Homogeneously assembled covalent organic framework membrane co-stitched by β-cyclodextrin and chitosan for dye separation

Covalent organic frameworks (COFs) based membranes have demonstrated great potential in molecular separation. However, COFs are usually synthesized as powders, and difficult to form large-area and highly crystalline membranes. There normally exists unfavorable crystal flaws and stacking defects in membranes, impairing their rejection performance. The severe reaction conditions of solvothermal synthesis also inhibit their fabrication. Here, a comprehensive strategy was developed to fabricate a homogeneously assembled COF membrane co-stitched by β-cyclodextrin (β-CD) and chitosan (CS). Specifically, the COF crystallites (named TATP) were homogeneously formed and assembled to be films at room temperature under the control of n-propylamine; The aminated CS chemically bonded the TATP crystallites on the substrate and helped assemble them to form dense films. β-CD molecules were subsequently embedded into the TATP layer and crosslinked to further stitch membrane defects. The prepared CD-TATP-NH2CS/nylon membrane demonstrated enhanced excellent rejection performance. It could reject 100 % of R250 (BB), Congo red, Direct blue15, and 99.4 % of Alcian blue. It also could selectively separate Methyl orange (MO) and BB mixed solutions with only MO passing through, owing to the co-stitching of the membrane defects by β-CD and CS. This study provides a significant concept and strategy for fabricating high-performance COF membranes.