Complete Defluorination and Mineralization of Perfluorooctanoic Acid by a Mechanochemical Method Using Alumina and Persulfate

Perfluorooctanoic acid (PFOA) is a persistent organic pollutant that has received concerns worldwide due to its extreme resistance to conventional degradation. A mechanochemical (MC) method was developed for complete degradation of PFOA by using alumina (Al 2 O 3 ) and potassium persulfate (PS) as comilling agents. After ball milling for 2 h, the MC treatment using Al 2 O 3 or PS caused conversion of PFOA to either 1-H-1-perfluoroheptene or dimers with a defluorination efficiency lower than 20%, but that using both Al 2 O 3 and PS caused degradation of PFOA with a defluorination of 100% and a mineralization of 98%. This method also caused complete defluorination of other C3∼C6 homologues of PFOA. The complete defluorination of PFOA attributes to Al 2 O 3 and PS led to the weakening of the C–F bond in PFOA and the generation of hydroxyl radical (•OH), respectively. During the MC degradation, Al 2 O 3 strongly anchors PFOA through COO – –Al coordination and in situ formed from Lewis-base interaction and PS through hydrogen bond. Meanwhile, mechanical effects induce the homolytic cleavage of PS to produce SO 4 •–, which reacts with OH group of Al 2 O 3 to generate •OH. The degradation of PFOA is initiated by decarboxylation as a result of weakened C–COO – due to Al 3+ coordination. The subsequent addition of •OH, elimination of HF, and reaction with water induce the stepwise removal of all carboxyl groups and F atoms as CO 2 and F –, respectively. Thus, complete defluorination and mineralization are achieved.