Equimolar CO Capture by Cuprous-Based Quaternary Deep Eutectic Solvents

Because of inefficient π-complexation of Cu+ sites, the CO solubilities of current available cuprous-based liquid absorbents are still unsatisfied and far away from equimolar CO capture. Herein, a novel cuprous-based quaternary deep eutectic solvent (DES) was prepared and employed as a superior absorbent for equimolar CO capture. It is found that the cuprous-based quaternary DES [Emim]Cl-CuCl-ZnCl2-EG showed a record CO uptake capacity (0.934 mol/mol, almost equimolar CO capture) and good ideal selectivities for CO/N2, CO/CO2, and CO/H2 at 1.0 bar and 298.2 K, which is by far the best liquid absorbent for efficient absorption of CO. The results of spectroscopic characterizations reveal that ZnCl2 and EG could weaken the Cu–Cl bond to have a significant red-shift, contributing to strengthen the Cu+ species interacting with more CO and thereby boosting CO capacity. Additionally, the CO absorption process was completely reversible, further demonstrating the good reusability of [Emim]Cl-CuCl-ZnCl2-EG. The cuprous-based quaternary DES thus shows good potential for efficient and selective absorption of CO.