Covalent organic frameworks (COFs) are prominent porous materials for molecules separation due to their desirable structures. However, very few COFs are reported for the separation of macromolecules such as low molecular-weight (MW) proteins. Here, two stable mesoporous COFs (Azo-COF and Tp-COF) with highly crystallized frameworks are synthesized, and their pore sizes are slightly-regulated via elaborate selection of pyrene knots and amino linkages. Benefiting from the pore size difference less than 4 Å, the tandem utilization of these two COFs exhibits efficiently size-selective separation ability towards low MW proteins cytochrome c and myoglobin with small MW difference of 2 kDa, in which protein adsorption possibilities are verified by computational calculations together with confocal laser scanning microscopy (CLSM). Furthermore, a simple COF-based separation device is designed and prepared to achieve effective and low-consumption proteins separation. This work has offered an optimized synthetic strategy for fine-tuned mesoporous COFs and expanded their applications on macromolecules separation.

Cationic azole-based metal-organic frameworks (MOFs) with remarkable stability and unique pore environment have aroused great research interests. Meanwhile, flexible MOFs which can undergo pore-structure changes upon exposure to external stimuli are ideal materials for gas separation. However, introducing flexibility into the framework of cationic azole-based MOFs is rarely reported. Herein, we synthesized two stable isomorphic cationic MOFs (M-btz-as, M = Co, Ni) based on a linear azole ligand. After activated at high temperature under vacuum, M-btz-ht (M = Co, Ni) were obtained and both MOFs exhibited flexible features in which Co-btz is more flexible than Ni-btz. Different solvent-mediated activation methods were employed to explore their effects on structural flexibility and produced MOFs with different phases. Continuous phase transformation of Co-btz-e was verified by powder X-ray diffraction. In addition, these MOF phases possessed different gas separation abilities affected by their flexible frameworks, and Co-btz-ht exhibited the highest CO₂/CH₄ separation ability.