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The electrochemical treatment of 100 mg L À1 nitrobenzene solutions in 0.05 M Na 2 SO 4 in the pH range 2.0-4.0 at 25 C has been comparatively studied in the presence of Fe 2þ , Cu 2þ and/or UVA light as catalysts using an undivided cell with a Pt anode and an O 2 -diffusion cathode able to electrogenerate H 2 O 2 . A quite slow degradation is found for the solution with 1 mM Cu 2þ due to the low production of oxidizing hydroxyl radical (OH ) from anodic oxidation of water and the action of the Cu 2þ /Cu þ system. Electro-Fenton treatment with 1 mM Fe 2þ leads to a high concentration of OH in the medium from Fenton's reaction, but less than 70% of the nitrobenzene is mineralized since stable complexes of Fe 3þ with products are formed. These complexes are quickly photodecomposed in the photoelectro-Fenton treatment of the same solution under UVA irradiation, leading to overall depollution at low currents. Complete degradation is also feasible using 1 mM Cu 2þ and 1 mM Fe 2þ at high current because OH can slowly destroy the complexes between Cu 2þ and intermediates. The positive synergetic effect of all catalysts allows the quickest nitrobenzene mineralization using 1 mM Cu 2þ and 1 mM Fe 2þ under UVA irradiation. The nitrobenzene decay always follows a pseudo-first-order reaction. Aromatic products such as o-nitrophenol, m-nitrophenol, p-nitrophenol and 4-nitrocatechol have been followed by reverse-phase chromatography. Nitrate ions are formed from oxidation of nitroaromatic products. Generated carboxylic acids such as maleic, fumaric and oxalic have been detected by ion-exclusion chromatography. The different evolution of complexes of oxalic with Cu 2þ and Fe 3þ explains the influence of the catalysts on nitrobenzene degradation.

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