Electrochemical Degradation of Methyl Red Using BDD and PbO2 Anodes

The electrocatalytic properties of lead dioxide (PbO2) and boron-doped diamond (BDD) anodes were compared for the electrochemical incineration of methyl red, an azo dye, using an electrolytic flow cell with parallel- plate electrodes. The effects of several operating parameters such as current density, hydrodynamic conditions, and pH on the degradation rate and current efficiency were determined. The experimental data indicate that, on PbO2 and BDD anodes, methyl red oxidation takes place by reaction with hydroxyl radicals electrogenerated from water discharge. The electro-oxidation of methyl red was found to behave as a mass-transfer-controlled process, so that the removal rate and current efficiency were enhanced by high flow rates and independent of the pH in the range of 3.0-7.0. It was also observed that the methyl red decay reaction followed pseudo- first-order kinetics with a rate constant that increased slightly with applied current at the PbO2 anode but was essentially independent of current at the BDD anode. From a comparison of the results, it was found that the BDD anode provided a higher oxidation rate and higher current efficiency; however, the two anodes required almost the same energy consumption for the mineralization of methyl red.