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 Mg2+ and Ca2+ 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. Membranes which extract lithium are critical to developing sustainable technologies. Here, the authors report a covalent organic framework featuring randomly oriented channels, separating lithium from a mixture of cations.