Enhancing natural gas purification in mixed matrix membranes: Stepwise MOF filler functionalization through amino grafting and defect engineering

Abstract

Efficient gas separations are crucial for sustainable energy production and industrial processes, yet membrane materials face a fundamental permeability–selectivity trade-off. Here, we overcome this limitation through a rational stepwise-functionalization strategy for metal–organic framework (MOF) fillers, which synergistically combines amino grafting (enhancing CO₂ affinity) with defect engineering (enabling accelerated transport). The resulting mixed matrix membrane exhibits exceptional CO₂/CH₄ separation performance—achieving a CO₂ permeability of 1900 Barrer and a selectivity of 63 (0.3 MPa, 25 °C)—surpassing membranes with pristine or solely amino-functionalized fillers and exceeding the 2019 Robeson upper bound. In-situ spectroscopy confirms the critical role of amino groups in CO₂ chemisorption, while transport modelling attributes enhanced permeation to engineered defects. Crucially, the separation performance is fully recoverable after thermal/pressure cycling and remains stable over 200 h of operation. The fundamental insights of this work establish a synergistic chemical–structural design route for next-generation separation membranes.