Kinetic modelling of electrochemical decolorization of diazo dyes on boron-doped diamond electrodes

The anodic oxidation of diazo dyes on boron-doped diamond (BDD) electrodes in the presence of chloride was investigated. Reactive Green 19 (RG19), a relatively new diazo dye of high structural complexity, was used as a model dye. To evaluate the effect of the operating parameters on decolorization, electrolyses under galvanostatic conditions were performed in a membrane-free reactor. The results obtained suggest the simultaneous occurrence of a reaction mediated by hydroxyl radicals and a reaction mediated by active chlorine. The first reaction was found to be favored by increasing current density and temperature, while the second was promoted by acidic pH and by increasing chloride concentration and stirring rate. Several kinetic models were tested for their ability to correlate the experimental data. The best results were obtained by a power-law model including all the parameters of interest and using the time required to achieve 50% or 99% color removal as response variables. From the estimated model coefficients, the contribution of each operating parameter to RG19 decolorization at shorter and longer times was determined.