The radicals involved in advanced oxidation process are the most important part of mechanism analysis, but radical quenching experiments and theoretical calculations cannot provide direct evidence for the generation, transformation and mechanism of radicals. Electron paramagnetic resonance (EPR) is a cutting-edge technology to prove the existence of various radicals, using different spectral characteristics to identify. However, the complexity of radical spectrum analysis and identification brings uncertainty and inconsistency to the mechanism explanation. The ignorance and difference of radical spectrum chart in previous studies had brought difficulties to the accurate identification of radical signals in EPR analysis. In addition, the application of EPR technology in the environmental field to analyze radicals in the process of environmental catalysis and pollutant conversion is still not mature enough. In this study, DMPO was selected as the trapping agent to capture various radicals commonly found in AOPs. By using EPR and MATLAB simulation as tools, a comprehensive study of the formation of radicals in different AOPs was carried out. Spectral width, line width, hyperfine coupling constant (AN and AH) and other typical parameters can accurately identify and judge the spectral signal characteristics of ●CH3, ●OH, ●O2-, ●OOH, SO4●- and ●OCH3 radicals in UV/H2O2, UV/PMS, UV/PDS, UV/PAA, and UV/IO4- system. In the H2O2 system, ●OH and ●O2- were recognized, and the transformation and recognition between ●O2- and ●OOH were discussed. In the peroxymonosulfate and peroxodisulfate system, SO4●- was firmly captured and simulated in aqueous solution. In the peracetic acid (PAA) system, carbon-center and oxygen-center radicals (●CH3, ●OH, CH3COO● and CH3COOO●) can be directly identified by AN/AH and total spectral width. In conclusion, the recognition of spectrum captured by DMPO was mainly determined by AN, AH, total spectral width, linewidth and solvent, caused by the electronegativity, molecular weight, hyperfine splitting coupling constant of the functional group in the radicals, which provided more accurate guidance for the mechanism analysis of advanced oxidation technology.

Radical analysis in advanced oxidation process of water treatment: Combination of experiment and simulation

ACS Spring 2022

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