A combined homogeneous and heterogeneous photocatalytic decolourisation and degradation of a chlorotriazine Reactive azo dye Reactive Orange 4 (RO4) have been carried out using ferrous sulphate/ ferrioxalate with H2O2 and TiO2-P25 particles. Solar/ferrous/H2O2/TiO2-P25 and solar/ferrioxalate/H2O2/TiO2-P25 processes are found to be more efficient than the individual photo-Fenton and solar/TiO2-P25 processes. A comparison of these two processes with UV/ferrous/H2O2/TiO2-P25 and UV/ferrioxalate/H2O2/TiO2-P25 reveals that ferrioxalate is more efficient in solar light whereas ferrous ion is more efficient in UV light. The experimental parameters such as pH, initial H2O2, Fe2+, ferrioxalate and TiO2-P25 concentration strongly influenced the dye removal rate in solar processes. The optimum operating conditions of these two combined processes are reported. (C) 2005 Elsevier B.V. All rights reserved.