Department of Civil and Environmental Engineering, Colorado School of Mines, Golden, Colorado 80401, United States.
Department of Chemistry, Colorado School of Mines, Golden, Colorado 80401, United States.
Environ Sci Technol. 2023 May 23;57(20):7849-7857. doi: 10.1021/acs.est.2c09451. Epub 2023 May 12.
Advanced reduction processes (ARPs) that generate hydrated electrons (e; e.g., UV-sulfite) have emerged as a promising remediation technology for recalcitrant water contaminants, including per- and polyfluoroalkyl substances (PFASs). The effectiveness of ARPs in different natural water matrices is determined, in large part, by the presence of non-target water constituents that act to quench e or shield incoming UV photons from the applied photosensitizer. This study examined the pH-dependent quenching of e by ubiquitous dissolved carbonate species (HCO*, HCO, and CO) and quantified the relative importance of carbonate species to other abundant quenching agents (e.g., HO, H, HSO, and O) during ARP applications. Analysis of laser flash photolysis kinetic data in relation to pH-dependent carbonate acid-base speciation yields species-specific bimolecular rate constants for e quenching by HCO*, HCO, and CO ( = 2.23 ± 0.42 × 10 M s, = 2.18 ± 0.73 × 10 M s, and = 1.05 ± 0.61 × 10 M s), with quenching dominated by HCO* (which includes both CO and HCO) at moderately alkaline pH conditions despite it being the minor species. Attempts to apply previously reported rate constants for e quenching by CO, measured in acidic solutions equilibrated with CO, overpredict quenching observed in this study at higher pH conditions typical of ARP applications. Moreover, kinetic simulations reveal that pH-dependent trends reported for UV-sulfite ARPs that have often been attributed to e quenching by varying [H] can instead be ascribed to variable acid-base speciation of dissolved carbonate and the sulfite sensitizer.
高级还原过程 (ARPs) 生成水合电子 (e; 例如，紫外线亚硫酸盐)，已成为一种有前途的修复技术，可用于处理顽固的水污染物，包括全氟和多氟烷基物质 (PFASs)。ARPs 在不同天然水基质中的有效性在很大程度上取决于非目标水成分的存在，这些成分会淬灭 e 或屏蔽入射的紫外线光子，使其远离应用的光敏剂。本研究考察了普遍存在的溶解碳酸物种 (HCO*、HCO 和 CO) 对 e 的 pH 依赖性猝灭作用，并量化了在 ARP 应用过程中，碳酸物种相对于其他丰富猝灭剂 (例如，HO、H、HSO 和 O) 的相对重要性。通过激光闪光光解动力学数据分析与 pH 依赖性碳酸酸碱形态分布的关系，得出了 e 被 HCO*、HCO 和 CO 猝灭的物种特异性双分子速率常数 (= 2.23 ± 0.42×10 M s、= 2.18 ± 0.73×10 M s 和 = 1.05 ± 0.61×10 M s)，尽管 HCO* 是少数物种，但在中等碱性 pH 条件下，HCO* (包括 CO 和 HCO) 主导了猝灭作用。尝试应用先前报道的在与 CO 平衡的酸性溶液中测量的 e 被 CO 猝灭的速率常数，会过高预测本研究中在更高 pH 条件下观察到的猝灭作用，因为这些条件更典型于 ARP 应用。此外，动力学模拟表明，通常归因于[H]变化导致的 UV-亚硫酸盐 ARPs 的 pH 依赖性趋势，实际上可以归因于溶解碳酸和亚硫酸盐敏化剂的酸碱形态变化。
