The photocatalytic degradation of catechol, resorcinol, m-cresol, o-cresol and phenol has been studied individually, in dual mixtures and in the presence of hydrogen peroxide to determine possible competition for adsorption and photoactive centres and for the radicals photogenerated. The obtained results have shown that in the presence of hydrogen peroxide degradation rates are determined by the localization of specific adsorption centres more than by the amount of adsorbed molecules or the number of aromatic ring activating positions generated by substituents. The interaction of catechol with the hydroxyls responsible for the formation of the more photoactive (OH)-O-center dot radicals slows down the degradation of the other phenolics. Additionally, the interaction of each compound with the surface of TiO2 results in the change of the photoadsorption of oxygen. Consequently, degradation rates of the mixtures are also determined by the photoadsorption of oxygen. (c) 2007 Elsevier B. V. All rights reserved.