(77g) Ultralow Surface Tension Solvents Enable Facile Cof Activation with Reduced Pore Collapse

Covalent Organic Frameworks (COFs) are organic, crystalline, highly porous materials linked by dynamic bonds. They are attractive for applications such as gas storage, gas separations, catalysis, contaminant adsorption and membrane filtration due to tunable functionality, porous crystalline structures and high surface areas. Activation of the COFs removes adsorbed solvents and impurities, and the most common method for activation is through solvent wash followed by vacuum drying. However, COFs can lose their porous structure and accessible surface areas during activation due to collapse of the pore structure. Here, we present a study of the impact of solvent surface tension on the activation proccess, and demonstrate that activation using the ultralow surface tension solvent perfluorohexane (PFH) is a simple and effective for a range of COF materials. We synthesized six different imine-based COFs through imine condensation reactions between tris(4-aminophenyl) benzene (TAPB) or 2,4,6-tris(4-aminophenyl)-1,3,5-triazine (TAPT) and multi-functional di- and tri-benzaldehydes with different aromatic substituents. For each COF, we performed through solvent wash followed by vacuum drying using six solvents varying in surface tension from 11.9 – 72.8 mN m^-1 and activation with supercritical CO₂ (ScCO₂). Through powder X-ray diffraction (PXRD) measurements combined with nitrogen adsorption and desorption analysis, we found that some COF chemistries were more fragile than others and readily lost their porosity during activation with higher surface tension solvents. However, all COFs could be effectively activated using PFH to produce materials with excellent crystallinity and high surface areas, comparable to those for samples activated using ScCO₂. This work demonstrates that the solvent surface tension used during activation has a strong impact on potential pore collapse, and activation using PFH provides a simple and effective activation route to produce COFs with excellent crystallinities and pore structures.