Enhanced nanofiltration membranes for Mg2+/Li+ separation: Development of a polyethyleneimine positively charged interlayer

Polyamide thin film composite (TFC) nanofiltration (NF) membrane possessing excellent permeance and monovalent/multivalent ions selectivity is eager for Mg 2+ /Li + separation. To achieve this purpose, we developed a TFC NF membrane with high water permeance, Mg 2+ rejection, as well as satisfied Mg 2+ /Li + separation factor by conducting the interfacial polymerization (IP) with polyethyleneimine (PEI600) and 1,3,5,-benzenetricarbonyl (TMC) on a positively charged interlayer constructed on PES/SPSF blending ultrafiltration substrate. On the one hand, the hydrophilic electropositivity interlayer can increase aqueous monomer adsorption capacity and inhibit the monomer diffusion rate, facilitating the formation of a thin separation layer. Therefore, the obtained NF-8 membrane exhibits the highest permeance of 8.8 L m −2 h −1 bar −1 , which is 2.8 times compared with the NF-0 membrane (3.1 L m −2 h −1 bar −1 ) prepared on PES-based substrate. On the other hand, the positively charged interlayer also imparts the NF-8 membrane a higher isoelectric point (IEP) of 7.9, as well as satisfied Mg 2+ rejection of 97.1 % and Mg 2+ /Li + separation factor of 87.1. This work demonstrates that the water permeance and ions selectivity of the TFC NF membrane can be enhanced by constructing a positively charged interlayer.