Structure and reactivity of the hydrated hematite (0001) surface

The structure of the hydroxylated hematite (0001) surface was investigated using crystal truncation rod diffraction and density functional theory. The combined experimental and theoretical results suggest that the surface is dominated by two hydroxyl moieties - hydroxyls that are singly coordinated and doubly coordinated with Fe. The results are consistent with the formation of distinct domains of these surface species; one corresponding to the hydroxylation of the surface Fe-cation predicted to be most stable under UHV conditions, and the second a complete removal of this surface Fe species leaving the hydroxylated oxygen layer. Furthermore, our results indicate that the hydroxylated hematite surface structures are significantly more stable than their dehydroxylated counterparts at high water partial pressures, and this transition in stability occurs at water pressures orders of magnitude below the same transition for α-alumina. These results explain the observed differences in reactivity of hematite and alumina (0001) surfaces with respect to water and binding of aqueous metal cations.