Defluorination of Per- and Polyfluoroalkyl Substances (PFASs) with Hydrated Electrons: Structural Dependence and Implications to PFAS Remediation and Management
Defluorination of Per- and Polyfluoroalkyl Substances (PFASs) with Hydrated Electrons: Structural Dependence and Implications to PFAS Remediation and Management
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DOI：
10.1021/acs.est.8b06648
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发表时间：
2019-04-02
影响因子：
11.4
通讯作者：
Liu, Jinyong
中科院分区：
文献类型：
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作者：
Bentel, Michael J.;Yu, Yaochun;Liu, Jinyong
本研究研究了34种具有代表性的全氟烷基和多氟烷基物质（PFASs）在紫外线产生的水合电子脱氟过程中的关键结构反应性关系。不同氟烷基链长（n = 2 ~ 10）的CnF2n+1-COO-表现出相似的母体化合物衰变和脱氟速率和程度，端粒CnF2n+1-CH2CH2-COO-和CnF2n+1-SO3-的反应明显依赖于氟烷基链的长度。交叉比较实验结果，包括特定PFAS类别的不同衰变率和脱氟率，大多数PFAS结构的不完全脱氟，以及令人惊讶的CF3COO- 100%脱氟，从而阐明了PFAS降解的新机理。对所有PFAS结构的C-F键离解能（BDEs）的理论计算揭示了以下方面的密切关系：(i)衰变和去氟化的速度和程度，（ii）头官能团，（iii）氟烷基链长度，以及（iv）低bde的C-F键的位置和数量。这些关系进一步得到了PFAS结构计算几何优化过程中特定键的自发裂解以及高分辨率质谱分析的支持。氢/氟交换、末端官能团解离、脱羧引发的HF消除和水解等多种反应途径可形成可变的脱氟产物。C-F键裂解的选择性和难易程度在很大程度上取决于分子结构。这些发现为开发PFAS处理工艺和技术以破坏范围广泛的PFAS污染物以及设计氟化学配方以避免将顽固性PFAS释放到环境中提供了重要信息。
This study investigates critical structure reactivity relationships within 34 representative per- and polyfluoroalkyl substances (PFASs) undergoing defluorination with UV-generated hydrated electrons. While CnF2n+1-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 CnF2n+1-CH2CH2-COO- and CnF2n+1-SO3- 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 CF3COO-, 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.