Comparison of Ti/Ti4O7, Ti/Ti4O7-PbO2-Ce, and Ti/Ti4O7 nanotube array anodes for electro-oxidation of p-nitrophenol and real wastewater

Abstract Three types of Magneli phase anodes (Ti/Ti4O7, Ti/Ti4O7-PbO2-Ce, and Ti/Ti4O7 nanotube arrays (NTA)) were fabricated, characterized, and compared with other typical active and non-active anodes (i.e., BDD, Ti/Pt, Ti/RuO2-IrO2, and Ti/IrO2-Ta2O5) for electro-oxidation treatment of p-nitrophenol (PNP) solution and a real coal chemical concentrated brine in this study. Characterization results indicate a nanotube array structure of Ti/Ti4O7 NTA, and a compact coating of Ti4O7 microparticles and PbO2-Ce nanocrystals on the Ti substrate for Ti/Ti4O7 and Ti/Ti4O7-PbO2-Ce, respectively. The three anodes present relatively high oxygen evolution potentials (2.16–2.44 V vs SCE), showing good capacity of electro-generating reactive oxidative species for pollutant degradation. After 30 min of EO treatment, Ti/Ti4O7 NTA and Ti/Ti4O7 removed 89–92% of PNP, which were 10–60% higher than Ti/Pt, Ti/RuO2-IrO2, and Ti/IrO2-Ta2O5, and were almost comparable with BDD (95%). Furthermore, Ti/Ti4O7 NTA and Ti/Ti4O7 kept very efficient for mineralization of PNP solution and real coal chemical concentrated brine. For Ti/Ti4O7-PbO2-Ce, its degradation efficiency was lower than other two Magneli phase anodes, but still competitive compared with other active anodes. Thanks to their high removal efficiencies, the three Magneli phase anodes required relatively low energy demand for pollutant mineralization. Besides, operational parameters such as electrolyte and current density were also very significant for efficient pollutant removal. The results of this study suggest Magneli phase electrodes as promising and cost-effective anode materials for industrial wastewater treatment, with Ti/Ti4O7 NTA and Ti/Ti4O7 being more efficient options.