Solution‐pH‐Modulated Rectification of Ionic Current in Highly Ordered Nanochannel Arrays Patterned with Chemical Functional Groups at Designed Positions

Abstract

A new ionic current rectification device responsive to a broad range of pH stimuli is established using highly ordered nanochannels of porous anodic alumina membrane with abrupt surface charge discontinuity. The asymmetric surface charge distribution is achieved by patterning the nanochannels with surface amine functional groups at designed positions using a two‐step anodization process. Due to the protonation/deprotonation of the patterned amine and the remaining intrinsic hydroxyl groups upon solution pH variation, the nanochannel‐array‐based device is able to regulate ion transport selectivity and has ionic current rectification properties. The rectification ratio of the device is mainly determined by the nanochannel size, and the rectification ratio is less sensitive to the patterned length of the amine groups when the nanochannels size is defined. Thus, the isoelectric point of nanochannels can be easily estimated to be the pH value with a unit rectification ratio. The present ionic device is promising for biosensing, molecular transport and separation, and drug delivery in confined environments.

Ionic Current Rectification of Porous Anodic Aluminum Oxide (AAO) with a Barrier Oxide Layer

“…Ionic transport governed by the space charge density gradient across the barrier oxide layer can be qualitatively supported by numerical calculation based on Poisson and Nernst–Planck equations coupled with the Navier–Stokes equation . To simplify the model, we only simulated a single nanopore by assuming that the AAO-BL membrane has a uniform pore structure and surface properties . The detailed information about the numerical simulation is described in the Supporting Information, including the simulation domain, the governing equations, and the boundary conditions.…”

A Solar Thermoelectric Nanofluidic Device for Solar Thermal Energy Harvesting

“…However, for a pH lower than 3, the TMP was reversed because the Al-OH was protonated at a solution pH lower than its isoelectric point, which turned the ion selectivity from cations to anions. 40 These results showed that the thermal-driven transport properties of cations and anions could be regulated effectively by simply tuning the surface charge density of the nanochannels, which again confirmed that the electrostatic interaction between the surface charge and the ions was a key factor for charge separation inside the nanochannels.…”

Beyond the Tradeoff: Dynamic Selectivity in Ionic Transport and Current Rectification

“…Briefly, we note that we have been concerned here with the ICR induced by continuous variations in the local Dukhin number and in the presence of surface charge of a single sign. This is in contrast to both classical bipolar diodes, containing regions of both positive and negative surface charge, for example, refs, ,,, and unipolar diodes, for example, refs, ,, containing regions of zero and nonzero surface charge. We term the latter intrinsic diodes, as in this case, the zone of depletion or accumulation is localized to the intrinsic discontinuity in either the local Dukhin number or the sign of the surface charge.…”