Efficient Ion Sieving in Covalent Organic Framework Membranes with Sub-2-Nanometer Channels

Area of Science:

• Materials Science
• Nanotechnology
• Separation Science

Background:

• Sub-2-nanometer channel membranes offer high ion transport rates but struggle with selective ion separation.
• Developing membranes with precise ion selectivity is crucial for various separation applications.

Purpose of the Study:

• To demonstrate covalent organic framework (COF) membranes with sub-2-nanometer channels for efficient ion sieving.
• To investigate the mechanism behind high ion selectivity in these COF membranes.

Main Methods:

• Fabrication of COF membranes with approximately 1.4 nm channels.
• Experimental measurements of ion permeation and selectivity.
• Theoretical simulations to understand cation-channel interactions.

Main Results:

• COF membranes exhibited high monovalent cation permeation (0.1-0.2 mol m⁻² h⁻¹).
• Achieved high selectivities for monovalent over divalent cations (e.g., K⁺/Mg²⁺ ≈ 765).
• Identified hydrogen bonding interactions as key to high selectivity and energy barriers for ion transport.

Conclusions:

• COF membranes with abundant hydrogen bonding sites enable efficient ion sieving.
• Hydrogen bonding interactions effectively control ion selectivity in sub-2-nanometer channels.
• This strategy is promising for developing high-performance membranes for ionic separation.