NO2 Solvation Structure in Choline Chloride Deep Eutectic Solvents-The Role of the Hydrogen Bond Donor

Deep eutectic solvents (DESs) are promising candidates as alternate media for industrial gas sequestration processes, such as denitrification via NO2 adsorption. Here, quantum chemical methods are employed to characterize the NO2 solvation structure and adsorption mechanism in choline chloride DES with urea, methylurea, and thiourea hydrogen bond donors. Our results show that the solvation structure of NO2 in bulk choline chloride DES is determined by the type of the hydrogen bond donor present. Changing the structure of the hydrogen bond donor not only changes its NO2 coordination mechanism but also changes that between NO2 and the choline and chloride ions in the DES. By using an energy decomposition analysis scheme, we show that the principle forces stabilizing NO2 in these DES are dispersion and polarization interactions and, consequently, that NO2 adsorption is most favorable in the choline chloride thiourea DES. These results highlight a potential route for the optimization of choline chloride DES for denitrification, by modulating the hydrogen bond donor structure.