Abstract
Water security is a pressing issue for global citizens in the 21st century. Concerns over clean water supply, and the environmental impact of industrial waste water, make water treatment a world-wide problem requiring a simple and effective solution. Membrane distillation is an emerging water purification technique that complements state-of-the-art reverse osmosis processes. Membrane distillation achieves high rejection over a range of salt concentrations while maintaining flux, using a temperature differential as opposed to pressure across the membrane. Importantly the process can be driven using low grade waste heat energy. Current membranes used in membrane distillation do not guarantee stable membrane performance under harsh (high salt and acid or base concentrations) conditions. Here we report, a permeable graphene membrane operating in harsh conditions with no observable degradation. A permeate of pH neutral water with a flux of 25 ± 1 L m−2 h−1 is produced by this membrane through near (99.9 ± 0.1%) ion rejection from 0.6 M sodium chloride at pH 1 and pH 13, over 144 h. More complex ion solutions, including real acid mine drainage waste-water, were also successfully purified. These findings may present a membrane that is suitable to improve water supply and reduce the environmental impact of industrial waste-water.
| Original language | English |
|---|---|
| Pages (from-to) | 240-247 |
| Number of pages | 8 |
| Journal | Carbon |
| Volume | 171 |
| Early online date | 9 Sept 2020 |
| DOIs | |
| Publication status | Published - 31 Jan 2021 |
Bibliographical note
Publisher Copyright:© 2020 Elsevier Ltd
Funding
To extend the capabilities of this graphene membrane, the performance of the membrane using a porous polymethylmethacrylate (PMMA) binder and a different support, polyvinylidene difluoride (PVDF), was tested (Fig. 4a and Fig. 4b). Direct use of the graphene with a porous PMMA binder (Fig. S14) removes the acetone cleaning step from the graphene transfer procedure [32]. Binders are commonly used to improve membrane robustness and prevent damage and therefore confirming the performance of the graphene film with a binder is important for implementing them in future applications. Furthermore, it enables the use of the graphene membrane on other supports than those tested. Graphene membranes with the binder and PVDF support produced a neutral pH permeate and rejected 99.9 ? 0.1% NaCl over the 48 h testing period (Fig. 4a). This is a similar result as the graphene on the PTFE support (Fig. 3a) indicating that the porous binder and new polymeric support have minimal impact on ionic rejection. Pristine PVDF membranes (initial flux of 25 ? 1 L m?2 h?1) exhibited rapid membrane performance degradation in less than 2 h, where the salt rejection decreased rapidly and the rapid permeate pH change was observed (Fig. 4b and Figs. S15?S17). We also note that the flux on PVDF supports is slightly lower than on PTFE supports (25?22 L m?2 h?1) potentially due to the lower permeability of PVDF or the presence of the PMMA binder. Exposure of harsh pH solutions to the PVDF membrane caused an observable change in surface properties, possibly leading to the significant degradation in membrane performance of PVDF based membrane. PVDF underneath the graphene layer acting as a support exhibited minimal surface property changes or degradation supporting the experimental results (Fig. 5 and Fig. S18). The porous PMMA with a thickness of ?240 nm (Fig. S19) may also potentially reduce the flux.A porous poly (methyl methacrylate) (PMMA)-binder was used to transfer the graphene sample prepared on Ni substrate onto different membrane substrates. PMMA binder was prepared by using 38 mg/mL of PMMA (Mw 996,000 Sigma Aldrich) dissolved in acetone which was spin-coated onto the permeable graphene sample on Ni foil (3000 rpm for 1 min). The sample was then dried on a hot plate for 10 min at 80 ?C. Subsequently, the underlying Ni foil was dissolved by placing in a bath of 0.5 M FeCl3 for 2 h. The PMMA/graphene film then floated to the surface. The sample was rinsed by exchanging FeCl3 for deionised water. For the preparation of PMMA binder/permeable graphene/PVDF support, a PMMA/permeable graphene sample was lifted out from the DI water bath and transferred onto the PVDF substrate and washed several times with DI water and dried. This was repeated for the graphene/PTFE support with an additional step where the PMMA binder was then dissolved by rinsing with acetone. After drying the sample is rinsed with DI water. A commercial PTFE membrane (Ningbo changqi, 0.45 ?m pore size, 450 ?m thick) was used as the substrate for the permeable graphene/PTFE membrane. For the PMMA binder/permeable graphene/PVDF support, the PVDF was fabricated using electrospinning methods [40]. The same transfer and preperation process was followed for the commercial graphene sample (Multi layer graphene on Nickel - Graphene supermarket) to prepare a commercial graphene/PTFE support membrane (Methods adapted from Seo et al. [23]).This work was supported by the CSIRO's Future Science Platform Program (CSIRO AIM-FSP), Australian Research Council (ARC) and CSIRO-QUT Joint Sustainable Processes and Devices Laboratory. D.H.S. S.Y. A.B. and A.T.M. acknowledge the CSIRO's Future Science Platform Program. S.Y. and A.T.M. acknowledge the CSIRO OCE Postdoctoral Fellowship Program. D. H. S. also acknowledges the UTS Chancellor's Postdoctoral research fellow scheme. Y.C.W. acknowledges the UTS International Research Scholarship (UTS IRS) from the University of Technology Sydney (UTS) and 2017 FEIT Post Thesis Publication Scholarship from UTS. M.X. acknowledges Vice Chancellor Research Fellowship from the Victoria University and Endeavour Australia Cheung Kong Research Fellowship. H. K. S. acknowledges the support from the ARC Future Fellowship (FT140101208). K. O. acknowledges the support from the ARC. The authors acknowledge the help from Dr. Christophe Comte for XRD measurements. This work was supported by the CSIRO’s Future Science Platform Program ( CSIRO AIM-FSP), Australian Research Council (ARC) and CSIRO- QUT Joint Sustainable Processes and Devices Laboratory. D.H.S., S.Y., A.B. and A.T.M. acknowledge the CSIRO’s Future Science Platform Program. S.Y. and A.T.M. acknowledge the CSIRO OCE Postdoctoral Fellowship Program. D. H. S. also acknowledges the UTS Chancellor’s Postdoctoral research fellow scheme. Y.C.W. acknowledges the UTS International Research Scholarship ( UTS IRS) from the University of Technology Sydney ( UTS ) and 2017 FEIT Post Thesis Publication Scholarship from UTS . M.X. acknowledges Vice Chancellor Research Fellowship from the Victoria University and Endeavour Australia Cheung Kong Research Fellowship. H. K. S. acknowledges the support from the ARC Future Fellowship (FT140101208). K. O. acknowledges the support from the ARC . The authors acknowledge the help from Dr. Christophe Comte for XRD measurements.
Keywords
- Chemical vapour deposition
- Graphene
- Harsh pH solution
- Membrane
- Water purification
ASJC Scopus subject areas
- General Chemistry
- General Materials Science
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