Covalent organic framework membranes through a mixed-dimensional assembly for molecular separations.

Area of Science:

• Materials Science
• Nanotechnology
• Chemical Engineering

Background:

• Covalent organic frameworks (COFs) offer tunable porous structures for molecular separations.
• Existing COFs often have pore sizes too large for small molecules, and weak intersheet interactions hinder membrane fabrication.
• Defect-free COF membranes with precise molecular sieving are needed.

Purpose of the Study:

• To fabricate advanced COF membranes with enhanced molecular sieving and stability.
• To address the limitations of large pore sizes and weak intersheet interactions in traditional COF membranes.
• To explore the potential of mixed-dimensional assembly for COF membrane design.

Main Methods:

• Mixed-dimensional assembly of 2D COF nanosheets and 1D cellulose nanofibers (CNFs).
• Characterization of membrane structure and pore size (0.45-1.0 nm).
• Performance evaluation for n-butanol dehydration and sodium sulfate removal.

Main Results:

• The CNF sheltering effect precisely controlled pore size, enabling molecular sieving.
• Enhanced interactions between COFs and CNFs improved membrane stability.
• Achieved high flux (8.53 kg m⁻² h⁻¹) and separation factor (3876) for n-butanol dehydration.
• Demonstrated high permeance (42.8 L m⁻² h⁻¹ bar⁻¹) and rejection (96.8%) for Na₂SO₄ removal.

Conclusions:

• Mixed-dimensional assembly of COFs and CNFs yields robust membranes with precise molecular sieving.
• The developed membranes show excellent performance in dehydration and salt removal.
• This design strategy offers a new pathway for fabricating high-performance COF membranes.