Surface Wettability of ZnO-Loaded TiO2 Nanotube Array Layers

Abstract

Herein we report on the synthesis and the effects of gradual loading of TiO2 nanotube array layers with ZnO upon surface wettability. Two-step preparation was chosen, where TiO2 nanotube layers, grown in a first instance by anodization of a Ti foil, were gradually loaded with controlled amounts of ZnO using the reactive RF magnetron sputtering. After crystallization annealing, the formerly amorphous TiO2 nanotubes were converted to predominantly anatase crystalline phase, as detected by XRD measurements. The as-prepared nanotubes exhibited a well-aligned columnar structure, 1.6 μm long and 88 nm in diameter, and a small concentration of oxygen vacancies. Ti2+ and Ti3+ occur along with the Ti4+ state upon sputter-cleaning the layer surfaces from contaminants. The Ti2+ and Ti3+ signals diminish with gradual ZnO loading. As demonstrated by the VB-XPS data, the ZnO loading is accompanied by a slight narrowing of the band gap of the materials. A combined effect of material modification and surface roughness was taken into consideration to explain the evolution of surface super-hydrophilicity of the materials under UV irradiation. The loading process resulted in increasing surface wettability with approx. 33%, and in a drastic extension of activation decay, which clearly points out to the effect of ZnO-TiO2 heterojunctions.

Correlation between the optical and microstructural characteristics and surface wettability transition of In2O3:Sn/ZnO nanostructured bilayer system for self-cleaning application

“…The variation in WCAs of the In 2 O 3 : Sn /ZnO thin films since UV treatment is shown in figure 13. Other research has also confirmed that UV illumination leads to a switching behavior from hydrophobic to hydrophilic [61,62]. The potential applications of the results obtained here are numerous, including the production of antifogging mirrors [1], self-cleaning exterior tiles [63], and biomedical fields where surface wettability has an important role in protein adsorption, cell adhesion, and proliferation [64].…”

“…This phenomenon can be attributed to the rod-like ZnO lattice [60]. This evolution follows the Cassie-Baxter model before ultraviolet illumination [61].…”

Adsorption Kinetics of NO2 Gas on Pt/Cr-TiO2/Pt-Based Sensors

“…A typical micro columnar structure of the sensing layer is observed with excellent adhesion [33,34]. From Figure 3d-i, it can be seen that these vertical columnar structures are around 2 μm in height.…”

Concentric double hollow grid cathode discharges. Spectral investigations and phenomenological approach

“…The presence of a mixture of oxide bonds from several elements in the thin films compositions indicates the possibility of obtaining different surface reactivity by customizing their ratio. Modifying the flow of Oxygen and thus its availability during layer growth can influence the stoichiometry of the layers and enhance the presence of suboxides, modifying the energy band configuration in such heterojunction materials [41,42]. This aspect is directly related to the surface reactivity of semiconductor materials (e.g.…”