Controlled transport of water molecules through membranes and capillaries is important in areas as diverse as water purification and healthcare technologies1,2,3,4,5,6,7. Previous attempts to control water permeation through membranes (mainly polymeric ones) have concentrated on modulating the structure of the membrane and the physicochemical properties of its surface by varying the pH, temperature or ionic strength3,8. Electrical control over water transport is an attractive alternative; however, theory and simulations9,10,11,12,13,14 have often yielded conflicting results, from freezing of water molecules to melting of ice14,15,16 under an applied electric field. Here we report electrically controlled water permeation through micrometre-thick graphene oxide membranes17,18,19,20,21. Such membranes have previously been shown to exhibit ultrafast permeation of water17,22 and molecular sieving properties18,21, with the potential for industrial-scale production. To achieve electrical control over water permeation, we create conductive filaments in the graphene oxide membranes via controllable electrical breakdown. The electric field that concentrates around these current-carrying filaments ionizes water molecules inside graphene capillaries within the graphene oxide membranes, which impedes water transport. We thus demonstrate precise control of water permeation, from ultrafast permeation to complete blocking. Our work opens up an avenue for developing smart membrane technologies for artificial biological systems, tissue engineering and filtration.
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This work was supported by the Royal Society, Engineering and Physical Sciences Research Council, UK (EP/K016946/1, EP/N013670/1 and EP/P00119X/1), British Council (award reference number 279336045), European Research Council (contract 679689) and Lloyd’s Register Foundation. We thank J. Waters for assisting with X-ray measurements and G. Yu for electrical measurements.
Nature thanks H. Fang, N. Koratkar, B. Mi and H. B. Park for their contribution to the peer review of this work.
The authors declare no competing interests.
Publisher’s note: Springer Nature remains neutral with regard to jurisdictional claims in published maps and institutional affiliations.
Extended data figures and tables
a, Fabrication procedure for the metal–GO–metal sandwich membrane. b, Photograph of one of our metal–GO–metal sandwich membranes attached to the PET sheet (step 2 in a). Scale bar, 6 mm. This was further attached onto another plastic disk to seal the metal container for gravimetric testing. c, SEM image showing the discontinuities and voids in a 10-nm gold thin film on a GO membrane. Scale bar, 150 nm. d, Water permeation rate of metal–GO–metal sandwiched membranes as a function of gold electrode thickness. The dotted line is a guide to the eye. Water permeation rates of a bare porous silver (Ag) support (red filled circle) and a commercial polyamide nanofiltration membrane (green filled circle) are provided for comparison. Inset, SEM image of a 50-nm-thick gold thin film on a GO membrane. Scale bar, 150 nm.
Extended Data Fig. 2 Conducting filament formation in a GO membrane and its electrical characterization.
a, I–V characteristics during the first voltage sweep show a sudden increase in the current for membranes exposed to humid conditions, suggesting partial electrical breakdown of the GO membrane and conducting filament formation. b, In-plane and out-of-plane I–V characteristics of the GO membrane after filament formation. Inset, out-of-plane I–V characteristics of the GO membrane at 100% RH and vacuum.
a, Topographical SEM image of a GO membrane after the formation of conducting filaments. b–d, Raman intensity ratio (ID/IG) mapping of D and G bands for a pristine GO membrane (b) and a GO membrane after conducting filaments have formed (c, d). c, Raman imaging from the membrane surface close to the positive electrode (about 200 nm away). d, Raman imaging from the membrane surface close to the negative electrode (about 100 nm away). e, f, The Raman spectra from the dark blue and green regions in c, respectively. g–j, Topography and the corresponding TUNA current image of pristine GO (g and h, respectively) and conducting GO (i and j) membranes (filament formed at 100% RH) exfoliated on a gold-thin-film-coated Si substrate. The conducting filaments are marked by red circles. Scale bars, 1 μm. k, Out-of-plane I–V characteristics of a conducting GO membrane with a diameter of about 7 mm before (parent membrane) and after dividing into four equal pieces. Inset, schematic of the structure of conducting carbon filaments in the GO membrane.
Extended Data Fig. 4 Influence of intercalated water and oxygen content on conducting filament formation in GO membranes.
a, b, Topography and the corresponding TUNA current images of GO membranes after filament formation at 40% RH (a and b, respectively) and inside liquid water (c and d). e, I–V characteristics of pristine and partially reduced (‘pr’) GO membranes during the first voltage sweep at 100% RH show partial breakdown. f, TUNA current image of a partially reduced GO membrane after filament formation. The conducting filaments are marked by red circles. Scale bars, 2 μm.
a, C 1s spectrum from a pristine GO membrane. b, c, C 1s spectra from GO membranes used for the electrically controlled permeation experiments after filament formation, from a freshly cleaved membrane surface close to the inner middle region (b) and close to the positive electrode (c). Black lines, raw data; red lines, the fitting envelope; blue lines, deconvolved peaks attributed to the chemical environments indicated.
a, Schematic of the experimental set-up for mass spectrometry measurements. A throttle valve (TV) controls the gas inlet with a capacitance gauge (CG) used to measure the upstream pressure. An isolation valve (IV) isolates upstream and downstream sides of the membrane. A rotary pump (RP1) evacuates the feed and the permeate side to 1 mbar. The quadrupole mass spectrometer (QMS) measures the downstream partial pressure. A turbomolecular pump (TP) backed by a rotary pump (RP2) evacuates the high-vacuum chamber of the mass spectrometer. An active ion gauge (IG) measures the pressure down to 1 × 10−9 torr in the high-vacuum side. b, The partial pressure of He, H2, O2 and H2O at the permeate side as a function of time at different currents through the membrane. No detectable change is observed in the partial pressures of He, H2 and O2 under different currents through the membrane. c, The partial pressure of H2O as a function of the current across the GO membrane and the corresponding I–V characteristics (colour-coded axes).The dotted lines are guides to the eye.
a, Schematic of the experimental set-up. b, I–V characteristics of a Au/GO/Ag membrane during the first voltage sweep while it is immersed in liquid water in the experimental set-up. c, Liquid water permeation rate as a function of current across the membrane after filament formation and the corresponding I–V characteristics (colour-coded axes). Sample-to-sample variation in the permeation is less than 30% (three samples measured).
a, Measured membrane temperature as a function of the current flowing across the membrane during the electrically controlled water permeation experiment. Error bars, standard deviation from 10 different measurements across the sample. b, The weight intake of a Au/GO/Ag membrane (1-μm-thick GO) at different humidity and electric current values. Weight intake is calculated with respect to the weight of the membrane at 0% RH. The shaded areas show the time during humidity sweeps.
a, Schematic of the application of a voltage V across an electrically conducting wire with radius a and length L; b is the point at which the potential decays to zero; r represents any point between a and b where the electric field E is calculated. b, Magnitude of E and its spatial distribution as a function of r and z around a conductive filament with 1-V potential difference across the ends and with 1-nA current flow.
a, Side view of our molecular dynamics simulation set-up used to study the flow of water mixed with H3O+ and OH− ions in the graphene capillary. The model contains two boxes connected by a graphene capillary. At the beginning of the simulation, water was mixed with H3O+ and OH− ions (red and white dots). By moving the left wall (subjected to external pressure) of the box towards the capillary, the water flow is created and the right box is gradually filled. The arrow indicates the direction of the external pressure applied on the left wall of the box. b, c, Number of water molecules in the capillary (b) and number of water molecules in the right box (c) for pure water and water with ions once pressure is applied to the left box (colour-coded labels). d, Water flow rate as a function of the concentration of ions inside the capillary.
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Zhou, K., Vasu, K.S., Cherian, C.T. et al. Electrically controlled water permeation through graphene oxide membranes. Nature 559, 236–240 (2018). https://doi.org/10.1038/s41586-018-0292-y
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