Abstract
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.