Insights on the Structural and Dynamic Properties of Corundum-Water Interfaces from First-Principle Molecular Dynamics

The interaction of water with hydroxylated mineral surfaces is central to numerous natural and technological processes; yet, at the atomic level much remains to be understood about the structure and dynamics of interfacial water and H-bonding networks. This work applies first-principle molecular dynamics to examine the relationship between surface structure and interfacial water behavior at four hydroxylated corundum (α-Al2O3) surfaces. The four surfaces studied include the (001), (012), (110), and (113) surfaces; they have distinct surface functional groups (-OH, μ-OH, and μ3-OH) and topography (planar, corrugated, and two-tiered). Interfacial H-bonding was investigated in detail by analyzing atomic density 1-D profiles, angular distribution of surface O-H bonds, and the dipole moment orientation of interface H2O molecules and by calculating vibrational density of states in the high-frequency region. Our results reveal distinct differences in the interaction of interfacial water and H-bonding networks at the four surfaces. Specifically, inter- and intramolecular H-bonding depends on surface site coordination geometry, neighboring functional groups, and surface topography. Moreover, intramolecular H-bonding involving in-plane surface hydroxyl groups may persist, thus limiting intermolecular H-bonding. Equally, first solvation layer water molecules are preferentially orientated at the (001), (012), and (113) surfaces, whereas water molecules at the (110) surface show minimal preferred orientation. The distinct differences in the behavior of interfacial water and H-bonding at the four surfaces may play a substantial role in determining the reactivity of the surfaces toward processes such as ion adsorption-desorption and dissolution-precipitation.