Crown-grafted loose nanofiltration membranes for the recovery of brine resources: Insights from molecular dynamics simulations

The increasing demand for lithium, driven by its essential role in battery technology, has warranted the need for effective recovery methods. Loose nanofiltration membranes (LNFMs) have shown great promise as a technology for extracting lithium from sustainable sources like seawater and brine. This study utilizes molecular dynamics simulations to probe the effectiveness of crown-grafted LNFMs in selectively recovering lithium from desalination brine. Tetraethylene pentaamine-based polyamide membranes (TEPA) were constructed through crosslinking with trimesoyl chloride (TMC) and further modified by grafting with various crown moieties, including 12-crown-4, 15-crown-5, and 18-crown-6. The resulting membranes demonstrated high compactness, high surface area, and significant solvent-accessible volumes. The pristine TEPA membrane showed high permeance for monovalent cations, while there were significant interactions with Na⁺ and K⁺ ions on the 12-crown-4 grafted membrane, facilitating the transport of Li⁺ ions, in consistent with reported experimental findings. When exposed to binary mixtures of Li⁺/Na⁺, Li⁺/K⁺, Li⁺/Mg²⁺, and Li⁺/Ca²⁺, the diffusion barrier for Li⁺ ion was lowered by the polyether heteroatoms in the 12-crown-4 grafted membrane, which continuously screened the competing ions. Herein, we highlight the inherent prospects of crown ethers in the development of advanced loose nanofiltration membranes specifically designed for targeted ion recovery, offering a pathway for further exploration.