A combined homogeneous and heterogeneous photocatalytic decolourisation and degradation of a chlorotriazine azo dye reactive orange 4 (RO 4) have been carried out using ferrous sulphate/ferrioxalate with H2O2, and TiO2-P25 nanoparticles. Enhancement in the photo-Fenton processes has been observed by the addition of TiO2-P25. UV/ferrous/H2O2/TiO2 and UV/ferrioxalate/H2O2/TiO2 processes are found to be more efficient than the individual photo-Fenton and UV/TiO2-P25 processes. The use of ferrioxalate in the combined process is found to be more advantageous. The effects of various experimental parameters such as pH, initial H2O2, Fe2+, Fe3+ and TiO2 concentrations on these combined photocatalytic processes have been investigated. All these parameters strongly influenced the removal rate. The optimum operating conditions of these combined processes are reported. (c) 2006 Published by Elsevier B.V.