Spatial Distributions of Single-Molecule Reactivity in Plasmonic Catalysis

Abstract

Plasmonic catalysts have the potential to accelerate and control chemical reactions with light by exploiting localized surface plasmon resonances. However, the mechanisms governing plasmonic catalysis are not simple to decouple. Several plasmon-derived phenomena, such as electromagnetic field enhancements, temperature, or the generation of charge carriers, can affect the reactivity of the system. These effects are convoluted with the inherent (nonplasmonic) catalytic properties of the metal surface. Disentangling these coexisting effects is challenging but is the key to rationally controlling reaction pathways and enhancing reaction rates. This study utilizes super-resolution fluorescence microscopy to examine the mechanisms of plasmonic catalysis at the single-particle level. The reduction reaction of resazurin to resorufin in the presence of Au nanorods coated with a porous silica shell is investigated in situ. This allows the determination of reaction rates with a single-molecule sensitivity and subparticle resolution. By variation of the irradiation wavelength, it is possible to examine two different regimes: photoexcitation of the reactant molecules and photoexcitation of the nanoparticle’s plasmon resonance. In addition, the measured spatial distribution of reactivity allows differentiation between superficial and far-field effects. Our results indicate that the reduction of resazurin can occur through more than one reaction pathway, being most efficient when the reactant is photoexcited and is in contact with the Au surface. In addition, it was found that the spatial distribution of enhancements varies, depending on the underlying mechanism. These findings contribute to the fundamental understanding of plasmonic catalysis and the rational design of future plasmonic nanocatalysts.

Electron transfer and energy exchange between a covalent organic framework and CuFeS2 nanoparticles

“…In general, the exfoliated, 2D materials hold promising aspects compared to bulk materials, such as higher carrier mobility and electron transfer, larger available surface areas and even the presence of defects, dopants or oxygenated functional groups are beneficial for the enhancement of their optical response by the accumulation of plasmonic nanoparticles on their substrates. 45,46 Systems of 2D materials have carriers with shorter diffusion lengths and easier migration to the surface. 47 This is the reason why before the hybrid assembly and while their emission states are the same, the pristine exfCOF has a higher fluorescence and, thus higher radiative recombination than the pristine bCOF, in accordance with previous work.…”

Thermometries for Single Nanoparticles Heated with Light

“…On the other hand, in cases such as in plasmon-assisted chemistry where reactions occur not only at the surface but also in near proximity of the illuminated NP, a nanoscale temperature map comprising both regions becomes crucial. This map could serve as a key to distinguish between thermal and nonthermal catalytic pathways and contribute to the understanding of the mechanisms governing the field. ,− In other cases, such as in the study of thermal stability and reshaping of NPs, the inner temperature of the material is the most relevant. Finally, the study of fluid dynamics and photothermal forces close to hot NPs requires mapping the thermal fields in a longer spatial range, and nanoscale resolution is not always necessary.…”

Photocatalysis on Hybrid Plasmonic Nanomaterials: From Catalytic Mechanism Study at Single-Particle Level to Materials Design

“…Furthermore, Ezendam monitored turnover rate of resazurin reduction on individual mSiO 2 -coated Au NRs under 647 nm laser or 561 nm laser illumination using super-resolution fluorescence microscopy (Figure 8b). 122 Surprisingly, the rate enhancement at 647 nm was found to be 20 times lower than that at 561 nm. By combined kinetic analysis, spatial distribution of reactivity, and the Finite Element Method, the authors proposed that the photoexcitation of the reactant molecule, not the enhanced absorption of SPR metals, might be a main contribution to the improvement of catalytic performance and highlighted the pivotal role of local field enhancement.…”

“…In this measurement, only the transversal resonance mode of Au NRs was excited, which is indistinguishable with the absorption and emission of resazurin and resorufin, thus limiting the study on plasmonic mechanism to a certain degree. Furthermore, Ezendam monitored turnover rate of resazurin reduction on individual mSiO 2 -coated Au NRs under 647 nm laser or 561 nm laser illumination using super-resolution fluorescence microscopy (Figure b) . Surprisingly, the rate enhancement at 647 nm was found to be 20 times lower than that at 561 nm.…”

“…(b) Activity enhancement of individual mSiO 2 -coated Au NRs under 647 nm irradiance. Reproduced with permission from ref . Copyright 2024 American Chemical Society.…”