Effect of capsaicin and urea-modified MIL-101(Cr) on the CO2 separation performance of PMP-based mixed matrix membranes

CO2 separation from the power plant's flares and the extracted natural gas is an important issue for the relevant industries. Membrane technology, due to its low energy consumption and process simplicity, has become a major focus of recent research. In this study, high-performance MMMs based on PMP were developed by incorporating capsaicin as a plant-derived CO2-philic modifier and urea-functionalized MIL-101(Cr) for further performance elevation. Introducing 5 wt.% capsaicin into PMP increased the membrane crystallinity from 35% in pure PMP to 41.85% in PMP/Capsaicin/MIL-Urea membrane. Subsequent incorporation of MIL-101(Cr) and MIL-101(Cr)-Urea (0–20 wt.%) further improved structural ordering, raising crystallinity up to 57.40% and strengthening interfacial interactions. The presence of MIL-101(Cr)-Urea also increased the glass transition temperature from 28.6 °C in PMP/Capsaicin membrane to 32 °C in mixed matric membranes and enhanced thermal stability, with the decomposition temperature rising from 250 °C in PMP/Capsaicin to 320 °C at 20 wt.% loading. Gas permeation results demonstrated that synergistic effects between capsaicin’s CO2-philic groups and the porous functionalized MOF structures significantly improved membrane performance. The CO2 permeability, CO2/CH4 and CO2/N2 selectivities of pure PMP membrane at 10 bar were 93.6 barrer, 9.26 and 12.31, respectively; while, in PMP/Capsaicin/MIL-Urea optimum membrane, these values was cosrrespondingly increased to 316.3 barrer, 25.92, and 31.63 at the same pressure. Overall, integrating a natural modifier with urea-functionalized MIL-101(Cr) provides a sustainable and effective strategy to simultaneously enhance permeability, selectivity, and stability in PMP-based MMMs, offering a promising pathway for next-generation CO2 separation technologies.