TiO₂/ZnO nanocomposite, ZnO/ZnO bi-level nanostructure and ZnO nanorod arrays: Microstructure and time-affected wettability change in ambient conditions

Wettability is an important property of surfaces and interfaces. Understanding the wetting behavior of semiconductors and its relationship with their microstructures has aroused much interest because of the great advantages this gives to various functional applications. Herein, we report the fabrication of ZnO-based nanoarrays, including ZnO nanorods, TiO₂/ZnO nanocomposites and ZnO/ZnO bi-level nanostructures, by hydrothermal growth and physical vapor deposition and also their wettability conversion. The ZnO matrix arrays consist of many hexagonal wurtzite nanorods. The microstructure and morphology of TiO₂/ZnO and ZnO/ZnO nanostructure arrays were studied. The wettability conversion of these ZnO-based nanoarrays in ambient conditions was monitored over a long period of time, and it was found that their surfaces transited from hydrophilic to hydrophobic without any external stimulation. It was also found that morphological features and surface chemical changes, such as replacing the hydroxyl groups and adding organic contaminants, affect their wettability behaving. Our results also demonstrated the possibility of slowing the loss of hydrophilic states by TiO₂ decoration.