Research ArticleChemistry

Paralyzed membrane: Current-driven synthesis of a metal-organic framework with sharpened propene/propane separation

See allHide authors and affiliations

Science Advances  26 Oct 2018:
Vol. 4, no. 10, eaau1393
DOI: 10.1126/sciadv.aau1393
  • Fig. 1 Synthesis of ZIF-8 membranes and the difference between ZIF-8_I Embedded Image and ZIF-8_Cm for propene/propane separation.

    (A) The electrochemical cell for membrane growth by FCDS. The substrate serves as a cathode in the electrochemcial system. (B) Schematic illustration of the ZIF-8 membrane growth via FCDS in comparison with solvothermal growth. In the solvothermal route, zinc ions and linkers assemble into the normal ZIF-8_I Embedded Image phase. With the local in situ electric field that formed around the support by the current, inborn lattice distortion occurs and the stiff polymorph ZIF-8_Cm is formed. (C to H) Schematic illustration and SEM images during ZIF-8 layer formation. Scale bars, 200 nm. (I) Difference between ZIF-8_I Embedded Image and ZIF-8_Cm for C3H6/C3H8 separation. Because the linkers of ZIF-8_I Embedded Image are easier to rotate than those of ZIF-8_Cm, during C3H6/C3H8 separation, the bigger propane molecules can permeate through the ZIF-8_I Embedded Image apertures more easily than through the ZIF-8_Cm apertures. Consequently, ZIF-8_Cm polymorph is expected to be more efficient for propene sieving.

  • Fig. 2 SEM characterization of FCDS membranes.

    (A to D) Cross-sectional SEM images of FCDS ZIF-8 membranes with different growth times. (E to H) Energy-dispersive x-ray spectroscopy (EDXS) mapping images of the membranes’ cross-sectional view at lower magnification (due to the difficulty to scan at higher magnification). Zn (red) is the tracer for the ZIF-8 layer, and Al (blue) is the tracer for the AAO support. The corresponding membrane SEM images with lower magnification are given in fig. S1.

  • Fig. 3 Membrane separation performance.

    (A) Binary C3H6/C3H8 separation performance of the ZIF-8 membranes as a function of growth time at room temperature. (B) Comparison of the C3H6/C3H8 separation performance of FCDS ZIF-8 membranes with literature data. Information on the data points is given in table S3. (C) Binary C3H6/C3H8 separation performances of the ZIF-8 membrane (grown for 20 min) as a function of temperature. The rectangular orange area shows the separation performance after cooling to 25° from 150°C. (D) Long-term stability of the ZIF-8 membrane (grown for 20 min) for C3H6/C3H8 separation at room temperature and 1 bar.

  • Fig. 4 XRD Rietveld refinement and MD simulations results.

    (A) Rietveld refinement of the XRD results of FCDS ZIF-8 membranes grown for 20 min. [Rwp (weighted profile R factor), 3.30%; Rexp (expected profile R factor), 1.74%; GoF (goodness of fit), 1.90]. The results show that the main phase in the as-synthesized membranes is ZIF-8_Cm, so the membrane separation performance is mainly determined by ZIF-8_Cm. a.u., arbitrary unit. (B) MD simulations of a propene/propane molecule passing through a ZIF-8_I Embedded Image or ZIF-8_Cm membrane with a thickness (along the z axis) of 200 nm, respectively. The passage rate (the inverse of passage time, averaged from five independent MD simulations in table S5) of both propene and propane through the ZIF-8_Cm membrane is slower than that through the ZIF-8_I Embedded Image membrane. This decrement is less significant for propene, leading to a considerably enhanced selectivity of propene over propane (increased from ~150 to ~530).

Supplementary Materials

  • Supplementary material for this article is available at http://advances.sciencemag.org/cgi/content/full/4/10/eaau1393/DC1

    Fig. S1. SEM images and XRD and FTIR results and change of membrane thickness with time.

    Fig. S2. Detection of the remaining metal ions and ligands in the spent growth solution.

    Fig. S3. Illustration of thin film interference and the excellent durability of ZIF-8 membranes.

    Fig. S4. Electrochemical characterization of growth mechanism.

    Fig. S5. Gas permeation setup and properties.

    Fig. S6. Rietveld refinement results of different ZIF-8 membranes.

    Fig. S7. MD simulation results.

    Fig. S8. LSCM characterization of self-elimination of defects.

    Fig. S9. Comparison of the time needed for the fabrication of MOF membranes.

    Fig. S10. SEM images and phase composition of the ZIF-8 layers grown on different conductive substrates and potential concept of hollow fiber formats.

    Table S1. C3H6/C3H8 separation properties for the ZIF-8 membranes prepared by FCDS grown at different times in a solution containing Zn(CH3COO)2 at room temperature and 1 bar with a 1:1 binary mixture of C3H6 and C3H8.

    Table S2. Detailed comparison of the synthesis time, methods, fabrication conditions, and their C3H6/C3H8 separation factors for different ZIF-8 membranes.

    Table S3. Detailed C3H6/C3H8 separation performance of different membranes listed in Fig. 3B.

    Table S4. Detailed results of MD simulations of gas passing through a single monolayer of ZIF-8 (each ZIF-8_I Formula/Cm + propene/propane system was simulated for five times, and the averaged result was reported).

    Table S5. Detailed results of MD simulations of gas passing through 200-nm-thick membranes of ZIF-8 (each ZIF-8_I Formula/Cm + propene/propane system was simulated for five times, and the averaged result was reported).

    Movie S1. Durability test by ultrasonic water bath treatment, shaking, and falling test.

    References (3759)

  • Supplementary Materials

    The PDF file includes:

    • Fig. S1. SEM images and XRD and FTIR results and change of membrane thickness with time.
    • Fig. S2. Detection of the remaining metal ions and ligands in the spent growth solution.
    • Fig. S3. Illustration of thin film interference and the excellent durability of ZIF-8 membranes.
    • Fig. S4. Electrochemical characterization of growth mechanism.
    • Fig. S5. Gas permeation setup and properties.
    • Fig. S6. Rietveld refinement results of different ZIF-8 membranes.
    • Fig. S7. MD simulation results.
    • Fig. S8. LSCM characterization of self-elimination of defects.
    • Fig. S9. Comparison of the time needed for the fabrication of MOF membranes.
    • Fig. S10. SEM images and phase composition of the ZIF-8 layers grown on different conductive substrates and potential concept of hollow fiber formats.
    • Table S1. C3H6/C3H8 separation properties for the ZIF-8 membranes prepared by FCDS grown at different times in a solution containing Zn(CH3COO)2 at room temperature and 1 bar with a 1:1 binary mixture of C3H6 and C3H8.
    • Table S2. Detailed comparison of the synthesis time, methods, fabrication conditions, and their C3H6/C3H8 separation factors for different ZIF-8 membranes.
    • Table S3. Detailed C3H6/C3H8 separation performance of different membranes listed in Fig. 3B.
    • Table S4. Detailed results of MD simulations of gas passing through a single monolayer of ZIF-8 (each ZIF-8_I 4¯3m/Cm + propene/propane system was simulated for five times, and the averaged result was reported).
    • Table S5. Detailed results of MD simulations of gas passing through 200-nm-thick membranes of ZIF-8 (each ZIF-8_I 4¯3m/Cm + propene/propane system was simulated for five times, and the averaged result was reported).
    • References (3759)

    Download PDF

    Other Supplementary Material for this manuscript includes the following:

    • Movie S1 (.mov format). Durability test by ultrasonic water bath treatment, shaking, and falling test.

    Files in this Data Supplement:

Navigate This Article