Trace PFOA synergistically intensifies nanoplastic-humic acid fouling in forward osmosis: Mitigation using a MXene-TiO2 substrate and a TA/Fe3+ interlayer

Multicomponent fouling arising from the coexistence of per- and polyfluoroalkyl substances (PFAS), nanoplastics (NPs), and natural organic matter (NOM) remains poorly understood and limits membrane-based water treatment. Here, these interactions and their mitigation are examined through coordinated substrate-interlayer engineering in forward osmosis membranes. A hydrogen-bonded MXene-TiO 2 (HMT) composite is incorporated into the polysulfone substrate to improve pore structure, hydrophilicity, and mass transfer, while a tannic acid/Fe 3+ interlayer regulates interfacial polymerization and surface chemistry. Control membranes are employed to decouple the individual and combined effects of these modifications. Fouling experiments under single, binary, and ternary conditions reveal that trace PFAS cause limited fouling independently whereas NPs and NOM produce stronger fouling individually and in combination, while PFOA synergistically intensifies this co-fouling when all three coexist. The modified membrane mitigates this behavior through enhanced hydration, reduced roughness, and a negative surface charge, resulting in lower foulant deposition under ternary conditions. As a result, the water flux of the optimized membrane increased from 5.7 to 11.3 L m -2 h -1 , the reverse salt flux decreased from 5.9 to 4.4 g m -2 h -1 , and the membrane exhibited lower flux decline during the 48-h ternary fouling test and ≥ 94% flux recovery during chemical-cleaning tests. Transport analysis ( A , B , and S ) confirms improved intrinsic selectivity and reduced internal concentration polarization, while microscopic observations verify reduced foulant deposition. These findings clarify how trace PFOA synergistically intensifies multicomponent co-fouling and offer a rational design strategy for next-generation membranes operating in complex water matrices.