The electrogeneration of hydroxyl radicals was studied at a synthetic boron-doped diamond ͑BDD͒ thin film electrode. Spin trapping was used for detection of hydroxyl radicals with 5,5-dimethyl-1-pyrroline-N-oxide and with salicylic acid using electron spin resonance and liquid chromatography measurements, respectively. The production of hydrogen peroxide and competitive oxidation of formic and oxalic acids were also investigated using bulk electrolysis. The results have shown that oxidation of salicylic acid leads to the production of hydroxylated products ͑2,3and 2,5-dihydroxybenzoic acids͒. These results demonstrate that the oxidation process on BDD electrodes involves hydroxyl radicals as electrogenerated intermediates.

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ABSTRACT. In the present work, herbicide 2,4,5-trichlorophenoxyacetic acid, more commonly known as 2,4,5-T herbicide, has been completely mineralized (i.e. transformed into CO 2 and H 2 O) in saturated aqueous solutions using a semi-industrial electrochemical cell that contains a boron doped diamond anode and a zirconium cathode. We have performed cyclic voltammetry, chronoamperometry and bulk electrolysis to give the optimization characteristics of the degradation of such a compound and its by-products. Bulk electrolysis in the potential region of electrolyte decomposition leads to the complete destruction of 2,4,5-T and its degradation intermediates by means of the electrogeneration of the highly reactive hydroxyl radicals. The evolution of the chemical oxygen demand (COD) and the instant current efficiency (ICE) during the degradation process is perfectly predicted by a theoretical mathematical model. HPLC and GC-MS have also been performed to highlight the evolution of the mother product and its degradation intermediates. Kinetic analysis of the obtained results has shown a fast destruction of the mother herbicide asserting a diffusion-controlled process. 2,4,5-trichlorophenol and quinonebased organic compounds have been depicted as aromatic intermediates, all of them transformed into short chains carboxylic acids before complete mineralization happens.

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