Thin‐Film Composite Polyionic Liquid Gel Membranes and Their Potential for Nanofiltration in Organic Solvents

Abstract Polymeric ionic liquid (PIL) gels can serve as a promising material for the fabrication of solvent resistance nanofiltration (SRNF) membranes, given the solubility and the high delocalization of the counterion of PILs in organic solvents. This research describes the fabrication of a new thin‐film composite membrane (TFC) with a crosslinked PIL (i.e., PIL gel) as an active layer and demonstrates its great potential as an SRNF membrane. A hydrophobic and positively charged thin‐film PIL gel (100–400 nm) is successfully grafted onto a polyethersulfone membrane. The grafting degree, surface charge, and cross‐linker density depend on the grafting conditions. This, it turn, governs the permeability and selectivity of the membranes tested in acetonitrile and ethanol solutions, good and poor solvents for the grafted PIL gel, respectively. These changes are attributed to the trade‐off between the membrane surface properties in the two solvents. In particular, the membrane that has a high grafting degree, surface charge, and cross‐linker density yields high permeance and rejection in acetonitrile. Furthermore, the membrane performance is stable in ethanol for one week. Due to the wide variety of PIL monomers, TFC membranes with different properties can be developed based on the solvent properties.