Development of Borate-Based Basic Ionic Liquid for Room Temperature CO₂ Capture

As part of CO₂ capture strategies, ionic liquid-based CO₂ absorbents have gained attention for their tunable properties to lower the energy costs for CO₂ capture. In this study, a series of borate-based nonamine functionalized ionic liquids (ILs), incorporated with magnesium acetylacetonate, were developed and investigated for its CO₂ capture capability at moderate temperature under ambient pressure. Nuclear magnetic resonance and Fourier transform infrared spectroscopy confirmed the successful incorporation of acetylacetonate ligands into the fluorinated-lithium borate ionic liquids. Comprehensive analyses of the physical and thermochemical properties revealed that the synthesized ILs remain stable below 200 °C, with the borate structure and acetylacetonate ligands intact. The ILs functionalized with fluorinated alcohol and magnesium acetylacetonate enhance the CO₂ uptake capacity by 55% in comparison with the original lithium borate ILs, suggesting the enhanced cooperative interactions responsible for improved CO₂ capture performance. The carbon capture mechanism was identified to proceed via physical absorption, as evidenced by minimal changes in the characterization results and viscosity after CO₂ absorption. The enthalpy of CO₂ absorption (ΔH _a) for the synthesized ILs were determined experimentally by using differential scanning calorimetry to be in the range from -12.4 kJ mol^-1 to -18.9 kJ mol^-1, which are much lower than that of conventional amine solutions (e.g., MEA: -82 kJ mol^-1) and amine-based ILs ((e.g., [Bmim]-[Ac]: -45.8 kJ mol^-1). These findings suggest that lithium borate-acetylacetonate ILs offer a promising approach for a CO₂ capture system under ambient conditions.