Polyamide nanofiltration membrane fine-tuned via mixed matrix ultrafiltration support to maximize the sieving selectivity of Li+/Mg2+ and Cl–/SO42–

Herein, we report polyamide (PA) nanofilms with nanostripe, fine-tuned aperture and surface charge, formed on the mixed matrix ultrafiltration (UF) membranes (MMMs) doped with ZIF-8 or UIO-66-NH2. Due to the increased polarity and the surface pore narrowed, the distribution and content of the aqueous amine molecules on the MMMs are different with that of the pristine UF membrane. The PA nanofilm formed on the MMMs thus exhibits a uniform nanostripe and a thinner thickness. The experimental data show that water fluxes of the PA nanofilms formed on the MMMs exhibited 2.18–2.67 times that of the PA nanofilm formed on the pristine UF membrane. And a significantly increased separation factor on Li+/Mg2+ (78.6 at Mg2+/Li+ ratio of 30.6, under mixed solution of 10.5 g L−1) and Cl−/SO42− (377.8 for the mixed solution containing 2.0 g L−1 NaCl and 2.0 g L−1 Na2SO4) was achieved, which surpassed some of the commercial PA membranes (NF 270, XC-N, DK, and DL) and most of the literature reported membranes. This work demonstrates that the MMMs uniformly loaded UIO-66-NH2 or ZIF-8 nanoparticles enable to tune the structure characteristic of the interfacially polymerized PA nanofilm, and then facilitate ion sieving.