Quantitative Single-Particle Fluorescence Imaging Elucidates Semiconductor Shell Influence on Ag@TiO2 Photocatalysis.

The understanding of the structure-reactivity relationship is helpful for the nanocatalyst (NC) design. However, though precisely parse, this information is challenging due to the heterogeneity of NCs and the complex mechanism of energetic charge carrier (e-/h+ pairs) generation and transfer within the catalysts upon light irradiation. Here, the effect of the semiconductor shell on the photocatalytic redox reaction is probed at the single-Ag@TiO2 NC level with single-molecule imaging. By engineering the TiO2 shell thickness, catalytic activities of the NCs are precisely controlled and quantitatively measured to show a parabolic-like distribution with increasing TiO2 thickness. Besides, the varied activity among different NCs and the dynamic activity fluctuation of single NCs during continuous redox conversion are observed. Mathematical analysis indicates that the TiO2 layer affects the activity of the core-shell NCs by simultaneously affecting the fate of photo-induced e-/h+ pairs and hot electrons generated at the Ag core. This work sheds light on molecular-scale elucidation of the impact of metal-semiconductor NC structures on their reactivities.