Harnessing Pore Size in COF Membranes: A Concentration Gradient-Driven Molecular Dynamics Study on Enhanced H₂/CH₄...

Area of Science:

• Materials Science
• Chemical Engineering
• Computational Chemistry

Background:

• Covalent organic frameworks (COFs) show promise for gas separation membranes.
• Accurate prediction of gas transport properties in COFs is crucial for material design.
• Existing simulation methods may yield different results for small-pore COFs.

Purpose of the Study:

• To present and validate a novel nonequilibrium molecular dynamics (NEMD) approach, concentration gradient-driven molecular dynamics (CGD-MD), for predicting COF membrane gas transport.
• To identify promising COF materials for hydrogen/methane (H2/CH4) separation.
• To compare CGD-MD predictions with traditional grand canonical Monte Carlo (GCMC) and equilibrium molecular dynamics (EMD) methods, especially for COFs with pore sizes below 10 Å.

Main Methods:

• Simulated H2 and CH4 flux across COF-300 and COF-320 membranes using CGD-MD.
• Validated CGD-MD results against experimental data for permeability and selectivity.
• Employed density functional theory (DFT) to investigate gas-COF interactions.

Main Results:

• CGD-MD simulations closely matched experimental gas permeability and selectivity for tested COF membranes.
• Identified several novel COF candidates (NPN-1, NPN-2, NPN-3, etc.) for efficient H2/CH4 separation.
• Demonstrated significant discrepancies between CGD-MD and GCMC+EMD for COFs with pore sizes < 10 Å, with CGD-MD favoring H2 selectivity while GCMC+EMD suggested CH4 selectivity.

Conclusions:

• CGD-MD provides accurate predictions of gas transport properties in COF membranes.
• The choice of simulation method critically impacts predicted performance for small-pore COFs (< 10 Å).
• Understanding the interplay between adsorption and diffusion, as highlighted by the adsorption-diffusion time relationship, is key for designing effective COF membranes.