Ionic liquid cobalt complex as O2 carrier in the PIM-1 membrane for O2/N2 separation

Abstract Ionic liquids (ILs) are attractive and prospective materials used in membranes due to the nonvolatility, structure tunability, and the ability to tune the interface compatibility. The cobalt IL Bmim2Co(NCS)4 possesses the porphyrin-like N4-coordinated cobalt center which could selectively and reversibly interact with O2. Herein the Bmim2Co(NCS)4 as liquid-phase oxygen carrier was used to fabricate thin-film composite (TFC) membrane with the polymer of intrinsic microporosity (PIM-1). The microstructures, properties and gas separation performance of the membrane were compared with the TFC membrane which takes cobalt porphyrin (T(4-Cl)PPCo) as a carrier. We found that the addition of a small amount of T(4-Cl)PPCo can enlarge the d-spacing of packed chains of PIM-1 and significantly increase the fractional free volume (FFV) and the gas permeability of the membrane, but the selectivity is unsatisfactory. It is worth noting that adding Bmim2Co(NCS)4 into the polymer can increase greatly the O2/N2 selectivity which is higher than that of the membrane with T(4-Cl)PPCo. Although the addition of Bmim2Co(NCS)4 decreases the d-spacing of packed chains of PIM-1, resulting in the slight decline of FFV and gas permeability of the membrane, the Bmim2Co(NCS)4/PIM-1 TFC membranes exhibit better O2/N2 separation performance than the T(4-Cl)PPCo/PIM-1 TFC membranes in consideration of the Robeson upper bound.