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Heterogeneous sub-continuum ionic transport in statistically isolated graphene nanopores

Nature Nanotechnology volume 10, pages 1053–1057 (2015)Cite this article

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Abstract

Graphene and other two-dimensional materials offer a new class of ultrathin membranes that can have atomically defined nanopores with diameters approaching those of hydrated ions1,2,3,4,5,6,7. These nanopores have the smallest possible pore volumes of any ion channel, which, due to ionic dehydration8 and electrokinetic effects9, places them in a novel transport regime and allows membranes to be created that combine selective ionic transport10 with ultimate permeance11,12,13 and could lead to separations14,15 and sensing16 applications. However, experimental characterization and understanding of sub-continuum ionic transport in nanopores below 2 nm is limited17,18. Here we show that isolated sub-2 nm pores in graphene exhibit, in contrast to larger pores, diverse transport behaviours consistent with ion transport over a free-energy barrier arising from ion dehydration and electrostatic interactions. Current–voltage measurements reveal that the conductance of graphene nanopores spans three orders of magnitude8 and that they display distinct linear, voltage-activated or rectified current–voltage characteristics and different cation-selectivity profiles. In rare cases, rapid, voltage-dependent stochastic switching is observed, consistent with the presence of a dissociable group in the pore vicinity19. A modified Nernst–Planck model incorporating ion hydration and electrostatic effects quantitatively matches the observed behaviours.

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Figure 1: Statistical isolation and conductance measurement of graphene nanopores.
Figure 2: Current–voltage (I–V) characteristics reflect ion hydration and electrostatic effects.
Figure 3: Hydration-based cation selectivity.
Figure 4: Voltage-activated switching of nanopore state.

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Acknowledgements

This work was supported by the US Department of Energy, Office of Basic Energy Sciences under award no. DE-SC0008059. The research made use of the Materials Research Science and Engineering Centers Shared Experimental Facilities supported by the National Science Foundation under award no. DMR-0819762 at the Massachusetts Institute of Technology. Scanning transmission electron microscopy was conducted at Oak Ridge National Laboratory's Center for Nanophase Materials Sciences (CNMS), which is a US Department of Energy, Office of Science User Facility.

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Authors and Affiliations

  1. Department of Mechanical Engineering, Massachusetts Institute of Technology, Cambridge, 02139, Massachusetts, USA

    Tarun Jain, Benjamin C. Rasera, Ricardo Jose S. Guerrero, Michael S. H. Boutilier, Sean C. O'Hern & Rohit Karnik

  2. Center for Nanophase Materials Sciences, Oak Ridge National Laboratory, Oak Ridge, 37831, Tennessee, USA

    Juan-Carlos Idrobo

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  1. Tarun Jain
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Contributions

T.J. and R.K. designed the experiments and wrote the manuscript. T.J., B.C.R. and R.J.S.G. performed ionic transport measurements. T.J., R.K. and M.S.H.B. developed the theoretical model and T.J. performed data analysis. S.C.O. and J.C.I. performed the scanning transmission electron microscopy experiments, and M.S.H.B compiled the histogram.

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Correspondence to Rohit Karnik.

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R.K. declares financial interest in a start-up company that aims to commercialize graphene membranes.

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Jain, T., Rasera, B., Guerrero, R. et al. Heterogeneous sub-continuum ionic transport in statistically isolated graphene nanopores. Nature Nanotech 10, 1053–1057 (2015). https://doi.org/10.1038/nnano.2015.222

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