Photocatalytic Surface Restructuring in Individual Silver Nanoparticles.

Light absorption and scattering by metal nanoparticles can drive catalytic reactions at their surface via the generation of hot charge carriers, elevated temperatures, and focused electromagnetic fields. These photoinduced processes can substantially alter the shape, surface structure, and oxidation state of surface atoms of the nanoparticles and therefore significantly modify their catalytic properties. Information on such local structural and chemical change in plasmonic nanoparticles is however blurred in ensemble experiments, due to the typical large heterogeneity in sample size and shape distributions. Here, we use single-particle dark-field and Raman scattering spectroscopy to elucidate the reshaping and surface restructuring of individual silver nanodisks under plasmon excitation and during photocatalytic CO hydrogenation. We show that silver nanoparticles reshape significantly in inert N atmosphere, due to photothermal effects. Furthermore, by collecting the inelastic scattering during laser irradiation in a reducing gas environment, we observe intermittent light emission from silver clusters transiently formed at the nanoparticle surface. These clusters are likely to modify the photocatalytic activity of silver nanodisks and to enable detection of reaction products by enhancing their Raman signal. Our results highlight the dynamic nature of the catalytic surface of plasmonic silver nanoparticles and demonstrate the power of single-particle spectroscopic techniques to unveil their structure-activity relationship both and in real time.