Electropumping Phenomenon in Modified Carbon Nanotubes

2023

J. Phys. Chem. C

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Ionic current rectification (ICR) in nanofluidic diodes is determined by a combination of channel geometry and surface charge, where most of the previous works have focused on charged asymmetric channels. In this work, through a series of molecular dynamics simulations, we find a surprising ICR phenomenon in a Janus graphene channel, whose geometry is symmetric, while the surface charge is asymmetric by tuning the ratio of cationic and anionic surface modification. A key observation is that when the electric field changes from positive to negative direction, the ionic current exhibits a switchable on−off state depending on whether the dipole moment of the channel's inner surface is parallel to the electrical force. Strikingly, the ICR ratio shows a maximum behavior with the increase in cationic modification, attributed to the change in the range of electrostatic repulsion under the negative electric field. Furthermore, for a given modification ratio, with the increase in graphene layer distance, the ICR ratio also displays a maximum behavior because of the reduced range of the electric double layer (EDL). For small layer distance, the EDL overlap leads to a Coulomb blockade effect under the positive electric field, corresponding to a small ionic current. However, the large layer distance reduces the influence of EDL on ion transport owing to the weakened electrostatic interactions, which ultimately leads to the decrease in ICR ratio. Our results shed light on the essential role of charge polarity in ICR performance, which could open a new window for the design of novel nanofluidic diodes based on symmetric Janus channels.

Section: Resultssupporting

confidence: 77%

Ionic Current Rectification Induced by Charge Polarity in Janus Graphene Channels

2023

J. Phys. Chem. C

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“…This phenomenon, known as the memristor effect, can be harnessed to build an elementary neuron. Furthermore, recent experiments and simulations have addressed some common results, such as the linear relationship between the ion flux and electric field or pressure difference, the linear or power law relation between the ion flux and salt concentration, and the linear relationship between the ion flux and temperature. − Thereby, the dynamic behavior of ion conduction through nanochannels has become an ongoing area of active research, which opens new possibilities for the design of novel nanofluidic devices, ranging from electropumping to desalination. − …”

Section: Introductionmentioning

confidence: 99%

Promoting Electroosmotic Water Flow through a Carbon Nanotube by Weakening the Competition between Cations and Anions in a Lateral Electric Field

Liu

2022

Langmuir

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Understanding the electroosmotic flow through a nanochannel is essential to the design of novel nanofluidic devices, ranging from desalination to nanometer water pumps. Nonetheless, the competition between cation and anion in electric fields inevitably leads to a limited pumping of water, and thus weakening their competition could be a new avenue for the fundamental control of water transport. In this work, through a series of molecular dynamics simulations, we find a surprising phenomenon in which under the drive of a traditional longitudinal electric field, an additional lateral electric field can significantly weaken the competitive transport of a cation and anion through a carbon nanotube, which spontaneously leads to a massive increase in electroosmotic water flux. Specifically, with the increase in the lateral electric field, the anion flux exhibits an almost linear reduction, and the cation flux is stable and can even be enhanced. As a result, the net water flux along the cation direction increases significantly. The key to this unexpected phenomenon lies in the size and mobility difference between the cation and anion. The anion is larger and has greater mobility and is thus more susceptible to the lateral electric field, which ultimately leads to the reduction of its flux. For different ion types and CNT lengths, we can observe similar electropumping phenomenon, where the friction force induced by the lateral electric field becomes nontrivial for long CNTs. Our results provide a new route to tune the competitive transport of cations and anions and should be useful for the design of novel electroosmotic pumps.

“…In general, the charged channels with appropriate surface charge density and symmetric structure are always counterionselective. 47 In the present GO channel, the ion selectivity (see the ESI †) is codetermined by both the channel geometry and electrostatic interactions. At low s (r 1.06 Àe nm À2 ), the ion selectivity mainly depends on the entrance effect.…”

Section: Normal Rectification At Low Surface Charge Densitymentioning

confidence: 99%

Surface charge density governs the ionic current rectification direction in asymmetric graphene oxide channels

Phys. Chem. Chem. Phys.

2023

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