Enhanced CO2 Separation Performance of a Modified Composite Membrane Based on a Covalent Organic Framework by Molecular Simulation

Abstract

This study investigates the mechanisms of CO₂ adsorption and separation in COF (covalent organic framework) membranes modified with ionic liquids and DESs (deep eutectic solvents) under varying temperature and humidity conditions by molecular dynamics simulations. The results indicate that higher temperatures enhance the CO₂ permeability, while an appropriate amount of water improves separation selectivity. The effects of DES and PEGIL (PEG-modified ionic liquid) solvents differ due to their distinct molecular structures. DES molecules are more uniform with shorter and less curved chains, resulting in denser membranes. In contrast, PEGIL molecules, characterized by longer and more curved chains, generate additional free volume. However, due to the strong interactions among PEGIL, COF, and CO₂ gas molecules, more adsorption space is provided for gas molecules, resulting in decreased gas permeability. Humidity plays a dual role. In DES@COF membranes, small amounts of water selectively enhance the transport of CO₂ while inhibiting N₂ transport; in PEGIL@COF membranes, excessive water causes phase separation, which impedes gas transport. These findings offer practical insights for optimizing COF-based composite membranes for efficient CO₂ separation in industrial applications.