Ionic liquid 1-butyl-3-methylimidazolium tetrafluoroborate (BMIMBF4) was utilized for preparation of composite membranes containing ZnO nanoparticles. The separation performance for CO2 molecules for these composite membranes was investigated. It was found that when ZnO nanoparticles were generated into BMIMBF4, the selectivity of CO2/N-2 and CO2 permeance of the composite were significantly enhanced to 42.1 and 101, respectively, compared to the neat BMIM+BF4- membrane that had a CO2/N-2 selectivity and CO2 permeance of 5.0 and 17.0, respectively. These enhancement for CO2 separation was attributable to two factors: (1) the oxide layer of ZnO and (2) free ions of BMIMBF4 to increase the CO2 solubility. The chemical and physical properties of the membrane were characterized using TEM, SEM, FT-Raman, and TGA. (C) 2017 Elsevier B.V. All rights reserved.