Multi-molar absorption of CO2 by a novel dual-functionalized ionic liquid solution: Experimental and DFT mechanistic study

Viscosity and absorption capacity are the main indexes to evaluate functionalized ionic liquids. Based on the precise design strategy of both anion and cation absorption, a dual-functionalized protic IL diethylenetriamine methylurea ([DETAH][MEUR]) for trapping CO₂ was successfully synthesized. The absorption and regeneration properties of the ILs solution were tested, and the changes in the physical properties of ILs before and after CO₂ absorption were compared. The experimental results showed that the [DETAH][MEUR] solution had relatively low viscosity, excellent absorption property with 2.05 mol CO₂/mol IL at 40 °C and 0.5 mol/L concentration, and its regeneration efficiencies still kept above 90.09 % after five cycles. In addition, the mechanism of the absorption reaction was explored by combining Fourier transform infrared (FT-IR) spectroscopy, carbon nuclear magnetic resonance (¹³C NMR) spectroscopy, and density functional theory (DFT) calculation methods. It shows that in [DETAH][MEUR] solution, the N atom losing proton (-NH) in the anion is the main absorption site, and the primary amine (-NH₂) in the protonated cation [DETAH]⁺ of secondary amine is used as an auxiliary cooperative trapping CO₂. Hopefully, this work can provide a new way for the research and development of green CO₂ absorbents.