Thermal Versus Nonthermal Pathways in Plasmonic Photocatalysis: Current Debates and Insights

Photocatalysis is well defined in the IUPAC Compendium of Chemical Terminology (Gold Book); however, photothermal catalysis remains insufficiently defined, and the relative contributions of thermal and nonthermal (photochemical) effects continue to be actively debated. In particular, the interpretation of plasmonic photocatalysis has raised fundamental questions regarding the roles of photothermal heating and generated hot carriers in light-driven processes over plasmonic metal nanoparticles. This perspective paper summarizes a recently recommended classification of thermo-photocatalysis, with specific emphasis on plasmonic photocatalytic systems. The elementary photo-induced processes occurring in plasmonic nanoparticles—including light absorption, localized surface plasmon resonance excitation, hot-carrier generation and relaxation, and nanoscale heat dissipation—are outlined. Representative experimental examples are discussed to illustrate synergistic interactions between thermal and nonthermal pathways in plasmonic photocatalysis. In addition, simple and widely accessible experimental strategies used to distinguish nonthermal contributions—such as analyses of light intensity effects, wavelength-dependent studies, competitive electron transfer reactions, and kinetic isotopic effects—are briefly discussed. By highlighting both the strengths and limitations of these experimental approaches, this paper aims to provide a conceptual framework for distinguishing thermal and nonthermal phenomena and to promote more rigorous mechanistic analyses in future studies of plasmonic and related photo-driven catalytic systems at elevated temperatures.