Monolithic Porous Magnéli-phase Ti4O7 for Electro-oxidation Treatment of Industrial Wastewater

Abstract

Electrochemical oxidation (EO) processes have been gaining a growing popularity in wastewater treatment. Their engineered applications inspire the search for conductive, stable, inexpensive, and sustainable electrode materials. Magnéli-phase titanium oxides have unique crystal and electron structure, which result in good electrical conductivity approaching that of metal and excellent corrosion resistance close to that of ceramics. We fabricated a monolithic porous Magnéli-phase Ti4O7 electrode for EO of refractory industrial dyeing and finishing wastewater (DFWW). The results demonstrated that the electrochemically active area of porous Ti4O7 electrode was 2–3 orders of magnitude higher than the apparent surface area of bulk electrode. The Ti4O7 electrode achieved efficient and stable abatement of recalcitrant organic pollutants on site without any extra addition of chemicals. The soluble chemical oxygen demand (COD) and dissolved organic carbon (DOC) were removed by 66.5% and 46.7%, respectively, at current density of 8 mA cm−2 after 2 h reaction. The bioavailability of treated wastewater was improved substantially, indicated by one order of magnitude increase in BOD5/COD. The Ti4O7 electrode had good long-term stability, with its maximum COD removal declined only slightly (<8%) at current density of 20 mA cm−2 during a 50-cycle operation. The organic pollutants appear most likely to be oxidized by electrochemically generated active species like physisorbed OH radical and aqueous ClO− species under mass transfer control condition. The current study provides important insights for achieving efficient and sustainable electrochemical wastewater treatment using the novel porous Ti4O7 electrode material.