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.

The practical application of the traditional Fenton system (Fe­(II)/H2O2) is seriously hampered by the sluggish Fe­(III)/Fe­(II) cycle and the stringent acidic reaction condition. In this work, we found that trace-dissolved S­(-II) (DS­(-II), 5 μM) could significantly accelerate the Fe­(III)/Fe­(II) cycle and trigger a rapid H2O2 activation process in the Fe­(III)/H2O2 system. Thus, more hydroxyl radicals (·OH) were generated for the rapid removal of various organic pollutants such as bisphenol A (BPA) and sulfamethoxazole (SMX) from water. Besides, the additive DS­(-II) effectively broadened the application pH range of the Fenton or Fenton-like system. The constructed Fe­(III)/DS­(-II)/H2O2 system showed extensive applicability to different water matrices and maintained high BPA removal in the actual water sources. Furthermore, the toxicity assessment revealed that the toxicity of the target contaminant was diminished. The harmless SO4 2– was the final product of DS­(-II) in the Fe­(III)/DS­(-II)/H2O2 system, and the residual DS­(-II) was less than the threshold limit value for fresh or saltwater (0.5 mg/L). This discovery is expected to promote the large-scale practical application of iron-based Fenton or Fenton-like systems in practical organic wastewater purification.

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