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Constructing Unique Cross-Sectional Structured Mixed Matrix Membranes by Incorporating Ultrathin Microporous Nanosheets for Efficient CO₂ Separation

Li, Xueqin, Hou, Jinpeng, Guo, Ruili, Wang, Zhongming, Zhang, Jianshu
ACS applied materials & interfaces 2019 v.11 no.27 pp. 24618-24626
carbon dioxide, gases, nanosheets, permeability, polymers, porous media, porphyrins, scanning electron microscopy
Ultrathin microporous nanosheets denoted as Zn-tetra-(4-carboxyphenyl)porphyrin (Zn-TCPP) were synthesized and incorporated into a Pebax MH 1657 (Pebax) polymer to fabricate mixed matrix membranes (MMMs) for efficient CO₂ separation. The Zn-TCPP nanosheets with a microporous structure provide high-speed channels for fast CO₂ transport and shorten the diffusion pathways, both contributing toward high CO₂ permeability. Furthermore, scanning electron microscopy results indicate that the ultrathin Zn-TCPP nanosheets with an ultrahigh aspect ratio (>200) tend to arrange horizontally in the Pebax matrix. The obtained unique cross-sectional structure of the MMMs functions as a selective barrier, allowing repeated discrimination of gases due to the tortuous interlayer of horizontal nanosheets, thus improving the selectivity of the MMMs. In addition, the horizontally arranged microporous nanosheets were found to strongly interact with the membrane matrix and endowed the MMMs with excellent interfacial compatibility, which improved the CO₂ permeability and eliminated unselective permeation pathways. Significantly, the optimized CO₂ separation performance of the MMMs surpassed the 2008 Robeson’s limit.