Comparative study of MMO and BDD anodes for electrochemical degradation of diuron in methanol medium

Abstract

Treating emerging pollutants at low concentrations presents significant challenges in terms of degradation efficiency. Anodic oxidation using active and non-active electrodes shows great potential for wastewater treatment. Thus, this study compared the efficiency of a commercial mixed metal oxide anode (MMO: Ti/Ti_0.7Ru_0.3O₂) and a boron-doped diamond anode (BDD) for the electrochemical oxidation of diuron in methanol, in chloride and sulfate media. The MMO anode achieved diuron removal rates of 94.9% and 92.8% in chloride and sulfate media, respectively, with pseudo-first-order kinetic constants of 0.0177 and 0.0143 min^-1. The BDD anode demonstrated slightly higher removal rates, achieving 96.2% in sulfate medium and 96.9% in chloride medium, with respective kinetic constants of 0.0193 min⁻¹ and 0.0177 min⁻¹. Increasing the current density enhanced diuron removal by up to 15% for both electrodes; however, excessively high current densities led to increased energy consumption due to side reactions. The present of water had antagonistic effects, resulting in removal rates of 91.1% for chloride media using the BDD anode; and 87.4% and 90.4% in sulfate media with MMO and BDD anodes, respectively. The MMO anode in chloride medium did not show significant difference in the degradation percentage, reaching 96% of diuron removals. The degradation mechanism was proposed based on the detection of various by-products. The primary reactions observed during the oxidation of diuron in methanol involved chlorine substitution in the aromatic ring and dealkylation. These processes generated several intermediates and by-products at low concentrations, ultimately leading to high diuron removal.