ABSTRACT Interface engineering is an effective strategy for improving the catalytic activity of electrocatalysts. Herein, an enhanced binder-free Ti 4 O 7 electrode doped with waste MOF-recycled N-doped carbon polyhedrons (Dr-CN) was developed and denoted as Dr-CN@Ti 4 O 7 . The chemical-bond formation at the interface of Ti 4 O 7 and Dr-CN led to a significant acceleration of charge transfer and higher •OH yield at 1.55-2.75 times rate in comparison with pristine Ti 4 O 7 . At 0.5%Dr-CN@Ti 4 O 7 electrode, the oxidation rate of tetracycline (TCH) was about 3 times that of pristine Ti 4 O 7 , especially when doped with 2 wt% Dr-CN, the kinetic rate can be comparable to that of BDD electrode. Furthermore, the 0.5%Dr-CN@Ti 4 O 7 anode exhibited desirable stability and durability in consecutive 20 cycle tests and was shown to effectively mineralize refractory organic matters in actual livestock and coking wastewater. Energy consumption for TCH removal by 0.5%Dr-CN@Ti 4 O 7 electrode was calculated as 3.02 kWh m -3 , with a 73.5-77.6% reduction compared to some previous electrodes. These results suggested that the interface chemical-bonded engineering strategy via doping MOF-derived carbon can effectively improve the Magnéli-phase Ti 4 O 7 electrode with satisfying electrochemical reactivity and stability.
Electro-oxidation is a promising technology for removal of refractory organic pollutants. While the appeal of this technology lies in its chemical-free nature, commercially scale-up application may be limited by the availability of electrode materials and mass transport. Here we report the development of a flow-through electro-oxidation system for removal of chlorophenols in water using Magnéli-phase (Ti 4 O 7 ) tubular anode and a 304 stainless steel (SS) tubular cathode. The key to this system was the porous and conductive Magnéli-phase Ti 4 O 7 anode, the structure and composition of which was confirmed by scanning electron microscopy, X-ray diffraction and X-ray photoelectron spectroscopy. System efficacy was evaluated by using 4-chlorophenol (4-CP) as a typical refractory contaminant and model chlorophenol. Under optimized conditions, a complete removal of 4-CP could be obtained within 120 min in 0.04 mol L −1 Na 2 SO 4 solution. Electro-produced HO • and direct electron transfer were both shown to contribute to the 4-CP electro-oxidation process due to the high selectivity and oxygen evolution potential of the Ti 4 O 7 anode. The intermediates of 4-CP degradation were identified and a pathway for its electro-oxidation was proposed. When challenged with industrial wastewater containing 4-CP, chemical oxygen demand (COD) and total organic carbon removal efficiencies of 67.5% and 63.1% respectively could be obtained, accounting for energy consumption of 85.1 kWh·kg COD −1 for degradation of 1 kg of COD in industrial wastewater. This study provides an effective and robust solution for the removal of refractory emerging contaminants from industrial wastewaters using a continuous-flow electro-oxidation system.
Huijiao Wang,Zhongyi Li,Fengyuan Zhang,Yuxiang Wang,Xian Zhang,Jianbing Wang,Xuwen He
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.
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