Extremely efficient electrochemical degradation of organic pollutants with co-generation of hydroxyl and sulfate radicals on Blue-TiO2 nanotubes anode

Efficient anode materials are essential to electrochemical advanced oxidation processes (EAOPs) for organic wastewater treatment. In this regard, blue TiO2 nanotube arrays (Blue-TNA) anode was prepared for the first time in formic acid electrolyte by electrochemical self-doping and applied for electrochemical degradation of contaminants. Characterized by XPS, Raman and Mott-Schottky curves, the formation of Ti3+ on Blue-TNA was confirmed. This anode was more efficient and had a higher hydroxyl radical production activity (1.7 × 10−14 M) than BDD (9.8 × 10-15 M), inducing a higher TOC and COD removal of 100 mg/L phenol with a lower energy consumption of 9.9 kW h/(kg COD) at current density 2.5 mA/cm2, pH 5 in 0.1 M Na2SO4, account for the lower accumulation of degradation intermediates. Both •OH and SO4•- were responsible for the degradation on Blue-TNA anode, while their contributions differed greatly with that of BDD, and could be affected and regulated by the operating parameters like current density, initial pH and Na2SO4 concentration. Blue-TNA anode represented a relative stable performance for 5 cycles degradation of 100 mg/L phenol for each cycle of 300 min, and such an oxidation capacity could be easily regenerated by electrochemical reduction in formic acid. Blue-TNA anode had an excellent performance on the TOC removal and MCE especially at low current density of 2.5 mA/cm2 when compared with other anodes. Therefore, Blue-TNA anode is hopeful a promising and cost-effective anode for electrochemical oxidation.