Double-Modified Composite Membranes with Organic Framework Nanoparticles for Nanoplastics Removal: Insights from Density Functional Theory Modeling

In this study, we developed a novel dual-modified composite membrane by integrating hydrogen-bonded organic framework (HOF) and metal–organic framework (MOF) nanoparticles to enhance water permeability, nanoplastics (NPs) removal and antifouling properties. Polysulfone (PSF) substrates were modified with 4,4′,4″,4‴-(pyrene-1,3,6,8-tetrayltetrakis(ethyne-2,1-diyl))tetrabenzoic acid-based HOF nanoparticles, improving substrate porosity and surface hydrophilicity. Simultaneously, the active polyamide (PA) layer was functionalized with MIL-101(Cr) MOF nanoparticles to achieve a smoother and more hydrophilic surface with increased negative charge. Optimal integration of 0.2 w/v % HOF and MOF nanoparticles into the substrate and selective layer, respectively, yielded a membrane with a remarkable water permeability of 1520 L m–2 h–1 bar–1, a 3.6-fold enhancement over pristine PSF membranes. The membrane achieved 99% removal efficiency for polystyrene and polyethylene NPs in synthetic wastewater, attributed to synergistic size exclusion, electrostatic repulsion and reduced foulant adsorption due to a robust hydration layer. Exceptional antifouling performance was demonstrated with a flux recovery ratio of 94% after 10 filtration cycles. Density functional theory calculations confirmed significant repulsive interactions between the composite membrane and NPs, validating the observed high removal efficiency. Furthermore, the composite membrane maintained stability under harsh conditions, withstanding a pH range of 4–10 and NaClO concentrations of 500–1500 ppm, without nanoparticle leaching. These findings highlight the innovative double modification approach for efficient NPs removal from wastewater while ensuring high permeability and fouling resistance.