Titanium Dioxide Photocatalysis: Interactions of band edge carriers with molecules by ultrafast photoemission spectroscopy and theory

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With this award from the Chemical Catalysis Program of the Chemistry Division of the National Science Foundation, Prof. Hrvoje Petek, his collaborator Dr. Jin Zhao and their students at the University of Pittsburgh will study by experiment and theory the electron driven processes in photocatalytic chemistry on rutile titanium dioxide surfaces. Excitation of carriers across the band gap of titanium dioxide with near-ultraviolet light is known to initiate a variety of photocatalytic processes involving interaction of adsorbed molecules with energetic electrons and holes. The timescales of photophysical and photochemical processes span femtoseconds to seconds. The interaction of photoexcited electrons with adsorbed molecules and defects will be studied for molecule covered single crystal titanium dioxide surfaces under ultrahigh vacuum conditions by time-resolved two-photon photoemission spectroscopy. The extension of the two-photon photoemission technique to 4.6 eV will enable the study of dynamics of the most chemically significant conduction band edge electrons with chemisorbed molecules. In parallel, advanced theoretical methods will be used to study how photoexcited carriers initiate chemical reactions of chemisorbed molecules.Titanium dioxide is a model photocatalyst of significant fundamental interest for the conversion of solar to chemical energy starting with abundant chemical feedstocks such as water and carbon dioxide. A central issue in photocatalysis is how photoexcited carriers (electrons and holes) interact with adsorbed molecules to initiate chemical reactions. Such knowledge can be used to design more efficient photocatalyst materials and practical solar energy conversion processes. The potential advances in harnessing solar energy can conceivably reduce our reliance on fossil fuels and convert potentially harmful byproducts of combustion into valuable chemical fuels. This research will be used to train the next generation of scientists since students will be exposed to high-level experimental and theoretical methods for investigation of ultrafast interfacial dynamics. They will explore research areas that can have major impacts on society, and will be exposed to international collaboration with colleagues at the University of Science and Technology of China.