Hydrazone-Linked Covalent Organic Frameworks for C ₂ H ₂ /C ₂ H ₄ Separation

Flexible covalent organic frameworks (COFs) are attractive due to their unique kinetic properties. However, their accessibility remains limited. In particular, it is challenging to control the flexibility of COFs, and the effects of different flexibilities on the properties of COFs are rarely revealed. In this work, three hydrazone-linked COFs with increasing flexibility were designed and synthesized by adjusting the flexibility of the hydrazide linker step-by-step. Through static adsorption and dynamic separation experiments, remarkable differences in adaptation among three COFs are revealed. The gas adsorption experiment shows that Ta-DMTH-COF has the best purification ability of C2H2/C2H4, and the selectivity of ideal adsorbed solution theory can reach 5.17, which is much higher than the other two COFs. This paper studied a flexible strategy of COFs by adjusting their connectors, and the influence of different flexibilities on the performance of COFs is analyzed, which provides an idea for the research and development of this kind of dynamic porous material.