Covalent organic framework-based materials for ion separation: A review

Separation and purification of valuable ions from water is an area of interest to deal with environmental pollution and energy crisis. Although various materials have been developed for the recovery of ions, they still face some drawbacks, such as low separation efficiency and low ion selectivity. As a class of emerging materials, covalent organic frameworks (COFs) have garnered enormous attention for the extraction and separation of ions from water sources. Compared with polymeric membranes, COFs have higher porosity and crystallinity, higher physical and chemical stability, and better functionality. Moreover, they show high specific surface areas and excellent adsorption capacities. This review discusses the properties, synthesis, fabrication and modification of COF-based materials (e.g., adsorbents and membranes). Different parameters affecting the performance of COFbased materials, including pore size, stability, and hydrophilicity/hydrophobicity are assessed. Moreover, the possible mechanisms for ion extraction and separation using COF-based materials are investigated. Finally, the advances, challenges, and prospects in developing COF-based materials with desirable properties for ions extraction and separation are assessed. This review provides significant insights into developing the next generation of high-performance COF-based adsorbents and membranes for sustainable ion separation and extraction.