Wetting behavior of hierarchical oxide nanostructures: TiO2 nanotubes from anodic oxidation decorated with ZnO nanostructures

Titania nanotubes (TiO₂ NTs) of 5 μm in length and 100 nm in the external diameter are easily formed by anodic oxidation. They are used as hollow substrates to deposit different ZnO nanostructures, such as nanoparticles and nanowires by employing two different techniques, electrodeposition and hydrothermal growth, respectively. In this way highly nanostructured and hierarchical sample surfaces were obtained, showing high level of crystallinity of both TiO₂ anatase and ZnO wurtzite materials. In addition, the wetting behavior drastically changed from the hydrophilic TiO₂ NTs surface to almost superhydrophobic surfaces of the hierarchical samples, thanks to the decoration with ZnO nanostructures. These results open interesting possibilities to employ our hierarchical TiO₂-ZnO nanostructured materials as self-cleaning, antireflective or anti-fogging surfaces. These hierarchical and composite nanostructures could be thus efficiently used in photocatalytic devices, which would also benefit from the combination of both metal oxides for improved performances and efficiencies.