Recycled use of a hydrophobic vitamin B 12, heptamethyl co-byrinate perchlorate, in the dechlorination of 1,1-bis(4-chlorophenyl)-2,2,2-trichloroethane (DDT) with a visible light irradiation system containing a [Ru(II)(bpy)(3)]Cl-2 photosensitizer was achieved using an ionic liquid as reaction medium.