Elucidating Facet-Dependent Photocatalytic Activities of Metastable CdS and Au@CdS Core-Shell Nanocrystals.

Controlling the crystal facets of semiconductor nanocrystals (NCs) has been proven as an effective approach to tune their physicochemical properties. However, the study on facet-engineering of metastable zinc blende CdS (-CdS) and its heterostructures is still not fully explored. In this study, the -CdS and Au@-CdS core-shell NCs with tunable terminating facets are controllably synthesized, and their photocatalytic performance for water splitting are evaluated. It is found that the {111} facets of the -CdS NCs display higher intrinsic activity than the {100} counterparts, which originates from these surfaces being much more efficient, facilitating electron transition to enhance the adsorption ability and the dissociation of the adsorbed water, as revealed by theoretical calculations. Moreover, the Au@-CdS core-shell NCs exhibit better photocatalytic performance than the -CdS NCs terminated with the same facets under visible light irradiation (≥400 nm), which is mainly ascribed to the accelerated electron separation at the interface, as demonstrated by femtosecond transient absorption (fs-TA) spectroscopy. Importantly, the quantum yield of plasmon-induced hot electron transfer quantified by fs-TA in the Au@-CdS core-shell octahedrons can be reached as high as 1.2% under 615 nm excitation, which is higher than that of the Au@-CdS core-shell cubes. This work unravels the face-dependent photocatalytic performance of the metastable semiconductor NCs via a combination of experiments and theoretical calculations, providing the understanding of the underlying mechanism of these photocatalysts.