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

Abstract

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.