The interaction of water with oxide mineral surfaces affects chemical reactions that are important to many environmental and geological systems, such as contaminant and nutrient transport, crystal growth and dissolution, microbial-promoted redox processes, and geologic CO<sub>2</sub> sequestration. These reactions predominantly occur in the mineral-water interfacial region, a chemical and structural transition zone where surface functional groups interact with both adsorbates and water. While past work clearly shows that interfacial water responds to chemical changes at the mineral surface, the role of water in controlling the reactivity of interfacial regions has not been systematically investigated. Surface X-ray scattering measurements on corundum (001) surfaces in the presence and absence of arsenate over a range of pH conditions have been used to determine the response of interfacial water structure to arsenate adsorption. In the absence of arsenate, relatively weak spatial ordering of water was observed that had little variation over the pH range of 5 to 9, suggesting surface charging alone is inadequate to induce extensive structural changes in interfacial water on this surface. In contrasts, interfacial water undergoes substantial restructuring in response to arsenate adsorption, suggesting that charged surface complexes perturbs interactions of water molecules and the corundum (001) surface. Interfacial water structure on this surface also shows a dependence on arsenate surface coverage, with a gradual structural transition to a more ordered one with increasing arsenate surface coverage. These observations demonstrate that the adsorption of arsenate directly affects the structural rearrangement of interfacial water molecules, possibly through the modification of mineral surface charge properties or by providing new sites to which water may form hydrogen bonds. Such adsorbate-induced restructuring of interfacial water suggests that water structure plays an important role in the energetics of chemical reactions at mineral-water interfaces.<br/><br/>

Impacts of pH and surface coverage on the response of interfacial water structure to the adsorption of arsenate

253rd National Meeting (2017)

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