ISSN print edition: 0366-6352 ISSN electronic edition: 1336-9075 Registr. No.: MK SR 9/7 Published monthly

Photo-Fenton and photo-Fenton-like processes for the degradation of methyl orange in aqueous medium: Influence of oxidation states of iron

L. Gomathi Devi, S. Girish Kumar, K. S. Anantha Raju, and K. Eraiah Rajashekhar

Department of Post Graduate Studies in Chemistry, Central College Campus, Dr. B.R. Ambedkar Veedi, Bangalore University, Bangalore, 560 001, India

E-mail: gomatidevi_naik@yahoo.co.in

Received: 22 May 2009  Revised: 5 August 2009  Accepted: 12 August 2009

Abstract: Degradation of methyl orange (MO) was carried out by the photo-Fenton process (Fe²⁺/H₂O₂/UV) and photo-Fenton-like processes (Fe³⁺/H₂O₂/UV, Fe²⁺/S₂O₈²⁻/UV, and Fe³⁺/S₂O₈²⁻/UV) at the acidic pH of 3 using hydrogen peroxide and ammonium persulfate (APS) as oxidants. Oxidation state of iron had a significant influence on the efficiency of photo-Fenton/photo-Fenton-like processes. It was found that a process with a source of Fe³⁺ ions as the catalyst showed higher efficiency compared to a process with the Fe²⁺ ion as the catalyst. H₂O₂ served as a better oxidant for both oxidation states of iron compared to APS. The lower efficiency of APS is attributed to the generation of excess protons which scavenges the hydroxyl radicals necessary for degradation. Further, the sulfate ions produced from S₂O₈²⁻ form a complex with Fe²⁺/Fe³⁺ ions thereby reducing the concentration of free iron ions in the solution. This process can also reduce the concentration of hydroxyl radicals in the solution. Efficiency of the various MO degradation processes follows the order: Fe³⁺/H₂O₂/UV, Fe³⁺/APS/UV, Fe²⁺/H₂O₂/UV, Fe²⁺/APS/UV.

Keywords: photo-Fenton process - photo-Fenton-like process - ammonium persulfate - methyl orange - degradation pathway

Full paper is available at www.springerlink.com.

DOI: 10.2478/s11696-010-0011-0

Chemical Papers 64 (3) 378–385 (2010)