Metal Oxide Electrode-Based Treatment of Industrial Dyes with Assessment of Performance and Oxidation Efficiency

This study evaluated the electrochemical and oxidative performance of titanium-supported RuO2–SnO2–Sb2O5 mixed metal oxide electrodes (hereafter denoted as RuO2–SnO2–Sb2O5/Ti) for degrading three aniline-based dyes and their mixture using electro-oxidation (EOx), electro-Fenton (EF), and photoelectron-Fenton (PEF) processes. Electrochemical characterization showed quasi-reversible redox behavior and fast electron-transfer kinetics, while SEM, AFM, and EDS analyses revealed a rough surface with fissures and agglomerates that increased the real electroactive area to 4.85 cm2, supporting the high catalytic activity. Spectroscopic analyses confirmed the functional groups typical of azo dyes, and RNO assays verified sustained hydroxyl-radical production during electrolysis. Current density was the main operational factor: at 50 mA cm−2, decolorization exceeded 90% due to enhanced •OH generation, whereas higher initial dye concentrations decreased reaction rates because of surface saturation and diffusion limitations. Among the oxidation processes, EF was most effective for Brown KK and Brown 5VR, EOx performed best for Brown NT, and PEF showed a slight advantage for the dye mixture owing to UV-assisted regeneration of reactive species. COD removal followed similar trends, with Brown KK mineralizing fastest and Brown 5VR showing the highest recalcitrance. Analysis of H2O2 and active chlorine indicated that EOx favors the accumulation of chlorine-derived oxidants, whereas PEF maximizes H2O2 conversion to •OH and reduces chlorinated by-products, positioning PEF as the most efficient and environmentally favorable option for treating chloride-containing wastewater.