Electrochemical Oxidation of Methyl Orange as a Model Azo Dye Pollutant: Comparative Electrode Performance, EIS Mechanistic Analysis, and Techno-Economic Assessment

Abstract

This study investigates the electrochemical oxidation (EO) of methyl orange (MO) as a model azo dye pollu tant representative of textile and industrial effluents, using boron-doped diamond (BDD) and dimensionally stable anode (DSA) electrodes under systematically optimized conditions. Model solutions were prepared in ultrapure water with 0.1 M Na2SO4 as the supporting electrolyte. Batch experiments were conducted in gal vanostatic mode at 25 ± 1 °C with constant stirring (300 rpm), varying current densities (10–50 mA/cm²), pH values (2–10), and initial methyl orange concentrations (50–500 mg/L). BDD anodes achieved 94.3 ± 2.1 % pollutant removal within 120 min at optimal conditions (30 mA/cm², pH 3.0, 200 mg/L), significantly outper forming DSA (87.6 ± 3.3 %) and platinum (68.7 ± 4.5 %) electrodes. Electrochemical impedance spectrosco py (EIS) using a Randles R(Cdl(RctW)) equivalent circuit revealed a 73 % decrease in charge transfer re sistance (Rct: 385 Ω → 104 Ω) with increasing anodic potential (1.0–2.5 V vs. Ag/AgCl), confirming Butler Volmer-controlled oxidation kinetics. The apparent rate constant kapp = 0.0315 ± 0.0018 min–1 for BDD was 1.68-fold greater than for platinum. Total organic carbon (TOC) analysis confirmed near-complete minerali zation (96.8 ± 1.5 % TOC reduction) with BDD. Specific energy consumption was minimized to 8.2 kWh/m3, indicating the potential competitiveness of this approach for treating dye-containing effluents. At Nigerian electricity tariffs (₦45/kWh), estimated treatment cost is ₦369/m³, suggesting feasibility for industrial appli cation in developing economies, pending validation with real effluent matrices.