Reductive defluorination of perfluorooctanoic acid by titanium(III) citrate with vitamin B 12 and copper nanoparticles.

•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.