Intrinsic Superhydrophilicity of Titania-Terminated Surfaces

The wettability of solid surfaces is of fundamental scientific interest and related to many diverse chemical and physical phenomena at the heart of practical technologies. In particular, the hydrophilicity of the photocatalytically active metal-oxide TiO2 has attracted considerable attention for many applications. However, the intrinsic hydrophilicity of Ti-oxide surfaces is not fully understood. In this work, we investigate the intrinsic hydrophilicity of Tioxide surfaces on the atomically stable (√13 × √13)-R33.7° SrTiO3 (001) surface. The surface has a TiOx double layer on a TiO2-terminated SrTiO3 (001) surface, which is available as a surface marker to assess the atomic-scale structural stability of the surface. Both experimental and theoretical results show that Ti-oxide surfaces are intrinsically superhydrophilic with a water contact angle of ∼0°. The results show that airborne surface contamination is the most significant factor affecting the wettability of titania surfaces, strongly supporting the contamination model for explaining the mechanism of photoinduced superhydrophilicity observed on titanate surfaces. We emphasize that the effect of airborne contamination has to be carefully evaluated when investigating the wettability of surfaces.