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.