Nonlinear Ion Transport through Ultrathin Metal–Organic Framework Nanosheet

Abstract

The rational design of artificial solid-state nanopores is of great importance in the discovery of intriguing ion transport phenomena. 2D metal-organic framework (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.

Artificial sodium-selective ionic device based on crown-ether crystals with subnanometer pores

“…Compared to synthetic artificial ion channels, solid-state artificial ionic devices consisting of nanochannels are much more robust and potentially more useful in applications 4 – 7 . To this end, metal-organic-frameworks, a highly porous material with a pore size precisely tunable from subnanometer to tens of nanometers 26 , were recently proposed to construct artificial ionic devices 27 – 30 . For example, by using a photosensitive organic linker, metal-organic-frameworks can be used as a photoresponsive ion channel or photodriven ion pump 29 .…”

Ultrafast rectifying counter-directional transport of proton and metal ions in metal-organic framework–based nanochannels

“…To study the metal ion rectifying mechanism, a 3D model was constructed to simulate the electro-kinetic metal ion transport inside the PET/MIL-53-COOH NC based on the Poisson-Nernst-Planck equation using COMSOL multiphysics solver ( 53 , 54 ), as shown in fig. S12.…”

Construction of Metal‐Organic Frameworks (MOFs)–Based Membranes and Their Ion Transport Applications

“…In addition to the light‐gated MOF hybrid membranes, the Gu group developed voltage‐responsive 2D MOF nanosheets, which were synthesized via an electrophoretic method supported by SiN x substrates (Figure 6c). [ 82 ] The fabricated MOF‐based composite nanopores exhibited a voltage‐activated gating phenomenon, with a large gap at 4 V. The high‐conductance state was achieved above 4 V and the low‐conductance state was achieved below 4 V. The emergence of this large gap and the asymmetry of the I – V curves could be explained by the hydrophobic effect and charge effect influenced by pH. The nonlinear ion transport phenomenon observed in the ultrathin 2D nanosheets offers an opportunity to explore further applications as an ionic diode in solid‐state nanopores.…”