An effective electroanalytical approach for the monitoring of electroactive dyes and intermediate products formed in electro-Fenton treatment

Reactive Black 5 (RB5) is an electroactive diazo dye compound derivate of H-acid (coupling reaction), which cannot be effectively degraded by conventional or biological processes. In this work, the feasibility of electroFenton (EF) process to treat a simulated effluent polluted by RB5 dye and the effectiveness of electroanalysis by Linear Sweep Voltammetry (LSV) to monitor RB5, intermediates and by-products during the EF treatment have been demonstrated. Several variables on the electrochemical behaviour of RB5 have been determined under EF experimental conditions. The key factors are scan rate and dye concentration (in the presence and the absence of iron) and their effect on shape, position and height of RB5 peaks have been determined to obtain the best sensitivity and selectivity in the voltammetric analysis. Moreover, the iron appears as a strong electrocatalyst that promotes the electron transfer for the oxidation reaction of RB5 on screen-printed carbon electrode, in part, due to a very stable coordinate complex formed with RB5. Besides that, the degradation profiles have revealed the main stages along the EF process and the voltammetric kinetic data has given selective information about the RB5 degradation and the evolution of the electroactive products generated. The formation of aromatic/cyclic organic intermediates, and evolution of carboxylic acids, as well as the inorganic ions released during the treatment were validated by other techniques and a plausible pathway is proposed based on the obtained results.