Fabrication of asymmetric charge distribution mosaic membranes for ionic current rectification

Abstract

The ion gating effect is crucial for numerous biological processes and provides valuable insights for the development of nanoscale artificial ion gates. Traditionally, ionic current rectification is achieved by designing asymmetric geometries or charge distributions via complex and cumulative procedures. Here, we report a simple aqueous immersion method for the fabrication of single-layer rectifying membranes. The prepared membrane exhibited a homogeneous distribution of positively and negatively charged groups in the interior and an asymmetric distribution of cationic and anionic groups on the two opposing surfaces, thereby enabling a satisfactory rectification effect for a variety of ions. These results indicate that the rectification ratio strongly correlates with the ion type and the ionic strength. The rectification ratios generally followed the order of Na₃PO₄ > Na₃C₆H₅O₇ > Na₂SO₄ > NaCl > KCl. Further analysis reveals that rectification efficiency is concentration-dependent. At lower concentrations (e.g., <100 mM), limited ion mobility reduces rectification performance, whereas higher concentrations (>100 mM) compress the electric double layer (EDL), diminishing charge selectivity. Optimal rectification is achieved at 100 mM ion concentration. This method provides a straightforward and viable solution for developing ion-selective membranes for ionic current rectification.