Nonlinear Ion Transport Through Ultrathin Metal-Organic Framework Nanosheet

The rational design of artificial solid-state nanopores is of great importance in the discovery of intriguing ion transport phenomena. 2D metal-organicframework (2D MOF) nanosheets with single crystallinity, aligned nanochannels, ultrathin thickness, and diverse functionalities are highly potential solid-state nanopores. An electrophoretic method is developed to successfully fabricate MOF nanopores supported by SiN(x)substrate, which is confirmed by high-resolution transmission electron microscopy. A giant gap around 4 V together with ionic current rectification is discovered in nonlinear voltage-activated current-voltage curves, revealing the synergy of the hydrophobic effect and charge effect in MOF nanopores. The charge effect embodies the different contribution current which results from the enrichment and depletion of ions in MOF nanopores by COMSOL simulation. Moreover, 2D MOF nanosheets with different surface charges, hydrophobicity, and pore sizes demonstrate the universality of nanopore fabrication and further confirm the synergistic mechanism. The nonlinear ion transport in the ultrathin MOF nanosheets will provide an opportunity to explore further applications in solid-state nanopores.