In-situ growth of anionic covalent organic frameworks efficaciously enhanced the monovalent selectivity of anion exchange membranes

The development of monovalent selective ion exchange membranes with excellent performance is required owing to the continuous refinement of electrodialysis technology. Here, a tailored strategy for the in-situ growth of a sulfonate-rich covalent organic framework (sCOF) on the anion exchange membrane (AEM) was proposed to construct an ideal platform (sCOF/aAEM3) for superior anion separation. Specifically, sCOF and AEM were covalently linked (-C=N-) to ensure the high stability of the modified layer, which is an important application parameter. The sCOF layer, with a thickness of approximately 2.97 μm, was formed using the Bottom-Up in-situ growth method. The appearance of sulfonate in the pores of sCOF induced a strong electronegativity of −38.85 eV at pH = 7. The periodic structure of sCOF achieved a regularly sulfonate arrangement, which maximized the utilization of the functional group, causing strong electrostatic repulsion on SO42−. The electrodialysis process showed that sCOF/aAEM3 exhibited a superior perm-selective performance (PSO42−Cl− =18.92). In addition, the unique open 1D channel of sCOF endowed sCOF/aAEM3 with an enhanced ion flux of Cl− from 2.96 to 3.35 × 10−8 mol cm2 s−1. This facile strategy has been used for two other commercial AEMs having elevated perm-selectivity, which indicates the great potential for extensive applications.