Different nanocrystalline photoactive TiO2 catalysts were prepared by the hydrolysis of titanyl sulphate (TiOSO4). Some important parameters in the preparation procedure, such as pH, calcination temperature, hydrolysing agent and temperature and ageing time were varied, leading to TiO2 with very different physical properties, i.e. crystalline phase composition, crystallite size, surface area, light absorption properties and bandgap energy. The photocatalytic activity of the TiO2 catalysts was evaluated using the photooxidation of dichloroacetic acid (DCA) as probe reaction. The experimental results revealed that the photocatalytic activity of the samples was greatly affected by their physical properties and therefore by the experimental conditions employed in their preparation. Using the optimum preparation parameters, TiO2 with an activity notably higher than the commercial TiO2 Degussa P-25 was obtained. Photoelectrochemical properties of both materials were studied for the hypothesis of enhanced activity. (c) 2005 Elsevier B.V. All rights reserved.