摘要：

This work reports a mechanochemical (MC) method for complete defluorination of perfluorooctanoic acid (PFOA) by using Al and Al₂O₃ as milling agents. Both the Al/Al₂O₃ molar ratio (r_e/r_dec.) and the pre-thermal treatment of Al₂O₃ strongly influenced the defluorination of PFOA. When commercial γ-Al₂O₃ was pre-treated at 1200 ºC, the use of Al and heat-treated γ-Al₂O₃ with 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-Al₂O₃ pre-heated at temperatures lower than 700 ºC. It was clarified that the carboxylate-mediated adsorption of PFOA on Al₂O₃ 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 increased the in-situ electron generation rate (r_e), and a higher heat-treatment temperature decreased OH−/H₂O adsorbed on Al₂O₃ to low the PFOA decarboxylation rate (r_dec). The r_e/r_dec 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_e/r_dec.

关键词：Perfluorooctanoic acid; mechanochemical degradation; defluorination; reduction;decarboxylation