Enhanced CO2 separation enabled by mesoporous fluoride-cerium nanosheets in ultrathin mixed-matrix composite membranes

Abstract

An ultrathin mixed-matrix composite membrane (MMCM) for efficient CO₂ separation is developed. A green bottom-up synthesis is employed to fabricate F-Ce two-dimensional nanosheets with a mesoporous structure and well-defined interlayer spacing. These nanosheets are incorporated into a Pebax 1657 polymer matrix to prepare a mixed-matrix coating solution. PDMS/PEI support membranes are fabricated by casting and subsequently modified by UVO₃ treatment to obtain hydrophilic PDMS(UVO₃)/PEI supports. The Pebax-F-Ce coating solution is uniformly deposited onto the modified support surface to produce Pebax-F-Ce/PDMS(UVO₃)/PEI composite membranes. The resulting membrane possesses an ultrathin separation layer (∼500 nm) and an intermediate layer (∼150 nm), enhancing gas transport while maintaining structural stability. Uniformly dispersed F-Ce nanosheets form mesoporous architectures that provide rapid CO₂ transport channels, while their −F functional groups enhance CO₂ solubility, further improving gas permeance. The 0.344 nm interlayer spacing provides a moderate size-exclusion effect on larger gas molecules, thereby contributing to improved CO₂/N₂ selectivity. The high aspect ratio and rigidity of F-Ce nanosheets induce more tortuous diffusion pathways for bulky molecules, further enhancing separation efficiency. Comprehensive characterization (SEM, TEM, FT-IR, XRD, XPS, BET, and gas permeation) confirms excellent performance, showing a CO₂ permeance of 662 GPU and a CO₂/N₂ selectivity of 59—representing 12% and 44% improvements over conventional Pebax/PDMS/PEI membranes, respectively. This study demonstrates that constructing an ultrathin separation layer and optimizing the composite structure significantly enhances the gas separation performance of MMCMs, providing an effective strategy for efficient CO₂ capture.