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

Herein, we report an asymmetric polyamide (PA) nanofilm formed by using trimesoyl-[4,4-dimethyl-5(4H)-azlactone] (TMDMA) and trimesoyl chloride (TMC) as mixed organic phase. Of which, the sublayer is dendrimer porous layer and the top layer is a nanostriped interfacial polymerization (IP) PA nanofilm. Due to the higher acidity coefficient (pKa) of the hydrolyzed TMDMA, the resultant optimized asymmetric PA nanofilms have coordinated surface charge and narrowed mean effective nanopore. Experimental data demonstrate that the 0.1TMC/0.0125TMDMA–0.8 piperazine (PIP)-15 had a high MgCl2 rejection (97.41 ± 0.29 %) and a lower LiCl rejection (34.94 ± 1.02 %), and the corresponding water permeances were 343.6 ± 4.90 and 396.6 ± 4.98 kg m–2h−1 MPa−1, respectively. Moreover, a significantly enhanced Li+/Mg2+ selectivity was achieved, up to 58.7 under a LiCl/MgCl2 solution of 10.5 g L–1, while the related water permeance was 174.66 kg m–2h−1 MPa−1, which was superior to the most literature reported membranes and part of common commercial PA membranes (DK, DL and NF 90). Besides, the resultant membranes also showed an excellent sieving performance of Cl–/SO42– (141.1). This work demonstrates that the azlactone-based monomer enables to coordination of the inner structure of the IP PA nanofilm, thus facilitating ion sieving.