Unveiling singlet oxygen spin trapping in catalytic oxidation processes using in situ kinetic EPR analysis

• Published in: Proceedings of the National Academy of Sciences - PNAS Vol. 120; no. 30; p. e2305706120
• Main Authors: Wu, Jing-Hang, Chen, Fei, Yang, Tian-Hao, Yu, Han-Qing
• Format: Journal Article
• Language: English
• Published: United States National Academy of Sciences 25.07.2023
• Subjects: Catalytic oxidation; Chemical synthesis; Decontamination; Electron paramagnetic resonance; Electron spin; Electron spin resonance; Molecular modelling; Oxidation; Physical Sciences; Reaction mechanisms; Singlet oxygen; Trapping; Water purification; kinetic study; electron paramagnetic resonance; singlet oxygen; catalytic oxidation processes; direct TEMP oxidation
• ISSN: 0027-8424; 1091-6490; 1091-6490
• DOI: 10.1073/pnas.2305706120

Singlet oxygen ( 1 O 2 ) plays a pivotal role in numerous catalytic oxidation processes utilized in water purification and chemical synthesis. The spin-trapping method based on electron paramagnetic resonance (EPR) analysis is commonly employed for 1 O 2 detection. However, it is often limited to time-independent acquisition. Recent studies have raised questions about the reliability of the 1 O 2 trapper, 2,2,6,6-tetramethylpiperidine (TEMP), in various systems. In this study, we introduce a comprehensive, kinetic examination to monitor the spin-trapping process in EPR analysis. The EPR intensity of the trapping product was used as a quantitative measurement to evaluate the concentration of 1 O 2 in aqueous systems. This in situ kinetic study was successfully applied to a classical photocatalytic system with exceptional accuracy. Furthermore, we demonstrated the feasibility of our approach in more intricate 1 O 2 -driven catalytic oxidation processes for water decontamination and elucidated the molecular mechanism of direct TEMP oxidation. This method can avoid the false-positive results associated with the conventional 2D 1 O 2 detection techniques, and provide insights into the reaction mechanisms in 1 O 2 -dominated catalytic oxidation processes. This work underscores the necessity of kinetic studies for spin-trapping EPR analysis, presenting an avenue for a comprehensive exploration of the mechanisms governing catalytic oxidation processes.