Preparation and gas separation properties of Si-MWCNT/polyimide mixed matrix membranes

Multi-walled carbon nanotubes (MWCNTs) have attracted much attention in the field of gas separation membranes due to their unique one-dimensional structure and high specific surface area. However, their poor compatibility with polymer matrices and easy agglomeration limit their application in mixed matrix membranes (MMMs). In this study, surface-functionalized Si-MWCNTs were prepared by combining acidification treatment with silane coupling agent (APTES) modification, and Si-MWCNTs/PI MMMs were prepared by blending Si-MWCNTs with fluorinated polyimide. The structure and properties of the filler and membrane materials were systematically studied by means of FTIR, TGA, XRD and gas permeability. The results show that the introduction of —OH and —NH₂ functional groups on the surface of Si-MWCNTs effectively enhances its interfacial compatibility with polyimide and avoids disordered agglomeration. Its tubular structure provides a fast diffusion channel for gas molecules and improves the permeability of the membrane material. When the loading amount of Si-MWCNTs was 2%, the CO₂ permeability coefficient increased to 35.63 Barrer, which was 69% higher than that of the pure membrane, and the CO₂/N₂ separation factor reached 24.83, an increase of about 85%; In particular, the O₂/N₂ separation performance exceeds the 1991 Robeson upper limit. The results show that Si-MWCNTs effectively break through the trade-off between permeability and selectivity of traditional polymer membranes in gas separation by synergistic structural regulation and interface optimization, showing good application potential.