Designing bioinspired nanofiltration membrane for enhanced water permeance and efficient ion sieving

The precise separation of molecules or ions using nanofiltration (NF) membranes at a sub-Angstrom scale is a crucial aspect of water purification. Drawing inspiration from the rapid water transfer phenomenon observed in aquaporins found in nature, in this study, the incorporation of bola-amphiphile-imidazole-ureido (IU) into the polyamide (PA) layer was carried out via interfacial polymerization (IP). IU groups provided hydrogen bonds, which facilitated the rapid water transfer, and enabled the appropriate physical confinement transport channels that mimic the confined cavity structures of the biological selectivity filter for ions sieving. When the loading of IU reached 1.0 mg mL−1 (8.5 wt% IU/PA), the water permeance reached its highest value of 7.65 L m−2h−1 MPa−1 at 25 ℃, which was 1.5 times that of the pristine PA membrane. The rejection rates of 1.0 mg mL−1 IU-containing PA membrane for Na2SO4, MgSO4, and NaCl were 99.67 %, 99.3 %, and 98.46 %, respectively. At varying NaCl concentrations of up to 4000 ppm and throughout 210-hour continuous test, the 1.0 mg mL−1 IU-containing PA membrane maintained close to 100 % NaCl rejection, highlighting its great applicability in industry. This work offered an effective and promising synthesis strategy to obtain bioinspired nanofiltration membrane with excellent water performance and efficient ion sieving performance.