Solar Energy Materials & Solar Cells 89 (2005) 61–74 Enhanced heterogeneous ferrioxalate photo-fenton degradation of reactive orange 4 by solar light K. Selvam, M. Muruganandham, M. Swaminathan à Department of Chemistry, Annamalai University, Annamalai Nagar—608 002, India Received 21 December 2004; accepted 10 January 2005 Available online 24 February 2005 Abstract A combined homogeneous and heterogeneous photocatalytic decolourisation and degrada- tion of a chlorotriazine Reactive azo dye Reactive Orange 4 (RO4) have been carried out using ferrous sulphate/ ferrioxalate with H 2 O 2 and TiO 2 -P25 particles. Solar/ferrous/H 2 O 2 /TiO 2 - P25 and solar/ferrioxalate/H 2 O 2 /TiO 2 -P25 processes are found to be more efficient than the individual photo-Fenton and solar/TiO 2 -P25 processes. A comparison of these two processes with UV/ferrous/H 2 O 2 /TiO 2 -P25 and UV/ferrioxalate/H 2 O 2 /TiO 2 -P25 reveals that ferriox- alate is more efficient in solar light whereas ferrous ion is more efficient in UV light. The experimental parameters such as pH, initial H 2 O 2 , Fe 2+ , ferrioxalate and TiO 2 -P25 concentration strongly influenced the dye removal rate in solar processes. The optimum operating conditions of these two combined processes are reported. r 2005 Elsevier B.V. All rights reserved. Keywords: Reactive orange 4; Photo-Fenton; Ferrous ion; Ferrioxalate; H 2 O 2 ; TiO 2 -P25; Solar light 1. Introduction Oxidation of organic compounds in the presence of Fe(II) and hydrogen peroxide was first observed by Fenton in 1894 [1]. But its mechanism was not known till 1934. ARTICLE IN PRESS www.elsevier.com/locate/solmat 0927-0248/$-see front matter r 2005 Elsevier B.V. All rights reserved. doi:10.1016/j.solmat.2005.01.002 à Corresponding author. Tel./fax: +914144220572. E-mail address: chemsam@yahoo.com (M. Swaminathan).