Efficient Reductive Defluorination of Branched PFOS by Metal-Porphyrin Complexes.

Vitamin B (VB) has been reported to degrade PFOS in the presence of Ti citrate at 70 °C. Porphyrin-based catalysts have emerged as VB analogues and have been successfully used in various fields of research due to their interesting structural and electronic properties. However, there is inadequate information on the use of these porphyrin-based metal complexes in the defluorination of PFOS. We have therefore explored a series of porphyrin-based metal complexes for the degradation of PFOS. Co-5,10,15,20-tetraphenyl-21,23-porphyrin (Co-TPP), Co-5,10,15,20-tetrakis(4-methoxyphenyl)-21,23-porphyrin (Co-M-TPP), and Co-M-TPP exhibited efficient reductive defluorination of the branched PFOS. Within 5-8 h, these compounds achieved the same level of PFOS defluorination as VB achieved in 7-10 days. For branched isomers, the specific removal rate of the Co-TPP-Ti citrate system is 64-105 times higher than that for VB-Ti citrate. Moreover, the Co-TPP-Ti citrate system displayed efficient (51%) defluorination for the branched PFOS (br-PFOS) in 1 day even at room temperature (25 °C). The effects of the iron and cobalt metal centers, reaction pH, and several reductants (NaBH, nanosized zerovalent zinc (nZn), and Ti citrate) were systematically investigated. Based on the analysis of the products and previously published reports, a new possible defluorination pathway of branched PFOS is also proposed.