Large-Area 2D Covalent Organic Framework Membranes with Tunable Single-Digit Nanopores for Predictable Mass Transport

Area of Science:

• Materials Science
• Chemical Engineering
• Nanotechnology

Background:

• Covalent organic frameworks (COFs) show promise for molecular separations but face challenges in scaling up to functional membranes.
• Current limitations include difficulties in fabricating large-area COF materials from nanoscale precursors.

Purpose of the Study:

• To synthesize large-area, ultrathin 2D COF membranes with tunable nanopore sizes for molecular separations.
• To investigate the mass transport properties and performance of these novel COF membranes in organic solvent nanofiltration.

Main Methods:

• Facile interfacial polymerization technique to create large-area (64 cm²) and ultrathin (24 nm) β-ketoenamine-linked 2D COFs.
• Angstrom-level control over single-digit nanopore size (1.4-2.0 nm) via monomer integration.
• Fabrication of COF membranes with variable thicknesses and supporting materials.

Main Results:

• Achieved high solvent fluxes and sharp molecular weight cutoffs in the fabricated 2D COF membranes.
• Demonstrated an order-of-magnitude greater permeance than state-of-the-art commercial polymeric membranes for organic solvent nanofiltration.
• Quantified mass transport using continuum models, revealing pore passage resistance dominance and a linear correlation between nanopore tortuosity, COF thickness, and solvent flux.

Conclusions:

• Tunable 2D COF properties enable precise control over membrane mass transport.
• The developed COF membranes offer superior performance for organic solvent nanofiltration.
• Continuum and pore flow transport models accurately predict COF membrane performance based on material properties.