Enhanced perfluorooctane acid mineralization by electrochemical oxidation using Ti³⁺ self-doping TiO₂ nanotube arrays...

Perfluorooctanoic acid (PFOA) is of increasing concern due to its worldwide application and extremely environmental persistence. Herein, we demonstrated the electrochemical degradation of PFOA with high efficiency using the Ti³⁺ self-doping TiO₂ nanotube arrays (Ti³⁺/TiO₂-NTA) anode. The fabricated Ti³⁺/TiO₂-NTA anode exhibited vertically aligned uniform nanotubes structure, and was demonstrated good performance on the electrochemical degradation of PFOA in water. The degradation rate, total organic carbon (TOC) removal rate and defluorination rate of PFOA reached 98.1 %, 93.3 % and 74.8 %, respectively, after electrolysis for 90 min at low current density of 2 mA cm^-2. The energy consumption (7.6 Wh L^-1) of this electrochemical oxidation system using Ti³⁺/TiO₂-NTA anode for PFOA degradation was about 1 order of magnitude lower than using traditional PbO₂ anodes. Cathodic polarization could effectively prolong the electrocatalytic activity of the anode by regenerating Ti³⁺ sites. PFOA molecular was underwent a rapidly mineralization to CO₂ and F^-, with only low concentration of short-chain perflfluorocarboxylic acids (PFCAs) intermediates identified. A possible electrochemical degradation mechanism of PFOA was proposed, in which the initial direct electron transfer (DET) on the anode to yield PFOA free radicals (C₇F₁₅COO•) and hydroxyl radicals (•OH) oxidation were greatly enhanced. This presented study provides a novel approach for the purification of the recalcitrant PFOA from wastewaters.