Reversible CO₂ Capture by Conjugated Ionic Liquids through Dynamic Covalent Carbon–Oxygen Bonds

Abstract

The strong chemisorption of CO2 is always accompanied by a high absorption enthalpy, and traditional methods to reduce the absorption enthalpy lead to decreased CO2 capacities. Through the introduction of a large π-conjugated structure into the anion, a dual-tuning approach for the improvement of CO2 capture by anion-functionalized ionic liquids (ILs) resulted in a high capacity of up to 0.96 molCO2 mol-1IL and excellent reversibility. The increased capacity and improved desorption were supported by quantum chemical calculations, spectroscopic investigations, and thermogravimetric analysis. The increased capacity may be a result of the strengthened dynamic covalent bonds in these π-electron-conjugated structures through anion aggregation upon the uptake of CO2 , and the improved desorption originates from the charge dispersion of interaction sites through the large π-electron delocalization. These results provide important insights into effective strategies for CO2 capture.

High Performing CO2 Capture by Smart Strategies in Functionalized Ionic Liquids

“…Proposed reaction between the first TSIL [apbim][BF4] and CO2. [6] Smart strategies including basicity tuning/dual tuning methods, [8,9] multi-site cooperative interactions, [10][11][12] and intramolecular hydrogen bonding/intra-molecular proton transfer [13,14] has been employed into ILs for CO2 capture. For examples, Dai et al [8] investigated the relationship between the enthalpy of CO2 absorption and the pKa value in a series of non-amino functionalized ILs and concluded that it is possible to achieve both efficient CO2 uptake and energy-saving release by simply tuning the basicity of the anion of IL.…”

“…For examples, Dai et al [8] investigated the relationship between the enthalpy of CO2 absorption and the pKa value in a series of non-amino functionalized ILs and concluded that it is possible to achieve both efficient CO2 uptake and energy-saving release by simply tuning the basicity of the anion of IL. Wang et al [9] disclosed that conjugated ILs could reversibly capture high molar capacity of CO2 through dynamic covalent carbon-oxygen bonds by taking advantage of the dual-tuning roles of large π-conjugated anions. Cui and co-workers [12] demonstrated a novel strategy based on cooperative interactions between CO2 and multiple active sites in the pre-organized anion for highly efficient and reversible capture of low-concentration CO2.…”

“…Structure of anion and cation in large π-conjugated anion-functionalized ILs for CO2 capture. [9] A class of tunable basic ILs such as [P66614][Triz] was developed for equimolar CO2 capture as well as excellent reversibility. 25 cycles of CO2 absorption and desorption demonstrate the CO2 capture process by [P66614][Triz] is highly reversible ( Figure 5).…”

“…With regard of the low stability of some anions such as phenolate and imidazolate during CO2 uptake, Pan et al [9] designed a dual-tuning strategy to achieve both enhanced molar capacity of CO2 and excellent cycling life by introduction of a large π-conjugated structure into the anion of IL (Scheme 6). The high molar capacity of CO2 may be as a result of the strengthened dynamic covalent bonds through anion aggregation and the excellent reversibility orginates from π-electron delocalization through charge dispersion.…”

Absorption and thermodynamic properties of CO2 by amido-containing anion-functionalized ionic liquids

“…[5][6][7][8][9] In light of the reaction mechanism of CO 2 in alkanolamine solutions and the outstanding properties of ILs, Davis et al 10 rst reported imidazolium ILs with amino-graed cation for the chemical absorption of CO 2 . Since the anion plays a key role in carbon capture, worldwide researchers have developed many kinds of task-specied ILs with the functionalized anions such as amino acids, [11][12][13][14] azolates, [15][16][17][18][19][20] phenolates, 7,[21][22][23] and acetate. 24 Compared with conventional ILs, these anion-functionalized ILs typically have high CO 2 absorption capacity and selectivity.…”