Do We Appropriately Detect and Understand Singlet Oxygen Possibly Generated in Advanced Oxidation Processes by Electron Paramagnetic Resonance Spectroscopy?

作者：Yang Zong, Long Chen, Yunqiao Zeng, Jun Xu, Hua Zhang, Xiaomeng Zhang, Wen Liu, Deli Wu · 发表于：Environmental Science & Technology · 年份：2023 · DOI：10.1021/acs.est.3c01553 · 被引用次数：180 · 研究领域：Advanced oxidation water treatment、Electrochemical Analysis and Applications、Electron Spin Resonance Studies

Electron paramagnetic resonance (EPR) spectroscopy using sterically hindered amine is extensively applied to detect singlet oxygen ( 1 O 2 ) possibly generated in advanced oxidation processes. However, EPR-detectable 1 O 2 signals were observed in not only the 1 O 2 -dominated hydrogen peroxide (H 2 O 2 )/hypochlorite (NaClO) reaction but surprisingly also the 1 O 2 -absent Fe(II)/H 2 O 2, UV/H 2 O 2, and ferrate [Fe(VI)] process with even stronger intensities. By taking advantage of the characteristic reaction between 1 O 2 and 9,10-diphenyl-anthracene and near-infrared phosphorescent emission of 1 O 2, 1 O 2 was excluded in the Fe(II)/H 2 O 2, UV/H 2 O 2, and Fe(VI) process. The false detection of 1 O 2 was ascribed to the direct oxidation of hindered amine to piperidyl radical by reactive species [e.g., • OH and Fe(VI)/Fe(V)/Fe(IV)] via hydrogen transfer, followed by molecular oxygen addition (forming a piperidylperoxyl radical) and back reaction with piperidyl radical to generate a nitroxide radical, as evidenced by the successful identification of a piperidyl radical intermediate at 100 K and theoretical calculations. Moreover, compared to the highly oxidative species (e.g., • OH and high-valence Fe), the much lower reactivity of 1 O 2 and the profound nonradiative relaxation of 1 O 2 in H 2 O resulted it too selective and inefficient in organic contaminant destruction. This study demonstrated that EPR-based 1 O 2 detection could be remarkably misled by common oxidative ...