Synthesis and CO2/N2 Separation Performance Analysis of Mixed Matrix Membrane (MMM) Based on Different Bimetallic Metal–Organic Frameworks (Ni-Cu-MOF-74, Ni-Co-MOF-74, and Ni-Zn-MOF-74)

Polydimethylsiloxane (PDMS) is commonly used in gas-separation studies because of its high CO2 permeability and stable mechanical properties. In this work, mixed matrix membranes (MMMs) were prepared by incorporating the bimetallic MOFs Ni-Cu-MOF-74, Ni-Co-MOF-74, and Ni-Zn-MOF-74 into a PDMS matrix. The membranes were fabricated by solution casting and characterized by SEM, XRD, FT-IR, and BET analyses, which confirmed uniform filler dispersion and the successful incorporation of the MOF-74 structures. Single-gas permeation tests showed clear performance improvements with MOF loading. The best results were obtained for the membrane containing 1 wt.% Ni-Cu-MOF-74, which reached a CO2 permeability of 3188.25 Barrer and a CO2/N2 selectivity of 35.10. The improvement is attributed to the accessible metal sites and high surface area provided by the MOF-74 framework, which enhanced adsorption–diffusion pathways for CO2 transport. These results show that PDMS/MOF-74 mixed-matrix membranes are effective for CO2/N2 separation, with Ni-Cu-MOF-74 achieving the highest performance.