Electrochemical incineration of glucose as a model organic substrate I. Role of the electrode material

In the frame of study on the electrochemical incineration of organic pollut ants, the reactivity of glucose toward mineralization was studied under dif ferent electrolysis conditions. The process was followed at Pt, SnO2-Pt com posite, and PbO2 electrodes, at different current densities and temperature s. In all cases, the supporting electrolyte was 2 N H2SO4. Chemical oxygen demand and total organic carbon content of the solutions and amount of oxyg en evolved were measured as functions of the electrolysis time. From these data, an initial electrochemical oxidation index (EOI) was evaluated follow ing standard methods. Larger values for this parameter were found at the Pb O2 electrodes under all conditions of current density and temperature. At P t and SnO2-Pt, in the room-temperature range, the efficiency of the electro chemical mineralization of glucose was low, particularly at longer electrol ysis times. The situation improved by increasing the temperature to 56 degr ees C. The extent of mineralization was quite low at SnO2-Pt electrodes und er all conditions explored. At Pt and SnO2-Pt electrodes, the main oxidatio n intermediate was glucaric acid, apparently quite stable toward further at tack at these electrodes. In the case of PbO2 electrodes, smaller concentra tions of intermediates were detected. Gluconic and 2-ketogluconic acids wer e also present in amounts comparable with that of glucaric acid. Study of t he initial electrochemical oxidation index for gluconic acid and glucaric a cid was also carried out, confirming the stability of the latter at Pt and SnO2-Pt electrodes. At PbO2, on the contrary, it was found to be even more reactive than glucose. An explanation for the reactivity of carboxylic acid s toward mineralization at the PbO2 electrodes is proposed. (C) 1999 The El ectrochemical Society. All rights reserved.