Metal oxide / liquid water interfaces are common in a wide range of research areas like mineralogy, colloid chemistry and electrochemistry. We present results from a direct comparison of in situ synchrotron X-ray scattering experiment with hybrid-functional molecular dynamics simulations for a model compound, the hematite (alpha-Fe2O3) / liquid water interface. We show that the solvation structure of the reactive yet common (1-102) termination is dynamically stabilised by frequent exchange of surface aquo groups with bulk water, giving rise to effective partial occupancies at the surface. This interconversion between aquo groups, adsorbed water and bulk water is visible on the picosecond time scale in DFT molecular dynamics calculations, while the effective distribution of the water molecules arising from this dynamic interconversion can be found in crystal truncation rod (CTR) experiments. This work explains why classical atomistic models of the interface were not able to draw a consistent picture of the solvent - surface interactions. Moreoever, this work is of particular importance to the interpretation of CTR measurements which are a commonly used tool due to their surface sensitivity. We demonstrate the applicability of CTR measurements (which assume a static averaged atomistic structure) even for highly dynamic interfaces like the one in question here. The particular appeal of this joint experimental and theoretical work is a common picture of both the crystal structure and the solvation structure at the interface.

Dynamic stabilization of metal oxide / liquid water interfaces through water exchange

255th National Meeting (2018)

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