Characterization of TiO₂ thin films for photocatalysis applications using photoacoustic spectroscopy

Abstract
Semiconductors thin films are being used to promote photocatalytic reactions in a very efficient way to decompose hydrocarbons such as aromatic hydrocarbons, chlorinated aromatics, surfactants, etc. Titanium dioxide is the most widely used oxide semiconductor for photocatalytic processes due to both its high photocatalytic activity and its chemical photocorrosion stability in the reaction conditions. The photocatalytic activity is determined by thin film growth parameters such as grain size, high active surface area, crystalline phase and doping of the semiconductor particles. In particular, the bandgap energy values of the semiconductor films are a fundamental parameter since it determines the portion of the visible spectra useful for the photocatalytic reactions. Using the sol-gel deposition technique, we have grown TiO₂ thin films on glass substrates to be applied in the decomposition of benzene and toluene pollutants. We used different growth conditions in terms of the precursors used for the sol-gel growth solution and the mol ratio of water, in order to control the crystalline phase, either the rutile or the anatase TiO₂ phases, and the film crystalline quality. The photoacoustic spectroscopy has been used to characterize the optical absorption spectra for these set of films, and determine precisely the bandgap energies. We also present results on the photocatalytic activity for these TiO₂ films evaluated in terms of the photobleaching of methylene blue, and their correlation to the photoacoustic spectra.