Titanium dioxide thin films deposited by the sol-gel technique starting from titanium oxy-acetyl acetonate: Gas sensing and photocatalyst applications

Titanium dioxide (TiO₂) thin films were deposited onto sodocalcic glass plates by the sol-gel technique, starting from a non-alkoxide route, namely, titanium oxy-acetyl acetonate as Ti precursor. Film thickness effect on both the gas sensing and photocatalytic degradation performance was studied. The as-deposited films were annealed in air at 400 °C. All the X-ray spectra of the films show a very broad-peak centered in a 2θ angle around 30°. In the case of the thinnest films the surface morphology is uniform and very smooth, whereas for the thickest films the corresponding surface is covered by grains with a rodlike shape with a length on the order of 140 nm. The films were tested both for two straightforward applications: ultraviolet assisted-degradation of methylene blue dissolved in water, at different times, as well as gas sensor in a controlled propane (C ₃H₈) atmosphere. As the film thickness increases, the degradation of methylene blue (MB) also increases. The thickest TiO₂ thin films after being exposed by 5 hours to the catalytic degradation, promoted by ultraviolet illumination, showed a final MB solution degradation in the order of 48 %. This reult can be associated with the increase in the effective exposed area of the TiO₂ thin films. On the other hand, the exposition of the films to a controlled propane atmosphere produced a significant change in the surface electrical resistance of the films at operating temperatures of 200 °C and above. In fact, in the case of the thickest TiO₂ films, a dramatic electrical resistance change of non-exposed and propane exposed - 560 to 0.7 MΩ -, was registered. The results show that TiO₂ films deposited by an economical deposition technique, as is the case of the sol-gel technique, could have an important potential in industrial applications.