Dual-electric layer nanofiltration membranes based on polyphenol/PEI interlayer for highly efficient Mg2+/Li+ separation

In recent years, the global demand for lithium resources has grown substantially due to the rapid development of the new energy industry. The nanofiltration (NF) technique is a feasible method to extract lithium from salt-lake brine, and the high Mg 2+ /Li + separation selectivity of the NF membrane is the crucial factor in the NF separation process. In this work, the polyamide (PA) layer was prepared on the polyphenol/PEI interlayer-modified polysulfone (PSF) substrate to endow the NF membrane with decreased pore size and weakened electronegativity. Enhanced steric hindrance effect and reduced electrostatic attraction between Mg 2+ and PA layer increased the Mg 2+ rejection, thereby improving the Mg 2+ /Li + separation factor of the NF membrane. Furthermore, the positively charged polyphenol/PEI interlayer hindered the permeation of Mg 2+ through the Donnan effect, further enhancing the Mg 2+ /Li + separation factor. A separation factor up to 50.7 for Mg 2+ /Li + was achieved by extracting lithium from simulated brine using the obtained NF membrane. In addition, the NF membrane exhibited a permeability of 18.6 L m −2 h −1 ·bar −1 and excellent long-term stability, which greatly improved the Mg 2+ /Li + separation efficiency and reduced energy consumption. Therefore, this work provides a simple strategy for preparing NF membranes with high Mg 2+ /Li + separation factor and permeability. • Dual-electric layer NF membranes with positively charged interlayer and negatively charged separation layer. • The high Mg 2+ /Li + separation selectivity is attributed to the synergy between the steric hindrance effect and Donnan exclusion. • The Mg 2+ /Li + selectivity of NF membranes can be adjusted by changing the preparation conditions of the interlayer. • Permeability - selectivity trade-off was well addressed.