Electrospun nanofiber substrates that enhance polar solvent separation from organic compounds in thin-film composites

Organic solvent nanofiltration (OSN) with thin film composite (TFC) membranes containing a thin selective layer on top of a porous substrate is key to lowering energy costs of high-speed chemical separations. Conventional TFC membranes wereoften built on phase inversion induced asymmetrical substrates, with high tortuosity that impede rapid solvent transport. Nanofiber as ultrapermeable substrate has enhanced water transport in forward osmosis, nanofiltration and otheraqueous separations. However, problems of solvent stability in harsh operating conditions prevent their exploitation in non-aqueous molecular separations. Here we show that by combining a simple solution-phase cross-linking process andelectrospinning, the instability of nanofibrous polyacrylonitrile (PAN), in industrially-important polar solvents can be overcome and harnessed to benefit the purification of polar solvents containing low molecular weight solutes. The low tortuosity of electrospun PAN nanofibrous substrates is key to uniform cross-linking, hence are more stable and mechanically stronger than cross-linked PAN asymmetrical substrates fabricated by the traditional approach of phase inversion. The low resistance offered by cross-linked nanofibrous substrates increased solvent permeation withoutsacrificing selectivity, for example, to 99.5 % rejection of negatively-charge Sudan 4 (MW:380 Da) dyes with a methanol permeance of 9.87 L m-2 h-1 bar-1 and water permeance of 22.40 Lm-2 h-1 bar-1. The enhanced stability of TFC membranes inpolar aprotic solvents such as dimethylsulfoxide highlight their potential application for molecular separations in pharmaceutical and chemical industries.