the charge transfer mechanism. In situ KPFM validated the surface potential difference between the ZnS QDs and ZnIn₂S₄ interfaces estimated about 55 mV which was approximately 2 times higher than ZnS NPs/ZnIn₂S₄. Theoretical calculation confirms the significant reduction in Gibbs free energy about -0.6 eV. Electron paramagnetic resonance (EPR) spectra suggest the development of a novel S-scheme mechanism and provides a unique insight into the charge transfer, separation and the surface photovoltage of heterostructure photocatalysts.