Dehydration‐enhanced Ion Recognition of Triazine Covalent Organic Frameworks for High‐resolution Li+/Mg2+ Separation

Abstract The precise and rapid extraction of lithium from salt‐lake brines is critical to meeting the global demand for lithium resources. However, it remains a major challenge to design ion‐transport membranes with accurate recognition and fast transport path for the target ion. Here, we report a triazine covalent organic framework (COF) membrane with high resolution for Li + and Mg 2+ that enables fast Li + transport while almost completely inhibiting Mg 2+ permeation. The remarkably high rejection of Mg 2+ by the COF membrane is achieved via imposed ion dehydration and the construction of the energy well. The proper hydrophilic environment of the COF channel promotes the dissociation of Li + from the negatively charged functional groups, allowing Li + for hopping transport supported by the sulfonate side‐chains to shorten the diffusion path of Li + . Under high‐salinity electrodialysis conditions, the COF membrane demonstrates robust Li + /Mg 2+ separation performance (No Mg 2+ were detected in the collected solution), achieving efficient lithium recovery and high product purity (Li 2 CO 3 : 99.3 %). This membrane design strategy enables high energy efficiency and powerful lithium extraction in the electrodialysis lithium extraction process, and can be generalized to other energy and separation related membranes.