Selective and asymmetric ion transport in covalent organic framework-based two-dimensional nanofluidic devices

Two-dimensional (2D) covalent organic framework (COF) membranes featuring well-aligned and programmable vertical nanochannels have emerged as a promising candidate for advanced nanofluidic devices and showcased vast potential in the fields of smart-gating, ion-separation, and energy-harvesting. However, the transverse interlayer nanochannels with a height of sub-nanometer-scale in 2D-COF membranes have scarcely been studied in comparison. Here, we report the ion transport characteristics in 2D interlayer nanochannels of protonated COF membranes. The distinct surface-charge-governed ionic conductance in domination of electrolyte concentration below 10(-3) M as well as the exceptional anion/cation (Cl-/K+) selectivity is revealed due to the pronounced charge and nano-confinement effects. Additionally, evident ion current rectification is witnessed when incorporating asymmetric geometry into the system, which is attributed to the dynamic process of ion enrichment and dissipation within the protonated nanochannels. This work offers immense prospects for 2D-COF membranes in the fields of biomimetic nanofluidic devices and cutting-edge electronic devices.