Research ArticleAPPLIED PHYSICS

Multifunctional wafer-scale graphene membranes for fast ultrafiltration and high permeation gas separation

See allHide authors and affiliations

Science Advances  23 Nov 2018:
Vol. 4, no. 11, eaau0476
DOI: 10.1126/sciadv.aau0476
  • Fig. 1 Creation of PG by bottom-up and top-down methods.

    (A) Schematic of growth of single-layer porous graphene on W/Cu. W is evaporated on Cu by e-beam evaporation. Annealing leads to dewetting of W on Cu, forming islands. Graphene is synthesized selectively on Cu but locally inhibited by W islands. (B) Schematic of patterning double-layer graphene by the BCP process. The s-BCP thin film is spin-coated on double-layer graphene on glass and developed into a porous polystyrene film. Anisotropic oxygen ion beam milling leads to the patterning of the underlying graphene. (C) Patterned and porous graphene are transferred to a PCTE support forming a graphene-PCTE membrane. A representative scanning electron microscopy (SEM) image of PG on PCTE is shown.

  • Fig. 2 Membrane characteristics and wafer-scale fabrication.

    (A and B) Porous graphene (A) and patterned graphene (B) on PCTE support with a diameter distribution for each respective PG type. The dashed line in the histogram outlines a normal distribution. Scale bars, 500 nm. (C) Average pore size and SD for porous (blue stars) and patterned (red circles) graphene with respect to the respective process parameter. (D) Average porosity and SD for porous (blue stars) and patterned (red circles) graphene with respect to the respective process parameter. (E) Raman spectra evolution of porous graphene from nonporous (bottom) to 10-nm W (top). a.u., arbitrary units. (F) I(D)/I(G) versus I(D′)/I(G) showing the different nature of defect in respective graphene films: ~3.3 for porous graphene reflects line defects (grain boundaries), and patterned graphene has an I(D)/I(D′) of ~6.7, indicating vacancy-like defects. (G) Raman spectra evolution of patterned graphene from unpatterned (bottom) to 30 s (top). (H) Photograph of wafer-scale porous graphene on PCTE support with pore formation in the middle and at the edge of the sample (I). (K) Wafer-scale patterned graphene on PCTE support (dashed circle) with pore formation in the middle and at the edge of sample (J).

  • Fig. 3 Mass transport and ultrafiltration characterization of PG on PCTE.

    (A and B) Nitrogen flow rate (A) and water flow rate (B) through porous (2-, 5-, and 10-nm W, blue squares) and patterned (10, 20, and 30 s, red circles) graphene. Error bars show the SD of permeances obtained from three samples per membrane type. The prediction of the flow rates are blue and red stars for porous and patterned graphenes, respectively. Error bar was obtained by error propagation calculation based on the graphene properties (section S12). (C) Comparison of highest-porosity PG membrane (30 s) with other membrane materials of the same size cutoff: PCTE, MF Millipore (commercially available), Wei et al. (20), and CNF-71 (32). (D) UV-vis spectra of 30-nm Au NP feed and permeate solutions, showing filtration by porous graphene membrane (2-nm W). The inset shows a photograph of feed and permeate solutions.

  • Fig. 4 Graphene-reinforced polymer nanofilm fabrication and characterization of gas transport through the membranes.

    (A) Schematic of synthesis of freestanding polymer nanofilm supported by triple-layer PG (1) and polycondensation reaction (i to iii). (B) Triple-layer PG suspended on Si3N4/Si before polymer synthesis (i) and after the synthesis of a 40-nm-thick film (ii). Scale bar, 1 μm. Schematic of synthesized polymer on PG (iii). (C) Top: Variation of the thickness of polymer films as a function of 6FDA monomer concentration. Scale bars, 100 nm. Bottom: Representative SEM image of a 20-nm-thick polymer nanofilm. Scale bar, 300 nm. (D) Comparison of separation factor of a 20-nm-thick polymer nanofilm with the theoretical (Graham) selectivity and bare triple-layer PG membrane (PGM). (E) Performance of the state-of-the-art polymer [green crosses (36, 40, 4345)] and graphene membranes [black square (46), blue diamond (4)] in comparison to the 20-nm-thick polymer-graphene nanofilm. The upper bound corresponds to a hypothetical 100-nm-thick polymer.

  • Table 1 Comparison of the membrane characteristics for both porous and patterned graphenes.

    The pore size, pore number density, and areal porosity of porous and patterned graphene membranes, all with standard deviation (SD), are shown. The pore statistics were obtained from the SEM graphs (section S5).

    PG typePorousPatterned
    Number of layers12
    Process parameterNoncatalytic domain sizeDry etching time
    Pore size19.4 (±7.7)–54.1 (±20.3) nm*18 (±7)–30.5 (±18.3) nm
    Areal porosity5.5–13.9%4.4–18%§
    Pore number density0.5–1.5 × 1010 cm−2 (~10–20% deviation)||1.25–2.1 × 1010 cm−2 (~20% deviation)||

    *Figure 2C, blue stars.

    Figure 2C, red circles.

    Figure 2D, blue stars.

    §Figure 2D, red circles.

    ||Section S7.

    Supplementary Materials

    • Supplementary material for this article is available at http://advances.sciencemag.org/cgi/content/full/4/11/eaau0476/DC1

      Section S1. NP formation of tungsten on copper

      Section S2. Patterning graphene using s-BCP/transfer to PCTE

      Section S3. Effect of circular cross section of pores in s-BCP

      Section S4. Graphene coverage on PCTE

      Section S5. Pore size evaluation

      Section S6. Full results of parameter study for patterned graphene

      Section S7. Pore number density of porous and patterned graphenes

      Section S8. TEM and SAED of porous graphene

      Section S9. Membrane preparation for gas and liquid flow measurements

      Section S10. Gas flow permeance measurement

      Section S11. Liquid flow permeance characterization

      Section S12. Calculation of flow impedances through graphene on PCTE

      Section S13. Gold NP filtration

      Section S14. Polymer film formation

      Section S15. Polymer film uniformity by AFM

      Section S16. Gas permeation and separation measurements

      Section S17. Properties of polymer/graphene membranes

      Fig. S1. NP formation of W on Cu.

      Fig. S2. Schematic of the manufacturing process of BCP patterning of graphene.

      Fig. S3. Effect of circular pore cross section in s-BCP on graphene pore formation.

      Fig. S4. Graphene coverage on PCTE.

      Fig. S5. Pore size evaluation using SEM graphs.

      Fig. S6. Full results of parameter study for patterned graphene.

      Fig. S7. Pore number density of porous and patterned graphenes.

      Fig. S8. TEM and SAED of porous graphene.

      Fig. S9. Membrane preparation for gas and liquid flow measurements.

      Fig. S10. Gas flow permeance measurement.

      Fig. S11. Liquid flow permeance measurement.

      Fig. S12. Extraction of liquid flow permeation from measurement.

      Fig. S13. Patterned double-layer graphene membrane (30 s) after DI water flow.

      Fig. S14. Polymer film formation on porous graphene.

      Fig. S15. Polymer film uniformity characterization by AFM.

      Table S1. Computed gas flow impedances for graphene and PCTE and the overall permeance based on the combined impedance model.

      Table S2. Computed liquid flow impedances for graphene and PCTE and the overall flow rate based on the combined impedance model.

      Table S3. Relative error functions based on the simplified error propagation model.

      Table S4. Relative error for gas and liquid permeances computed based on the functions in table S3.

      Table S5. Gas permeation and separation results of polymer/graphene membranes.

    • Supplementary Materials

      This PDF file includes:

      • Section S1. NP formation of tungsten on copper
      • Section S2. Patterning graphene using s-BCP/transfer to PCTE
      • Section S3. Effect of circular cross section of pores in s-BCP
      • Section S4. Graphene coverage on PCTE
      • Section S5. Pore size evaluation
      • Section S6. Full results of parameter study for patterned graphene
      • Section S7. Pore number density of porous and patterned graphenes
      • Section S8. TEM and SAED of porous graphene
      • Section S9. Membrane preparation for gas and liquid flow measurements
      • Section S10. Gas flow permeance measurement
      • Section S11. Liquid flow permeance characterization
      • Section S12. Calculation of flow impedances through graphene on PCTE
      • Section S13. Gold NP filtration
      • Section S14. Polymer film formation
      • Section S15. Polymer film uniformity by AFM
      • Section S16. Gas permeation and separation measurements
      • Section S17. Properties of polymer/graphene membranes
      • Fig. S1. NP formation of W on Cu.
      • Fig. S2. Schematic of the manufacturing process of BCP patterning of graphene.
      • Fig. S3. Effect of circular pore cross section in s-BCP on graphene pore formation.
      • Fig. S4. Graphene coverage on PCTE.
      • Fig. S5. Pore size evaluation using SEM graphs.
      • Fig. S6. Full results of parameter study for patterned graphene.
      • Fig. S7. Pore number density of porous and patterned graphenes.
      • Fig. S8. TEM and SAED of porous graphene.
      • Fig. S9. Membrane preparation for gas and liquid flow measurements.
      • Fig. S10. Gas flow permeance measurement.
      • Fig. S11. Liquid flow permeance measurement.
      • Fig. S12. Extraction of liquid flow permeation from measurement.
      • Fig. S13. Patterned double-layer graphene membrane (30 s) after DI water flow.
      • Fig. S14. Polymer film formation on porous graphene.
      • Fig. S15. Polymer film uniformity characterization by AFM.
      • Table S1. Computed gas flow impedances for graphene and PCTE and the overall permeance based on the combined impedance model.
      • Table S2. Computed liquid flow impedances for graphene and PCTE and the overall flow rate based on the combined impedance model.
      • Table S3. Relative error functions based on the simplified error propagation model.
      • Table S4. Relative error for gas and liquid permeances computed based on the functions in table S3.
      • Table S5. Gas permeation and separation results of polymer/graphene membranes.

      Download PDF

      Files in this Data Supplement:

    Stay Connected to Science Advances

    Navigate This Article