A Gd³⁺-doped blue TiO₂ nanotube array anode for efficient electrocatalytic degradation of iohexol

Hongxiang Li ^{a, c, 1}, Haiou Song ^{a, c, d, 1*}, Qian Lai ^{a, c}, Yun Li ^{a, d}, Gusunkiz Egabaierdi ^{a, d}, Zhe Xu ^{a, c, d}, Shaogui Yang ^{a, c, d}, Shiyin Li ^{a, c, d}, Huan He ^{a, c, d}, Shupeng Zhang ^{b, *}

ABSTRACT

A Gd³⁺-doped blue TiO₂ nanotube array anode (Gd-BTNA) was successfully fabricated by the processes of anodization, Gd doping and cathodization. The electrocatalytic activity of a blue TiO₂ nanotube array anode (BTNA) can be improved by Gd doping, which introduced oxygen vacancies into the material and increases the specific surface area of the anode. Gd-BTNA is used to eliminate iohexol (IOH) in water, and the optimal operating parameters for electrochemical degradation of IOH are a current density of 15 mA cm^–2, initial solution pH of 6.5 and initial IOH concentration of 10 ppm. Coexisting components in wastewater have adverse effects on the treatment process, including Cl^–, HCO₃^–, NH₄⁺ and humic acid. Under the optimal conditions, complete degradation of IOH was obtained within 18 min and more than 52.1% total organic carbon (TOC) was removed after 60 min of reaction time, which outperforms the BTNA and several commercial electrodes. The excellent efficiencies in electrochemical degradation of iohexol show that Gd-BTNA was a promising anode to treat iodinated contrast media contaminants.

In this study, a Gd-BTNA was successfully fabricated using anodization, Gd doping and cathodization. Gd doping improved the electrocatalytic performance of BTNA in that more oxygen vacancies and increased active area were introduced. Under optimal conditions, IOH could be eliminated completely within 18 min and the TOC removal extent could reach 52.1% within 60 min by Gd-BTNA, and ·OH was the critical active species in this system. The degradation of IOH mainly experienced deiodination, amide hydrolysis, amino oxidation and C–OH oxidation and addition of –OH. This study may provide a new idea for the electrochemical degradation of ICM in a water environment.