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.
Harvesting energy from biogas is a potential way to retard the depletion of fossil fuels and fight against global warming simultaneously. Membrane technology holds great promise to achieve cost-effective biogas upgrading, along with advantages of low energy consumption and environmental friendliness, which leads to extensive exploration in fabricating CO 2 membranes with high separation performance. In this study, mixed matrix membranes are fabricated by incorporating exfoliation-free layered double hydroxides laminates intercalated with amino acids (Phe with hydrophobic side chains and Glu with hydrophilic side chains) into a low-cost commercial Pebax (poly (amide-b-ethylene oxide)) polymer. Both amino and carboxyl groups can facilitate the transport of CO 2 through quadrupole moment interaction, enlarged interlayer spacing and reversible reaction. Particularly, MMM containing 5 wt% AA-LDH exhibits an optimal permeability of 790 Barrer and a promising CO 2 /CH 4 selectivity of 31, which is 64.6% and 83.9% higher than the pristine Pebax membrane, respectively. The distinct advantages in terms of facile fabrication and processability confer the LDH-based membrane with great potential for large-scale CO 2 capture and separation.
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