Molecular Foundry Seminar
"Reaction of Oxides in Water at the Molecular Scale"
Professor Bill Casey, Departments of Chemisty and Geology, UC Davis,Tuesday, October 20th at 1:30 pm, Room 67-3111
Abstract:
Understanding the corrosion of oxide materials is key to many fields, including geochemistry, nuclear power, the stability of glasses, human health, design of photoelectric cells and the fluxes of contaminants through watersheds. Predictive models for these reactions range from thermodynamic treatments and step-flow models to those that emphasize activated bond ruptures in molecular-scale clusters. Molecular details, however, are largely speculative because it is unclear what functional groups are present at the surface, how they are arranged and how they interact with water and each other during reaction. Establishing the surface structures themselves is a research problem of great difficulty.
As an alternative, my group examines hydrolytic and isotope-exchange reactions in nanometer-size aqueous oxide ions that are 40-2000 atoms in size. Unlike the glass or mineral interface, the structures of these large ions in solution can be known with complete confidence. The pathways for dissociations and isotope-exchanges can be followed spectroscopically with unprecedented clarity. With them, I show how metastable forms of the structures probably dominate the chemistry at the molecular scale and that little about the reaction pathways could be anticipated from the ground-state properties. The pathways are not intuitive.
I begin the seminar by reviewing the broad reactivity trends for dissolution of insulating oxide materials in water and show that many aspects of glass and mineral dissolution resemble familiar reactions, such as ester hydrolysis and isotopic exchange in sugars. Some important classes of reactions, such as ligand substitutions at surface functional groups, can be estimated with confidence; others remain so wildly speculative that only repetition in a loud voice provides any measure of an idea's value.
