Inverse Adsorption Separation of CO₂/C₂H₂ Mixture in Cyclodextrin-Based Metal-Organic Frameworks

The demand for CO₂/C₂H₂ separation, especially the removal of CO₂ impurity, continues to grow because of the high-purity C₂H₂ required for various industrial applications. The adsorption separation of C₂H₂ and CO₂ via porous materials is gaining a considerable attention as it is more energy-efficient compared with cryogenic distillation. The ideal porous materials are those that preferentially adsorb CO₂ over C₂H₂; however, very few adsorbents meet such requirement. Herein, two isostructural cyclodextrin-based CD-MOFs (CD-MOF-1 and CD-MOF-2) were demonstrated to have an inverse ability to selectively capture CO₂ from C₂H₂ by single-component adsorption isotherms and dynamic breakthrough experiments. These two MOFs showed excellent adsorption capacity and benchmark selectivity (118.7) for CO₂/C₂H₂ mixture at room temperature, enabling the pure C₂H₂ to be obtained in only one step. This work revealed that these materials were promising adsorbents for obtaining high-purity C₂H₂ via selectively capturing CO₂ from C₂H₂.