Photocatalytic hydrogen evolution over monolayer H1.07Ti1.73O4•H2O nanosheets: Roles of metal defects and greatly enhanced performances

Monolayer H1.07Ti1.73O4 center dot H2O nanosheets with the thickness about 0.67 nm were prepared and developed as an efficient photocatalyst for hydrogen evolution. The prepared sample exhibits greatly improved photocatalytic activity with more 10.5 times higher than its layered counterpart. The morphologies, microstructures, superficial properties and electronic structures of the sample were characterized by XRD, TEM, AFM, BET, and UV-vis DRS in detail. Moreover, EXAFS, FTIR, XPS and in-suit FTIR of D2O absorption results suggested that Ti vacancies result in the formation of abundant active O species around vacancies sites, which can be exposed fully in the monolayer nanosheets and bind with water molecules in the formation of surface coordination via hydrogen bonds. An efficient electron transition from nanosheets to surficial coordinated H2O molecules takes place. Finally, a synergistic effect between titanium vacancies and ultrathin 2D structure was proposed to elucidate that the enhanced photocatalytic performance over metal defects may be attributed to efficient exposure of active species and transition of photo-electrons from surface to H2O molecules.