| Abstract
| - Understanding the interaction of water with metal oxide surfaces is important to a diverse array of fields and isessential to the interpretation of surface charging and ion adsorption behavior. High-resolution specular X-ray reflectivitywas used to determine the termination of and water adsorption on the α-Al2O3 (012)-aqueous solution interface.Interference features in the reflectivity data were used to identify the likely termination, consisting of a full Al2O3layer plus an additional oxygen layer that completes the coordination shell of the upper aluminum site. This was furtherinvestigated through a model-independent inversion of the data using an error correction algorithm, which also revealedthat there are two sites of adsorbed water above the surface. Characteristics of these two water sites were quantifiedthrough a model-dependent structural refinement, which also revealed additional layering in the interfacial water thatgradually decays toward disordered bulk water away from the surface. Although the termination observed in this studydiffers from that assumed in past studies of surface charging, the density of key surface functional groups is unchanged,and thus, predictions of surface charging behavior are unchanged. As the pHpzc of this surface has yet to be modeledaccurately, a full 3-dimensional surface structural analysis based on the termination observed in this study is neededso that the effects of surface functional group bond length changes on the pKa values can be incorporated. Considerationof the termination and sites of water adsorption suggest that singly coordinated oxygen groups will be the primarysites of ion adsorption on this surface.
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