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 H-2 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.