Electrochemical oxidation of Acid Orange 7 azo dye using a PbO₂ electrode: Parameter optimization, reaction mechanism...

In this study, electrochemical oxidation of Acid Orange 7 (AO 7) azo dye has been investigated using a Fe-doped PbO₂ electrode. The degradation of AO 7 followed pseudo-first-order reaction kinetics. The removals of AO 7, chemical oxygen demand (COD) and total organic carbon (TOC) were 87.15%, 49.88% and 44.94% after 60 min of electrolysis at the optimal conditions (Na₂SO₄ concentration 0.1 M, initial pH 5, initial AO 7 concentration 100 mg L^-1 and applied current density 20 mA cm^-2), respectively. And the corresponding degradation rate constant was 0.035 min^-1. The intermediates formed during electrochemical process were identified, and a possible degradation pathway was proposed, which was initiated by the oxidation of azo bond (-NN-), hydroxylation and substitution reaction of -NH₂ and -SO₃H under the attack of OH, and ended with the formation of mineralization products such as NH₄⁺, NO₃^-, SO₄^2-, CO₂ and H₂O. The toxicity of treated AO 7 solution towards Vibrio fischeri increased slightly at first and then rapidly reduced to non-toxicity with prolonging time. The results indicate that electrochemical oxidation of AO 7 using Fe-doped PbO₂ electrode is a promising way.