Improving the Separation of CO₂/N₂ Using Impregnation of a Deep Eutectic Solvent on a Porous MOF

As the partial pressure of CO₂ in flue gas is 0.1-0.2 bar, CO₂ capture at a low pressure needs more attention. Under low pressure conditions, the functional metal-organic framework (MOF) is powerful for CO₂ capture. One of the effective methods to increase the absorption capacity of the MOF is impregnation with deep eutectic solvents. In this research, NH₂-MIL101(Cr) is impregnated with a deep eutectic solvent of choline chloride:urea (DES ChCl:urea) to enhance the adsorption capacity. The CO₂ and N₂ adsorption capacity of NH₂-MIL101(Cr) and DES/NH₂-MIL101(Cr) was investigated at temperatures of 288.15-303.15 K and pressures up to 1 bar. The obtained results indicate that the adsorption capacity of the MOF increases by 1.7 and 3 times with the impregnated DES for CO₂ and N₂, respectively. Nevertheless, the pore volume of the MOF decreased after impregnation, but the adsorption capacity of the MOF increased due to the interaction of the adsorbate with the confined DES in pores. The contribution of the impregnated DES to adsorption capacity is explained according to Henry's law. Also, high heats of adsorption are attributed to the strong interaction between modified NH₂-MIL101(Cr) and CO₂. Also, the sample was refined at 298 K and vacuum and was reused without considerable reduction of the CO₂ capture capacity after 6 times. Moreover, the impregnation of ChCl:urea into NH₂-MIL101(Cr) nanostructures was studied using density functional theory-based approaches.