The oxidation of nitrobenzene and phenylamine has been carried out by heterogeneous photocatalysis in aqueous suspensions of commercial TiO2. The photoreactivity results indicate that two reaction pathways occur in parallel with both substrates from the start of irradiation: partial oxidation to monohydroxy derivatives and mineralization. The first pathway involves the entering of radical HO center dot into the aromatic ring giving rise to monohydroxy derivatives, and the second one involves the total oxidation of the substrates to CO2. The partial oxidation of nitrobenzene produces all the three possible monohydroxy derivatives, while that of phenylamine only produces the ortho- and para-isomers. The extent of adsorption in the dark was found to be about 8% mol for nitrobenzene, while the amounts were not detectable for phenylamine. The Langmuir-Hinshelwood approach has been satisfactorily applied for modeling the photoreactivity results, and the values of the kinetic model parameters have been determined. (c) 2007 American Institute of Chemical Engineers.