Breathing Effect of Flexible Metal-Organic Frameworks Drives C₂H₂/CO₂ Separation

One of the biggest challenges in industrial gas purification is the separation of CO₂ from C₂H₂. This work presents a flexible MOF, CUPMOF-70, for efficiently separating C₂H₂/CO₂ mixtures via a unique "breathing" gating mechanism. CUPMOF-70 exhibits a relatively high C₂H₂ adsorption capacity (up to 59.73 cm³·g^-1), especially with a much lower adsorption threshold pressure of C₂H₂ than that of CO₂, thereby enabling effective separation of C₂H₂/CO₂ mixtures. Strong affinity and selectivity for C₂H₂ are confirmed by the isosteric heat of adsorption (Q_st) (65.62 kJ·mol^-1) and ideal adsorbed solution theory selectivity (7.69). And in situ single-crystal X-ray diffraction experiments and simulations clarify the molecular-level separation mechanism, where CO₂ contacts weakly while C₂H₂ is immobilized through numerous C-H···π and supramolecular interactions. Moreover, dynamic breakthrough experiments demonstrated the actual efficient separation performance of CUPMOF-70 for the C₂H₂/CO₂ mixtures.