Asymmetric polyamide nanofilm with coordinated charge and nanopore, tuned by azlactone-based monomer to facilitate ion separation

•Asymmetric polyamide nanofilm doped with azlactone based monomer exhibited an obvious bilayer structure.•The resultant membrane had varied charge and nanopore with increase of the doping content of the TMDMA.•MgCl2 rejection is as high as 97.41 ± 0.29 %, and LiCl rejection is 34.94 ± 1.02 %.•The water permeance on MgCl2 and LiCl are 343.6 ± 4.90, 396.6 ± 4.98 kg m–2h−1 MPa−1.•A good ion selectivity (141.1 for Cl–/SO42–, 58.7 for Li+/Mg2+) was achieved.