Department of Chemical & Environmental Engineering and ‡Materials Science & Engineering Program , University of California , Riverside , California 92521 , United States.
Department of Civil & Environmental Engineering , ∥Metabolomics Lab of Roy J. Carver Biotechnology Center , and ⊥Institute for Genomic Biology , University of Illinois at Urbana-Champaign , Urbana , Illinois 61801 , United States.
Environ Sci Technol. 2019 Apr 2;53(7):3718-3728. doi: 10.1021/acs.est.8b06648. Epub 2019 Mar 15.
This study investigates critical structure-reactivity relationships within 34 representative per- and polyfluoroalkyl substances (PFASs) undergoing defluorination with UV-generated hydrated electrons. While C F-COO with variable fluoroalkyl chain lengths ( n = 2 to 10) exhibited a similar rate and extent of parent compound decay and defluorination, the reactions of telomeric C F-CHCH-COO and C F-SO showed an apparent dependence on the length of the fluoroalkyl chain. Cross comparison of experimental results, including different rates of decay and defluorination of specific PFAS categories, the incomplete defluorination from most PFAS structures, and the surprising 100% defluorination from CFCOO, leads to the elucidation of new mechanistic insights into PFAS degradation. Theoretical calculations on the C-F bond dissociation energies (BDEs) of all PFAS structures reveal strong relationships among (i) the rate and extent of decay and defluorination, (ii) head functional groups, (iii) fluoroalkyl chain length, and (iv) the position and number of C-F bonds with low BDEs. These relationships are further supported by the spontaneous cleavage of specific bonds during calculated geometry optimization of PFAS structures bearing one extra electron, and by the product analyses with high-resolution mass spectrometry. Multiple reaction pathways, including H/F exchange, dissociation of terminal functional groups, and decarboxylation-triggered HF elimination and hydrolysis, result in the formation of variable defluorination products. The selectivity and ease of C-F bond cleavage highly depends on molecular structures. These findings provide critical information for developing PFAS treatment processes and technologies to destruct a wide scope of PFAS pollutants and for designing fluorochemical formulations to avoid releasing recalcitrant PFASs into the environment.
本研究考察了 34 种代表性的全氟和多氟烷基物质（PFAS）在 UV 产生的水合电子作用下进行脱氟反应时的关键结构-反应性关系。具有可变氟烷基链长度（n=2 至 10）的 C F-COO 表现出相似的母体化合物衰减和脱氟速率和程度，而端基 C F-CHCH-COO 和 C F-SO 的反应则明显依赖于氟烷基链的长度。实验结果的交叉比较，包括不同特定 PFAS 类别的衰减和脱氟速率、大多数 PFAS 结构的不完全脱氟以及 CFCOO 的惊人 100%脱氟，揭示了对 PFAS 降解的新的机制见解。对所有 PFAS 结构的 C-F 键离解能（BDE）的理论计算表明，（i）衰减和脱氟的速率和程度、（ii）头官能团、（iii）氟烷基链长度以及（iv）具有低 BDE 的 C-F 键的位置和数量之间存在很强的关系。这些关系还得到了在计算带有一个额外电子的 PFAS 结构的几何优化过程中特定键自发断裂的支持，以及通过高分辨率质谱进行的产物分析。多种反应途径，包括 H/F 交换、端基官能团的解离以及脱羧引发的 HF 消除和水解，导致形成不同的脱氟产物。C-F 键的选择性和断裂的容易程度高度取决于分子结构。这些发现为开发 PFAS 处理工艺和技术以破坏广泛的 PFAS 污染物以及设计避免将难降解的 PFAS 释放到环境中的含氟化学品配方提供了关键信息。
