Facet engineered interface design of NaYF4:Yb,Tm upconversion nanocrystals on BiOCl nanoplates for enhanced near-infrared photocatalysis.

The combination of upconversion nanocrystals with a wide-bandgap semiconductor is an efficient strategy to develop near-infrared (NIR)-responsive photocatalysts. The photocatalytic activity of the hybrid structures is greatly determined by the efficiency of the energy transfer on the interface between upconversion nanocrystals and the semiconductor. In this work, we demonstrate the interface design of a NaYF4:Yb,Tm-BiOCl hybrid structure based on the choice of suitable BiOCl facets in depositing NaYF4:Yb,Tm upconversion nanocrystals. It was found that the selective deposition of NaYF4:Yb,Tm nanocrystals on the BiOCl(110) facet can greatly enhance the photocatalytic performance in dye degradation compared with the sample with NaYF4:Yb,Tm nanocrystals loaded on the BiOCl(001) facet. Two effects were believed to contribute to this enhancement: (1) a stronger UV emission absorption ability of the BiOCl(110) facet from NaYF4:Yb,Tm in generating more photo-induced charge carriers resulted from the narrower bandgap; (2) a shorter diffusion distance of photogenerated charge carriers to the BiOCl(110) reactive facet for surface catalytic reactions owing to the spatial charge separation between different facets. This work highlights the rational interfacial design of an upconversion nanocrystal-semiconductor hybrid structure for enhanced energy transfer in photocatalysis.