Highly CO2 selective membranes by potassium cations as carriers for facilitated transport with Ag2O particles and free ions in ionic liquid

•CO2 separation membranes consisting of ionic liquid BMIMBF4/Ag2O/KF composite.•Potassium cations as CO2 carriers for facilitated transport.•Enhanced solubility of CO2 molecules by both Ag2O particles and free ions in ionic liquid.

The highly selective composite membranes consisting of ionic liquid 1-butyl-3-methyl imidazolium tetrafluoroborate (BMIM+BF4−)/Ag2O/KF were prepared for CO2 separation. When Ag2O and KF were incorporated into BMIM+BF4−, the ideal selectivities of CO2/N2 and CO2/CH4 reached 105 and 52, respectively, with a CO2 gas permeance of 31 GPU. These enhanced separation performance were attributable to synergistic effect of (1) K+ cations in KF as CO2 carriers for facilitated transport and (2) the oxide layer of the well-dispersed Ag2O and free ions in ionic liquid for improvement in CO2 solubility. The coordinative interactions in the BMIM+BF4−/Ag2O/KF membrane were characterized by TGA, XPS, and FT-Raman spectroscopy.