Origin of Superlinear Power Dependence of Reaction Rates in Plasmon-Driven Photocatalysis: A Case Study of Reductive Nitrothiophenol Coupling Reactions

Abstract

The superlinear dependence of the reaction rate on the power of the excitation light, which may arise from both thermal and nonthermal effects, has been a hallmark of plasmon-driven photocatalysis on nanostructured metal surfaces. However, it remains challenging to distinguish and quantify the thermal and nonthermal effects because even slight uncertainties in measuring the local temperatures at the active surface sites may lead to significant errors in assessing thermal and nonthermal contributions to the overall reaction rates. Here we employ surfaceenhanced Raman scattering as a surface-sensitive in situ spectroscopic tool to correlate detailed kinetic features of plasmon-mediated molecular transformations to the local temperatures at the active sites on photocatalyst surfaces. Our spectroscopic results clearly reveal that the superlinearity in the power dependence of the reaction rate observed in a plasmon-driven model reaction, specifically the reductive coupling of para-nitrothiophenol adsorbates on Ag nanoparticle surfaces, originates essentially from photothermal heating rather than nonthermal plasmonic effects.

Thermometries for Single Nanoparticles Heated with Light

“…The portion of the spectrum corresponding to lower energies than the excitation is known as Stokes, while the higher energy portion is known as anti-Stokes (Figure d). The Stokes spectrum of some compounds adsorbed onto plasmonic NPs is known to change with respect to temperature, , but this feature was not exploited yet at the single particle level. For an anti-Stokes scattering event to be possible, the initial state of molecule should be vibrationally excited, and therefore, its probability to occur is temperature dependent and proportional to a Boltzmann population distribution .…”

Photo-enhanced dehydrogenation of formic acid on Pd-based hybrid plasmonic nanostructures

“…Although the decoupling of these effects is greatly limited by the extended timescales and highly conned space, some studies and reviews have focused on this key question. 59,97,120,121 The contribution of hot carriers, local eld, and local heat was distinguished through accurate temperature detection, optimized catalytic system design, or the application of in situ spectroscopy. In addition, excessive heating may also lead to poor product selectivity, generating carbon monoxide during HCOOH decomposition.…”

Au@C/Pt core@shell/satellite supra-nanostructures: plasmonic antenna–reactor hybrid nanocatalysts

“…12,14,[18][19][20][21] Plasmonic hot carriers, if not harvested by molecular adsorbates, may become thermalized by interacting with phonons to generate heat, a process known as photothermal transduction. 14,20,[27][28][29] Local-eld enhancements, 30 hot carriers, 12,31,32 and photothermal heating [33][34][35] derived from excitation and decay of plasmons may all provide critical contributions to the kinetic enhancements of photocatalytic reactions. Although the great promise of plasmon-mediated photocatalysis has been well-recognized by both nanoplasmonics and heterogeneous catalysis communities, nanocatalysts composed of ideal plasmonic metals can only efficiently catalyze a limited number of industrially relevant chemical reactions.…”