Bimetallic nanostructures possess unique catalytic reactivity and selectivity in plasmon-driven reactions. Such nanostructures are typically composed of plasmonic and catalytic metals. A growing body of evidence suggests that unique catalytic reactivity and selectivity of bimetallic nanostructures are determined by the intensity of the rectified electric field, the nature of the catalytic metals, and the interplay between catalytic and plasmonic metals at the nanoscale. However, the actual impact of all these factors remains unclear. In this talk, I will demonstrate how tip-enhanced Raman spectroscopy (TERS) can be used to determine the underlying physical cause of catalytic reactivity and selectivity of gold−platinum (Au@PtNPs) and gold−palladium (Au@PdNPs) bimetallic nanoplates. I will discuss the results of nanoscale imaging of plasmon-driven oxidation of 4-mercapto-phenyl-methanol (MPM) to 4-mercaptobenzoic acid (MBA) and a reversed plasmon-driven reduction of MBA to MPM on Au@PtNPs, Au@PdNPs, and their monometallic analogues, AuNPs. Our results show that plasmondriven reduction of MBA to MPM is evident only for Au@PdNPs, whereas Au@PtNPs exclusively possess oxidation properties enabling MPM to MBA conversion. These results show that the nature of the catalytic metal determines redox properties of bimetallic nanostructures. At the same time, none of these redox reactions are evident for AuNPs. Instead, we observe only C−C cleavage of both MPM and MBA that yields thiophenol. These findings suggest that the rectified electric field determines the reactivity of plasmon-driven reactions, whereas its intensity can be used to predict chemical transformations on these mono- and bimetallic nanostructures.

Probing the redox selectivity and catalytic reactivity of gold-platinum and gold-palladium bimetallic nanoplates by tip-enhanced Raman spectroscopy

ACS Spring 2022

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