Thin films of single-crystalline SrTiO3 nanorod arrays and their surface wettability conversion

Thin films of single-crystalline SrTiO3 nanorod arrays were synthesized by ion-exchange and annealing titanate nanotube arrays. The diameter of the SrTiO3 nanorods ranged from 10 to 20 nm, and the long length axis of these nanorods was oriented in the [110] direction of the perovskite phase. These nanorod arrays were optically semitransparent and adhered well to the substrates. Due to their surface nanostructures, these nanorod surfaces exhibited superhydrophilicities with water contact angles (theta) below 3 degrees. In addition, these surfaces turned into high-hydrophobic states (theta = 140 degrees) when oleic acid was applied. UV illumination caused these hydrophobic thin films to become superhydrophilic states because single-crystalline SrTiO3 nanorods have strong photocatalytic oxidative activities, which decomposed the surface-adsorbed oleic acid.