Correlation between ligand-mediated silver species on TiO2 nanosheet with the photocatalytic hydrogen evolution activities

Metal oxide photocatalysts loaded with metal species are extremely important in photocatalysis. The physicochemical states of metal species, as well as the interaction between metal species and support, determine the transfer of charge carriers between the heterointerface, which has a significant impact on photocatalytic activity. Here, we prepared anatase TiO₂ nanosheets (TIO) modified with different Ag species, including single atoms, clusters, and nanoparticles, using a ligand-mediated method. The existence of different forms of Ag species on TIO was verified by high-angle annular dark field scanning transmission electron microscope (HAADF-STEM) and high-resolution transmission electron microscope (HRTEM); Electron paramagnetic resonance (EPR) and diffuse reflectance infrared Fourier transform spectroscopy (DRIFTS) confirmed the changed electronic properties in heterointerface and charge carrier transfer channels caused by the Ag species in different existence states; X-ray absorption fine structure (XAFS) in depth differentiated the valence states, coordination environments, and charge densities of Ag species. It is intriguing that the photocatalytic hydrogen evolution activity exhibits a hump shape, which can be attributed to the changes in the physicochemical properties of silver species in different states. In addition, the combination of density functional theory (DFT) calculations and experimental results demonstrated that the Ag single atom acted as an active site for water splitting, while the Ag cluster tended to attract electrons and promoted charge separation efficiency. This work delves into the relationship between the microscopic changes of metal species anchored on the surface of photocatalysts and their photocatalytic performance, providing further insights into precise surface engineering and performance optimization by adjusting the metal presence state on the photocatalyst surface.