This work reports on a promising strategy for the development of novel grafted ionic liquid membranes (GILMs) in which phosphonate-based ILs are confined within the pores of a mesoporous gamma-Al2O3 ceramic membrane by chemical grafting. The effect of both the chemical nature (i.e., alkyl versus ether) of the organic spacer chain and the presence of phosphonate coupling functions were evidenced as crucial parameters influencing CO2 transport through the membranes. The effectiveness of the grafting procedure yielding GILMs was clearly demonstrated by Fourier transform infrared spectroscopy and high resolution-magic angle spinning NMR, and attractive membrane performance was evidenced through both the CO2/N-2 ideal selectivity (similar to 140) and CO2 permeability (similar to 130 Barrer).