Fabrication of Stable and Flexible Nanocomposite Membranes Comprised of Cellulose Nanofibers and Graphene Oxide for Nanofluidic Ion Transport

Two-dimensional membranes with nanofluidic channels and a high chemical stability are strongly needed in many practical applications. We present a facile vacuum filtration method to fabricate a lamellar hybrid microstructure with cellulose nanofibers and graphene oxide sheets. The flexible and free-standing composite membrane obtained has uniformly distributed interstitial voids that provide nanofluidic channels for ion transport. The systematic measurement of the ionic currents through the nanofluidic channels with various electrolytes at different concentrations establish the surface-charge-governed ion-transport behavior. The ionic conductivity through the nanofluidic channels at lower concentrations (<= 10(-4) M) can be enhanced by several orders of magnitude and appears to be independent of the concentration of the bulk electrolytes because of the successful hybridization of the negatively charged and permselective nanochannels. The resulting devices have an excellent chemical stability and maintain a stable ionic conductivity even after immersion in basic or acidic solutions at high concentrations (1 M) for half a month. Moreover, the activation energy and proton mobility provide additional confirmations that the hybrid nanofluidic channels lower the energy barrier for ion transport. The excellent performance of the membrane makes it an outstanding candidate for stable and flexible nanofluidic devices as well as other potential applications.