Recent advances on covalent organic framework-based membranes for ion selective sieving and wastewater resource utilization

Precise and ultra-fast ion selective sieving technology can be applied to solution purification, strategic element extraction, valuable ion recovery, and other ion fractionation fields, which are crucial to the sustainable development of the economy and society. As a key link for achieving specific ion selective sieving, the emerging membrane materials constructed by modified covalent organic frameworks (COFs) has been attracted extensive attention and become a hot spot in recent years. As a typical class of crystalline porous materials, COFs contain periodically extended and covalently bound network structures. The specific structures and the tailorable organic linkers endow COFs with tunable pore size and structure as well as facilely-tailored functionality so that it can contribute to achieve precise ion sieving. Herein, we trace recent developments in COF membranes in the context of selective ion sieving, aim to elaborated on the design ideas and synthesis strategies of COF membranes based on ion separation mechanisms such as pore size sieving, electrostatic repulsion, chemical affinity, and biomimetic ion channels. Moreover, the demonstrated applications of COF membranes for mono/polyvalent metal cation sieving, halogen/inorganic acid ion sieving, and acid wastewater recovery are discussed, which have achieved excellent ion sieving effect in the laboratory testing process. Finally, the application prospects and challenges (membrane stability, crystallinity, and antifouling performance) facing COF membrane development in the context of ion sieving are summarized.