A steric hindrance-driven amorphization strategy on MOF/COF for boosting CO2 separation in mixed matrix membranes

Abstract

In the field of gas separation using mixed matrix membranes (MMMs), amorphous fillers have attracted attention due to their excellent gas separation performance. However, the transformation of crystalline fillers into amorphous fillers requires severe conditions; there is still a lack of amorphization strategies without relying on external energy. In this work, we synthesize an amorphous MOF/COF composite by using a steric hindrance-driven amorphization strategy. Due to the integration of COFs onto an MOF sheet, steric hindrance between adjacent COFs leads to lattice stress that can destroy the crystalline structure. Subsequently, the incorporation of an amorphous MOF/COF into the Pebax matrix is employed to fabricate MMMs for CO₂/CH₄ separation. A significant increase can be observed in CO₂ separation performance in comparison with the Pebax membrane when the crystalline MOF/COF filler is transformed into the amorphous MOF/COF filler. The amorphous MOF/COF weakens π-electron delocalization and then exposes more Lewis basic sites and open metal sites, thereby enhancing CO₂ selectivity in MMMs. This strategy provides a new perspective for the application of amorphous MOF/COF fillers in MMMs for CO₂ separation.