Banayan Esfahani Ehsan, Asadi Zeidabadi Fatemeh, Jafarikojour Morteza, Mohseni Madjid
Department of Chemical and Biological Engineering, University of British Columbia, 2360 East Mall, Vancouver, Canada.
Department of Chemical and Biological Engineering, University of British Columbia, 2360 East Mall, Vancouver, Canada.
Sci Total Environ. 2024 Nov 15;951:175796. doi: 10.1016/j.scitotenv.2024.175796. Epub 2024 Aug 25.
The present study investigated the photo-reduction of perfluorooctane sulfonate (PFOS) and its alternatives, focusing on decomposition mechanisms, active species involvement, the influence of background water constituents, and kinetic model development. The decomposition and defluorination rates followed the order of PFOS > PFHxS > 6:2 FTSA > PFBS, with shorter chains and CH linkers enhancing the resistance of PFOS alternatives against the attack of hydrated electrons (e). Two primary pathways were identified during the photodegradation of PFAS: (i) H/F exchange at CF bonds with the lowest bond dissociation energies (BDEs) and (ii) functional group cleavage followed by short-chain PFCAs formation, with OH playing a crucial role in transforming intermediates. Adding iodide and elevated temperatures demonstrated a synergistic effect on PFBS decomposition and defluorination, with high temperatures promoting functional group cleavage as the preferred defluorination pathway. The study examined the impact of background water constituents in different aqueous environments, from surface waters to wastewater streams and ion-exchange brine concentrates. Chloride exhibited a concentration-based dual impact on the UV/VUV/sulfite process: promotive effects at low dosages (1-10 mM) by acting as a secondary e mediator, and adverse effects at high dosages (20-500 mM) due to the scavenging effect of generated chlorine radicals (Cl). High ionic strength adversely affected e quantum efficiency. Additionally, bicarbonate and natural organic matter (NOM) had opposing effects on PFOS photo-reduction, primarily through e scavenging and pH alteration. Kinetic modeling revealed reaction rate constants of the studied PFAS with e ranging from 1.8 × 10 to 1.3 × 10 M s, corroborating the concentration profiles of active species and highlighting the reductive nature of sulfite-mediated processes.
本研究调查了全氟辛烷磺酸（PFOS）及其替代品的光还原作用，重点关注分解机制、活性物种参与情况、背景水成分的影响以及动力学模型的建立。分解和脱氟速率遵循PFOS＞全氟己烷磺酸（PFHxS）＞6:2氟调聚磺酸（FTSA）＞全氟丁烷磺酸（PFBS）的顺序，较短的链和-CH-连接基增强了PFOS替代品对水合电子（e）攻击的抗性。在全氟烷基磺酸（PFAS）的光降解过程中确定了两条主要途径：（i）在具有最低键解离能（BDEs）的CF键处进行H/F交换，以及（ii）官能团裂解，随后形成短链全氟羧酸（PFCA），其中OH在中间体转化中起关键作用。添加碘化物和升高温度对PFBS的分解和脱氟表现出协同效应，高温促进官能团裂解作为首选的脱氟途径。该研究考察了从地表水到废水流和离子交换盐水浓缩物等不同水环境中背景水成分的影响。氯离子对UV/VUV/亚硫酸盐过程表现出基于浓度的双重影响：低剂量（1-10 mM）时通过作为二级电子介质起到促进作用，高剂量（20-500 mM）时由于生成的氯自由基（Cl）的清除作用产生不利影响。高离子强度对电子量子效率有不利影响。此外，碳酸氢盐和天然有机物（NOM）对PFOS光还原有相反的影响，主要通过电子清除和pH改变。动力学建模揭示了所研究的PFAS与电子的反应速率常数范围为1.8×10至1.3×10 M⁻¹ s⁻¹，证实了活性物种的浓度分布，并突出了亚硫酸盐介导过程的还原性质。
