Understanding the electrochemical oxidation of dyes on platinum and boron-doped diamond electrode surfaces: experimental and computational study

Anodic oxidation (AO) approach proceeds via direct and indirect electrochemical pathways and their subsequent reactions. The interest to elucidate the mechanisms for removing dyes from water contributes to the understanding of more complex reactions involving organic pollutants towards anode surfaces. The present study was motivated by the reports that promote the use of AO for removing different organic compounds but no considerations about the influence of different functional groups in their structure have been discussed. Therefore, we have evaluated the influence of different functional groups in the dye structure (Reactive Orange 16, Reactive Violet 4, Reactive Red 228, and Reactive Black 5) by potentiodynamic measurements and by computational analyzes using density functional theory (DFT). The computational studies have allowed to carry out morphological studies on the frontier orbitals where the electrons are more energetic and then, the electron-transfer to electrode surface is achieved, which was associated to the electrochemical measurements (current-potential profiles). Also, the theoretical studies were used to understand the bulk electrolysis, in terms of mineralization. The results clearly demonstrate that organic molecules can be degraded in different way and level due to the oxidants electrochemically generated as well as the interaction of dyes with anode surface by adsorbed/non-adsorbed intermediates. Conversely, the decolorization mechanisms, which are related to the fragmentation of chromophore group, are associated to the direct AO approach, favoring different order of elimination, as already reported in our previous work. The results were discussed in light of the existing literature.