CO2 Separation Membranes Consisting of Ionic Liquid/CdO Composites

CdO nanoparticles were utilized in the fabrication of a composite membrane containing the ionic liquid 1-butyl-3-methylimidazolium tetrafluoroborate (BMIM+BF4-) for CO2 separation. The use of BMIM+BF4- containing CdO nanoparticles as a CO2 separator greatly improved separation performance. The ideal selectivity for CO2/N-2 was 32.5 with a CO2 permeance of 57.1 GPU when CdO nanoparticles were incorporated into the BMIM+BF4- liquid. The enhanced separation performance was attributed to increased CO2 solubility facilitated by both the free ions in BMIM+BF4- and the oxide layer of the CdO nanoparticle. The CdO nanoparticles were identified with transmission electron microscopy and the physical and chemical properties of the membranes were investigated using scanning electron microscopy, Raman spectroscopy and TGA. Interestingly, we found a correlation between CO2 permeance and electronegativity differences between the metal and oxygen for CO2 separation membrane. The electronegativity differences between the metal and oxygen was ZnO (1.79) > CdO (1.75) > CuO (1.54) > AgO (1.51). The order of CO2 permeance was ZnO in BMIM+BF4- (101 GPU) > CdO in BMIM+BF4- (57.1 GPU) > CuO in BMIM+BF4- (52.4 GPU) > AgO in BMIM+BF4- (14.1 GPU).