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

Three types of Magnéli phase anodes (Ti/Ti 4 O 7 , Ti/Ti 4 O 7 -PbO 2 -Ce, and Ti/Ti 4 O 7 nanotube arrays (NTA)) were fabricated, characterized, and compared with other typical active and non-active anodes (i.e., BDD, Ti/Pt, Ti/RuO 2 -IrO 2 , and Ti/IrO 2 -Ta 2 O 5 ) 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/Ti 4 O 7 NTA, and a compact coating of Ti 4 O 7 microparticles and PbO 2 -Ce nanocrystals on the Ti substrate for Ti/Ti 4 O 7 and Ti/Ti 4 O 7 -PbO 2 -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/Ti 4 O 7 NTA and Ti/Ti 4 O 7 removed 89–92% of PNP, which were 10–60% higher than Ti/Pt, Ti/RuO 2 -IrO 2 , and Ti/IrO 2 -Ta 2 O 5 , and were almost comparable with BDD (95%). Furthermore, Ti/Ti 4 O 7 NTA and Ti/Ti 4 O 7 kept very efficient for mineralization of PNP solution and real coal chemical concentrated brine. For Ti/Ti 4 O 7 -PbO 2 -Ce, its degradation efficiency was lower than other two Magnéli phase anodes, but still competitive compared with other active anodes. Thanks to their high removal efficiencies, the three Magnéli 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 Magnéli phase electrodes as promising and cost-effective anode materials for industrial wastewater treatment, with Ti/Ti 4 O 7 NTA and Ti/Ti 4 O 7 being more efficient options.