Molecular transformation of dissolved organic matter during persulfate-based advanced oxidation: Response of reaction pathways to structure

•FT-ICR MS was used to reveal the transformation mechanism of DOM.•Spectral changes of three types of DOM exhibit obvious differences during PS oxidation.•Response of oxidation degree in DOM to free radicals was prior to molecular weight.•Pathways involved in PS oxidation were revealed based on 26 types of reactions.•FA and NOM are more prone to the reactions of carboxylic acid and amine, respectively. Persulfate (PS)-based advanced oxidation is an effective technology for remediating organically contaminated groundwater, which could induce the structural transformation of dissolved organic matter (DOM). Although the influences of DOM components on its structural transformation have been studied extensively, a comprehensive understanding, particularly at the molecular level, is still lacking. Here, selecting different DOM components including humic acid (HA), fulvic acid (FA), and natural organic matter (NOM), we comparatively analyzed the changes in structural characteristics during PS oxidation using optical spectroscopy and high-resolution mass spectrometry. The results showed a reduction in aromaticity and molecular weight of DOM during PS oxidation, with the largest decrease observed in NOM. The fluorescence intensity in HA increased, that of FA showed a decreasing and then increasing trend, while that of NOM significantly decreased after PS oxidation. Sequential oxidation responses of functional groups in DOM followed a specific order, with C-O of aromatic esters → C = O of polysaccharides or alcohols → C-C of quinone rings → C-O of aromatic ethers. The removal of low oxygen molecules (O/C