Microplastic-derived dissolved organic matter mediates phenol oligomerization via coupled photo-redox pathways

Pollutant removal through polymerization represents a promising strategy for reducing carbon emissions and improving energy efficiency during water treatment. Given the ubiquitous presence of microplastics in aquatic ecosystems, however, it remains unclear whether such polymerization pathways emerge when dissolved organic matter derived from microplastics (MP-DOM) coexists with organic pollutants. Here, biodegradable and non-biodegradable microplastics, poly (butylene adipate-co-terephthalate) (PBAT) and polyethylene (PE), were selected as representative microplastics, with phenol employed as a model pollutant to investigate MP-DOM-mediated transformation mechanisms. By integrating Fourier transform ion cyclotron resonance mass spectrometry (FT-ICR-MS), UPLC-MS/MS, and FTIR, we simultaneously resolved MP-DOM molecular evolution and phenol transformation products. The results demonstrate that PBAT-DOM increased phenol removal from 22.8% (direct photolysis) to 91.1% under irradiation, likely involving the synergistic action of ¹O₂-mediated oxidation and photo-redox electron transfer, while itself undergoing carboxylation, methylation, and dehydration, suggesting its role as a photo-redox-active matrix. This process yielded hydroquinone and trimers, alongside an increased signal intensity of polymers ((C₆H₂)_n)-species in phenol photolysis with PBAT-DOM. Analogous polymerization products were observed with electron-withdrawing substituted phenols (e.g., p-Nitrophenol), indicating the generalizability of this pathway across structurally related contaminants. This study uncovers a previously overlooked function of MP-DOM as an active mediator of photochemical oligomerization via coupled photo-redox processes, offering novel mechanistic insights into microplastic-driven photochemistry and an improved framework for assessing the environmental behavior and ecological risks of microplastics in aquatic systems.