Synergistic structure-microenvironment design of polyamide membranes for efficient extraction of lithium from brine

Synergistic regulation of PA layer cross-linking and hydrogen-bonding environment. • Enhanced interfacial polymerization degree based on pre-crosslinked structure. • Enhanced H-bond network via TA and MMTNS for ultrafast water transport. • A promising scalable route to break permeability-Li + /Mg 2+ selectivity trade-off. Polyamide (PA) membrane has become a promising material for direct lithium extraction from salt lake brine, but it faces the trade-off between permeability and Li + /Mg 2+ selectivity. Here, we propose a strategy to resolve this limitation by synergistic regulation of the crosslinked structure of the PA layer and the internal hydrogen-bonding environment. The pre-crosslinking of tannic acid (TA)-modified montmorillonite nanosheets (MMTNS) and polyethyleneimine (PEI) promoted the formation of a PA composite layer with narrow pore size, thereby enhancing Mg 2+ rejection. Their synergistic effect also achieves precise regulation of PEI: MMTNS inhibits PEI diffusion in the bulk phase, while TA facilitates its interfacial diffusion. The resulting heterogeneous polymerization dynamics forms a thin and dense PA layer, which enables high Li + /Mg 2+ selectivity and ultrafast water transport. In addition, MMTNS and TA construct a rich hydrogen-bonding network that improves the water transport environment and further enhances transport efficiency. The optimized membrane achieves a permeance of 10.08 L m −2 h −1 bar −1 and a Li + /Mg 2+ separation selectivity of 49.5, exceeding most currently reported selective Li + extraction membranes. This work provides insights into the control of the PA layer structure and mass transfer environment, facilitating the design of next-generation selective ion separation membranes. Download: Download high-res image (398KB) Download: Download full-size image