More stringent regulations concerning effluent release into rivers and streams have made it necessary to develop new technologies for effluent mineralization, with heterogeneous photocatalysis as an attractive option. The aim of the present work was to investigate the influence of thermal treatment on the structure and photocatalytic activity of TiO2 P25. The TiO2 was calcined at different temperatures (0, 200, 300, 400, 500, 600 and 700 degrees C) and used for phenol degradation (50 mg l(-1)) under visible and near-UV irradiation for 5 h. Characterization analyses (textural analysis, acidity and X-ray diffraction (XRD)) showed that the specific surface area decreased with increasing calcination temperature from 500 to 700 degrees C, while the catalyst acidity increased after thermal treatment. The anatase-rutile phase transformation occurred at 600 degrees C. In this process, both direct and sensitized photocatalysis occurred and uncalcined TiO2 showed the highest level of phenol degradation. An increase in calcination temperature led to a reduction in TiO2 activity, which may be related to the presence of rutile and anatase phases, as well as to surface adsorbed water and hydroxyl groups on the TiO2. (c) 2005 Elsevier B.V. All rights reserved.