Zhu Dongyang, Verduzco Rafael
Department of Chemical and Biomolecular Engineering, Rice University, 6100 Main Street, MS-362, Houston, Texas 77005, United States.
Department of Materials Science and Nanoengineering, Rice University, 6100 Main Street, MS-325, Houston, Texas 77005, United States.
ACS Appl Mater Interfaces. 2020 Jul 22;12(29):33121-33127. doi: 10.1021/acsami.0c09173. Epub 2020 Jul 13.
Covalent organic frameworks (COFs) are organic, crystalline, highly porous materials attractive for applications such as gas storage, gas separations, catalysis, contaminant adsorption, and membrane filtration. Activation of COFs removes adsorbed solvents and impurities, but common methods for COF activation can result in the collapse of porous structure and loss of accessible surface areas. Here, we present a study of the impact of solvent surface tension on the activation process and demonstrate that activation using the ultralow surface tension solvent perfluorohexane (PFH) is 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 multifunctional di- and tri-benzaldehydes with different aromatic substituents. For each COF, we performed a solvent wash followed by vacuum drying using six solvents varying in surface tension from 11.9 to 72.8 mN m. Through powder X-ray diffraction (PXRD) measurements combined with nitrogen adsorption and desorption analysis, we found that some COF chemistries readily lost their porosity during activation with higher surface tension solvents while others were more robust. 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 supercritical CO. This work demonstrates that the solvent surface tension used during activation has a strong impact on the potential pore collapse, and activation using PFH provides a simple and effective activation method to produce COFs with excellent crystallinities and pore structures.
共价有机框架（COFs）是有机、晶体、高度多孔的材料，在气体存储、气体分离、催化、污染物吸附和膜过滤等应用方面具有吸引力。COFs的活化可去除吸附的溶剂和杂质，但常用的COF活化方法可能导致多孔结构坍塌和可及表面积损失。在此，我们展示了一项关于溶剂表面张力对活化过程影响的研究，并证明使用超低表面张力溶剂全氟己烷（PFH）对一系列COF材料进行活化既简单又有效。我们通过三（4-氨基苯基）苯（TAPB）或2,4,6-三（4-氨基苯基）-1,3,5-三嗪（TAPT）与具有不同芳族取代基的多功能二醛和三醛之间的亚胺缩合反应合成了六种不同的基于亚胺的COFs。对于每种COF，我们使用六种表面张力从11.9到72.8 mN/m不等的溶剂进行溶剂洗涤，然后真空干燥。通过粉末X射线衍射（PXRD）测量结合氮气吸附和解吸分析，我们发现一些COF化学组成在用较高表面张力溶剂活化过程中容易失去孔隙率，而其他的则更稳定。然而，所有COFs都可以用PFH有效活化，以生产出具有优异结晶度和高表面积的材料，与使用超临界CO2活化的样品相当。这项工作表明，活化过程中使用的溶剂表面张力对潜在的孔坍塌有很大影响，并且使用PFH活化提供了一种简单有效的活化方法，以生产具有优异结晶度和孔结构的COFs。
