Thin-film composite membranes featuring open-chain crown ether aromatic diacyl chloride for monovalent/divalent ion separation

Precise ion separation is crucial for applications such as wastewater treatment, energy storage, and resource recovery, but challenges arise due to the similar properties of metal ions. To address this, a monomer with crown ether-like properties, o-phenyldioxydiacetyl chloride (OPDC), was synthesized for ion-selective membrane design via interfacial polymerization. The resulting membrane exhibited seven times higher Li⁺ flux compared to conventional thin-film composite (TFC) membranes. Electrodialysis and crossflow filtration experiments revealed that OPDC-enhanced TFC membranes play a key role in selective Li⁺ separation. The OPDC monomer enables both chemical complexation and physical sieving, improving Li⁺/Mg²⁺ selectivity. Density Functional Theory (DFT) simulation reveals the thermodynamically favorable binding preferences of the OPDC monomer. The strong complexation ability of OPDC towards Mg²⁺ led to the formation of a stable state, reducing Mg²⁺ permeability through the membrane and thereby improving the Li⁺/Mg²⁺ separation performance of the membrane. This work advances the understanding of ion transport mechanisms and paves the way for the development of ion-selective TFC membranes.