(104f) Optically-Tunable, Metallic Nanomaterials for Chemical Sensing and Catalytic Studies

Understanding the reaction mechanisms and catalytic activity of metallic nanoparticles is frequently hindered by our inability to identify and probe surface chemical species under reactive conditions. Techniques such as IR and Raman can be used for in situ chemical analysis and sensing; unfortunately, these methods lack sufficient sensitivity to study catalytic surfaces and active sites at the nanoscale. In such venues, Raman scattering is potentially more useful than IR because the chemical signature (or scattering cross-section) of an analyte molecule or adsorbate can be enhanced by coupling of probe radiation with optically-active metallic nanostructures. Although the Raman enhancement approach can potentially provide a wealth of chemical information about reactions at surfaces, it is not easily implemented because most metals are not plasmonically active in the visible or IR range. As such, having the ability to tailor the optical and chemical behavior of a catalyst, by blending a catalytically-active (noble) metal with an optically-active metal, would allow for in situ spectroscopic investigations of surface adsorbates and catalytic mechanisms.

In this talk, we will highlight several synthetic routes to realize bi-metallic nanomaterials with tunable optical properties that are catalytically active. Specifically, we will discuss the synthesis, characterization, and reactivity of AgAu, CuAu, and PtAu nanomaterials created via co-reduction, digestive ripening, plasma reduction of metal-containing micelles, and nanosphere lithography techniques. For instance, using digestive ripening to alloy gold and silver nanoparticles with decylamine ligands, the plasmon frequency could be tuned over a wide range while keeping the particles crystalline with sizes smaller than 10 nm. We will also discuss in situ Raman investigations of catalytic processes, such as selective oxidation and CO scrubbing of H₂, on these bi-metallic nanoparticles. With such an approach, operando optical methods, aided by optically- tunable, catalytically-active nanoparticles, can potentially provide deeper understanding of reaction intermediates and chemical processes at nanoparticle surfaces and active sites under realistic conditions.