Blue Hierarchical TiO2 Nanotube Array for Significantly Enhanced Electrochemical Oxidation Performance and Stability of Tetracycline Degradation

Blue TiO2 exhibited excellent electrocatalytic activity for degrading various organic pollutants in wastewater. However, its crystal structure and morphology considerably affected the electrocatalytic activity of blue TiO2. In this study, a blue hierarchical TiO2 nanotube array (B-HTNA) was synthesized utilizing Ti foam by ice–water bath anodic oxidation and cathodic reduction. Benefiting from a higher concentration of doped Ti3+, the prepared B-HTNA exhibited greater electron transport capability. B-HTNA effectively degraded tetracycline with a high removal rate of more than 90% within 60 min under 20 mA cm–2. The results of free radical quenching experiments revealed the effects induced under different experimental conditions, wherein the electrochemical oxidation of pollutants with B-HTNA mainly relied on the oxidation of hydroxyl radicals. In addition, B-HTNA exhibited a longer service life of up to 85.4 h, surpassing other anodes with a bare and fragile nanotube array. B-HTNA displayed enhanced stability owing to the hierarchical structure with uniform nanoparticles adhering to a porous layer, which could prevent chemical erosion of the anode and charge leakage from the top of the nanotube during cathodic polarization, thereby enhancing self-doping and stability.