The use of mixed matrix membranes (MMMs) comprising metal–organic frameworks (MOFs) for the separation of COsub.2 from flue gas has gained recognition as an effective strategy for enhancing gas separation efficiency. When incorporating porous materials like MOFs into a polymeric matrix to create MMMs, the combined characteristics of each constituent typically manifest. Nevertheless, the inadequate dispersion of an inorganic MOF filler within an organic polymer matrix can compromise the compatibility between the filler and matrix. In this context, the aspiration is to develop an MMM that not only exhibits optimal interfacial compatibility between the polymer and filler but also delivers superior gas separation performance, specifically in the efficient extraction of COsub.2 from flue gas. In this study, we introduce a modification technique involving the grafting of poly(ethylene glycol) diglycidyl ether (PEGDE) onto a UiO-66-NHsub.2 MOF filler (referred to as PEG-MOF), aimed at enhancing its compatibility with the 6FDA-durene matrix. Moreover, the inherent COsub.2-philic nature of PEGDE is anticipated to enhance the selectivity of COsub.2 over Nsub.2 and CHsub.4. The resultant MMM, incorporating 10 wt% of PEG-MOF loading, exhibits a COsub.2 permeability of 1671.00 Barrer and a COsub.2/CHsub.4 selectivity of 22.40. Notably, these values surpass the upper bound reported by Robeson in 2008.