pH-responsive nanofiltration membrane with color monitoring for efficient Mg2+/Li+ separation

Achieving precise pore size tuning in nanofiltration membranes for Mg 2+ /Li + separation remains challenging due to the similar hydrated radii of the ions and the lack of real-time monitoring for dynamic adjustments. In this study, we developed a novel pH-responsive color-changing nanofiltration membrane with tunable pore sizes, enabling real-time monitoring and enhanced separation efficiency. By incorporating γ-cyclodextrin during interfacial polymerization, we achieved angstrom-level pore size tuning and reduced pH sensitivity. The color response of the membrane enables dynamic adjustments to the feed solution pH, optimizing pore radii to ∼0.41 nm, leading to a separation factor of 35.5. Molecular dynamics simulations and weight cut-off experiments confirmed that γ-cyclodextrin enhanced pore uniformity, resulting in a denser, more efficient membrane. This innovative approach offers a flexible and precise solution for Mg 2+ /Li + separation, demonstrating high permeance (15.5 L m −2  h −1 bar −1 ) and potential for applications in seawater desalination, resource recovery, and industrial ion separation.