Two-Dimensional Nanochannel Arrays Based on Flexible Montmorillonite Membranes

Abstract

Two-dimensional (2D) nanochannel arrays are constructed by bottom-up reassembly of montmorillonite monolayers that are obtained by liquid-phase exfoliation of 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 °C 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 eight to nine times that of anions, which is consistent with the fact that the montmorillonite monolayers are negatively charged and the nanochannels are permselective. Last, ionic 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 a bias between −1 and +1 V because of the asymmetric electrostatic potential through the nanochannels.

Strategic Design of Clay‐Based Multifunctional Materials: From Natural Minerals to Nanostructured Membranes

“…Therefore, cations are the dominant charge carriers, so the surface charge density has a greater impact on the concentration of the cations in the nanochannels than the bulk electrolyte concentration. Shao and co‐workers fabricated a reconstructed MMT membrane (RMM) with a similar process (Figure f) . Surface charge‐governed ion transport behavior was also detected through the nanochannels of the RMM with KCl electrolyte.…”

“…Compared with other 2D materials, clays have significant advantages for fabricating lamellar membranes for molecule and ion transport because of their ease of exfoliation, sufficient surface charge, and structural diversity . Recently, Huang and co‐workers reported self‐assembled VMT‐based 2D nanofluidic channels with surface charge‐governed proton conductivity .…”

“…g) Schemes of nanofluidic channels with asymmetric bulk electrolyte concentrations (top) and asymmetric geometry shape (down) and h,i) their corresponding I−V responses. Reproduced with permission . Copyright 2017, American Chemical Society.…”

Atomic scale understanding of ion exchange in atomically thin clays and micas by STEM

“…The simplified crystal structure, approximate unit cell dimensions and chemical formula for the materials are given in Table S2. S2| Indicative crystal structure and unit cell dimensions of the source materials [1][2][3] . Chemical formulas are expressed in the form of interlayer cation, octahedral layer and tetrahedral layer with associated -OH, and water molecules.…”

“…Yi-Chao Zou 1,2 , Lucas Mogg 3,4,5 , Nick Clark 2,3 , Cihan Bacaksiz 6 , Slavisa Milanovic 6 , Vishnu Sreepal 3,7 , Guang-Ping Hao 3,4 , Yi-Chi Wang 2,8 , David G. Hopkinson 2,3 , Roman Gorbachev 3,4 , Samuel Shaw 9 , Kostya S. Novoselov 3,4 , Rahul Raveendran-Nair 3,7 , Francois M. Peeters 6 , Marcelo Lozada-Hidalgo 3,4 *, Sarah J. Haigh 2,3 * 1 Supplementary Figure S17|Imaging adsorbed surface ions in cross-sectional ADF-STEM images. a, Left panel, ADF-STEM image of a Cs-3L muscovite flake (graphite above and silica substrate below) with Cs + ions visible only at the interface between muscovite and Gr.…”