Photothermal Effect, Local Field Dependence, and Charge Carrier Relaying Species in Plasmon-Driven Photocatalysis: A Case Study of Aerobic Nitrothiophenol Coupling Reaction

摘要

Optical excitation of plasmonic electron oscillations confined by metallic nanoparticles provides a unique means of driving unconventional photocatalytic transformations of molecular adsorbates on the nanoparticle surfaces. Photothermal heating, local-field enhancement, and hot carrier generation have been identified as three major plasmon-induced photo physical effects, all of which are directly relevant to plasmon-driven photocatalysis. However, delineation of the contribution of each effect has long been challenging due to the strong synergy among the three effects and the mechanistic complexity of plasmon-driven molecular transformations. Aiming at unambiguously elucidating the photothermal effect, local-field dependence, and hot carrier channeling mechanisms that underpin plasmon-driven photocatalysis, we conducted a detailed case study on the aerobic reductive coupling of p-nitrothiophenol chemisorbed on Ag nanocube surfaces under near-infrared excitations. We used surface-enhanced Raman scattering (SERS) as a plasmon-enhanced, molecular fingerprinting spectroscopic tool to track the plasmon-driven structural evolution of molecular adsorbates in real time, based on which we were able to correlate the molecule-transforming kinetics with local-field intensities and photothermal heating at the nanoparticle surfaces. The information extracted from the time-resolved SERS results allowed us not only to clarify several controversial issues regarding the photothermal effect and local field dependence but also to unravel a unique function of surface-adsorbed molecular oxygen as an interfacial charge carrier relaying cocatalyst that works in conjunction with the plasmonic Ag photocatalysts to mediate the multistep coupling reaction.