Cocatalyst-free photocatalysts for efficient visible-light-induced H ₂ production: Porous assemblies of CdS quantum dots and layered titanate nanosheets

Highly efficient, visible-light-induced H₂ generation can be achieved without the help of a Pt cocatalyst by new hybrid photocatalysts, in which CdS quantum dots (QDs) (particle size ≈2.5 nm) are incorporated in the porous assembly of sub-nanometer-thick layered titanate nanosheets. Due to the very-limited crystal dimension of component semiconductors, the electronic structure of CdS QDs is strongly coupled with that of the layered titanate nanosheets, leading to an efficient electron transfer between them and the enhancement of the CdS photostability. As a consequence of the promoted electron transfer, the photoluminescence of CdS QDs is nearly quenched after hybridization, indicating the almost-suppression of electron-hole recombination. These Pt-cocatalyst-free, CdS-layered titanate nanohybrids show much-higher photocatalytic activity for H₂ production than the precursor CdS QDs and layered titanate, which is due to the increased lifetime of the electrons and holes, the decrease of the bandgap energy, and the expansion of the surface area upon hybridization. The observed photocatalytic efficiency of these Pt-free hybrids (≈1.0 mmol g^-1 h^-1) is much greater than reported values of other Pt-free CdS-TiO₂ systems. This finding highlights the validity of 2D semiconductor nanosheets as effective building blocks for exploring efficient visible-light-active photocatalysts for H ₂ production.