Synergistic confinement–coordination mechanism of crown ether-grafted chitosan polymer inclusion membranes for selective lithium recovery

Two crown ether grafted chitosan PIMs were separately fabricated. • PIM-CTS-15 exhibits superior Li + selectivity and >95% cycling stability. • Confinement–coordination synergy enables hopping-like Li + migration. • XPS, DFT and Danesi model reveal the Li + transport mechanism. Selective Li + recovery from complex industrial leachates is hindered by the intrinsic trade-off between ion flux and permselectivity. Herein, we propose a confined ion-recognition transport strategy based on two distinct crown ether-functionalized chitosan (CTS) polymer inclusion membranes (PIMs), namely PIM-CTS-15 and PIM-CTS-18 incorporating benzo-15-crown-5 (B15C5) and dibenzo-18-crown-6 (DB18C6), respectively. Covalent immobilization of crown ether moieties within the CTS matrix creates spatially confined recognition sites, enabling selective Li + coordination and transport. Under optimized conditions, PIM-CTS-15 achieves a high Li + flux of 4.8 mol h −1  m −2 and maintains over 95% cycling stability after ten cycles, with ion permselectivity follows the order of Li + ≫Mg 2+ >Ca 2+ >K + , demonstrating preferential Li + migration. Furthermore, PIM-CTS-15 exhibits competitive Li + permselectivity over competing coexisting ions, with P Li/Mg  = 2.6, P Li/Ca  = 3.5, and P Li/K  = 2.3. Mechanistic investigation reveals that Li + transport proceeds through coordination-assisted hopping within confined crown ether sites, while the applied electric field promotes ion migration. Danesi kinetic analysis indicates a diffusion-coupled facilitated transport mechanism, and XPS/DFT calculations confirm the preferential interaction between Li + and O/N containing sites, as well as the stronger Li + binding affinity of PIM-CTS-15 compared with PIM-CTS-18. Notably, lowest Li + migration barrier among the studied cations, quantitatively supporting the hopping-like pathway. This work offers a molecular design principle for ion-recognition membranes by integrating host-guest confinement and coordination chemistry, achieving a favorable balance among Li + selectivity, transport efficiency, and operational stability for lithium recovery from complex industrial waste streams. Separation performance and mechanism of the PIM-CTS-15 membrane for Li + over competing metal ions. Download: Download high-res image (250KB) Download: Download full-size image