Effect of Hydrogen Bonds on CO₂ Capture by Functionalized Deep Eutectic Solvents Derived from 4-Fluorophenol

Abstract

Deep eutectic solvents (DESs) have received a great amount of attention for CO 2 uptake due to their unique properties. Here, deep eutectic solvents (DESs) based on 4-fluorophenol-derived superbase ionic liquid are studied for CO 2 capture. The ionic liquid used is [DBUH][4-F-PhO], formed by 1,8-diazabicyclo[5.4.0]undecane-7-ene (DBU) and 4-fluorophenol (4-F-PhOH). The DESs are obtained by mixing [DBUH][4-F-PhO] with ethylene glycol (EG) or 4-F-PhOH. Surprisingly, [DBUH][4-F-PhO]-EG DESs present a much higher CO 2 capacity (∼1.0 mol CO 2 /mol solvent) than [DBUH][4-F-PhO]-4-F-PhOH (∼0.10 mol CO 2 /mol solvent) at 25 °C and 1.0 atm. However, after EG is added into [DBUH][4-F-PhO]-4-F-PhOH, the ternary solvents [DBUH][4-F-PhO]-4-F-PhOH-EG exhibit an unexpected high capacity, although both EG and [DBUH][4-F-PhO]-4-F-PhOH exhibit a low capacity. Moreover, the capacities of ternary solvents [DBUH][4-F-PhO]-4-F-PhOH-EG decrease with increasing concentration of 4-F-PhOH in the solvents. NMR and Fourier transform infrared (FTIR) results demonstrate that CO 2 reacts with EG in [DBUH][4-F-PhO]-EG or [DBUH][4-F-PhO]-4-F-PhOH-EG by forming a carbonate species, while [DBUH][4-F-PhO]-4-F-PhOH binary mixtures are chemically inert to CO 2 . NMR analysis and theoretical calculations evidence that the strength of hydrogen bonds between [4-F-PhO] − and hydrogen-bond donors (EG and 4-F-PhOH) governs the CO 2 absorption behaviors, and the strength of the hydrogen bond between the anion [4-F-PhO] − and 4-F-PhOH is much stronger than that between [4-F-PhO] −and EG. Moreover, the desorption behaviors of the DESs studied can also be controlled by tuning the strength of the hydrogen bonds in the solvents. This work highlights the important role of hydrogen bonds in CO 2 capture, which may be useful for the rational design of efficient solvents for carbon capture in the future.

Electrocatalysis in deep eutectic solvents: from fundamental properties to applications

“…The presence of versatile interactions in DESs significantly increases the solubility for small molecules, which is favorable for the adsorption and conversion of small molecules in electrocatalytic reactions. 62–65 Besides, interactions in DESs could construct supramolecular networks to control the growth direction of materials and could also play significant roles in activating reactants and stabilizing intermediates, 30,40,66–68 making DESs promising candidates as electrolytes for electrocatalysis.…”

Rapid Absorption and Desorption of CO2 by Deep Eutectic Solvents via Reversible CO2-Triggered Proton Transfer Process

“…In general, DESs are prepared by simply mixing of two or more components, including both hydrogen bond acceptors (HBAs) and hydrogen bond donors (HBDs), to form a solution with a melting point lower than that of any of its components by means of hydrogen bonding interactions. Organic amines and azoles are widely used to synthesize ILs to capture CO 2 , which can also be used as HBDs and HBAs. − Three types of the most studied DESs for CO 2 capture are as follows: amino-based functionalized DESs, − azole-based functionalized DESs, − and super base functionalized DESs. − Due to the low cost and highly efficient capture of CO 2 by amines, amino-based functionalized DESs have been widely investigated. Zhang et al selected monoethanolamine (MEA) as a HBD and synthesized several 1-butyl-3-methylimidazolium chloride (BmimCl):MEA DESs.…”

“…For example, the mole absorption capacity of [TETA]­Cl/EG DES increased from 0.75 mol CO 2 /mol [TETA]Cl to 1.456 mol CO 2 /mol [TETA]Cl as the molar ratio of EG to [TETA]Cl increased from 1:1 to 3:1. Additionally, EG has also been reported to be involved in the chemical capture of CO 2 in super base functionalized DESs, in which EG acted as a chemical interaction site and formed carbonate with CO 2 after being deprotonated by the super base. , So, in this work, EG was selected as the HBD to form DES with aromatic amines.…”

CO2 Capture Mechanism by Deep Eutectic Solvents Formed by Choline Prolinate and Ethylene Glycol

“…Nevertheless, for the [Et 4 N][Car]-4CH 3 -Im (4CH 3 -Im: 4-methylimidazole) system, CO 2 reacted with the anion [Car] − , but did not react with 4CH 3 -Im. In addition, superbase-derived anion-functionalized DESs were also explored for CO 2 capture, such as [DBUH][Im]-EG (DBU: 1,8-diazabicyclo-[5,4,0]undec-7-ene) [ 42 ], [DBUH][MLU]-EG (MLU: methyl urea) [ 43 ], [DBNH][Triz]-EG (DBN: 1,5-Diazabicyclo[4.3.0]non-5-ene) [ 44 ], [DBUH][Car]-EG [ 45 ], DBN-EU (EU: 2-imidazolidone) [ 46 ], [DBUH][4-F-PhO]-EG(4-F-PhO:4-Fluorophenolate) [ 47 ], ternary DESs [DBUH][4-F-PhO]-4-F-PhOH-EG [ 47 ], and DBN-BmimCl-Im [ 48 ]. According to the results reported in the literature, it can be found that the components of DESs greatly affect the CO 2 absorption behaviors of functionalized DESs.…”