Supplementary material for Sheath, P., Majumder, M., 2015, Flux accentuation and improved
rejection in graphene-based filtration membranes produced by capillary-force-assisted self-assembly,
Phil. Trans. R. Soc. A. doi: 10.1098/rsta.[paper ID in form xxxx.xxxx e.g. 10.1098/rsta.2014.0049]
Supplementary material
RGO calibration curve
Supplementary Figure S1: RGO calibration curve. The calibration curve equation is y=0.041x-0.025.
Note that the data is strongly linear with R2=0.997.
Membrane testing
Supplementary Figure S2: Schematic of dead end pressure cell.
© The Authors under the terms of the Creative Commons Attribution License http://creativecommons.org/licenses/by/3.0/, which
permits unrestricted use, provided the original author and source are credited.
Supplementary material for Sheath, P., Majumder, M., 2015, Flux accentuation and improved
rejection in graphene-based filtration membranes produced by capillary-force-assisted self-assembly,
Phil. Trans. R. Soc. A. doi: 10.1098/rsta.[paper ID in form xxxx.xxxx e.g. 10.1098/rsta.2014.0049]
SEM characterisation
Cross sections of the membranes were prepared by immersing small rectangular cut pieces of the
membrane into liquid nitrogen for several minutes and cleaving them in half with flat tweezers.
Cleaved sections were mounted onto the side of a stub and gold coated. SEM images were taken
with an FEI Nova NanoSEM 450 FEGSEM. SEM images of the top surfaces and cross sections of
tested membranes in comparison to bare Nylon are shown in Figure S4.
Supplementary Figure S3: SEM images of the tops (left panes: a, c, e) and the cross sections (right
panes b, d, f) for bare Nylon, vacuum filtration membranes and CAS membranes.
© The Authors under the terms of the Creative Commons Attribution License http://creativecommons.org/licenses/by/3.0/, which
permits unrestricted use, provided the original author and source are credited.
Supplementary material for Sheath, P., Majumder, M., 2015, Flux accentuation and improved
rejection in graphene-based filtration membranes produced by capillary-force-assisted self-assembly,
Phil. Trans. R. Soc. A. doi: 10.1098/rsta.[paper ID in form xxxx.xxxx e.g. 10.1098/rsta.2014.0049]
AFM images
AFM images were taken with a Dimension Icon AFM using ScanAsystTM mode and NanoScope
Analysis software to analyse and render the images. The images correspond to the SEM images
which show that RGO deposited onto Nylon produces smoother topologies compared to the bare
Nylon and that CAS appears to have a less rough surface topology compared to vacuum filtration.
Supplementary Figure S4: Typical surface AFM for bare Nylon (top), vacuum filtration membranes
(middle) and CAS membranes (bottom).
FTIR characterisation
FTIR was taken using a PerkinElmer 100 ATR-FTIR. Characteristic peaks of Nylon [1] are
superseded by an RGO coating. Irrespective of the coating method (CAS or vacuum filtration), the
RGO chemistry is identical. Peaks corresponding to residual oxygen groups carbonyl (1736 cm -1) and
hydroxyl (1313 cm-1) groups are evident, as is the characteristic peak for sp2 aromatic carbon (1667
cm-1) [2].
Supplementary Figure S5: FTIR of pristine Nylon and of RGO loaded onto Nylon.
© The Authors under the terms of the Creative Commons Attribution License http://creativecommons.org/licenses/by/3.0/, which
permits unrestricted use, provided the original author and source are credited.
Supplementary material for Sheath, P., Majumder, M., 2015, Flux accentuation and improved
rejection in graphene-based filtration membranes produced by capillary-force-assisted self-assembly,
Phil. Trans. R. Soc. A. doi: 10.1098/rsta.[paper ID in form xxxx.xxxx e.g. 10.1098/rsta.2014.0049]
Polarised light microscopy
The order parameter provides a means to quantitatively compare the degree of order from
measurement of the azimuth angle (the angle of maximum transmittance):
where θ is the angle between the director (the mean azimuth) and the local azimuth. The Abrio
software produces azimuth value per pixel along a user defined line (or series of lines) from which the
order parameter per pixel may be determined and then averaged to provide the final result.
Optical images of the top surface of membranes on Nylon and after transfer to glass reveal that the
transfer appears to have a negligible effect on the morphology of the membranes and therefore it is
presumed that the order parameter is not adversely affected by the transfer onto glass.
Supplementary Figure S6: Optical images showing that transfer onto glass appears to have a
negligible effect on the morphology of RGO depositions. This indicates that the order parameter is not
likely to be greatly affected by the transfer and subsequent drying process.
© The Authors under the terms of the Creative Commons Attribution License http://creativecommons.org/licenses/by/3.0/, which
permits unrestricted use, provided the original author and source are credited.
Supplementary material for Sheath, P., Majumder, M., 2015, Flux accentuation and improved
rejection in graphene-based filtration membranes produced by capillary-force-assisted self-assembly,
Phil. Trans. R. Soc. A. doi: 10.1098/rsta.[paper ID in form xxxx.xxxx e.g. 10.1098/rsta.2014.0049]
Flow paths for solute
Supplementary Figure S7: Schematic of possible flow paths within stacked RGO membranes.
Permeance data for dye solutions
Supplementary Figure S8: Pure water and dye solution permeance of CAS and vacuum filtration
membranes.
© The Authors under the terms of the Creative Commons Attribution License http://creativecommons.org/licenses/by/3.0/, which
permits unrestricted use, provided the original author and source are credited.
Supplementary material for Sheath, P., Majumder, M., 2015, Flux accentuation and improved
rejection in graphene-based filtration membranes produced by capillary-force-assisted self-assembly,
Phil. Trans. R. Soc. A. doi: 10.1098/rsta.[paper ID in form xxxx.xxxx e.g. 10.1098/rsta.2014.0049]
UV-vis spectroscopy spectra
Supplementary Figure S9: Typical UV-visible spectra of dye solutions showing the differences
between feed and permeate for a) MB, b) DY and c) OG. See Table 1 in the main text for a list of the
peak wavelengths for each dye.
© The Authors under the terms of the Creative Commons Attribution License http://creativecommons.org/licenses/by/3.0/, which
permits unrestricted use, provided the original author and source are credited.
Supplementary material for Sheath, P., Majumder, M., 2015, Flux accentuation and improved
rejection in graphene-based filtration membranes produced by capillary-force-assisted self-assembly,
Phil. Trans. R. Soc. A. doi: 10.1098/rsta.[paper ID in form xxxx.xxxx e.g. 10.1098/rsta.2014.0049]
Salt rejection
We also tested the rejection of selected salts (Na2SO4, MgCl2 and K3[Fe(CN)6]) over CAS and
vacuum filtration membranes All tests were conducted at 3 bar with salt concentration of 20 mM. An
Ocean Optics USB4000 UV-vis spectrometer was used to determine the concentration of K3[Fe(CN)6]
(λmax= 220 nm) whilst a PS Aqua C 10 mm immersion probe with k=1.0 sensor and automatic
temperature compensation (Thermo Fisher Scientific) was used to determine the concentration of
Na2SO4 and MgCl2 salt solutions.
CAS and vacuum membranes both exhibited small salt rejections (Supplementary Figure S10). This
is not surprising considering that the channel dimensions are larger than the size of the salts. Donnan
exclusion has been attributed as the predominant mechanism responsible for the rejection of salts by
GO/RGO membranes [3, 4].
Supplementary Figure S10: Rejection character for three salt solutions over CAS and vacuum
filtration membranes.
The pure-water normalised permeance for salt solutions is shown in Figure S11. We attribute the
reduction in permeance of K3[Fe(CN)6] to concentration polarisation, a phenomena responsible for
flux decline in membranes and which is enhanced by larger diameter solutes and concentration [5].
Concentration polarisation effects can be mitigated by using cross-flow filtration [6] or related
shear/turbulence inducing techniques[7]. Flux decline was not significant for the dye probes (Figure
S9) since the concentrations used were much smaller.
© The Authors under the terms of the Creative Commons Attribution License http://creativecommons.org/licenses/by/3.0/, which
permits unrestricted use, provided the original author and source are credited.
Supplementary material for Sheath, P., Majumder, M., 2015, Flux accentuation and improved
rejection in graphene-based filtration membranes produced by capillary-force-assisted self-assembly,
Phil. Trans. R. Soc. A. doi: 10.1098/rsta.[paper ID in form xxxx.xxxx e.g. 10.1098/rsta.2014.0049]
Supplementary Figure S11: Relative pure water and salt solution permeance through CAS and
vacuum filtration membranes. Permeance has been normalised with respect to the pure water
permeance of vacuum/CAS.
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© The Authors under the terms of the Creative Commons Attribution License http://creativecommons.org/licenses/by/3.0/, which
permits unrestricted use, provided the original author and source are credited.