Nanomorphogenesis of interlayered polyamide membranes for precise ion sieving in lithium extraction

Nanofiltration (NF) offers a scalable and energy-efficient method for lithium extraction from salt lakes. However, the selective separation of lithium from magnesium, particularly in brines with high magnesium concentrations, remains a significant challenge due to the close similarity in their hydrated ionic radii. The limited Li⁺/Mg²⁺selectivity of current NF membranes is primarily attributed to insufficient control over pore size and surface charge. In this study, we report the development of an interlayered thin-film composite (iTFC) membrane incorporating functionalized sulfonated carrageenan to regulate the interfacial polymerization process. This integrated interlayer plays a crucial role in controlling the diffusion and spatial distribution of amine monomers, leading to the formation of dense, nano-striped polyamide networks. These structural improvements including refined pore size and reduced negative charge significantly enhanced Li⁺/Mg²⁺selectivity (133.5) and increased permeance by 2.5 times compared to conventional TFC membranes. Additionally, the nano-striped structure optimized the membrane filtration area while minimizing ion transport resistance, effectively overcoming the traditional trade-off between ion selectivity and permeability. This study highlights the potential of iTFC membranes for achieving both high lithium purity and recovery, offering a promising avenue for large-scale lithium extraction from brines.