Abstract
Recently, deep eutectic solvents (DESs), a new type of solvent, have been studied widely for CO2 capture. In this work, the anion-functionalized deep eutectic solvents composed of phenol-based ionic liquids (ILs) and hydrogen bond donors (HBDs) ethylene glycol (EG) or 4-methylimidazole (4CH3-Im) were synthesized for CO2 capture. The phenol-based ILs used in this study were prepared from bio-derived phenols carvacrol (Car) and thymol (Thy). The CO2 absorption capacities of the DESs were determined. The absorption mechanisms by the DESs were also studied using nuclear magnetic resonance (NMR), Fourier transform infrared (FTIR), and mass spectroscopy. Interestingly, the results indicated that CO2 reacted with both the phenolic anions and EG, generating the phenol-based carbonates and the EG-based carbonates, when CO2 interacted with the DESs formed by the ILs and EG. However, CO2 only reacted with the phenolic anions when the DESs formed by the ILs and 4CH3-Im. The results indicated that the HBDs impacted greatly on the CO2 absorption mechanism, suggesting the mechanism can be tuned by changing the HBDs, and the different reaction pathways may be due to the steric hinderance differences of the functional groups of the HBDs.
Highlights
The climate crisis has been one of the most serious issues threatening the environment, animals, and humankind, which is regarded as the feedback of global warming
The four anion-functionalized deep eutectic solvents (DESs) based on bio-derived phenols could efficiently capture CO2, up to 0.90 mol CO2/mol solvent
Hydrogen bond donors ethylene glycol (EG) and 4CH3-Im impact greatly on the absorption mechanism by these DESs, and the reaction pathway between CO2 and absorbents can be tuned by changing hydrogen bond donors (HBDs)
Summary
The climate crisis has been one of the most serious issues threatening the environment, animals, and humankind, which is regarded as the feedback of global warming. Letters from a to i are the labels of hydrogen or carbon atoms of [Car] or [Thy] anion. Letters m and k are the labels of hydrogen or carbon atoms of [Et4N] cation. As seen in the 1H NMR spectra, two new peaks at 3.53 (H-2) and 3.80 (H-3) ppm can be observed after CO2 absorption. The similar new peaks can be found in the 1H and 13C NMR spectra of [Et4N] [Thy]:EG (1:2) after absorption (Figure S3). Compared to the FTIR spectrum of the virgin [E [Car]:EG (1:2), a new peak appeared near at 1635 cm−1, and a shoulder was observe around 1614 cm−1. Thermo-gravimetric analysis (TGA) was performed using a Mettler Toledo TG 3+ (Mettler Toledo, Greifensee, Switzerland) instrument from 25~400 ◦C at a heating rate of 10 ◦C/min under N2 atmosphere
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