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

Due to low cost and high efficiency, amino-based functionalized deep eutectic solvents (DESs) have been widely investigated in CO2 capture. The amino group reacted with CO2 in a quantized ratio of 2:1 to form a carbamate and quaternary ammonium cation, which not only limited the absorption capacity of the amino group but also led to a dramatic increase in viscosity. In this work, we proposed a new strategy to improve the absorption capacity of amino-based functionalized DESs and inhibit viscosity increase by changing the proton transfer site from -NH2 to -N & boxH; to prevent the formation of -NH-COO- and -NH3+ using aromatic amines and ethylene glycol (EG). EG exhibited significant activation effect on 4-aminopyridine (AP). The absorption capacity of AP was enhanced from 0.10 mol of CO2/mol of DES to 0.60 mol of CO2/mol of DES at 303.15 K and 101.3 kPa after forming DES with EG. In addition, the saturated DES could be rapidly regenerated within 20 min at 353.15 K, and the absorption performance was maintained after six cycles. Results of proton nuclear magnetic resonance and carbon nuclear magnetic resonance spectra revealed the formation of carbamate and the protonation of pyridine nitrogen. The new reaction path effectively reduced the increase in viscosity. The viscosity of AP/EG (1:3) DES increased slightly from 29.17 to 68.40 mPas after absorption.