MOF-808/Polyamide Thin-Film Nanocomposite Membranes for Efficient Nanofiltration

Metal-organic frameworks (MOFs) have attracted tremendous interest in preparing a thin-film nanocomposite (TFN) membrane. Especially, the membrane performance could be optimized by using MOFs as modifying agents, which takes advantage of their adjustable and regular pore structure, good compatibility with polymers, and superb functional designability. In this study, a tailored TFN polyamide membrane for nanofiltration was successfully fabricated via interfacial polymerization by incorporating MOF-808 into the selective layer on top of a poly(m-phenylene isophthalamide) (PMIA) substrate. An MOF-808 nanoparticle with a size of approximately 60 nm and a high specific surface area of 1666 m²·g^-1 was synthesized using a two-step green method and embedded into the polyamide layer. The surface morphology of the resultant TFN membrane evolved from the nodular structure to a particle aggregation configuration with increased roughness and enhanced hydrophilicity when adding more MOF-808. In particular, the membrane prepared with 0.02 wt % MOF-808 exhibited exceptional water permeance with 17.63 LMH·bar^-1 with a well-maintained Na₂SO₄ rejection of 97.67%, which is superior to commercial membranes and most TFN membranes reported in the literature. The molecular dynamics simulation results showed that the introduction of the MOF-808 filler can significantly enhance the mass transfer of water in the TFN membrane. In addition, the newly designed TFN membrane possessed excellent ion separation performance and superior long-time stability. The findings in this study demonstrate a strategy to regulate the membrane structure, which will provide an impetus for the MOF-based TFN membrane in water treatment and desalination applications.