Abstract
Plasmonic nanoparticle catalysts offer improved light absorption and carrier transport compared to traditional photocatalysts. However, it remains unclear how plasmonic excitation affects multi-step reaction kinetics and promotes site-selectivity. Here, we visualize a plasmon-induced reaction at the sub-nanoparticle level in-situ and in real-time. Using an environmental transmission electron microscope combined with light excitation, we study the photocatalytic dehydrogenation of individual palladium nanocubes coupled to gold nanoparticles with sub-2 nanometer spatial resolution. We find that plasmons increase the rate of distinct reaction steps with unique time constants; enable reaction nucleation at specific sites closest to the electromagnetic hot spots; and appear to open a new reaction pathway that is not observed without illumination. These effects are explained by plasmon-mediated population of excited-state hybridized palladium-hydrogen orbitals. Our results help elucidate the role of plasmons in light-driven photochemical transformations, en-route to design of site-selective and product-specific photocatalysts.
Highlights
Plasmonic nanoparticle catalysts offer improved light absorption and carrier transport compared to traditional photocatalysts
The enhanced photoreactivity of plasmonic nanoparticles is attributed to their localized surface plasmon resonances (LSPR), collective oscillations of the conduction band electrons which enable strong optical absorption and scattering in the subwavelength regime, with the ability to be tuned by the size, shape, material, and the surrounding medium of the nanoparticle
The sample is mounted on a cryo-cathodoluminescence (CL) holder which allows us to illuminate the sample while imaging it in an environmental TEM (ETEM)
Summary
Plasmonic nanoparticle catalysts offer improved light absorption and carrier transport compared to traditional photocatalysts. We find that plasmons increase the rate of distinct reaction steps with unique time constants; enable reaction nucleation at specific sites closest to the electromagnetic hot spots; and appear to open a new reaction pathway that is not observed without illumination These effects are explained by plasmon-mediated population of excited-state hybridized palladium-hydrogen orbitals. Important and often surprising structure-function relations have been observed with single and sub-particle plasmon catalysis measurements Utilizing techniques such as dark-field optical spectroscopy[20], super-resolution microscopy[21,22,23], and exsitu scanning electron microscopy[24], researchers have monitored sitespecific reaction rates and identified the reactive sites of an individual particle, indicating large particle-to-particle variability. This configuration has been recently shown useful for inducing plasmonic fields in the non-plasmonic though chemically active metal, promoting chemical reactions with light[22,23]
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