There is a lot of potential for energy-efficient separation in membranes made up of covalent organic frameworks (COF). It has been reported that COFs are able to separate dyes, salts, bacteria, and nanoparticles based on size-selective transport through ordered pore structure. They have recently emerged as promising membranes for separations involving organic liquids. In the last decade, organic solvent nanofiltration (OSN) has received a lot of attention since it is an energy- and waste-efficient method for separating mixtures down to the molecular level. Although the number of OSN publications has increased in recent years, there is a need to search for new membrane materials with a combination of excellent solvent stability and adequate separation performances. In this work, continuous TpPa-1 COF membranes were synthesized on polyether ether ketone (PEEK) supports via the interfacial polymerization (IP) method, in a similar way to the standard IP process used for the synthesis of polyamide (PA) membranes. A conformal TpPa-1 COF membrane was formed on the porous substrate within a minute owing to the fast reaction between amine and aldehyde monomers, which were dissolved in the aqueous and organic solutions, respectively. The separation performances of the TpPa-1 membranes were evaluated in water and organic solvent systems with ethanol as the polar organic solvent and with dye molecules as the model solutes. Anionic dyes such as methyl blue and fast green (FG) dye molecules were rejected at a rate of 95% with a permeance of 229.88 L m–2 hr–1 bar–1 and 86.55% with a permeance of 48 L m–2 hr–1 bar–1 for aqueous system. The molecular weight cut off (MWCO) of the membranes for OSN in the ethanol system was ~780 g?mol–1. The rejection mechanism of TpPa-1 COF membrane in the polar solvent has also been discussed. Moreover, solvothermal synthesis was used to synthesize TpPa-1 COF powder, and their structural stability was examined using polar and nonpolar solvents. Covalent organic framework materials along with highly stable polyether ether ketone substrate appear to have great potential for OSN applications.
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机译：在由共价有机框架 （COF） 组成的膜中，节能分离的潜力很大。据报道，COF 能够基于通过有序孔结构的尺寸选择性运输来分离染料、盐、细菌和纳米颗粒。它们最近成为有前途的膜，用于涉及有机液体的分离。在过去十年中，有机溶剂纳滤 （OSN） 受到广泛关注，因为它是一种将混合物分离到分子水平的节能和浪费方法。尽管近年来 OSN 出版物的数量有所增加，但仍需要寻找兼具出色溶剂稳定性和足够分离性能的新型膜材料。在本工作中，通过界面聚合 （IP） 方法在聚醚醚酮 （PEEK） 载体上合成连续 TpPa-1 COF 膜，其方式类似于用于合成聚酰胺 （PA） 膜的标准 IP 工艺。由于胺和醛单体之间的快速反应，它们在多孔基材上形成保形 TpPa-1 COF 膜，它们分别溶解在水溶液和有机溶液中。在水和有机溶剂体系中，以乙醇为极性有机溶剂，以染料分子为模型溶质，评价了 TpPa-1 膜的分离性能。对于水性体系，甲基蓝和固绿 （FG） 染料分子等阴离子染料分子的去除率为 95%，渗透率为 229.88 L m–2 hr–1 bar–1，渗透率为 86.55%，渗透率为 48 L m–2 hr–1 bar–1。乙醇系统中 OSN 膜的截留分子量 （MWCO） 为 ~780 g？mol–1。还讨论了 TpPa-1 COF 膜在极性溶剂中的截留机制。此外，采用溶剂热合成合成 TpPa-1 COF 粉末，并使用极性和非极性溶剂检查其结构稳定性。共价有机框架材料以及高度稳定的聚醚醚酮基材似乎在 OSN 应用中具有巨大的潜力。
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