Crumpled polyethyleneimine nanofiltration membranes regulated by thermocapillary effect for efficient...

The advancement of lithium (Li) extraction from brines is crucial for boosting Li production capacity and meeting the growing demands of emerging energy markets. However, the presence of symbiotic ions, particularly magnesium ions (Mg²⁺), poses significant challenges. Although conventional nanofiltration (NF) membranes have demonstrated considerable potential in magnesium-lithium (Mg²⁺/Li⁺) separation, they often face the inherent trade-off between membrane permeance and salt rejection. In this study, NF membranes with desirable ridge-like structures were fabricated via temperature-gradient-assisted interfacial polymerization. Notably, under the action of thermocapillary effect, the surface morphology of the membranes can be precisely controlled by adjusting the amount of residual aqueous film on the substrate. The separation performances revealed that the unique microscale hollow ridges provided a larger effective filtration area, leading to a substantial improvement in membrane permeance. Compared to conventional polyethyleneimine-based NF membranes, the optimized membrane exhibited a threefold increase in permeance (17.6 L·m^-2·h^-1·bar^-1) while exhibiting a higher Mg²⁺ rejection rate (97.6 %) and exceptional Mg²⁺/Li⁺ selectivity (S_Li⁺_/Mg²⁺ = 32.2). Additionally, the membrane demonstrated excellent long-term operational and storage stability. These crumpled membranes displayed advantages such as ease of production and high separation efficiency, making them highly promising for practical applications in Mg²⁺/Li⁺ separation.