Composite nanofiltration membranes via the co-deposition and cross-linking of catechol/polyethylenimine

High performance nanofiltration (NF) membranes are facilely fabricated via the co-deposition of catechol (CCh) and polyethylenimine (PEI) on the surface of a polysulfone (PSf) ultrafiltration membrane, with subsequent cross-linking by glutaraldehyde (GA). The surface properties of the studied membranes have been investigated in detail by Fourier transform infrared spectroscopy, X-ray photoelectron spectroscopy, scanning election microscopy, atomic force microscopy, zeta potential, and water contact angle. The NF performance of the membranes are dependent on the CCh/PEI ratio, co-deposition time and cross-linking condition. Results reveal that the optimum membrane yields a rejection of 88% and a permeation flux of 25 L m−2 h−1 when filtrating the 1000 mg L−1 MgCl2 solution at 0.6 MPa. And the negatively charged membrane surface is related to the following salt rejection sequence: MgSO4 > Na2SO4 > MgCl2 > CaCl2 > NaCl. Meanwhile, the membranes show excellent operation stability during a 240 h consistent filtration test.