Ying Yunpan, Tong Minman, Ning Shoucong, Ravi Sai Kishore, Peh Shing Bo, Tan Swee Ching, Pennycook Stephen John, Zhao Dan
Department of Chemical and Biomolecular Engineering, National University of Singapore, 4 Engineering Drive 4, Singapore 117585, Singapore.
School of Chemistry and Materials Science, Jiangsu Normal University, No. 101 of Shanghai Road, Xuzhou 221116, China.
J Am Chem Soc. 2020 Mar 4;142(9):4472-4480. doi: 10.1021/jacs.9b13825. Epub 2020 Feb 21.
Covalent organic frameworks (COFs) are a promising category of porous materials possessing extensive chemical tunability, high porosity, ordered arrangements at a molecular level, and considerable chemical stability. Despite these advantages, the application of COFs as membrane materials for gas separation is limited by their relatively large pore apertures (typically >0.5 nm), which exceed the sieving requirements for most gases whose kinetic diameters are less than 0.4 nm. Herein, we report the fabrication of ultrathin two-dimensional (2D) membranes through layer-by-layer (LbL) assembly of two kinds of ionic covalent organic nanosheets (iCONs) with different pore sizes and opposite charges. Because of the staggered packing of iCONs with strong electrostatic interactions, the resultant membranes exhibit features of reduced aperture size, optimized stacking pattern, and compact dense structure without sacrificing thickness control, which are suitable for molecular sieving gas separation. One of the hybrid membranes, TpEBr@TpPa-SONa with a thickness of 41 nm, shows a H permeance of 2566 gas permeation units (GPUs) and a H/CO separation factor of 22.6 at 423 K, surpassing the recent Robeson upper bound along with long-term hydrothermal stability. This strategy provides not only a high-performance H separation membrane candidate but also an inspiration for pore engineering of COF or 2D porous polymer membranes.
共价有机框架材料（COFs）是一类很有前景的多孔材料，具有广泛的化学可调性、高孔隙率、分子水平上的有序排列以及相当高的化学稳定性。尽管有这些优点，但COFs作为气体分离膜材料的应用受到其相对较大的孔径（通常>0.5纳米）的限制，这超过了大多数动力学直径小于0.4纳米的气体的筛分要求。在此，我们报告了通过逐层（LbL）组装两种孔径不同且电荷相反的离子共价有机纳米片（iCONs）制备超薄二维（2D）膜的方法。由于具有强静电相互作用的iCONs的交错堆积，所得膜呈现出孔径减小、堆积模式优化和致密结构紧凑的特点，同时不影响厚度控制，适用于分子筛分气体分离。其中一种混合膜TpEBr@TpPa-SONa，厚度为41纳米，在423K时表现出2566气体渗透单位（GPUs）的H渗透率和22.6的H/CO分离因子，超过了最近的罗伯逊上限，同时具有长期的水热稳定性。该策略不仅提供了一种高性能H分离膜候选材料，也为COF或二维多孔聚合物膜的孔工程提供了灵感。
