Covalent Organic Framework Membranes with Regulated Orientation for Monovalent Cation Sieving

Area of Science:

• Materials Science
• Chemical Engineering
• Nanotechnology

Background:

• Continuous covalent organic framework (COF) thin membranes are recognized for their low energy consumption, operational simplicity, environmental friendliness, and high separation efficiency.
• Developing advanced membranes for selective ion separation remains a critical challenge in various industrial applications.

Purpose of the Study:

• To fabricate distinct, self-supporting COF membranes from identical building blocks using solvent modulation.
• To investigate the impact of pore alignment (random vs. vertical) on COF membrane separation performance.
• To achieve selective separation of lithium ions (Li+) over sodium (Na+) and potassium (K+) ions.

Main Methods:

• Fabrication of two distinct COF membranes from identical building blocks via solvent modulation.
• Characterization of COF membrane structure, focusing on pore orientation and layer stacking.
• Evaluation of membrane performance for selective ion transport, specifically Li+ over Na+ and K+.

Main Results:

• Successfully fabricated two distinct COF membranes by altering solvent conditions.
• Demonstrated that vertically aligned pores significantly enhance membrane separation precision compared to random orientations.
• The membrane with vertically aligned pores achieved Li+/K+ selectivity of 38.7 and Li+/Na+ selectivity of 7.2.

Conclusions:

• Strategic solvent selection enables control over pore orientation and layer stacking in COF membranes.
• This work presents a potent strategy for developing specialized membranes for highly selective Li+ ion separation.
• The findings contribute to the advancement of membrane technology for efficient ion separation processes.