Preliminary exploration of the dye/salt separation performance of 2D and 3D covalent organic frameworks/nylon 6 membranes prepared by layer-by-layer strategy

Covalent organic frameworks (COFs) had been widely studied as high-performance separation membrane materials because of their uniform pore size, high porosity and good stability. In this work, 1,3,5-tris(4-aminophenyl)benzene (TAPB) - 1,3,5-triformylphloroglucinol (Tp)-12/nylon 6 membrane, a two-dimensional (2D) COFs membrane, and 4-[tris(4-aminophenyl)methyl]aniline (TAPM) -Tp-6/nylon 6 membrane, a three-dimensional (3D) COFs membrane, were prepared by layer-by-layer strategy. During the experiment, these COFs/nylon 6 membranes showed good properties, such as high water permeance (4522 L m−2 h−1 bar−1 for TAPB-Tp-12/nylon 6 membrane, and 4840 L m−2 h−1 bar−1 for TAPM-Tp-6/nylon 6 membrane), excellent dye rejection (methylene blue rejection>99.7 %), low salt rejection (<3.4 %), good chemical stability and reusability, which might be due to the hydrophilicity and electrical properties of these materials and the support of nylon 6 skeleton. Moreover, the possible reasons for these differences between 2D COFs membrane and 3D COFs membrane were analysed by summarizing and comparing the data obtained from these COFs/nylon 6 membranes. Therefore, this work not only provided a universal method for the synthesis of different types of COFs membranes, but also supplied a reference for researchers in the same field to compare the performance of 2D and 3D COFs membranes.