Two-Dimensional Nanochannel Arrays Based On Flexible Montmorillonite Membranes (Vol 10, Pg 44915, 2018)

Two-dimensional (2D) nanochannel arrays are constructed by a bottom-up re-assembly montmorillonite monolayers that are obtained by liquid phase exfoliating its layered crystals, and the as-constructed interstitial space between these monolayers is uniform and provides ions with nanoscale transport channels. Surface charge-controlled ion transport behavior is observed through these nanochannels as the electrolyte concentration reduces to 10-4 M at room temperature. Furthermore, the nanochannel structure remains even after 400 ºC heat treatment, and nanofluidic devices based on the annealed nanochannel arrays still exhibit surface charge-governed ion transport at low electrolyte concentrations. In addition, a drift-diffusion experiment is conducted to investigate the mobility ratio of cations/anions through the nanochannels with asymmetric bulk electrolyte concentrations, and the results show that the mobility of cations is about 8~9 times that of anions, which is consistent with the fact that the montmorillonite monolayers are negatively-charged and the nanochannels are permselective. Last, ion current rectification is observed in the nanofluidic system of asymmetric geometric shape, and rectification factors of ~2.6 and ~3.5 can be obtained in KCl and HCl electrolytes, respectively, at bias between -1 and +1 V because of the asymmetric electrostatic potential through the nanochannels.