Interface-regulated NH₂-UiO-66/ladder polysilsesquioxane hybrid membranes for synergistically enhanced CO₂/CH₄ separation and plasticization resistance

Plasticization induced by high-pressure CO₂ remains a central challenge for polymer membranes in natural gas upgrading, because excessive CO₂ sorption can increase chain mobility and eventually deteriorate separation selectivity and operational stability. Herein, we report an interface-regulated hybrid membrane platform by integrating amino-functionalized UiO-66 (NH₂-UiO-66) nanoparticles into a side-chain-engineered ladder polysilsesquioxane matrix (LPG40). In this design, the semirigid ladder-like siloxane backbone provides an intrinsically stable framework against segmental relaxation, while NH₂-UiO-66 contributes preferential CO₂ sorption sites and microporous transport pathways. More importantly, the coupling between the MOF surface and the epoxy-containing side chains of LPG40 generates an interfacial confinement effect, which reduces non-selective interfacial defects and suppresses local chain mobility under elevated CO₂ pressure. As a result, the optimized hybrid membrane containing 15 wt% NH₂-UiO-66 exhibited a CO₂ permeability of about 56.3 Barrer and a CO₂/CH₄ selectivity of 48.2, together with a plasticization pressure of 22.5 bar. Compared with the pristine LPG40 membrane, both gas transport performance and resistance to CO₂-induced plasticization were simultaneously improved. Mixed-gas measurements further demonstrated stable separation behavior and enhanced tolerance to plasticization at reduced CO₂ concentrations, indicating the potential of the membrane for elevated-pressure natural gas upgrading. The improved performance is attributed to the cooperative effects of the semirigid ladder backbone, CO₂-preferential sorption in NH₂-UiO-66, and interface-regulated confinement that promotes selective transport while mitigating chain relaxation. This work provides an effective strategy for designing robust hybrid membranes with balanced permeability, selectivity, and plasticization resistance.