Hierarchical PEG-PA/Fe3O4@PNF composite membrane with synergistic sieving-adsorption effect for efficient removal of aged nanoplastics

A hierarchical PEG-PA/Fe 3 O 4 @PNF composite membrane was fabricated for aged nanoplastics removal. • Synergistic surface sieving and depth adsorption achieve 99.89% removal of aged nanoplastics. • Fe 3 O 4 provides strong coordination sites for aged nanoplastics. Aged nanoplastics, characterized by their small size, abundant oxygen-containing functional groups, are high colloidal stability. These features make them difficult to remove by conventional membrane processes. Efficient removal usually requires membranes with very small pore sizes. This requirement causes a severe permeability and selectivity trade-off. Herein, a hierarchical PEG-PA/Fe 3 O 4 @PNF composite membrane was rationally engineered via electrospinning coupled with interfacial polymerization to achieve efficient removal of aged polystyrene nanoplastics (PSNPs). The membrane features a three-layer architecture consisting of a PEG-modified polyamide (PEG-PA) selective layer, a Fe 3 O 4 -loaded polyacrylonitrile nanofibrous (Fe 3 O 4 @PNF) adsorption layer, and a nonwoven support, enabling the integration of surface sieving and depth adsorption within a single membrane. PEG modification markedly improved surface hydrophilicity, reducing the water contact angle from 28.07° to 9.84%. As a result, water flux increased by 54.2% while simultaneously enhancing antifouling performance. Meanwhile, Fe 3 O 4 nanoparticles introduced abundant adsorption sites that effectively captured aged PSNPs through specific coordination interactions. Density functional theory (DFT) calculations further supported this proposed mechanism. Benefiting from the synergistic coupling of selective sieving and adsorption, the optimized membrane achieved an aged PSNP removal efficiency of 99.89% while maintaining a water flux of approximately 1142–1059 L m −2  h −1 at 0.4 MPa (the pure-water flux is 1199 L m −2  h −1 under the same pressure). Moreover, the membrane maintained a high removal efficiency under neutral and alkaline conditions (pH 7–11), exhibited good tolerance toward common inorganic ions except phosphate, and demonstrated satisfactory reusability. This study presents an effective strategy for integrating selective separation and targeted adsorption into thin-film composite membranes. The proposed design also provides new insights into the efficient remediation of aged nanoplastics with broad size distributions in complex aqueous environments.