Crown ether-incorporated polyesteramide membrane enabling efficient ion separation through synergistic size sieving and host-guest recognition

Achieving efficient monovalent/divalent cation separation remains challenging due to the trade-off between membrane permeability and selectivity. Herein, we report a novel polyesteramide (PEA) nanofiltration membrane incorporating cyclic di(hydroxybenzo)-18-crown-6 (DHB18C6) via interfacial polymerization (IP) of piperazine (PIP), DHB18C6, and trimesoyl chloride (TMC). Molecular dynamics (MD) simulations reveal that DHB18C6 retards PIP diffusion via hydrogen bonding, yielding a thinner separation layer with narrower pore size distribution (mean pore diameter = 0.46 nm, σ p  = 1.348) compared to conventional PA membranes. The optimized PIP@DHB18C6-TFC membrane achieves exceptional MgCl 2 rejection (>99.0%) through size exclusion, while the 18-crown-6 cavities provide facilitated transport channels for K + due to optimal radius matching. In mixed-salt filtration tests (2000 ppm, mass ratio of 20:1), the membrane exhibits outstanding selectivities of 106.7 for K + /Mg 2+ , 90.0 for Na + /Mg 2+ , and 57.2 for Li + /Mg 2+ , significantly surpassing most reported nanofiltration membranes. The membrane maintains stable performance over 72-h continuous operation. This work demonstrates that integrating cyclic crown ethers into PEA networks offers a promising strategy for developing high-performance ion-selective membranes, with particular advantages for potassium recovery applications.