Efficient C2H2/CO2 separation in two 2-fold interpenetrating metal-organic frameworks with ultrahigh C2H2 packing density

Adsorptive separation of C2H2/CO2 is industrially important and feasible but the design of highly efficient adsorbents remains very challenging owing to the almost identical physicochemical properties of the two gases. Herein, we constructed two new microporous metal–organic frameworks (MOFs), termed CTGU-39/40 (CTGU = China Three Gorges University), with 2-fold interpenetrating frameworks and unique pore geometry/chemistry for C2H2/CO2 separation. Both the activated MOFs (CTGU-39/40-a) can preferentially adsorb C2H2 over CO2 with excellent selectivity of 8.4 and 3.3 at 298 K and 100 kPa, respectively, as verified by static adsorption measurements. More importantly, attributed to the suitable pore aperture size (∼5 Å) and abundant adsorption sites, CTGU-39-a combines exceptionally high packing density of C2H2 (0.41 g mL−1) and moderate isosteric heat of adsorption (Qst) for C2H2 (26.8 kJ mol−1), outperforming most previously reported adsorbents. Theoretical calculations reveal that the preferential adsorption of C2H2 within two MOFs is driven by cooperative adsorption behavior through multiple H-bonding and Coulomb interactions. Experimental breakthrough results further confirmed their practical separation ability and recyclability toward an equimolar C2H2/CO2 mixture at different feeding rates. This work may offer new insights into the design of advanced porous materials for C2H2 purification and potentially other gas separations.