Insight into Ion Transfer through the Sub‐Nanometer Channels in Zeolitic Imidazolate Frameworks

Abstract A crack‐free sub‐nanometer composite structure for the study of ion transfer was constructed by in situ growth of ZIF‐90 Zn(ICA) 2 , ICA=Imidazole‐2‐carboxaldehyde on the tip of a glass nanopipette. The potential‐driven ion transfer through the sub‐nanometer channels in ZIF‐90 is strongly influenced by the pH of the solution. A rectification ratio over 500 is observed in 1 m KCl solution under alkaline conditions (pH 11.58), which is the highest value reported under such a high salt concentration. Fluorescence experiments show the super‐high rectification ratio under alkaline conditions results from the strong electrostatic interaction between ions and the sub‐nanometer channels of ZIF‐90. In addition to providing a general pathway for further study of mass‐transfer process through sub‐nanometer channels, the approach enable all kinds of metal–organic frameworks (MOFs) to be used as ionic permselectivity materials in nanopore‐based analysis.