Graphene oxide membranes show exceptional molecular permeation properties, with promise for many applications1,2,3,4,5. However, their use in ion sieving and desalination technologies is limited by a permeation cutoff of ∼9 Å (ref. 4), which is larger than the diameters of hydrated ions of common salts4,6. The cutoff is determined by the interlayer spacing (d) of ∼13.5 Å, typical for graphene oxide laminates that swell in water2,4. Achieving smaller d for the laminates immersed in water has proved to be a challenge. Here, we describe how to control d by physical confinement and achieve accurate and tunable ion sieving. Membranes with d from ∼9.8 Å to 6.4 Å are demonstrated, providing a sieve size smaller than the diameters of hydrated ions. In this regime, ion permeation is found to be thermally activated with energy barriers of ∼10–100 kJ mol–1 depending on d. Importantly, permeation rates decrease exponentially with decreasing sieve size but water transport is weakly affected (by a factor of <2). The latter is attributed to a low barrier for the entry of water molecules and large slip lengths inside graphene capillaries. Building on these findings, we demonstrate a simple scalable method to obtain graphene-based membranes with limited swelling, which exhibit 97% rejection for NaCl.
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This work was supported by the Royal Society and the Engineering and Physical Sciences Research Council, UK (EP/K016946/1 and EP/M506436/1). K.G. acknowledges Marie Curie International Incoming Fellowship. K.S.V. and R.R.N. acknowledge support from BGT Materials Limited.
The authors declare no competing financial interests.
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Abraham, J., Vasu, K., Williams, C. et al. Tunable sieving of ions using graphene oxide membranes. Nature Nanotech 12, 546–550 (2017). https://doi.org/10.1038/nnano.2017.21
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