Reduced colloidal metal-oxide nanocrystals as novel redox reagents

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James M. Mayer of the University of Washington is supported by an award from the Macromolecular, Supramolecular and Nanochemistry Program in collaborative research that seeks to examine the chemical reactivities and physical properties of colloidal oxide semiconductor nanoparticles containing extra electrons. Pure and doped ZnO and TiO2 nanoparticles of different sizes, band gaps, and with different surface-capping groups will be studied. Photoexcitation of these particles followed by hole trapping yields stable solutions of reduced nanoparticles, containing electrons in conduction-band orbitals or in "trap states". Synthetic, analytical, and spectroscopic techniques will be integrated to develop a fundamental understanding of the structure/function relationships that govern the reactivities of these nanoparticles. The nanoparticle charging chemistries will be examined by tracking the organic products and protons that are formed upon hole trapping, and by following the evolution of the photoexcited nanoparticles spectroscopically. The ability of the reduced particles to perform multi-electron/multi-proton reactions will be examined using molecular and nanocrystal substrates. The influence of nanocrystal doping and surface modification will be examined. Connections among the spectroscopic, thermochemical, and kinetic properties of the reduced particles will be developed. This research will yield new fundamental scientific insights that could alter the ways such materials are understood and applied in various technologies including the oxide/solution interfaces of photoelectrochemical cells or batteries.This research will address fundamental reactivities of metal-oxide nanostructures. Such nanostructures are ubiquitous in energy conversion, energy storage, and photocatalysis technologies, and the information gleaned from the proposed research will have broad implications in each of these technologies. This project could furthermore result in the development of inexpensive, robust, and environmentally sound multi-electron reducing reagents with tunable potentials for application in a variety of scientific contexts from fundamental research to catalysis. Finally, this research will provide new fundamental insights into general electron transfer chemistries and will deepen our understanding of this important class of reactions. In addition to yielding new fundamental scientific insights and new materials, this research will also provide undergraduate and graduate students with opportunities for advanced interdisciplinary education and training to prepare them for future careers in science and engineering. Emphasis will be placed on integration of research and education at the undergraduate level through involvement of undergraduates in the research, incorporation of experiments and concepts from the research into the undergraduate laboratory curriculum, collaboration with faculty and students from undergraduate institutions, and outreach activities at regional community colleges and high schools.