Electrochemical oxidation of methyl orange by a Magnéli phase Ti₄O₇ anode

In this study, high quality Magnéli phase Ti₄O₇ bulks with electrical conductivity up to 961.5 S cm^-1 were successfully prepared by spark plasma sintering (SPS) and then served as electrode materials for electrochemical oxidation of azo dye methyl orange (MO). The influences of current density and initial dye concentration on the removal rates of MO and chemical oxygen demand (COD) were studied. Removal of MO and COD exhibited an increase with increasing current density and decreasing initial concentration of MO. Complete removal of MO was realized within a short time under all experimental conditions. The removal rate of COD reached 91.7% when current density was 10 mA cm^-2 and initial dye concentration was 100 mg L^-1. In addition, the electrochemical oxidation rate could be described through a pseudo-first-order kinetic constant k, and the obtained experimental results could be well fitted with a proposed kinetic model in all the examined conditions. Possible degradation mechanisms for electrochemical oxidation of MO by Ti₄O₇ electrode were proposed on the basis of intermediate products analysis. Tests were also conducted with other commercial electrodes for comparison, including commercial graphite, stainless-steel and dimension stable anode (DSA) electrodes. The results showed that Ti₄O₇ anode exhibited the fastest electrochemical oxidation rates than those of the other electrodes. This study provides a feasible method for realizing high efficiency of electrochemical oxidation degradation by Ti₄O₇ electrode.