Reductive defluorination of perfluorooctanoic acid by titanium(III) citrate with vitamin B₁₂ and copper nanoparticles

Highlights: • Reductive defluorination of PFOA using titanium(III) citrate with vitamin B₁₂ and Cu⁰ was investigated. • The combination of B₁₂ and Cu⁰ generate extraordinary reactive radicals for PFOA removal. • The performance of reductants for PFOA removal was titanium(III) citrate ≫ nano zero-valent Iron > NaBH4. • Mechanisms of PFOA hydrodefluorination through sequential electron transfer pathways were proposed. - Abstract: Perfluorooctanoic acid (PFOA) is widespread in the environment, which causes serious health and safety concerns. A mechanistic study on reductive defluorination of PFOA by titanium(III) citrate in the presence of catalysts was conducted. Vitamin B₁₂ was used to catalyze reduction reactions by shuttling electrons from a reducing agent (electron donor) to PFOA to produce a Co-carbon bond intermediates. In the presence of copper nanoparticles, a precursor complex, B₁₂-C₇F₁₄COOH, adsorbed on the metal surface, followed by a hydrogenolytic reaction to form less-fluorinated products. The synergistic effect between vitamin B₁₂ and copper nanoparticles enhances the reductive activities by electron-transfer reactions and hydrogenolysis. The efficient reduction of PFOA to less-noxious compounds was demonstrated with a copper dose of 2 g L⁻¹, titanium(III) citrate (45 mM), and vitamin B₁₂ (0.2 mM) with an initial pH of 9.0 and 70 °C. In this anoxic aqueous solution, the biomimetic reductive system effectively removed 65% of PFOA. The mass balance on fluoride matched the observed degradation of PFOA, while no short-chain intermediates were detected.