Complete mechanochemical defluorination of perfluorooctanoic acid using Al2O3 and Al powders through matching electron-mediated reduction with decarboxylation. (November 2022)

• Record Type: Journal Article
• Authors: Zhou, Yuqi; Lv, Hanqing; Lin, Jin; Lv, Tianyu; Wang, Nan; Tang, Heqing; Zhu, Lihua
• Is Part Of: Chemosphere. Volume 307:Part 2(2022)
• Publication Date: 2022-11
• Subjects: Perfluorooctanoic acid -- Mechanochemical degradation -- Defluorination -- Reduction -- Decarboxylation; Pollution -- Periodicals; Pollution -- Physiological effect -- Periodicals; Environmental sciences -- Periodicals; Atmospheric chemistry -- Periodicals; 551.511
• DOI: 10.1016/j.chemosphere.2022.135872
• Languages: English
• ISSNs: 0045-6535

Abstract

Abstract: This work reports a mechanochemical (MC) method for complete defluorination of perfluorooctanoic acid (PFOA) by using Al and Al2 O3 as milling agents. Both the Al/Al2 O3 molar ratio ( n Al / n Al 2 O 3 ) and the pre-thermal treatment of Al2 O3 strongly influenced the defluorination of PFOA. When commercial γ -Al2 O3 was pre-treated at 1200 °C, the use of Al and heat-treated γ -Al2 O3 with n Al / n Al 2 O 3 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 -Al2 O3 pre-heated at temperatures lower than 700 °C. It was clarified that the carboxylate-mediated adsorption of PFOA on Al2 O3 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 n Al / n Al 2 O 3 increased the in-situ electron generation rate ( r e ), and a higher heat-treatment temperature decreased OH − /H2 O adsorbed on Al2 O3 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 . Graphical abstract: Image 1 Highlights: The use of Al2 O3 and Al caused full defluorination of PFOA in 26 min ball milling. The Al/Al2 O3 molar ratio and pre-heating of γ -Al2 O3 affected PFOA defluorination. The carboxylate-mediated adsorption on Al2 O3 controlled PFOA decarboxylation. In-situ generated electrons on milled Al promoted reductive defluorination of PFOA. Rate ratio of electron generation to decarboxylation determined PFOA defluorination.