Role of pH in the Transformation of Perfluoroalkyl Carboxylic Acids by Activated Persulfate: Implications from the Determination of Absolute Electron-Transfer Rates and Chemical Computations
Role of pH in the Transformation of Perfluoroalkyl Carboxylic Acids by Activated Persulfate: Implications from the Determination of Absolute Electron-Transfer Rates and Chemical Computations
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pH 在活化过硫酸盐转化全氟烷基羧酸中的作用：绝对电子转移速率测定和化学计算的启示
DOI：
10.1021/acs.est.1c02389
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发表时间：
2021
影响因子：
11.4
通讯作者：
Vyas, Shubham
中科院分区：
文献类型：
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作者：
Carre-Burritt, Asa E.;Van Hoomissen, Daniel J.;Vyas, Shubham
全氟烷基羧酸（PFCA）是普遍存在的污染物，已知其生物累积性，毒理学危害和抗降解性。修复水中的全氟乙酸是一项持续的挑战，现有技术不足或需要额外的处置。一种紧急的方法是使用活化过硫酸盐，它通过连续切断CF2当量产生短链同系物CO2和F-来降解PFCA。这种转化被认为是由PFCA到活化氧化剂SO 4·-的单电子转移（SET）引发的。一个显着的pH值效应已观察到热活化过硫酸盐PFCA转化。为了评估pH在SET过程中的作用，我们使用激光闪光光解在pH 0.5-4.0的范围内直接测定了SO 4·-氧化全氟丁酸和三氟乙酸的绝对速率常数。在所有pH值下，两种底物的速率常数平均值为9 ± 2 × 103 M-1 s-1（±2σ），这表明热过硫酸盐活化的酸催化可能是观察到的pH效应的主要原因，而不是pH影响SET步骤。此外，利用密度泛函理论研究了SO 4·-质子化对PFCA相变动力学的影响.我们发现，当计算包括明确的水分子，直接SO 4·-质子化不会发生。
Perfluoroalkyl carboxylic acids (PFCAs) are ubiquitous contaminants known for their bioaccumulation, toxicological harm, and resistance to degradation. Remediating PFCAs in water is an ongoing challenge with existing technologies being insufficient or requiring additional disposal. An emergent approach is using activated persulfate, which degrades PFCAs through sequential scission of CF2equivalents yielding shorter-chain homologues, CO2and F–. This transformation is thought to be initiated by single electron transfer (SET) from the PFCA to the activate oxidant, SO4•–. A pronounced pH effect has been observed for thermally activated persulfate PFCA transformation. To evaluate the role of pH during SET, we directly determined absolute rate constants for perfluorobutanoic acid and trifluoroacetic acid oxidation by SO4•–in the pH range of 0.5–4.0 using laser flash photolysis. The average of the rate constants for both substrates across all pH values was 9 ± 2 × 103M–1s–1(±2σ), implying that acid catalysis of thermal persulfate activation may be the primary culprit of the observed pH effect, instead of pH influencing the SET step. In addition, density functional theory was used to investigate if SO4•–protonation might enhance PFCA transformation kinetics. We found that when calculations include explicit water molecules, direct SO4•–protonation does not occur.