Polyamide-based nanofiltration membranes with acicular leaf-like structure for rapid and selective separation of mono-divalent salts

Conventional polyamide-based nanofiltration (NF) membranes frequently encounter significant trade-off constraints between selectivity and permeability, which impedes their widespread adoption. In this study, we present a method for the construction of membrane surfaces with regular acicular leaf-like structures via interfacial polymerization reactions. This approach involves the induction of KCl crystal growth and the sacrifice of crystal templates, resulting in the formation of NF membranes with enhanced water permeability and pleasing mono-divalent salts selectivity. The molecular dynamics simulation and the observation of the membrane surface morphology revealed that the orderly grown KCl crystal templates successfully helped to form a regular acicular leaf-like structure on the membrane surface after the sacrificial treatment. As a result, polyamide-based NF membranes with a high permeable area were produced. The enhanced permeable area, diminished membrane thickness, and concentrated pore size distribution were identified as the key factors for the high permeability of 14.6 LMH/bar. And the mono-divalent salts separation coefficients (α(NaCl/Na 2 SO 4 )) of the membranes reached 97.8, which is outstanding compared to most currently reported polyamide-based NF membranes. The ultrahigh permselectivity NF membranes prepared by means of crystal template sacrifice are expected to provide a powerful aid for ion separation, desalination and drinking water treatment.