Regulating the Positive Localized Electric Field in Mixed Matrix Membranes by Charge Reversal of ILs‐COF for Boosting CO₂ Separation

Abstract

Covalent organic frameworks (COFs), characterized by their high porosity and stability, hold great potential for applications in gas separations. However, achieving precise size sieving without hindering the gas diffusion rate is challenging. This study presents a novel approach to establishing tunable localized electric fields in COF channels to achieve efficient CO2 separation in Pebax‐based mixed matrix membranes (MMMs). Different charge densities of the localized electric field are achieved by the host–guest interaction between COF and varying charged ionic liquids (ILs). Remarkably, the MMM with a positive localized electric field attains the optimal CO2/CH4 separation performance with a significantly enhanced permeability (≈38%) and selectivity (≈99%), surpassing the Robeson upper bound. Through density functional theory (DFT) calculations, the enhanced CO2/CH4 selectivity of MMM is due to the “sieving effect” of a positive localized electric field on CO2 over CH4. Specifically, the negatively charged O atom in CO2 exhibits stronger electrostatic interaction than the positively charged H atom of CH4. Therefore, the strategy of regulating the localized electric field can be employed as an efficient design for CO2 separation in MMMs.