Defluorination of perfluorooctanoic acid and perfluorooctane sulfonic acid by heterogeneous catalytic system of Fe-Al2O3/O3: Synergistic oxidation effects and defluorination mechanism

• Published in: The Science of the total environment 2024-03, Vol.915, p.169675-169675, Article 169675
• Main Authors: Zhang, Yumin, Guan, Zhijie, Liao, Xiaojian, Huang, Yu, Huang, Zhenhua, Mo, Zhihua, Yin, Baixuan, Zhou, Xingfan, Dai, Wencan, Liang, Jialin, Sun, Shuiyu
• Format: Article
• Language: English
• Subjects: Defluorination; Ozonation catalytic oxidation; Perfluorooctane sulfonic acid; Perfluorooctanoic acid; Synergistic oxidation effects
• ISSN: 0048-9697; 1879-1026
• DOI: 10.1016/j.scitotenv.2023.169675

In this study, catalytic ozonation by Fe-Al2O3 was used to investigate the defluorination of PFOA and PFOS, assessing the effects of different experimental conditions on the defluorination efficiency of the system. The oxidation mechanism of the Fe-Al2O3/O3 system and the specific degradation and defluorination mechanisms for PFOA and PFOS were determined. Results showed that compared to the single O3 system, the defluorination rates of PFOA and PFOS increased by 2.32- and 5.92-fold using the Fe-Al2O3/O3 system under optimal experimental conditions. Mechanistic analysis indicated that in Fe-Al2O3, the variable valence iron (Fe) and functional groups containing C and O served as important reaction sites during the catalytic process. The co-existence of 1O2, OH, O2− and high-valence Fe(IV) constituted a synergistic oxidation system consisting of free radicals and non-radicals, promoting the degradation and defluorination of PFOA and PFOS. DFT theoretical calculations and the analysis of intermediate degradation products suggested that the degradation pathways of PFOA and PFOS involved Kolbe decarboxylation, desulfonation, alcoholization and intramolecular cyclization reactions. The degradation and defluorination pathways of PFOA and PFOS consisted of the stepwise removal of -CF2-, with PFOS exhibiting a higher defluorination rate than PFOA due to its susceptibility to electrophilic attack. This study provides a theoretical basis for the development of heterogeneous catalytic ozonation systems for PFOA and PFOS treatment. [Display omitted] •Fe-Al2O3 showed excellent catalytic performance.•Using DFT calculations to find specific attack sites for PFOA and PFOS.•The co-existence of ROS and Fe(IV) constituted a synergistic oxidation system.•The degradation and defluorination pathways of PFOA and PFOS had been revealed.•PFOS exhibited a higher DeF rate due to its susceptibility to electrophilic attack.