Efficient CO₂ Separation of Multi-Permselective Mixed Matrix Membranes with a Unique Interfacial Structure Regulated...

A facile strategy to elevate gas separation performances of polymers is to introduce a versatile particle. In this study, the novel F-Ce nanosheets are synthesized, and then F-Ce is functionalized with 1-ethyl-3-methylimidazole thiocyanate (ionic liquids, ILs), obtaining multifunctional f-F-Ce nanosheets by the facile and environment-friendly methods. The multifunctional f-F-Ce nanosheets are incorporated into the Pebax (Pebax 1657) matrix to fabricate mixed matrix membranes (MMMs) for efficient CO₂ separation. The f-F-Ce nanosheets play versatile parts in elevating membrane gas separation performance. On the one hand, f-F-Ce tends to arrange horizontally and constructs a unique interfacial structure for cross-layer CO₂ transport in MMMs. On the other hand, the abundant mesopores from f-F-Ce construct high-speed CO₂ transport channels in MMMs and notably elevate the gas permeability. Moreover, the as-prepared MMMs separate CO₂ efficiently due to the comprehensive improvements of diffusivity selectivity, solubility selectivity, and reactivity selectivity. First, the high aspect ratio of f-F-Ce provides the tortuous pathways for gas transport and generates the rigid interface between the Pebax matrix and f-F-Ce nanosheets, increasing the diffusivity selectivity. Second, SCN^- groups from ILs show excellent affinity to CO₂, enhancing the solubility selectivity. Third, amine groups from ILs with abundant methylimidazole generate reversible reaction with CO₂ to elevate reactivity selectivity. Consequently, the f-F-Ce-doped MMMs display excellent CO₂ permeability and CO₂/CH₄ selectivity. In particular, the MMM incorporated with 8 wt % f-F-Ce displays a CO₂ permeability of 1823 Barrer and a CO₂/CH₄ selectivity of 35, overcoming the Robeson upper bound line (2008).