To screen the efficient media for CO2 capture of flue gas from power plants, a strategy for improving the CO2 capture capacity by dual functionalized ionic liquids (ILs) with multiple active sites is proposed. Three phosphonium dual functionalized ILs ([aP(4443)] [2-Np], [aP(4443)] [2-Op], and [aP(4443)][Triz]) have been prepared. The sorption capacities of the synthesized ILs under pure CO2 atmosphere and the supported ILs under different loading amounts from 10 to 50%, temperatures of 30-80 degrees C, and CO2 partial pressure varied from 10 to 15% were determined. Fourier transform infrared (FTIR) spectroscopy was applied to reveal the interaction between CO2 and ILs, and the pseudo-second-order model and the intraparticle diffusion model were used for a better understanding of the CO2 adsorption behavior. The results showed that a high capacity up to 1.88 mol of CO2/mol of IL for [aP(4443)][2-Np] is achieved, and 30% IL-MCM-41 can reach 3.19 mmol/g with excellent reversibility under the atmosphere of CO2:N-2 (159/0:85%) at 30 degrees C and 0.1 MPa. Raising the temperature or decreasing the CO2 concentration is not conducive to improving the CO2 capacity. FTIR spectroscopy demonstrated that the amino and hydroxyl react with CO2 to form NHCOO- or CO3-. Combined with the activation energy calculation, the kinetic analysis revealed that the CO2 capture of supported ILs is an internal diffusion controlled physical adsorption.