Combined experimental and computational studies on preferential CO2 adsorption over a zinc-based porous framework solid†
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 CH4 etc. [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.