Fabrication of composite polyamide/Kevlar aramid nanofiber nanofiltration membranes with high permselectivity in water desalination

Conventional piperazine (PIP)-based nanofiltration (NF) membranes feature a high water flux and a high retention for divalent salt ions. However, it remains a challenge to obtain permselective NF membranes with high water permeance and a good selectivity for monovalent ions. In this work, a new m-phenylenediamine (MPD)-based thin-film composite (TFC) NF membrane with excellent desalination performance was developed by interfacial polymerization on a solvent resistant Kevlar nanofibrous hydrogel substrate. The desalination performance of the ANF TFC membrane shifted from reverse osmosis (RO) into NF with a facile solvent treatment. The decreased membrane surface roughness, reduced surface zeta potential and increased surface hydrophilicity after solvent treatment yielding a high water permeability (14.4 L m−2 h−1 bar−1) for ANF TFC membrane, which is one order of magnitude higher than that of the pristine membrane and the hand-cast poly (m-phenylene isophthalamide) (PMIA) TFC membrane. The ANF TFC membrane showed an outstanding water-salt separation performance, with excellent rejections for multivalent salts (Na2SO4, 100%; MgSO4, 99.4%; MgCl2, 92.7%) and a high rejection for monovalent salt (NaCl, 80.3%), which is competitive with reference commercial membranes (NF90, NF270) tested in cross-flow filtration with 1000 mg L−1 salt solution at 6 bar, 25 °C. The newly developed TFC membrane was demonstrated to have great potential applications in water desalination, separation of organic compounds and dye wastewater treatment.