Efficient metal ion sieving in rectifying subnanochannels enabled by metal-organic frameworks

Area of Science:

• Materials Science
• Nanotechnology
• Supramolecular Chemistry

Background:

• Biological ion channels possess unique selectivity and permeability, serving as inspiration for artificial systems.
• Developing artificial analogues with comparable ion transport properties remains a significant challenge in nanotechnology.

Purpose of the Study:

• To engineer a metal-organic framework-based subnanochannel (MOFSNC) with heterogeneous structure and surface chemistry.
• To achieve high ion selectivity and permeability comparable to biological ion channels.

Main Methods:

• Fabrication of a metal-organic framework-based subnanochannel (MOFSNC) with an asymmetric structure.
• Characterization of ion transport properties, including selectivity and conductivity for various ions (K+, Na+, Li+, Ca2+, Mg2+).
• pH-dependent tuning of ion selectivity.
• Theoretical simulations to elucidate the mechanism of ion transport.

Main Results:

• The MOFSNC demonstrated rapid conduction of monovalent cations (K+, Na+, Li+) over divalent cations (Ca2+, Mg2+), achieving a conductivity difference of three orders of magnitude.
• A high mono/divalent ion selectivity of 10^3 was observed.
• Ion selectivity was further tunable by a factor of 10^2 to 10^4 by adjusting pH from 3 to 8.
• Theoretical simulations revealed that ion-carboxyl interactions significantly lower the energy barrier for monovalent cation passage.

Conclusions:

• The developed MOFSNC successfully mimics biological ion channel properties, offering ultrahigh ion selectivity.
• The tunable ion selectivity based on pH presents a novel approach for advanced ion separation technologies.
• This research paves the way for developing efficient ion-selective devices for applications in energy storage and power generation.