Physical properties and photocatalytic efficiencies of TiO2 films prepared by PECVD and sol–gel methods

TiO2 thin-film photocatalysts coated onto glass were prepared either by plasma enhanced chemical vapour deposition (PECVD) deposition or by a dip-coating process using sol–gel solutions. The influence of the addition of a polymer and of a highly viscous solvent on physical properties (thickness, crystallite size and porosity) of TiO2 thin films and on their photocatalytic efficiency was evaluated. lm thickness obtained after a single dipping was proportional to the viscosity of the dip-coating solution. The presence of highly viscous solvent such as α-terpineol did not modify the TiO2 crystallite size, while smaller crystallites were formed in presence of a polymer. Both additives increased the porosity of the single dipping TiO2 film. About twice higher TiO2 crystallite sizes were formed by using PECVD method. All TiO2 films prepared in this work by sol–gel methods were of the anatase phase and were orientated along the (1 0 1) plane. In contrast, anatase films prepared by PECVD and 520 nm thick were orientated along the (0 0 4) crystallographic plane was obtained in 520 nm film thickness. otocatalytic activities of the TiO2 thin films were evaluated by the photoxidation rate of 2-hydroxybutanedioı̈c acid (malic acid). They were strongly dependent on the film thickness, suggesting the participation of all the inner part of the film in the generation of e−/h+ pair. No influence of the TiO2 film porosity, in the range 10–70%, was observed because of a sufficient porosity to allow the total diffusion of organic compounds within the film. However, smaller TiO2 particles seemed to slightly increase the photocatalytic activity, probably because of the increase in the surface area of the particulate film. PECVD TiO2 films present smaller efficiencies than those prepared by the sol–gel method. luence of textural properties on the photocatalytic mechanism was observed.