Gelled Graphene Oxide-Ionic Liquid Composite Membranes with Enriched Ionic Liquid Surfaces for Improved CO2 Separation

Blends containing ionic liquid (IL) 1-ethyl-3-methyimidazolium tetrafluoroborate [emim][BF4] gelled with Pebax 1657 block copolymers were modified by adding graphene oxide (GO) and fabricated in the form of thin film composite hollow fiber membranes. Their carbon dioxide (CO2) separation performance was evaluated using CO2 and N-2 gas permeation and low-pressure adsorption measurements, and the morphology of films was characterized using scanning electron microscopy, atomic force microscopy, and transmission electron microscopy. Upon small addition of GO into the IL-dominated environment, the interaction between IL and GO facilitated the migration of IL to the surface while suppressing the interaction between IL and Pebax, which was confirmed using Fourier transform infrared spectroscopy and X-ray photoelectron spectroscopy. Amplified migration of IL to the surface and better dispersion of GO stacks were further achieved under alkaline conditions. With the enriched IL on the surface, the gas permeation through the films at 0.5 wt GO and approximately 80 wt % IL loading reached 1000 GPU for CO2 with their CO2/N-2 selectivity (up to 44) approaching that of pure IL.