Photocatalytic degradation of single and binary phenol and m-nitrophenol (m-NP) in aqueous solutions by commercial TiO2 powders (Degussa P-25) under UV irradiation was examined. The influences of various operating parameters including the initial reactant concentration (0.13-0.71 mM), solution pH (4.1-12.7), and the presence of the second reactant on photodegradation were studied. The effect of TiO2 pre-wetting with aqueous solution on phenol photodegradation was also studied. It was shown that the degradation rates of phenol and m-NP decreased with increasing initial reactant concentrations. The optimal solution pH for the photodegradation of single phenol and m-NP was at around 7.4 and 8.9, respectively. Compared to the single systems, the photodegradation rates of phenol and m-NP in binary systems decreased, particularly when the second reactant was in excess. Moreover, the photodegradation of either single or binary reactants in aqueous solutions satisfactorily followed the pseudo-first-order kinetics. (c) 2008 Elsevier B.V. All rights reserved.