Heterogeneous Catalysis on Plasmonic Metallic Nanostructures: Selective Catalytic Conversion at Lower Temperatures co-Driven by Solar and Thermal Energy

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In this project funded by the Chemical Catalysis program of the Chemistry Division, Professor Suljo Linic of The University of Michigan (Ann Arbor) is developing a new generation of photocatalysts that use solar energy to drive chemical transformation. These new photocatalysts are small nanoparticles of silver, copper and gold, which are on one hand characterized by their strong interaction with solar light (i.e., these concentrate the solar energy) and on the other hand by their high chemical activity (i.e., activate a number of desired chemical transformations). This new generation of photocatalysts will complement semiconductor photocatalysts, which are traditionally used in this field. An outreach program developed by Professor Linic to area high schools is allowing local high school students the opportunity to participate in this research and to learn about sustainable energy transformations. The broader impacts of this work include potential societal benefits from the discovery of new generation of photocatalysts as well as the development of training opportunities for students and teachers. It was demonstrated recently that when illuminated with low intensity light, plasmonic metal nanoparticles can activate electron-driven chemical reactions at meaningful rates. The characteristic of plasmonic nanostructures (Ag, Au, and Cu were used) that makes them fundamentally different than extended metal surfaces (metal bulk), is their strong resonant interaction with UV-vis light through the excitation of localized surface plasmon resonance (LSPR). While these initial studies led to a very vibrant field of photochemistry on plasmonic metals, there are many unanswered critical issues. The project focuses on a number of these issues, including identification of: (i) the mechanism by which plasmons transfer energetic electrons to the adsorbates and in doing so induce chemical transformations, (ii) the mechanisms responsible for the reported non-linear dependency between reaction rate and light intensity, and (iii) the nature of the active sites responsible for the observed photochemistry on plasmonic metal nanoparticles. Addressing these issues is critical for the development of predictive relationships between optical properties of metal nanoparticles, their geometric structure (at the single particle and a cluster level), and their photocatalytic activity. This is important for our understanding of the surface photo-chemistry taking place on these materials, the extent to which these processes can be controlled, and the parameters that influence the design of optimal photo-catalytic systems.