Electrochemical Degradation of the Reactive Red 141 Dye Using a Boron-Doped Diamond Anode
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The electrochemical degradation of the Reactive Red 141 azo dye was done using a one-compartment filter-press flow cell with a boron-doped diamond anode. The response surface methodology (with a central composite design) was used to investigate the effect of current density (10–50 mA cm−2), pH (3–11), NaCl concentration ([NaCl]) (0–2.34 g L–1), and temperature (15–55 °C) on the system’s performance. The charge required for 90 % decolorization (Q90), the fraction of chemical oxygen demand removal after 6 min of electrolysis (COD6), and the fraction of total organic carbon removal after 90 min of electrolysis (TOC90) were used to model the obtained results. The lowest values of Q90 were attained at pH <4 in the presence of higher values of [NaCl] (>1.5 g L−1), due to the electrogeneration of active chlorine, present mainly as HClO. The value of COD6 was not affected by the solution pH, but increased with [NaCl] up to 1.5 g L−1. Higher temperatures (>40 °C) led to a decrease in COD6, as a consequence of side reactions. Higher values of TOC90, which can be reached only with strong oxidants (such as ·OH and Cl·), were efficiently attained at low [NaCl] values (<0.7 g L−1) in acidic solutions that inhibit the formation of ClO3− and ClO4−. Finally, the obtained results allow inferring that most probably the mineralization of the dye starts with an attack on the chromophore group, followed by the degradation of intermediate species.