The catalytic behavior of the Fe3+/Fe2+ System in the electro-Fenton degradation of the antimicrobial drug chlorophene has been studied considering four undivided electrolytic cells, where a Pt or boron-doped diamond (BDD) anode and a carbon felt or O-2-diffusion cathode have been used. Chlorophene electrolyses have been carried out at pH 3.0 under current control, with 0.05 M Na2SO4 as supporting electrolyte and Fe3+ as catalyst. In these processes the drug is oxidized with hydroxyl radical ((OH)-O-center dot) formed both at the anode from water oxidation and in the medium from electrochemically generated Fenton's reagent (Fe2+ + H2O2, both of them generated at the cathode). The catalytic behavior of the Fe3+/Fe2+ system mainly depends on the cathode tested. In the cells with an O-2-diffusion cathode, H2O2 is largely accumulated and the Fe3+ content remains practically unchanged. Under these conditions, the chlorophene decay is enhanced by increasing the initial Fe3+ concentration, because this leads to a higher quantity of Fe2+ regenerated at the cathode and, subsequently, to a greater (OH)-O-center dot production from Fenton's reaction. In contrast, when the carbon felt cathode is used, H2O2 is electrogenerated in small extent, whereas Fe2+ is largely accumulated because the regeneration of this ion from Fe3+ reduction at the cathode is much faster than its oxidation to Fe3+ at the anode. In this case, an Fe3+ concentration as low as 0.2 mM is required to obtain the maximum (OH)-O-center dot generation rate, yielding the quickest chlorophene removal. Chlorophene is poorly mineralized in the Pt/O-2 diffusion cell because the final Fe3+-oxalate complexes are difficult to oxidize with (OH)-O-center dot. These complexes are completely destroyed using a BDD anode at high current thanks to the great amount of (OH)-O-center dot generated on its surface. Total mineralization is also achieved in the Pt/carbon felt and BDD/carbon felt cells with 0.2 mM Fe3+, because oxalic acid and its Fe2+ complexes are directly oxidized with (OH)-O-center dot in the medium. Comparing the four cells, the highest oxidizing power regarding total mineralization is attained for the BDD/carbon felt cell at high current due to the simultaneous destruction of oxalic acid at the BDD surface and in the bulk solution. (c) 2006 Elsevier B.V. All rights reserved.