Crown ether regulated nanocomposite membrane with lithium channels for highly selective Li+/Mg2+ separation

Efficient extraction of lithium from salt lakes is gaining more and more attention because it is regarded as a strategic resource. However, the poor Li+/Mg2+ selectivity of traditional polymer membrane hampers its application. Herein, with concerns over worldwide demands for lithium resource, we developed a novel GO-based nanocomposite membrane with crown ether for efficient lithium recovery. The positively-charged polyethyleneimine (PEI) and negatively-charged graphene oxide (GO) are alternately assembly on substrate, combining with the post-crosslinking with trimesoyl chloride (TMC), which guarantees the formation of ultrathin and dense separation layer with a thickness of around 15 nm. Importantly, crown ether which has a specific recognition to Li+ is subsequently introduced into the membrane to construct lithium channels for fast transport of Li+. Based on the tailor-made design, the optimal membrane exhibits a low rejection of 33.3% to LiCl, while a high rejection of 94.8% to MgCl2. Moreover, excellent Li+/Mg2+ selectivities with separation factors of 16.6 and 17.5 for the simulated salt lakes with Mg2+/Li+ mass ratios of 20 and 1, respectively are achieved. The high-performance nanocomposite membrane with lithium channels shows a promising application associated with lithium extraction from salt lakes.