Rational Pore Design of a Cage-like Metal–Organic Framework for Efficient C2H2/CO2 Separation

Considering the importance of C2H2 in industry, it is of great significance to develop porous materials for efficient C2H2/CO2 separation. Besides the high selectivity, the C2H2 adsorption capacity is another vital factor in C2H2/CO2 separation. However, the "trade-off" between these two factors is still perplexing. Rational pore design of metal-organic frameworks (MOFs) has been proven to be an effective way to solve the above problem. In this work, we have appropriately combined three kinds of strategies in the design of the MOF (FJI-H33), i.e., the introduction of open metal sites, construction of cage-like cavities, and adjustment of moderate pore size. As anticipated, FJI-H33 exhibits both outstanding C2H2 adsorption capacity and high C2H2/CO2 selectivity. At 298 K and 100 kPa, the C2H2 storage capacity of FJI-H33 is 154 cm3/g, while the CO2 uptake is only 80 cm3/g. The ideal adsorbed solution theory (IAST) selectivity of C2H2/CO2 (50:50) is calculated as high as 15.5 at 298 K. More importantly, the excellent practical separation performance was verified by breakthrough experiments. In addition, the calculation of adsorption sites and relevant energy by density functional theory (DFT) provides a good explanation for the excellent separation performance and pore design strategy.