The Origin of Superhydrophobicity for Intrinsically Hydrophilic Metal Oxides: A Preferential O2 Adsorption Dominated by Oxygen Vacancies.

The superhydrophobicity of intrinsically hydrophilic materials is still not well understood. Now, intrinsically hydrophilic metal oxides with different topographic structures are taken as model materials to reveal the origin of their superhydrophobicity. These metal oxides show enhanced hydrophobicity or superhydrophobicity in O2 relative to that in air, but exhibit superhydrophilic behavior in N2 . The presence of rich oxygen vacancies greatly enhanced the adsorption of O2 with an adsorption energy larger than N2 and H2 O, resulting in a stable O2 adsorption rather than air-trapping within grooves of rough-textured surfaces, which endows these intrinsically hydrophilic oxides with superhydrophobicity. Our results highlight a further understanding of the origin of superhydrophobicity for intrinsically hydrophilic materials, and is of great significance for designing novel devices with desired wettability.