@article {CHEN2022118747,
	title = {Accurate identification of radicals by in-situ electron paramagnetic resonance in ultraviolet-based homogenous advanced oxidation processes},
	journal = {Water Research},
	volume = {221},
	year = {2022},
	pages = {118747},
	abstract = {Accurate identification of radicals in advanced oxidation processes (AOPs) is important to study the mechanisms on radical production and subsequent oxidation-reduction reaction. The commonly applied radical quenching experiments cannot provide direct evidences on generation and evolution of radicals in AOPs, while electron paramagnetic resonance (EPR) is a cutting-edge technology to identify radicals based on spectral characteristics. However, the complexity of EPR spectrum brings uncertainty and inconsistency to radical identification and mechanism clarification. This work presented a comprehensive study on identification of radicals by in-situ EPR analysis in four typical UV-based homogenous AOPs, including UV/H2O2, UV/peroxodisulfate (and peroxymonosulfate), UV/peracetic acid and UV/IO4- systems. Radical formation mechanism was also clarified based on EPR results. A reliable EPR method using organic solvents was proposed to identify alkoxy and alkyl radicals (CH3C(=O)OO{\textperiodcentered}, CH3C(=O)O{\textperiodcentered} and {\textperiodcentered}CH3) in UV/PAA system. Two activation pathways for radical production were proposed in UV/IO4- system, in which the produced IO3{\textperiodcentered}, IO4{\textperiodcentered}, {\textperiodcentered}OH and hydrated electron were precisely detected. It is interesting that addition of specific organic solvents can effectively identify oxygen-center and carbon-center radicals. A key parameter in EPR spectrum for 5,5-dimethyl-1-pyrroline N-oxide (DMPO) spin adduct, AH, is ranked as: {\textperiodcentered}CH3 (23~G) \&gt;{\textperiodcentered}OH (15~G) \&gt;IO3{\textperiodcentered} (12.9~G) \&gt;O2{\textperiodcentered}- (11~G) >={\textperiodcentered}OOH (9{\textendash}11~G) >=IO4{\textperiodcentered} (9{\textendash}10~G) >=SO4{\textperiodcentered}- (9{\textendash}10~G) \&gt;CH3C(=O)OO{\textperiodcentered} (8.5~G) \&gt; CH3C(=O)O{\textperiodcentered} (7.5~G). This study will give a systematic method on identification of radicals in AOPs, and shed light on the insightful understanding of radical production mechanism.},
	keywords = {Advanced oxidation processes, Electron paramagnetic resonance, Homogeneous, Radical, Ultraviolet},
	issn = {0043-1354},
	doi = {https://doi.org/10.1016/j.watres.2022.118747},
	url = {https://www.sciencedirect.com/science/article/pii/S004313542200700X},
	author = {Long Chen and Duan, Jun and Du, Penghui and Weiliang Sun and Bo Lai and Liu, Wen}
}
