Research ArticleMATERIALS SCIENCE

Etching gas-sieving nanopores in single-layer graphene with an angstrom precision for high-performance gas mixture separation

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Science Advances  25 Jan 2019:
Vol. 5, no. 1, eaav1851
DOI: 10.1126/sciadv.aav1851
  • Fig. 1 Schematic of the partially decoupled defect nucleation and pore expansion.

    (A) Evolution of graphene lattice after subsequent exposures to O2 plasma and O3. (B) Fabrication procedure for nanoporous graphene membrane. The ozone treatment was carried out in situ.

  • Fig. 2 Characterization of the as-synthesized and the plasma-treated graphene.

    (A) Scanning electron microscopy (SEM) image of the as-synthesized graphene on a Cu foil. Histograms of (B) ID/IG and (C) I2D/IG from the as-synthesized graphene. (D) Evolution of D, G, D′, and 2D peaks as a function of the plasma time (baseline subtracted from the Raman spectra). Corresponding evolution of (E) ID/IG, I2D/IG, and (F) ID/ID′ with respect to the plasma time. a.u., arbitrary units.

  • Fig. 3 Characterization of the NPC-supported graphene and the resulting membrane.

    (A) Transmission electron microscopy (TEM) image of the NPC/graphene revealing porous structure of NPC. (B) ED pattern of typical single-layer graphene observed throughout the sample. (C to E) SEM images of the NPC/graphene film on the macroporous W substrate with different magnifications. Graphene is sandwiched between the NPC film and the W substrate. The region surrounded by the white square in (C) represents a 1-mm2 porous area on the W substrate. The circular features in (D) represent the arrays of 5-μm–sized macropores on the W substrate, visible in the SEM images because of electron beam–related charging effects. The porous structure of the NPC film is visible in (E). (F) Cross section of the NPC/graphene film revealing the thickness and the porous structure of the NPC film.

  • Fig. 4 Gas separation performance of graphene membranes from the intrinsic defects and from the pores generated by the plasma treatment.

    (A) Average H2 permeance of graphene membranes as a function of temperature. The error bars correspond to SD across several membranes (four for intrinsic defects, seven for 1-s plasma, and two for 2-s plasma). (B) Corresponding ideal selectivities (ISs) at 150°C. The error bars correspond to SD across several membranes. (C) Activation energies for gases as a function of kinetic diameter and the plasma exposure time. The error bars correspond to SD across several membranes.

  • Fig. 5 Gas separation performance of graphene membranes before and after the O3 treatment.

    (A) H2 permeance and ideal gas selectivities of 1-s plasma-treated graphene M9 and M10 after O3 treatment at 60°C (85 s) or 150°C (10 s). (B) H2 permeance and ideal gas selectivities of M2 (intrinsic defects) after repeated O3 treatments at 150°C (10 s). (C) H2 permeance and ideal gas selectivities of M4 (intrinsic defects) after O3 treatments at 25° C (120 s) and 150°C (10 s). The permeance and selectivity data were measured at 150°C.

  • Fig. 6 Evolution of graphene nanopores and its impact on the separation performance.

    (A) H2/CH4 separation performance from the nanopores incorporated using the methods developed here. The data were obtained at 150°C. Data for the intrinsic defects and 1- and 2-s plasma were obtained by averaging the results of several membranes. The error bars correspond to the SD across several membranes (four for the intrinsic defects, seven for the 1-s plasma, and two for the 2-s plasma). (B) Evolution of the pore density and the percentage of pores larger than 0.38 nm.

  • Fig. 7 Mixture separation performance of graphene membranes.

    (A) Comparison of graphene membrane performance in the single- and mixed-gas (equimolar) permeation tests (membrane M9 exposed to 60°C O3 for 85 s). (B) Comparison of graphene membranes in this work with other membranes in the literatures in terms of the separation of H2/CH4 mixture (the gray line is the polymer upper bound assuming a 1-μm-thick selective layer). The performance of graphene membranes in this work is shown with the data from the single-gas permeation test, which is reasonable since the SF is equal or higher than the corresponding IS while the H2 permeance does not change.

Supplementary Materials

  • Supplementary material for this article is available at http://advances.sciencemag.org/cgi/content/full/5/1/eaav1851/DC1

    Note S1. High-resolution TEM (HRTEM)–based characterization of graphene.

    Note S2. Calculation of activation energy.

    Note S3. Estimation of the percentage of the nonselective nanopores in graphene.

    Note S4. Estimation of the defect density from Raman.

    Note S5. Measurement of the O3 residence time.

    Note S6. Desorption of contaminants before permeation test.

    Fig. S1. The correlation between Ld, nd, and ID/IG.

    Fig. S2. HRTEM image of graphene after 6-s plasma treatment.

    Fig. S3. Gas permeation performance of 1-s plasma-treated graphene M7 after 60°C O3 treatment for 85 s.

    Fig. S4. The rise of O3 concentration in membrane module.

    Fig. S5. Schematic of the setup for gas permeation test.

    Fig. S6. Gas permeation performance of 1-s plasma-treated graphene M14.

    Table S1. Gas permeance from M1 to M13 at 150°C.

    Table S2. Gas permeance from M1 to M13 at 100°C.

    Table S3. Gas permeance from M1 to M13 at 30°C.

    Table S4. Estimated percentage of large nanopores in graphene after O2 plasma exposure for different gas molecules.

    Table S5. Gas permeance from M9 before and after O3 etching at 60°C for 85 s.

    Table S6. Gas permeance from M7 before and after O3 etching at 60°C for 85 s.

    Table S7. Gas permeance from M10 before and after O3 etching at 150°C for 10 s.

    Table S8. Percentage of nanopores larger than 0.38 nm after post cycles of O3 etching.

    Table S9. Gas permeance from M2 before and after O3 etching at 150°C for 10 s.

    Table S10. Gas permeance from M4 before and after O3 etching.

    Table S11. Comparison of H2/CH4 separation performance in this work with that in other literatures.

    Table S12. Gas permeance from M14 (1-s plasma-treated membrane) before and after 150°C treatment used to remove contaminants.

    References (4051)

  • Supplementary Materials

    This PDF file includes:

    • Note S1. High-resolution TEM (HRTEM)–based characterization of graphene.
    • Note S2. Calculation of activation energy.
    • Note S3. Estimation of the percentage of the nonselective nanopores in graphene.
    • Note S4. Estimation of the defect density from Raman.
    • Note S5. Measurement of the O3 residence time.
    • Note S6. Desorption of contaminants before permeation test.
    • Fig. S1. The correlation between Ld, nd, and ID/IG.
    • Fig. S2. HRTEM image of graphene after 6-s plasma treatment.
    • Fig. S3. Gas permeation performance of 1-s plasma-treated graphene M7 after 60°C O3 treatment for 85 s.
    • Fig. S4. The rise of O3 concentration in membrane module.
    • Fig. S5. Schematic of the setup for gas permeation test.
    • Fig. S6. Gas permeation performance of 1-s plasma-treated graphene M14.
    • Table S1. Gas permeance from M1 to M13 at 150°C.
    • Table S2. Gas permeance from M1 to M13 at 100°C.
    • Table S3. Gas permeance from M1 to M13 at 30°C.
    • Table S4. Estimated percentage of large nanopores in graphene after O2 plasma exposure for different gas molecules.
    • Table S5. Gas permeance from M9 before and after O3 etching at 60°C for 85 s.
    • Table S6. Gas permeance from M7 before and after O3 etching at 60°C for 85 s.
    • Table S7. Gas permeance from M10 before and after O3 etching at 150°C for 10 s.
    • Table S8. Percentage of nanopores larger than 0.38 nm after post cycles of O3 etching.
    • Table S9. Gas permeance from M2 before and after O3 etching at 150°C for 10 s.
    • Table S10. Gas permeance from M4 before and after O3 etching.
    • Table S11. Comparison of H2/CH4 separation performance in this work with that in other literatures.
    • Table S12. Gas permeance from M14 (1-s plasma-treated membrane) before and after 150°C treatment used to remove contaminants.
    • References (4051)

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