High-pressure electrochemical advanced oxidation: boosting azo dye removal through in-situ generation of reactive species

The contamination of aquatic ecosystems by synthetic azo dyes from industrial effluents poses a critical environmental challenge, necessitating the development of efficient and sustainable treatment technologies. While electrochemical advanced oxidation processes (EAOPs) are recognised as promising tools for degrading recalcitrant organic pollutants, their efficiency is often limited by mass transfer and the low solubility of reactive gases under ambient conditions. This study introduces a novel approach for the intensification of azo dye degradation by employing a high-pressure electrochemical advanced oxidation process. The indirect electrochemical oxidation of the model pollutant, Mordant Yellow 3 (MY) azo dye, was investigated in a NaCl electrolyte under elevated oxygen pressure up to 0.6 MPa. The results demonstrate that increased oxygen pressure significantly enhances the in-situ generation of reactive species. Voltammetric study revealed that pressure boosts both the anodic formation of active chlorine (hypochlorite) and the cathodic reduction of oxygen to hydrogen peroxide. Kinetic studies showed a 1.5-fold increase in the initial oxidation rate at the anode and a 3.0-fold increase in cathodic activity under pressure. Quantum-chemical calculations elucidated the energetic pathway of chlorine hydrolysis, confirming the feasibility of the proposed mechanism.