Surface Ti³⁺/ Ti⁴⁺ Redox Shuttle Enhancing Photocatalytic H₂ Production in Ultrathin TiO₂ Nanosheets/CdSe Quantum Dots

Constructing unique nanocomposites to facilitate charge transfer and promote catalytic activity provides a promising approach for enhancing solar-to-hydrogen efficiency. However, revealing the catalytic surface state and understanding their roles in the photocatalytic process remain elusive. Here, we develop a facile and mild solution method for ultrathin TiO₂ nanosheets with a large specific surface area and enhanced surface Ti³⁺ accumulation. Moreover, we demonstrate a hybrid nanosystem composed of ultrathin 2D TiO₂ nanosheets directly coupled with 0D CdSe QDs for hydrogen generation. The 0D CdSe QDs increase visible light absorption ability after being coupled with the TiO₂ nanosheets. Owing to the synergistic effect between the quantum dots and nanosheets, the apparent quantum efficiency increases to 45% at 380 and 450 nm, and the H₂ evolution exhibits a 10-fold enhancement. EPR results indicate that the surface Ti³⁺ greatly promotes H free radical production due to the redox couple Ti³⁺/Ti⁴⁺ providing an efficient route for the photoexcited electron-hole separation. Our findings provide new insights toward understanding and exploiting highly efficient photocatalyst.