Facilitated O2 transport membrane containing Co(II)-salen complex-based ionic liquid as O2 carrier

Abstract

Novel metal-containing ionic liquids (MCILs) with O2 absorbability were synthesized by mixing a N,N′-bis(salicylidene)ethylenediamine cobalt(II) (Co(salen)) complex and ionic liquid-based ligands. The couple of anions of the ionic liquid-based ligands, trihexyl(tetradecyl)phosphonium N-methylglycinate and trihexyl(tetradecyl)phosphonium bis(trifluoromethanesulfonyl)imide, coordinated to Co(salen) complex and gave negative charge to the neutral Co(salen). The negatively chaged Co(salen) complex with the ionic liquid-based ligands and the bulky trihexyl(tetradecyl)phosphonium cation allowed to form Co(salen) complex-based MCILs. The MCILs could chemically and selectively absorb a large amount of O2 and could function as an O2 carrier in supported MCIL membranes. The O2 permeability of the MCIL-based facilitated O2 transport membranes were higher than those of conventional fixed-O2 carrier membranes as well as polymer membranes. The fast O2 transportation could be realized from the high diffusivity of the O2 complex, which was formed via the reaction between MCIL and O2, owing to the liquidity of the MCILs.