Research ArticleAPPLIED SCIENCES AND ENGINEERING

Design and function of biomimetic multilayer water purification membranes

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Science Advances  05 Apr 2017:
Vol. 3, no. 4, e1601939
DOI: 10.1126/sciadv.1601939
  • Fig. 1 Coarse-grained computational MD simulations of SNF/HAP assembly and deposition.

    Elastic network models are built on mechanics and geometry feature of the unit building blocks. HAP-SNF surface energy γ (J/m2) is not certain because it depends on the molecular structure and the hierarchy structure of the interface in contact. This is important in forming the layered structure. For the SNF/HAP model, HAP and SNF particles were randomly distributed initially and then subjected to a gravity field that accounts for the drag force from the water flow. (A to C) Snapshots of the HAP/SNF assembly process during deposition, with γ set as 0 (A), 0.217 J/m2 (B), and 0.53 J/m2 (C).

  • Fig. 2 The pathway to fabricate the SNF/HAP membranes and visualization of typical multilayer structures formed.

    (A) Schematic of the preparation steps of SNF/HAP membranes. Step 1: Silk was assembled to SNFs in aqueous solution. The bottom image in the first row is an atomic force microscopy (AFM) image of SNFs; the top image in the second row is the SNF solution under polarized light, indicating the presence of a nematic phase of SNFs. Step 2: The SNFs were used as templates to induce the growth of HAP nanocrystals. The bottom image in the third row is an image of SNF/HAP solution; the top image in the fourth row is a scanning electron microscopy (SEM) image of biomineralized HAP nanocrystals. Step 3: SNF/HAP dispersions were assembled into membranes via vacuum filtration. (B) Multilayer structures of the membranes. The third image is an SNF/HAP membrane with a thickness of 4 μm. This membrane was directly moved from the supporting substrate after filtration of the SNF/HAP dispersion in a process that took 9 s. The second image is the cross-sectional SEM image of SNF/HAP membrane, which shows nacre-like, highly ordered multilayer structures. The first image is the high-resolution cross-sectional SEM of an SNF/HAP membrane. The clear SNF- and HAP-rich layers can be observed. False color was used in AFM and SEM images.

  • Fig. 3 The well-organized multilayer structures of SNF/HAP membranes.

    (A to D) The double-layer structure of the SNF/HAP membranes was formed through vacuum filtration of 1 ml of dispersion. (A) Schematic of double-layer structures. The top layer is the SNF-rich layer with small pore sizes. The bottom layer is the HAP layer with larger pore sizes. (B) Cross-sectional SEM image of a double-layer membrane. (C and D) Top-view SEM images of SNF-rich (C) and HAP-rich (D) layers. (E to G) The multilayer structure of the SNF/HAP membrane was generated from 3-ml SNF/HAP dispersion using a 3.5-cm-diameter mold. (E) Schematic of multilayer structures. (F) Cross-sectional SEM image of a multilayer membrane. (G) High-resolution cross-sectional SEM image of a multilayer membrane. False color is used in SEM images.

  • Fig. 4 Separation performance of SNF/HAP membranes.

    (A) Cross-sectional representation of a multilayer SNF/HAP membrane to filter compounds. (B) Image of the SNF/HAP-based syringe nanofilter, which successfully rejected Alcian Blue 8GX with a rejection of 98%. The detailed structures of SNF/HAP membranes formed on microfilters can be found in fig. S16B. (C) SNF/HAP nanofiltration membrane before (top) and after (bottom) filtration with 20 ml of 5 mM Rhodamine B solution. (D) Linear relationship between film thickness and film formation processing time. (E) Thickness-dependent changes in permeability to pure water for the SNF/HAP membranes and other previously reported membranes. The blue dash-dot line is a fitted curve using the Hagen-Poiseuille equation with uniform structure (9, 44). The red solid line is a fitted curve using Eq. 1 for multilayer membrane (see also section S8). (F) Time-dependent changes in the flux of water and dye solution within 24 hours of flow. (G) Separation performance of 7-μm-thick SNF/HAP membranes for dyes, proteins, and colloids after 10 min, 2 hours, and 24 hours of flow. The flux listed in the table was calculated from the filtration of model compound solutions. The filtration pressure was kept at 80 kPa in all these tests. Several dye solutions have lower flux than pure water, likely because of their large molecular size, which would be responsible for blocking the pores of membranes. (H) Comparison of the 5-nm gold nanoparticle separation performance of SNF/HAP membranes to that of other filtration membrane materials. The rejection is represented by the color of the pattern. The blue and red are 0 and 100% rejection, respectively. Cd(OH)2, Cu(OH)2, and Zn(OH)2 are Cd(OH)2, Cu(OH)2, and Zn(OH)2 nanofibers. Cellulose, cellulose nanofibers; SPEK-C, sulfonated polyetherketone with cardo groups; WS2, chemically exfoliated tungsten disulfide nanosheets; PS NP, polystyrene nanoparticles; GO, graphene oxide sheets; CNF, carbonaceous nanofiber; PP2b, 5,5′-bis(1-ethynyl-7 polyethylene glycol-N,N′-bis(ethylpropyl) perylene-3,4,9,10-tetracarboxylic diimide)-2,2′-bipyridine.

  • Fig. 5 Removal and recycling of heavy metal ions by SNF/HAP membranes.

    (A) Image of SNF/HAP dispersion-adsorbed metal ions at 0 and 24 hours (see section S10 for more details). (B) Image of an SNF/HAP membrane after metal ions were adsorbed through flux-controllable filtration. (C) Schematic of a general route for recycling metal ion contaminants by redispersion of saturated SNF/HAP membrane (see section S11 for more details). (D) Table of separation and adsorption performance of SNF/HAP nanocomposites for heavy metal ions (see section S10 for more details). The adsorbent capacity of Ag+ and Pb2+ is not listed quantitatively because Ag+ and Pb2+ interacted with Cl to yield a precipitate. The maximum adsorption capabilities of SNF/HAP composite for metal ions were calculated from equilibrium adsorption isotherms data (see section S10 for details). IARC, International Agency for Research on Cancer. (E) Gold contaminants can be reused after facile and green postprocessing (see section S11 for more details about postprocessing for metal ions). (F) Cost and adsorption capacity estimates for the most-studied nanomaterials. The detailed calculations and comparisons of these materials are shown in section S12. TEMPO, 2,2,6,6-tetramethylpiperidine 1-oxyl; MWCNT, multiwalled carbon nanotube; SWCNT, single-walled carbon nanotube.

Supplementary Materials

  • Supplementary material for this article is available at http://advances.sciencemag.org/cgi/content/full/3/4/e1601939/DC1

    movie S1. Movie of MD simulation of the SNF/HAP assembly process during deposition, with surface energy γ set as 0 J/m2.

    movie S2. Movie of MD simulation of the SNF/HAP assembly process during deposition, with surface energy γ set as 0.217 J/m2.

    movie S3. Movie of MD simulation of the SNF/HAP assembly process during deposition, with surface energy γ set as 0.53 J/m2.

    movie S4. Movie of preparation of SNF/HAP syringe ultrafilters.

    movie S5. Movie showing that top-down prepared SNF dispersions are directly passing through the 5-μm syringe macrofilter.

    section S1. Experimental section

    section S2. Coarse-grained computational model for SNF/HAP assembly and deposition

    section S3. The self-assembly process and structure of SNFs

    section S4. Synthesis of HAP nanocrystals via biomineralization approach

    section S5. Multilayer membrane formation and their properties

    section S6. Multilayer structure of SNF/HAP membrane

    section S7. Multitypes of SNF/HAP multilayer membranes

    section S8. Mechanical model of SNF/HAP membrane for water filtration

    section S9. Dye separation and adsorption performance of SNF/HAP membranes

    section S10. Heavy metal ion removal performance of SNF/HAP membranes

    section S11. Recycling of metal ion contaminants captured by SNF/HAP membrane via green postprocessing approaches

    section S12. Comparing the costs and maximum sorption capacities of SNF/HAP membranes with other nanoadsorbents

    fig. S1. Schematic figure of the coarse-grained computational model for HAP and SNF.

    fig. S2. Simulation setups and related parameters for SNF/HAP assembly and deposition modeling.

    fig. S3. Distributions of the mass ratio between HAP and SNF as functions of the coordinate along the membrane thickness direction for the three membranes assembled with different γ values.

    fig. S4. Distributions of the mass ratio between NP and NF as functions of the coordinate along the membrane thickness direction for the 15 membranes assembled with different γ values.

    fig. S5. Visual appearance and AFM image of SNFs.

    fig. S6. XRD profile and Fourier transform infrared spectrum of biomineralized HAP nanocrystals.

    fig. S7. SEM image of biomineralized HAP nanocrystals.

    fig. S8. SF solution induced the growth of HAP at 37°C for 1 week.

    fig. S9. Mesostructure of SNF/HAP solution after liquid nitrogen freezing and freeze-drying.

    fig. S10. Linear relationship between the volume of SNF/HAP solution and the resultant membrane thickness.

    fig. S11. Images of SNF/HAP membranes after moving from the substrate with a thickness of 4 μm.

    fig. S12. Stress-strain curves of as-cast SNF/HAP membrane with a thickness of 37 μm.

    fig. S13. Multilayer structure of nacre.

    fig. S14. SEM images of SNF/HAP membranes.

    fig. S15. Elemental analysis of the cross-sectional SNF/HAP membranes.

    fig. S16. Multitypes of SNF/HAP multilayer membranes.

    fig. S17. Schematic of SNF/HAP multilayer filtration membrane.

    fig. S18. Calculation of SNF and HAP thickness via power-law fittings.

    fig. S19. Comparison of theory fluxes of pure SNF, HAP, and SNF/HAP membranes with similar thicknesses.

    fig. S20. Rejection of 10 ml of 5 μM Rhodamine B aqueous solution with different thicknesses of the SNF/HAP membranes.

    fig. S21. Relationship between pressure and pure water flux of ejection of 37-μm-thick SNF/HAP membrane.

    fig. S22. The rejection of 10 ml of 5 μM Rhodamine B aqueous solution for 37-μm-thick SNF/HAP membrane with different applied pressures.

    fig. S23. Relationship between membrane thickness and adsorbed dye content.

    fig. S24. Equilibrium adsorption isotherms of dye adsorption on SNF/HAP membranes.

    fig. S25. UV-vis spectra of starting and retentate solution of Rhodamine B and Congo Red.

    fig. S26. SNF/HAP membrane used for large-volume permeate filtration.

    fig. S27. Equilibrium adsorption isotherms of Au3+, Cu2+, Ni2+, and Cr3+ adsorption on SNF/HAP nanocomposites.

    fig. S28. Kinetic curves of SNF/HAP nanocomposites for removing metal ions.

    fig. S29. Redispersion of SNF/HAP membranes after filtration with Au3+ ions.

    fig. S30. Recycling of metal ion contaminants via green postprocessing approaches.

    table S1. Numerical values of the physical parameters of the coarse-grained model.

    table S2. Numerical values of the physical parameters of the five coarse-grained models of NF and NP with the variation of the stiffness and density.

    table S3. Numerical values of the membrane.

    table S4. Langmuir and Freundlich isotherm parameters of dye adsorption on SNF/HAP nanocomposites.

    table S5. Langmuir and Freundlich isotherm parameters of metal ion adsorption on SNF/HAP nanocomposites.

    table S6. Kinetic parameters of second-order adsorption kinetic models for metal ions on SNF/HAP nanocomposites.

    table S7. Estimated total cost for preparing 1 g of nanoadsorbents.

    table S8. Maximum sorption capacities of metal ions with different nanomaterials.

    References (54101)

  • Supplementary Materials

    This PDF file includes:

    • Legends for movies S1 to S5
    • section S1. Experimental section.
    • section S2. Coarse-grained computational model for SNF/HAP assembly and deposition.
    • section S3. The self-assembly process and structure of SNFs.
    • section S4. Synthesis of HAP nanocrystals via biomineralization approach.
    • section S5. Multilayer membrane formation and their properties.
    • section S6. Multilayer structure of SNF/HAP membrane.
    • section S7. Multitypes of SNF/HAP multilayer membranes.
    • section S8. Mechanical model of SNF/HAP membrane for water filtration.
    • section S9. Dye separation and adsorption performance of SNF/HAP membranes.
    • section S10. Heavy metal ion removal performance of SNF/HAP membranes.
    • section S11. Recycling of metal ion contaminants captured by SNF/HAP membrane via green postprocessing approaches.
    • section S12. Comparing the costs and maximum sorption capacities of SNF/HAP membranes with other nanoadsorbents.
    • fig. S1. Schematic figure of the coarse-grained computational model for HAP and SNF.
    • fig. S2. Simulation setups and related parameters for SNF/HAP assembly and deposition modeling.
    • fig. S3. Distributions of the mass ratio between HAP and SNF as functions of the coordinate along the membrane thickness direction for the three membranes assembled with different γ values.
    • fig. S4. Distributions of the mass ratio between NP and NF as functions of the coordinate along the membrane thickness direction for the 15 membranes assembled with different γ values.
    • fig. S5. Visual appearance and AFM image of SNFs.
    • fig. S6. XRD profile and Fourier transform infrared spectrum of biomineralized HAP nanocrystals.
    • fig. S7. SEM image of biomineralized HAP nanocrystals.
    • fig. S8. SF solution induced the growth of HAP at 37°C for 1 week.
    • fig. S9. Mesostructure of SNF/HAP solution after liquid nitrogen freezing and freeze-drying.
    • fig. S10. Linear relationship between the volume of SNF/HAP solution and the resultant membrane thickness.
    • fig. S11. Images of SNF/HAP membranes after moving from the substrate with a thickness of 4 μm.
    • fig. S12. Stress-strain curves of as-cast SNF/HAP membrane with a thickness of 37 μm.
    • fig. S13. Multilayer structure of nacre.
    • fig. S14. SEM images of SNF/HAP membranes.
    • fig. S15. Elemental analysis of the cross-sectional SNF/HAP membranes.
    • fig. S16. Multitypes of SNF/HAP multilayer membranes.
    • fig. S17. Schematic of SNF/HAP multilayer filtration membrane.
    • fig. S18. Calculation of SNF and HAP thickness via power-law fittings.
    • fig. S19. Comparison of theory fluxes of pure SNF, HAP, and SNF/HAP membranes with similar thicknesses.
    • fig. S20. Rejection of 10 ml of 5 μM Rhodamine B aqueous solution with different thicknesses of the SNF/HAP membranes.
    • fig. S21. Relationship between pressure and pure water flux of ejection of 37-μm-thick SNF/HAP membrane.
    • fig. S22. The rejection of 10 ml of 5 μM Rhodamine B aqueous solution for 37-μm-thick SNF/HAP membrane with different applied pressures.
    • fig. S23. Relationship between membrane thickness and adsorbed dye content.
    • fig. S24. Equilibrium adsorption isotherms of dye adsorption on SNF/HAP membranes.
    • fig. S25. UV-vis spectra of starting and retentate solution of Rhodamine B and Congo Red.
    • fig. S26. SNF/HAP membrane used for large-volume permeate filtration.
    • fig. S27. Equilibrium adsorption isotherms of Au3+, Cu2+, Ni2+, and Cr3+ adsorption on SNF/HAP nanocomposites.
    • fig. S28. Kinetic curves of SNF/HAP nanocomposites for removing metal ions.
    • fig. S29. Redispersion of SNF/HAP membranes after filtration with Au3+ ions.
    • fig. S30. Recycling of metal ion contaminants via green postprocessing approaches.
    • table S1. Numerical values of the physical parameters of the coarse-grained model.
    • table S2. Numerical values of the physical parameters of the five coarse-grained models of NF and NP with the variation of the stiffness and density.
    • table S3. Numerical values of the membrane.
    • table S4. Langmuir and Freundlich isotherm parameters of dye adsorption on SNF/HAP nanocomposites.
    • table S5. Langmuir and Freundlich isotherm parameters of metal ion adsorption on SNF/HAP nanocomposites.
    • table S6. Kinetic parameters of second-order adsorption kinetic models for metal ions on SNF/HAP nanocomposites.
    • table S7. Estimated total cost for preparing 1 g of nanoadsorbents.
    • table S8. Maximum sorption capacities of metal ions with different nanomaterials.
    • References (54–101)

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    Other Supplementary Material for this manuscript includes the following:

    • movie S1 (.mov format). Movie of MD simulation of the SNF/HAP assembly process during deposition, with surface energy γ set as 0 J/m2.
    • movie S2 (.mov format). Movie of MD simulation of the SNF/HAP assembly process during deposition, with surface energy γ set as 0.217 J/m2.
    • movie S3 (.mov format). Movie of MD simulation of the SNF/HAP assembly process during deposition, with surface energy γ set as 0.53 J/m2.
    • movie S4 (.mov format). Movie of preparation of SNF/HAP syringe ultrafilters.
    • movie S5 (.mov format). Movie showing that top-down prepared SNF dispersions are directly passing through the 5-μm syringe macrofilter.

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