Amine-impregnated adsorbents are promising alternatives to aqueous amines for CO2 capture. However, the diffusion-controlled CO2 adsorption process is a significant issue associated with them, resulting in the insufficient utilization of amine groups. Herein, we propose the use of functionalized ionic liquids 1-ethyl-3-methylimidazolium acetate ([emim][Ac]) with chemical reactivity to CO2 and low viscosity as the additive to amine-impregnated adsorbents. The key is that [emim][Ac] does not show drastic increase in viscosity after reacting with CO2. Taking the polyethyleneimine (PEI)-impregnated SBA-15 as a model system, it is found that the CO2 capacities of PEI/SBA-15 composites are improved by 86%, and the active site efficiencies are improved by 270%, after the addition of [emim][Ac]. The addition of [emim][Ac] to PEI/SBA-15 composites also helps improve the CO2 adsorption rate and recycling stability of composites. Therefore, [emim][Ac] offers the opportunity to fabricate amine-impregnated adsorbents with simultaneously improved CO2 capacities, adsorption kinetics, and recycling stability. (c) 2018 American Institute of Chemical Engineers AIChE J, 64: 3671-3680, 2018