Complete mechanochemical defluorination of perfluorooctanoic acid using AlO and Al powders through matching electron-mediated reduction with decarboxylation.

This work reports a mechanochemical (MC) method for complete defluorination of perfluorooctanoic acid (PFOA) by using Al and AlO as milling agents. Both the Al/AlO molar ratio ( [Formula: see text] ) and the pre-thermal treatment of AlO strongly influenced the defluorination of PFOA. When commercial γ-AlO was pre-treated at 1200 °C, the use of Al and heat-treated γ-AlO with [Formula: see text] of 1: 1 led to PFOA defluorination of 100% after ball milling for 26 min at 350 rpm, being much higher than those (8.3%-58.1%) for using singlet milling agents or binary milling agents containing γ-AlO pre-heated at temperatures lower than 700 °C. It was clarified that the carboxylate-mediated adsorption of PFOA on AlO was essential for the MC decarboxylation as a degradation initiation step, and the in-situ generated electron on milled Al consequently caused the reductive dissociation of C-F bonds in the decarboxylation intermediate. A larger [Formula: see text] increased the in-situ electron generation rate (r), and a higher heat-treatment temperature decreased OH/HO adsorbed on AlO to low the PFOA decarboxylation rate (r). The r/r ratio determined defluorination pathways, and the percentage of the defluorination of PFOA in its total degradation including the generation of any degradation intermediates increased linearly with increasing r/r.