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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The electrochemical behavior of synthetic boron-doped diamond thin-film electrode ͑BDD͒ has been studied in acid media containing 4-chlorophenol ͑4-CP͒ by cyclic voltammetry, chronoamperometry, and bulk electrolysis. The results have shown that in the potential region of supporting electrolyte stability occur reactions involving the oxidation of 4-CP to phenoxy radical and 1,4-benzoquinone. Polymeric materials, which result in electrode fouling, are also formed in this potential region. Electrolysis at high anodic potentials, in the region of electrolyte decomposition, complex oxidation reactions can take place involving electrogenerated hydroxyl radicals, leading to the complete incineration of 4-chlorophenol. Electrode fouling is inhibited under these conditions. The experimental results have been also compared with a theoretical model. This model is based on the assumption that the rate of the anodic oxidation of 4-CP is a fast reaction. Finally, high-pressure liquid chromatographic analyses revealed that the main intermediate products of 4-CP oxidation were 1,4-benzoquinone, maleic acid, formic acid, and oxalic acid.

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