Abstract:four kinds of imidazolium-based anion-functionalized ionic liquids were prepared with ethyl tributylphosphonium ([P4442]+) as cation and imidazole ([Im]-), 4-methylimidazole ([4-MeIm]-),4-bromimidazole ([4-BrIm]-) or 4-nitroimidazole ([4-NO2Im]-) as anions. The density, viscosityand carbon capture properties of ILs were measured. The effects of substituents on the 4th position of ani⁃ons on carbon capture properties of ILs were investigated. The carbon capture mechanism of [P4442][Im]was studied by13C NMR and FT-IR. The results showed that the order of carbon capture capacity of ILsat 30 °C and 0.1 MPa was as follows: [P4442][Im] > [P4442][4-MeIm] > [P4442][4-BrIm]>[P4442][4-NO2Im], indicating that the weak electron-pushing effect of methyl group could notimprove the carbon capture performance, while the electron-withdrawing effect of bromine or nitrogroup could significantly inhibit carbon capture capacity by dispersing negative charge density ofanions. The substituents on 4th position increased the density and viscosity of ILs. The saturated CO2absorption of [P4442][Im] was as high as 1.0 mol CO2/mol IL. [Im]-could chemically interact with CO2, thereby enhancing the carbon capture ability. Close-