Low-viscous fluorine-substituted phenolic ionic liquids with high performance for capture of CO2

• The viscosities of the phenolic ionic liquids are less than 64.8 cP at 303.2 K.
• The absorption equilibrium times are within 230 s at 313.2 K.
• The CO2-absorption molar ratio of [P4444][4-F-PhO] is as high as 0.842.
• The ILs could be carried out with no obvious loss in the absorption of CO2.

Three fluorine-substituted phenolic ionic liquids, namely tetrabutylphosphonium 2-fluorophenolate ([P4444][2-F-PhO]), tetrabutylphosphonium 3-fluorophenolate ([P4444][3-F-PhO]), and tetrabutylphosphonium 4-fluorophenolate ([P4444][4-F-PhO]), were synthesized in this work. The ionic liquids prepared were characterized by 1H NMR, 13C NMR, FT-IR, and ESI-MS spectroscopies and their physical properties including densities, viscosities and decomposition temperatures were also determined. The viscosities of the three fluorine-substituted phenolic ionic liquids are not more found to be less than 64.8 cP at 303.2 K. As a result, the rate of CO2 absorption is very fast and the absorption equilibrium time is within 230 s at 313.2 K. The CO2-absorption capacity of [P4444][2-F-PhO], [P4444][3-F-PhO], [P4444][4-F-PhO] at 1.0 bar and 313.2 K are as high as 0.673, 0.741, 0.842 in molar ratio, respectively. Furthermore, the ionic liquids were carried out for five cycles with no obvious loss in the absorption capacity of CO2. Quantum chemical calculations and spectrum study are also used to investigate the interaction between phenolic ionic liquids and CO2 molecules.