Tandem CdS/TiO2(B) nanosheet photocatalysts for enhanced H2 evolution

A conventional TiO2 photocatalyst cannot respond to visible light due to its large band gap. Here, we describe the construction of tandem CdS/TiO2(B) nanosheet architectures with visible light H2 evolution. A type II heterojunction of hexagonal CdS/TiO2(B) (PCT) was constructed by photodeposition and CdS dots, with size about 6 nm, were anchored on TiO2(B) nanosheets. A second type I heterojunction of cubic CdS/TiO2(B) (HCT) was fabricated by a hydrothermal method and CdS nanoparticles, with size about 50 nm, were dispersed on TiO2(B) nanosheets. Both heterojunction systems display remarkable enhancement of H2 evolution activity under full spectrum irradiation, with highest H2 evolution rate of 1776 μmol·g−1·h−1 for the photodeposited catalyst and 1494 μmol·g−1·h−1 for the hydrothermal process. The different heterojunction systems show very different H2 evolution under just visible light irradiation. The highest H2 evolution (1577 μmol·g−1·h−1) for the type II system is far much higher than the type I (48 μmol·g−1·h−1). The type II system shows more effective utilization of full spectrum with the apparent quantum efficiency in the wavelength range extended from 300 to 500 nm, matching well with the optical absorbance spectrum of the composite catalyst. The structure, morphology, and photocatalytic mechanism of the CdS/TiO2(B) composites are discussed.