Combined experimental and computational studies on preferential CO2 adsorption over a zinc-based porous framework solid

Abstract

Here, we report the preferential CO₂ adsorption on a new zinc-based porous 3D framework compound, [Zn₂(H₂O)(nic)(pyrz)]_n·nH₂O, which has solvent accessible void space. Upon dehydration the porosity of the framework compound was enhanced significantly. At 298 K, the as-synthesized and dehydrated compound showed an uptake of carbon-dioxide of 2.2 and 5.7 wt% at 0.15 bar and 5.3 and 12.2 wt% at 1 bar, respectively, which increased to 5.6 and 11.7 wt% at 0.15 bar and 10.2 and 23.6 wt% at 1 bar, respectively, upon cooling to 273 K. The selectivity of CO₂ with respect to CH₄ at 273 K is calculated to be 22.4. The framework compound and its dehydrated product show very selective CO₂ adsorption with respect to other small gas molecules like H₂, N₂, and CH₄ at low partial pressure. The low pressure selective CO₂ adsorption is quite impressive with respect to other reported framework systems where selectivity was found particularly over one or two small gas molecules amongst H₂, N₂, and CH₄etc. [Zn₂(H₂O)(nic)(pyrz)]_n·nH₂O exhibits fairly strong CO₂–framework interactions as evidenced from the measured heat of adsorption, ∼50 kJ mol⁻¹ at low loading. Molecular dynamics and Monte Carlo simulations explain the selective CO₂ adsorption over other small gas molecules (H₂, N₂ and CH₄) in the framework compound.