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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The electrochemical behavior of lead dioxide and synthetic boron-doped diamond thin film electrodes ͑BDDs͒ has been studied in acid media containing 4-chlorophenol ͑4-CP͒ by bulk electrolysis under different experimental conditions. In order to quantify the electrochemical activity of a given electrode, for the electrochemical oxidation of organic compounds ͑4-CP͒, the current efficiency of the anodic oxidation has been normalized taking into consideration mass-transport limitations. The normalized current efficiency ͑͒ has been defined as the ratio between the current efficiency of the investigated anode to the current efficiency of an ideal anode which has a very fast oxidation rate, resulting in a complete combustion of organics to carbon dioxide. The results have shown that even if the complete combustion of 4-chlorophenol has been achieved at both lead dioxide and boron-doped diamond anodes, the latter give higher . The difference in reactivity of the electrogenerated hydroxyl radicals on the anode surface, has been proposed to explain the high values obtained using boron-doped diamond anodes.