Ch. Comninellis

Electrogeneration of Hydroxyl Radicals on Boron-Doped Diamond Electrodes

The electrogeneration of hydroxyl radicals was studied at a synthetic B-doped diamond (BDD) 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 ESR and liq. chromatog. measurements, resp. The prodn. of H2O2 and competitive oxidn. of formic and oxalic acids were also studied using bulk electrolysis. Oxidn. of salicylic acid gives hydroxylated products (2,3- and 2,5-dihydroxybenzoic acids). The oxidn. process on BDD electrodes involves hydroxyl radicals as electrogenerated intermediates. [on SciFinder (R)]

Anodic oxidation of phenol for waste water treatment

The electrochemical oxidation of phenol for waste water treatment was studied at a platinum anode. Analysis of reaction intermediates and a carbon balance has shown that the reaction occurs by two parallel pathways; chemical oxidation with electrogenerated hydroxyl radicals and direct combustion of adsorbed phenol or/and its aromatic intermediates to CO2.

Electrochemical oxidation of phenol at boron-doped diamond electrode

The electrochemical behaviour of a synthetic boron-doped diamond thin film electrode (BDD) has been studied in acid media containing phenol using cyclic voltammetry and bulk electrolysis. The results have shown that in the potential region of water stability direct electron transfers can occur on BDD surface resulting in electrode fouling due to the formation of a polymeric film on its surface. During electrolysis in the potential region of oxygen evolution, complex oxidation reactions can take place due to electrogenerated hydroxyl radicals. Electrode fouling is inhibited under these conditions. Depending on the experimental conditions, the electrogenerated hydroxyl radicals can lead to the combustion of phenol or to the selective oxidation of phenol to benzoquinone. The experimental results have also been compared to a theoretical model that permits the prediction of the evolution with time of phenol concentration, during its combustion, or during its selective oxidation to benzoquinone.

Anodic oxidation of phenol in the presence of NaCl for wastewater treatment

The electrochemical oxidation of phenol in the presence of NaCl for wastewater treatment was studied at Ti/SnO2 and Ti/IrO2 anodes. The experimental results have shown that the presence of NaCl catalyses the anodic oxidation of phenol only at Ti/IrO2 anodes due to the participation of electro-generated ClO− in the oxidation. Analysis of the oxidation products has shown that initially organo-chlorinated compounds are formed in the electrolyte which are further oxidized to volatile organics (CHCl3).

Electrochemical oxidation of phenol for wastewater treatment using SnO2 anodes

The electrochemical oxidation of phenol for waste water treatment was studied on doped SnO2 anodes. Analysis of reaction intermediates and a carbon balance has shown that the main reaction is oxidation of phenol to CO2. This unexpected behaviour of the SnO2 anode is explained by a change of the chemical structure of the electrode surface during anodic polarization.

Anodic oxidation of 2-naphthol at boron-doped diamond electrodes

Abstract The anodic oxidation of 2-naphthol in acid media was investigated at a synthetic boron-doped diamond thin film electrode (BDD) using cyclic voltammetry and bulk electrolysis. The results have shown that in the potential region, where the supporting electrolyte is stable, reactions involving simple electron transfer, such as oxidation of 2-naphthol to naphthoxy radical and 1,4-naphthoquinone occur. Polymeric materials, which lead to electrode fouling, are also formed in this potential region. Electrolysis at high positive potentials in the region of electrolyte decomposition causes complex oxidation reactions by electrogenerated hydroxyl radicals leading to the complete incineration of 2-naphthol. 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 2-naphthol is a fast reaction and it is under diffusion control.

Oxidation of 4-Chlorophenol at Boron-Doped Diamond Electrode for Wastewater Treatment

The electrochem. behavior of synthetic B-doped diamond thin-film electrode (BDD) was studied in acid media contg. 4-chlorophenol (4-CP) by cyclic voltammetry, chronoamperometry, and bulk electrolysis. The results showed that in the potential region of supporting electrolyte stability occur reactions involving the oxidn. 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 decompn., complex oxidn. reactions can take place involving electro-generated hydroxyl radicals, leading to the complete incineration of 4-chlorophenol. Electrode fouling is inhibited under these conditions. The exptl. results were compared with a theor. model. This model is based on the assumption that the rate of the anodic oxidn. of 4-CP is a fast reaction. HPLC analyses revealed that the main intermediate products of 4-CP oxidn. were 1,4-benzoquinone, maleic acid, formic acid, and oxalic acid. [on SciFinder (R)]

CHARACTERIZATION OF DSA-TYPE OXYGEN EVOLVING ELECTRODES : CHOICE OF A COATING

In the search for a DSA®-type electrode for oxygen evolution in acidic solutions, nine binary coatings with IrO2, RuO2, Pt as conducting component, and TiO2, ZrO2, Ta2O5 as inert oxides, have been deposited on titanium, examined for their microstructural properties and tested for their electrocatalytic activity and anodic stability. Electrochemical “true” surfaces of the coatings were found to be dependent on structure and morphology: the mixtures that form a solid solution (RuO2−TiO2), or allow limited miscibility (IrO2−TiO2), show the lowest dispersion of active material. Differences in service lives, were attributed to differences in wear mechanism of the electrodes. It was found that Ti/IrO2 (70 mol%)-Ta2O5 (30 mol%) is by far the best electrode.

Theoretical model for the anodic oxidation of organics on metal oxide electrodes

A theoretical model describing the electrochemical oxidation of organics at oxide electrodes (MOx) forming the higher oxide (MOx+1) is described. In this model both organics oxidation and O2 evolution are mediated by the higher oxide (MOx+1) which is electrogenerated at the anode surface. The effect of concentration polarization in the electrolyte is also included in the theoretical model.

Electrochemical oxidation of water on synthetic boron-doped diamond thin film anodes

Electrolysis in aqueous 1 M HClO4 and 1 M H2SO4 solutions has been carried out under galvanostatic conditions using boron-doped diamond electrodes (BDD). Analyses of the oxidation products have shown that in 1 M HClO4 the main reaction is oxygen evolution, while in H2SO4 the main reaction is the formation of H2S2O8. In both electrolytes small amounts of O3 and H2O2 are formed. Finally, a simplified mechanism involving hydroxyl radicals formed by water discharge has been proposed for water oxidation on boron-doped diamond anodes.