Quantitative super-resolution imaging uncovers reactivity patterns on single nanocatalysts

Abstract

Metal nanoparticles are used as catalysts in a variety of important chemical reactions, and can have a range of different shapes, with facets and sites that differ in catalytic reactivity. To develop better catalysts it is necessary to determine where catalysis occurs on such nanoparticles and what structures are more reactive. Surface science experiments or theory can be used to predict the reactivity of surfaces with a known structure, and the reactivity of nanocatalysts can often be rationalized from a knowledge of their well-defined surface facets. Here, we show that a knowledge of the surface facets of a gold nanorod catalyst is insufficient to predict its reactivity, and we must also consider defects on the surface of the nanorod. We use super-resolution fluorescence microscopy to quantify the catalysis of the nanorods at a temporal resolution of a single catalytic reaction and a spatial resolution of ∼40 nm. We find that within the same surface facets on the sides of a single nanorod, the reactivity is not constant and exhibits a gradient from the centre of the nanorod towards its two ends. Furthermore, the ratio of the reactivity at the ends of the nanorod to the reactivity at the sides varies significantly from nanorod to nanorod, even though they all have the same surface facets.

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

“…S4 and S5). This is comparable resolution to related superresolution optical microscopy techniques (2,11). Furthermore, the wide-field imaging format of our approach offers the capability to study multiple nanorods in the same frame, thus providing higher data collection efficiency.…”

“…Our superresolution imaging of catalytic reactions is based on wide-field single-molecule fluorescence microscopy of two fluorogenic catalytic reactions (2,4,18). For the first experiment, we chose high aspect ratio, Sb-doped TiO 2 nanorods (diameter, ∼3 nm; length, 90∼150 nm, Fig.…”

“…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)(3)(4)(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.…”

“…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)(7)(8)(9)(10)(11)(12)(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.…”

“…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 the nanocatalysts, possibly owing to the different types of surface atoms (14,15).…”