Transient Chemiluminescence Assay for Real-Time Monitoring of the Processes of SO32–-Based Advanced Oxidation Reactions

The hydroxyl radical (·OH) is a strong oxidizing agent in situ generated in advanced oxidation processes (AOPs) and crucial for assessing the performances of AOPs toward organic contaminants' degradation. Herein, we developed a specific luminescent probe, APDI (N′ N′-di(propylethylenediamine)-perylene-3,4,9,10-tetracarboxylic diimide), to selectively detect ·OH among diverse reactive oxygen species and other radicals. Based on the transient chemiluminescence (TCL) spectra, the in situ concentration profile of ·OH within 0.01 s interval time in classical Fenton reactions and four kinds of SO32–-based AOPs was obtained, which provides insights into the high dynamic processes of the whole ·OH generation and consumption processes. Besides, compared with acidic conditions, reduced degradation efficiencies in Fe2+–SO32– and Fe2+–SO32––H2O2 systems were found under neutral conditions. The complete depletion of active free radicals due to SO2–̇ radicals generated from Fe2+ and SO32– should account most for decreased degradation efficiencies evidenced by a new SO2* TCL signal discovered in the TCL spectra. In addition, similar phenomena have also been found in other M(n–1)+–SO32–-related AOPs. As SO32– and HSO3– often exist naturally in wastewater, more efforts are needed to improve the performance of Fe2+–H2O2 systems. This discovery has important significance for organic contaminant degradation in a natural environment.