Abstract:
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Rare-earth oxides (REOs) possess a remarkable
intrinsic hydrophobicity, making them candidates for a myriad
of applications. Although the superhydrophobicity of REOs has
been explored experimentally, the atomistic details of the
structure at the oxide−water interface are still not well
understood. In this work, we report a density functional theory
study of the interaction between water and CeO2, Nd2O3, and
α-Al2O3 to explain their different wettability. The wetting of the
metal oxide surface is controlled by geometric and electronic
factors. While the electronic term is related to the acid−base
properties of the surface layer, the geometric factor depends on
the matching between adsorption sites and oxygen atoms from
the hexagonal water network. For all the metal oxides
considered here, water dissociation is confined to the first
oxide-water layer. Hydroxyl groups on α-Al2O3 are responsible for the strong oxide−water interaction, and thus, both Al- and hydroxyl-terminated wet. On CeO2, the intrinsic hydrophobicity of the clean surface disappears when lattice hydroxyl groups (created by the reaction of water with oxygen vacancies) are present as they dominate the interaction and drive wetting. Therefore, hydroxyls may convert a intrinsic nonwetting surface into a wetting one. Finally, we also report that surface modifications, like cation substitution, do not change the acid−base character of the surface, and thus they show the same nonwetting properties as native CeO2 or Nd2O3. |