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.