Multiple-site absorption of CO2 in 2-hydroxypyridium ionic liquids based task-specific deep eutectic solvents

Global warming caused primarily by excessive emissions of CO 2 has attracted worldwide attention. Herein, three 2-hydroxypyridium ionic liquids (ILs) based task-specific deep eutectic solvents (DESs) were synthesized to absorb CO 2 and physical properties including density, viscosity, and melting points were measured to explore the effect on CO 2 absorption. The CO 2 absorption capacities of the ILs-based task-specific DESs were investigated at different pressures and temperatures, which showed that the maximum absorption capacity of the DES was up to 1.48 mol CO2 ·mol DES −1 or 0.233 g CO2 ·g DES −1 at the atmospheric pressure and 25 °C. The plausible absorption mechanism was also proposed by a combination of 1:1 and 2:1 stoichiometric reactions of CO 2 and the IL-based task-specific DES via multiple-site absorption, which was confirmed by 13 C and 1 H nuclear magnetic resonance (NMR), Fourier transform infrared (FT-IR) spectroscopy, quantum chemical calculation, and reaction equilibrium thermodynamic modeling. The thermodynamic properties, including absorption Gibbs free energy, absorption enthalpy, and absorption entropy were rationally deduced and explained. Furthermore, the excellent CO 2 absorption capacity and regenerability of multiple-site task-specific DES make it a new environmentally eco-friendly choice for highly efficient CO 2 absorption and subsequent CO 2 transformation. • Three ILs-based task-specific DESs were prepared for CO 2 absorption. • ILs-based task-specific DESs have multiple-site CO 2 absorption. • Absorption mechanism was proposed by combined 1:1 and 2:1 reactions of CO 2 and DES. • Reaction equilibrium thermodynamic modeling was clarified. • The multiple-site task-specific DESs exhibited excellent absorption capacity and regenerability.