Performance of MOF-containing active layer and HOF-based support layer of ultrafiltration membrane for nanoplastics removal from secondary effluent

Nanoplastics (NPs) are an emerging environmental contaminant of global concern due to their persistence and harmful effects on aquatic ecosystems. A novel dual-modified ultrafiltration membrane was developed for enhanced removal of NPs from secondary effluent collected from three wastewater treatment plants. The membrane was engineered with MIL-101(Cr), a metal-organic framework, in the active layer and a hydrogen-bonded organic framework derived from 4,4′,4″,4‴-(pyrene-1,3,6,8-tetrayltetrakis(ethyne-2,1-diyl))tetrabenzoic acid in the substrate layer. This study further identified and quantified the presence of three specific NPs in the collected effluent: poly(methyl methacrylate), polyethylene terephthalate, and polyvinyl chloride. Initial identification was performed using nanoparticle tracking analysis, and subsequently verified by using UV–Vis spectroscopy at specific absorbance peaks. Crossflow filtration tests showed excellent performance, achieving a permeability of ~1550 Lm −2 h −1 bar −1 and 97% NPs removal. This high efficiency arose from synergistic mechanisms of size-exclusion sieving, electrostatic repulsion, and the formation of a robust hydration layer that limited foulant adhesion. The membrane also exhibited excellent antifouling behaviour, maintaining a 97% flux recovery ratio after ten filtration cycles, while no chromium leaching was observed within pH 4–10, and 500–1500 ppm of NaOCl solution. These findings demonstrate the potential of dual-modified membranes as robust, high-efficiency filtration systems for long-term NPs removal in wastewater treatment plants.