Tetra-PEG Ion-Gel Thin-Film-Composite Hollow-Fiber Membrane

A hollow-fiber membrane with a thin poly(ethylene glycol) (PEG) layer containing an ionic liquid termed tetra-PEG ion-gel thin-film-composite (TFC) hollow-fiber membrane was fabricated in this study. The key strategy to form a thin PEG layer on the surface of the hollow-fiber membrane was using tetra-PEG hydrogel nanoparticles fabricated through the reaction between thiol-terminated tetra-PEG (tetra-PEGSH) and an excess molar amount of maleimide-terminated tetra-PEG (tetra-PEGMA). Tetra-PEG nanogels were filtered through a hollow-fiber membrane for forming a thin hydrogel cake layer on the inner wall. Although the CO2 permeability of the tetra-PEG layer was low because of the semicrystalline structure of the tetra-PEG network, impregnation with an ionic liquid (1-ethyl-3-methylimidazolium tricyanomethananide; [Emim][C(CN)3]) suppressed crystalline formation and increased CO2 permeability. The thickness of the ion-gel layer was controlled by varying the concentration of the tetra-PEG nanogel suspension and the filtration time. The [Emim][C(CN)3] content in the ion-gel layer was controlled by optimizing the [Emim][C(CN)3] impregnation conditions. The hollow-fiber membrane prepared under optimized conditions had a CO2 permeance of 207 GPU and a CO2/N2 permselectivity of ∼45. The large specific membrane area can compensate for the low CO2 permeance if an ion-gel tetra-PEG layer is formed on a thinner hollow-fiber membrane.