Randomly oriented covalent organic framework membrane for selective Li+ sieving from other ions

Certain biological channels exhibit remarkable selectivity, effectively distinguishing between competing cations. If artificial membranes could achieve similar precision in differentiating competing ions from Li + , it could advance sustainable technologies in lithium extraction. In this study, we present a covalent organic framework (COF) membrane featuring a randomly oriented structure that enables selective separation of major competing ions from Li + . The random orientation results in narrow pores, which impart size-based selectivity among alkaline ions. Additionally, the COF incorporates sulfonic groups that preferentially bind to Na + and K + , facilitating their transport while retaining Li + . These synergistic mechanisms endow the membrane with a selectivity beyond detection limit for K + and Na + over Li + . When driven by an electrical potential, the ion flux through the membrane is enhanced by over an order of magnitude. Notably, the membrane also permits the transport of Mg 2+ and Ca 2+ while still rejecting Li + , leveraging differences in their ion mobility. This work should advance the design and construction of biomimetic materials for the extraction of valuable species from seawater and other aqueous sources.