Polyamide Nanofiltration Membranes by Sulfonated Covalent Organic Framework Nanosheet Interlayer

To address uncontrollable layer thickness and "permeability-selectivity" trade-off in traditional interfacial polymerization （IP） process for polyamide （PA） nanofiltration membranes, sulfonated covalent organic framework （COF） nanosheets with ordered nanochannels were used as functionalized interlayers to prepare high-performance nanofiltration membranes. Based on the morphological and structural evolution, the functional groups within the sulfonated COF nanosheet interlayer could uniformly enrich piperazine （PIP） monomers, while its confined nanochannels could mitigate piperazine （PIP） transport kinetics. This synergy effectively regulated the IP process, inducing an ultra-thin （<30 nm） PA layer with finely nodular morphology and high cross-linking degree （72.73%）. At 5 μg·cm⁻² loading, the PAN-COF-PA membrane achieved 44.3 L·m⁻²·h⁻¹·bar⁻¹ water permeability （3-fold increase over PAN-PA） and 96.2% Na₂SO₄ rejection. The membrane showed excellent compact resistance and long-term stability. This COF-mediated interfacial polymerization provides a strategy for fabricating next-generation high-permeability nanofiltration membranes.