Dehydration‐enhanced Ion Recognition of Triazine Covalent Organic Frameworks for High‐resolution Li<sup>+</sup>/Mg<sup>2+</sup> Separation
Wentong Meng, Sifan Chen, Ming Wu, Feng Gao, Yang Hou, Xiaoli Zhan, Wei Hu, Lijun Liang, Qinghua Zhang
Abstract
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.