Revealing the Key Impact of Microplastic-Derived Dissolved Organic Matter Properties on Aromatic Pollutant Adsorption and the Underlying Mechanisms

Microplastics (MPs)-derived dissolved organic matter (MP-DOM) is pervasive in aquatic environments, yet its mechanisms influencing organic pollutant adsorption remain insufficiently understood. Herein, MP-DOM from polyethylene (PE), polystyrene (PS), and poly(ethylene terephthalate) (PET) was examined for its effects on bisphenol A (BPA) and naphthalene (NAP) adsorption onto covalent triazine frameworks (CTF), with humic acid (HA) as a conventional DOM reference. Adsorption experiments demonstrated that MP-DOM substantially suppressed the adsorption of aromatic pollutants onto CTF compared to HA. Correlation analysis indicated that DOM aromaticity and hydrophobicity predominantly governed BPA and NAP affinity (R2 = 0.90–0.99), outweighing molecular weight effects. Three-dimensional excitation and emission matrix (3DEEM) fluorescence spectra and two-dimensional correlation spectroscopy (2D-COS) analyses revealed that low-aromaticity, protein-like constituents in MP-DOM exhibit enhanced affinity toward pollutants. MP-DOM enhanced the maximum fluorescence intensity ratio (Fmax/F0) of protein-like substances by 2.61-fold to 5.65-fold relative to DOM-free samples, exceeding that of HA and indicating a greater affinity of MP-DOM that restricts contaminant diffusion. Moreover, MP-DOM facilitated pollutant desorption via a strong hydrophobic interaction. Overall, MP-DOM inhibited the adsorption of pollutants onto CTF, through reducing diffusion and enhancing desorption. These findings provide new insights into the mechanisms by which MP-DOM regulates the environmental behavior of aromatic contaminants in aquatic systems.