The development of alternative CO2 capture solvents such as ionic liquids(ILs) and nanoparticle organic hybrid materials(NOHMs) have provided interesting options for CO2 capture. In this study, CO2 interactions with 1,3-dimethylimidazolium dimethylphosphate([MMIM]DMP),1-ethyl-3-methylimidazolium dimethylphosphate([EMIM]DMP) and 1-ethyl-3-methylimidazolium diethylphosphate([EMIM]DEP) that contain inorganic ester groups based on phosphate, were investigated using ATR FT-IR spectroscopy. CO2-induced swelling, CO2 diffusivity and CO2 capture capacity were simultaneously measured to identify CO2 capture mechanisms, kinetics and diffusion behaviors as a function of the alkyl chain length of the cation. Henry’s law constants of CO2 were found to be in the range of 4-11 MPa, which is in agreement with those reported in other studies.