PREDICTING THE IMPACT OF THE ENVIRONMENT ON THE STRUCTURE AND CHEMISTRY OF METAL OXIDE SURFACES: THE ROLE OF ELECTRONIC STRUCTURE

Metal oxides play an important role in contaminant sequestration and speciation in groundwater aquifers and soils, in catalysis, and in corrosion. A key factor in understanding the reactivity of metal oxides is how bulk water interacts with the surfaces. Water exhibits a range of interactions with metal oxide surfaces, from physisorption to dissociation to dissolution. Which process dominates the interaction is determined by the electronic structure of the metal oxide, the exposed surface structure and stoichiometry, and whether experimental conditions reflect a geological or laboratory surface science environment. Unravelling the complexities of metal oxide surfaces under hydrated conditions is challenging, and has required an integrated approach of experiment and models capable of atomic resolution. In particular, crystal truncation rod diffraction spectroscopy and ab initio thermodynamics based on electronic structure calculations together have enabled the determination of how surface structures and stoichiometry change as a function of environmental conditions. To determine the physical and chemical principles underlying these changes, we have focused on a comparative study of hematite and alumina surfaces because they are isostructural, yet exhibit significant differences with respect to their interactions with water and contaminants. This presentation will focus on the role of the energy and occupancy of Fe d-band states in hematite and their absence in alumina in determining the chemical reactivity of water with respect to dissociation and dissolution processes at the surface.