TiO(2) 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 TiO(2) thin films and on their photocatalytic efficiency was evaluated. The film thickness obtained after a single clipping was proportional to the viscosity of the dip-coating solution. The presence of highly viscous solvent such as alpha-terpineol did not modify the TiO(2) crystallite size, while smaller crystallites were formed in presence of a polymer. Both additives increased the porosity of the single dipping TiO(2) film. About twice higher TiO(2) crystallite sizes were formed by using PECVD method. All TiO(2) 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. The photocatalytic activities of the TiO(2) thin films were evaluated by the photoxidation rate of 2-hydroxybutanedioic 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 TiO(2) 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 TiO(2) particles seemed to slightly increase the photocatalytic activity, probably because of the increase in the surface area of the particulate film. PECVD TiO(2) films present smaller efficiencies than those prepared by the sol-gel method. No influence of textural properties on the photocatalytic mechanism was observed. (C) 2004 Elsevier Ltd. All rights reserved.