Atmospheric pressure dielectric barrier discharge synthesis of morphology-controllable TiO2 films with enhanced photocatalytic activity

Atmospheric plasma technology is a promising next-generation alternative for replacing thermal chemical vapor deposition or wet chemical processes for the deposition of functional coatings. In this work, TiO2 films with various morphologies and thicknesses are synthesized in a controllable way by atmospheric Dielectric Barrier Discharges (DBD) under argon/oxygen ambient conditions. This method allows varying the density of the deposited coatings, from low density powders to dense compact anatase layers simple tuning of the parameters. The surface morphology and cross section of the as-synthesized films are observed by scanning electron microscopy (SEM). It is demonstrated that the total flow rate together with the absorbed power have a significant effect on the morphology of the film, which changes from granular to compact film by increasing the total flow rate or decreasing the power. In other words, changing the energy density (Ed) in the plasma allows to control the morphology of the TiO2 films. A deposition mechanism is proposed to explain the effect of the synthesis parameters on the formed films. The chemical and phase composition of these films before and after annealing for 2 h in air at 673 K are comparatively studied. The photocatalytic activities and the reusability of the TiO2 films is investigated by degrading a methylene blue (MB) solution under Ultra-Violet (UV) light. It is compared to the activity of a P25 film, deposited by drop-casting. The photocatalytic rate of the annealed TiO2 film synthesized at a total flow rate of 2.5 slm turns out to be about 2 and 15 times higher than the one of P25 and as-synthesized TiO2 films, respectively. The annealed TiO2 film were shown to be reusable for at least three cycles, without significant loss of photocatalytic activity.