Studies on the heterogeneous photocatalytic oxidation of 2,6-dinitrophenol with different catalysts like TiO2, TiO2-P25, CdS, WO3 and ZnO indicated aqueous TiO2-P25 suspensions exhibit maximum efficiency in photodegradation at the wavelength of 254 nm using an annular-flow type photo reactor with a 8 W low pressure mercury lamp as a UV light source. Operational parameters like variation of catalyst load, initial concentration of 2,6-DNP, irradiation time, pH, oxygen supply and nitrogen supply on the efficiency of degradation was also investigated and optimum conditions were established. All the experiments were carried out in a batch recirculation mode. The possible mechanisms for the photocatalytic degradation of 2,6-DNP are discussed. (C) 2004 Elsevier B.V. All rights reserved.