Fe2+-NTA synergized UV254 photolytic defluorination of perfluorooctane sulfonate (PFOS): Enhancing through intramolecular electron density perturbation via electron acquisition,Water Research

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Fe2+-NTA synergized UV254 photolytic defluorination of perfluorooctane sulfonate (PFOS): Enhancing through intramolecular electron density perturbation via electron acquisition
Water Research ( IF 11.4 ) Pub Date : 2024-03-05 , DOI: 10.1016/j.watres.2024.121421
Yihua Chen ₁ , Jiaxin Zhu ₁ , Hang Ma ₁ , Yurong Gu ₂ , Tongzhou Liu ₁

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Perfluorooctane sulfonate (PFOS) is a persistent organic pollutant posing a risk in environmental persistence, bioaccumulation and biotoxicity. This study was to reach a comprehensive and deeper understanding of PFOS elimination in a UV254 photolytic treatment with the co-presence of Fe2+ and nitrilotriacetic acid trisodium salt (NTA). PFOS defluorination was noticeably enhanced in the UV/Fe2+-NTA treatment compared with UV/NTA, UV/Fe2+ and our previously studied UV/Fe3+ treatments. UV–vis, FTIR, and UPLC/MS-MS results indicated the formation of PFOS-Fe2+-NTA complex in PFOS, Fe2+ and NTA mixture. The transition energy gap of PFOS-Fe2+-NTA decreased below the excitation energy supplied by UV254 irradiation, corresponding with red shift appearing in UV–vis scanning spectrum. This favored intramolecular electron transfer from Fe2+-NTA to PFOS under UV254 irradiation to form electron-accepting PFOS. Molecular electrostatic potential and atom charge distribution analyses suggested electron density rearrangement and perturbation in the perfluorinated carbon chain of electron-accepting PFOS, leading to the decrease in bond dissociation energies. Intermediate products detection suggested the parallel defluorination pathways of PFOS desulfonation, middle carbon chain scission and direct C-F cleavage. NTA exhibited crucial functions in the UV/Fe2+-NTA treatment by holding Fe2+/Fe3+ in soluble form as a chelant and favoring water activation to generate hydrated electrons (eaq−) under UV irradiation as a photosensitizer. Fe2+ acting as the conduit for electron transfer and the bridge of PFOS anion and NTA was thought functioning best at 200 µM in this study. The degree of UV/Fe2+-NTA -synergized PFOS defluorination also depended on eaq− yield and UV254 photon flux. The structure dependence on the electron transfer process of PFOS and PFOA was explored incorporating molecular structure descriptors. Because of possessing greater potential to acquire electrons or less likeliness to donate its electrons than PFOA, PFOS exhibited faster defluorination kinetics in the published “reduction treatments” than “oxidation” ones. Whereas, PFOA defluorination kinetics were at similar level in both “reduction” and “oxidation” treatments.

中文翻译：

Fe2+-NTA 协同 UV254 全氟辛烷磺酸 (PFOS) 光解脱氟：通过电子采集通过分子内电子密度扰动增强

全氟辛烷磺酸（PFOS）是一种持久性有机污染物，具有环境持久性、生物蓄积性和生物毒性的风险。本研究旨在全面、深入地了解 Fe2+ 和次氮基三乙酸三钠盐 (NTA) 共存的 UV254 光解处理中 PFOS 的消除。与 UV/NTA、UV/Fe2+ 和我们之前研究的 UV/Fe3+ 处理相比，UV/Fe2+-NTA 处理中的 PFOS 脱氟效果显着增强。 UV-vis、FTIR 和 UPLC/MS-MS 结果表明，在 PFOS、Fe2+ 和 NTA 混合物中形成了 PFOS-Fe2+-NTA 复合物。 PFOS-Fe2+-NTA 的跃迁能隙降低到低于 UV254 照射提供的激发能，这与 UV-vis 扫描光谱中出现的红移相对应。这有利于在 UV254 照射下从 Fe2+-NTA 到 PFOS 的分子内电子转移，形成电子接受的 PFOS。分子静电势和原子电荷分布分析表明，电子接受 PFOS 的全氟化碳链中存在电子密度重排和扰动，导致键解离能降低。中间产物检测表明PFOS脱磺、中间碳链断裂和直接CF断裂的平行脱氟途径。 NTA 在 UV/Fe2+-NTA 处理中表现出关键功能，作为螯合剂将 Fe2+/Fe3+ 保持在可溶形式，并作为光敏剂有利于水活化在紫外线照射下产生水合电子 (eaq−)。在本研究中，Fe2+ 充当电子转移的导管以及 PFOS 阴离子和 NTA 的桥梁，被认为在 200 µM 时发挥最佳作用。 UV/Fe2+-NTA 协同 PFOS 脱氟程度还取决于 eaq− 产率和 UV254 光子通量。通过结合分子结构描述符，探索了 PFOS 和 PFOA 电子转移过程的结构依赖性。由于与 PFOA 相比，PFOS 具有更大的获取电子的潜力或不太可能提供电子，因此在已发表的“还原处理”中，PFOS 表现出比“氧化”处理更快的脱氟动力学。然而，PFOA 脱氟动力学在“还原”和“氧化”处理中处于相似的水平。

更新日期：2024-03-05

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