The Confinement Effect of Angstrom-Sized Pores in Asymmetrical Membrane Constructed by Zeolitic Imidazolate Frameworks: Partially Dehydrated Ion Transport Performance.

The confinement effect in asymmetrical biological ion channels makes the state of molecules and ions differs from that in the external environment, and the mass transfer confined in the biological ion channels is in a single strand form. Herein, an asymmetrical membrane with angstrom-sized pores is constructed by growth of ZIF-90 membrane on the porous anodic aluminum oxide film. Due to the confinement effect of angstrom-sized pores of ZIF-90, ions transport through the pores of ZIF-90 suffer from multiple dehydration-hydration-dehydration process in the form of a single ionic chain. Molecular dynamics simulations imply that ions inside the pores of ZIF-90 are partially dehydrated. In alkaline condition, high rectification ratios of 237, 295, and 357 can be achieved in 10 × 10-3 m KCl, NaCl, and LiCl electrolyte, respectively. Besides, the strong electrostatic interaction between ions and the confined ZIF-90 pores makes the ions transport through the asymmetrical membrane suffer from an energy barrier, and the energy barrier is different with different ion species. This work helps to understand the ions transfer mechanism through angstrom-sized pores, which can provide guidance for the design of asymmetrical membrane and boost their applications.