Enhancing CO ₂ Separation in Mixed Matrix Membranes Through Entropy and Enthalpy Regulation

ABSTRACT Metal organic framework (MOF) fillers endow mixed matrix membranes (MMMs) with tunable pore structures and functional sites, rendering them highly promising for CO 2 /CH 4 separation. However, currently the design of fillers for MMMs still relies predominantly on empirical trial‐and‐error method and there lacks an efficient design strategy to achieve simultaneous enhancement of both permeability and selectivity. Guided by transition‐state‐theory (TST), we that increasing the diffusion‐related activation entropy (ΔS diff ) while decreasing the adsorption‐related activation enthalpy (ΔH ads ) of the MOF fillers can cooperatively reduce the activation free‐energy barrier (ΔG) for CO 2 transport. This insight thermodynamic insight into gas transport enables the formulation of a promising strategy for rational filler design. Here, we validate this strategy by constructing [R‐T]‐MIL‐125‐NH 2 (Ti) fillers featuring both hierarchical pores and exposed unsaturated Ti sites. When incorporated into a Pebax matrix, the hierarchical pores enhance ΔS diff , whereas the unsaturated Ti sites reduce ΔH ads . The as‐prepared Pebax/[110‐300]‐MIL‐125‐NH 2 MMM exhibits a 100% increase in CO 2 permeability and a 70% enhancement in CO 2 /CH 4 selectivity compared with the unmodified Pebax/MIL‐125‐NH 2 MMM. This work establishes an efficient filler design strategy centered on the synergistic regulation of ΔS diff and ΔH ads , offering a thermodynamic pathway to transcend the performance upper bound of MMMs.