CAREER: Mapping the Chemical Reactivity of Metal Oxide Photocatalysts by Correlative Single-Molecule Fluorescence and Electron Microscopy

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Nanocrystal photocatalysts are tiny, synthetic crystals that use light to accelerate chemical reactions. Photocatalysts that make fuels, such as methane, using only carbon dioxide, water and sunlight would have significant benefit to society. However, developing photocatalysts capable of sunlight-to-fuel conversion is a challenging problem that requires a fundamental understanding of the chemical reactions taking place on the nanocrystal surface. With support from the Macromolecular, Supramolecular and Nanochemistry Program of the NSF Division of Chemistry, Professor Sadtler at Washington University in St. Louis is developing microscopy methods to watch individual, light-driven reactions as they occur on single nanocrystal photocatalysts. Together, Professor Sadtler and his students are gaining new insights into why some atomic sites on the surface of nanocrystals are particularly active for catalysis. Professor Sadtler is also infusing his research into education. He is developing new courses that use atomic structure and chemical bonding as a basis to teach the frontiers of chemistry and materials science, as well as working with high school teachers and students in the St. Louis area.Metal oxide semiconductor nanocrystals with tunable stoichiometry are promising photocatalysts to produce liquid fuels through solar water splitting, partial methane oxidation, and the reduction of carbon dioxide. However, the contribution of specific structural and morphological features among individual catalyst particles to their ensemble activity is not well understood because each particle is different and possesses a variety of potential reaction sites. This project uses super-resolution fluorescence microscopy and redox-active fluorogenic probes to monitor photoinduced charge-transfer events on individual metal oxide nanocrystals with nanoscale spatial resolution. Correlation of the reactivity maps with the atomic resolution of scanning transmission electron microscopy performed on the same particles reveals how the distribution of oxygen vacancies in individual particles affects their reactivity. To further develop structure-activity relationships in metal oxide photocatalysts, the single-molecule, single-particle data are compared to measurements of bulk photocatalytic activity for methane oxidation and carbon dioxide reduction.This award reflects NSF's statutory mission and has been deemed worthy of support through evaluation using the Foundation's intellectual merit and broader impacts review criteria.