The absorption of carbon dioxide (CO2) in an amino-cation and amino-anion dual functionalized ionic liquid (IL) (3-aminopropyl) tributyl phosphonium glycinate ([aP(4443)][Gly]) in aqueous medium was tested at temperatures (278.14 to 348.05) K and pressures (0.103 to 7.747) MPa. The water mass fractions of the tested aqueous solution were 0.599, 0.801, 0.900, and 0.950, respectively. It is found that the CO2 solubility in the bulk solution of this IL is considerably depressed by the deactivation of amino-cations and amino-anions due to the IL ion aggregation, when water content and temperature are low. The degree of deactivation of the IL ions was defined with an inactive factor of IL ion aggregation. In rich water content, the deactivation of the amino-ions reacting with CO2 can be overcome considerably. The carbonation in the solution can be doubled due to the neutralization of the dual amino-bases. The equilibrium constant of the acid-base reaction was determined by a potentiometric titration. A modified electrolyte nonrandom two-liquid (eNRTL) model was proposed for correlation of the experimental data by taking into account the inactive factor of IL ion aggregation and a correlative coefficient of the Henry's law constant of CO2 in the functionalized IL solution.