Superresolution fluorescence mapping of single-nanoparticle catalysts reveals spatiotemporal variations in surface reactivity

Abstract

For the practical application of nanocatalysts, it is desirable to understand the spatiotemporal fluctuations of nanocatalytic activity at the single-nanoparticle level. Here we use time-lapsed superresolution mapping of single-molecule catalysis events on individual nanoparticles to observe time-varying changes in the spatial distribution of catalysis events on Sb-doped TiO 2 nanorods and Au triangle nanoplates. Compared with the active sites on well-defined surface facets, the defects of the nanoparticle catalysts possess higher intrinsic reactivity but lower stability. Corners and ends are more reactive but also less stable than flat surfaces. Averaged over time, the most stable sites dominate the total apparent activity of single nanocatalysts. However, the active sites with higher intrinsic activity but lower stability show activity at earlier time points before deactivating. Unexpectedly, some active sites are found to recover their activity ("selfhealing") after deactivation, which is probably due to desorption of the adsorbate. Our superresolution measurement of different types of active catalytic sites, over both space and time, leads to a more comprehensive understanding of reactivity patterns and may enable the design of new and more productive heterogeneous catalysts.single-molecule nanocatalysis | optical superresolution imaging | photocatalysis | surface restructuring A ll kinds of nanoparticles, such as metals, metal oxides, and even nonmetals, are used as catalysts in a variety of chemical processes (1). In support of developing better and less-expensive nanoparticle catalysts, single-molecule mapping of nanocatalyst activity using superresolution imaging at the single-nanoparticle level can determine active site locations on nanoparticles and which structures are most reactive (2-5). For example, defects, corners, and edges on nanoparticle surfaces have been shown by singlemolecule, superresolution imaging of single nanocatalysts to be more active than other sites. The relative abundance of these sites on nanoparticle catalysts is important for explaining their observed reactivity (2, 4, 6-13).However, prior reports are based on longtime integrations of catalytic activity and thus do not provide information about any dynamic changes in catalytic activity, such as the time-dependent evolution of different active sites. Studies of time-varying catalytic activity are thus arguably more informative than time-averaged observations.The temporal fluctuation of catalytic activity on nanocatalysts or electrodes has been previously observed in situ at both the ensemble and single-nanoparticle level (14-17). More recently, superresolution imaging techniques have been applied to identify the spatial distribution of catalytic activity on a few different nanocatalysts including Au@SiO 2 nanorods, Au@SiO 2 nanotriangles (2, 4) and Au-CdS nanohybrids (6). The observed spatial variations in catalytic activity between different catalysts were merely attributed to possible reaction-driven surface reconstruction of...

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Intermittent photocatalytic activity of single CdS nanoparticles

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