Fabrication of dual-charged MOF-based ultrafiltration membrane to remove charged nanoplastics from wastewater

The presence of nanoplastics (NPs) in municipal and industrial wastewater has raised significant concerns regarding their potential toxic effects on humans and various organisms. Herein, we synthesized dual-charged metal-organic framework (MOF)-based nanoparticles by anchoring ethylenediamine (ED) to the unsaturated metal sites of the MIL-101(Cr). These nanoparticles were then incorporated into a polyethersulfone (PES)/polyamide (PA) composite to fabricate ultrafiltration (UF) membrane for achieving an enhanced removal of charged NPs (polystyrene and polyethylene with positive and negative charge) from wastewater with high water permeability. The lab-scale tests on synthetic wastewater showed that the increased availability of water channels within the nanoparticle structure enhanced water permeability by 27 % compared to PES/PA-based membranes, attributed to the shortened pathways for water molecules. An optimum nanoparticle concentration of 0.2 % ( w / v ) yielded a membrane with exceptional permeability of 769 Lm −2 h −1 bar −1 . This membrane also effectively removed >99 % of both charged NPs using crossflow filtration. The grafting of ED onto the nanoparticles enhanced the repulsion of hydrophobic and charged NPs, effectively complementing the membrane-sieving mechanism. Furthermore, the membrane's hydrophilic and smooth surface provided excellent antifouling properties as indicated by a 92 % flux recovery ratio at the 10th cycle. The Composite membranes fabricated from PA/PES, incorporating uniformly dispersed MOF nanoparticles exhibited excellent stability and durability across a pH range of 4–10 and sodium hypochlorite concentrations ranging from 500 to 1500 ppm, under which nanoparticle leaching was effectively prevented. This research highlighted the potential of ED-MIL-101(Cr)-based PES/PA composite UF membranes for NPs removal while maintaining high water permeability. • Ethylenediamine grafting onto the MOF resulted in the synthesis of dual-charged MOF. • The ED-MIL-101(Cr) membrane effectively removed over 99 % of charged NPs. • Electrostatic repulsion and sieving were the dominant mechanisms for NPs removal. • The membrane maintained a negative surface charge across a wide pH range of 2–10. • The membrane demonstrated a 92 % flux recovery ratio after the 10th filtration cycle.