TiO2-SiO2 mixed oxides were synthesized by the sol-gel technique using three different acids, i.e., acetic, sulfuric, or chlorhydric acid. Their photocatalytic behavior was evaluated on the phenol oxidation in liquid phase and correlated with the characterization results. It was found that the kind of acid used during the preparation strongly influences the phase composition and stability of the TiO2 phases incorporated in the silica structure as well as the photocatalytic activity. In all cases, silica introduced a dispersive effect that stabilized the TiO2 crystalline phases upon calcination at 700 degrees C. SO42- and CH3COO- ions stabilized the anatase phase at high calcination temperatures (700 degrees C) leading to samples with the highest photoactivities. Cl- ions induced the formation of traces of rutile and brookite resulting in a lower photoactivity. The highest photoactivity was achieved with the catalyst synthesized with acetic acid and calcined at 700 degrees C (TS1-700-ace). The photocatalytic performance of this material was even better than that obtained with the commercial catalyst Degussa P-25. (C) 2013 Elsevier B.V. All rights reserved.