Selectivity of ion transport in narrow carbon nanotubes depends on the driving force due to drag or drive nature of their active hydration shells

Gao, Haiqi; Wang, Jing; Liu, Yuzhen; Xie, Yannan; Lu, Ruifeng

doi:10.1063/5.0038662

Cited by 20 publications

(15 citation statements)

References 54 publications

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“…This can be attributed to the interplay between ion and water transport, i.e., the pressure-induced water motion drags adjacent ions to transport through the CNT . As further illustrated in the previous work, an ion may escape from its hydration shell, forming a new hydration shell by reconstruction, and eventually results in a slower transport of ions than water. However, higher pressure creates more stable hydrogen-bond structures in the CNT, where the ions are stably trapped in the hydration shell and hardly escape.…”

Section: Resultsmentioning

confidence: 78%

“…As a result of flux behavior, Figure 6d shows a monotonous decay for the NaCl rejection with the increase in the CNT diameter, indicating that the ion selectivity is highly dependent on the pore size. 63 Notably, despite massively reduced salt rejection for larger CNTs, the rejection enhancement by E x is still universal in all selected diameters. For larger diameters of D = 1.35 and 1.62 nm, the enhancement can be almost twice from E x = 0.1 to 1.0 V/nm.…”

Section: ■ Results and Discussionmentioning

confidence: 97%

“…Meanwhile, the decrease in the water flux by E x becomes trivial when compared to ion flux. As a result of flux behavior, Figure d shows a monotonous decay for the NaCl rejection with the increase in the CNT diameter, indicating that the ion selectivity is highly dependent on the pore size …”

Section: Resultsmentioning

confidence: 99%

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Enhanced Ion Rejection in Carbon Nanotubes by a Lateral Electric Field

Zhang

2022

Langmuir

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Reverse osmosis membranes hold great promise for dealing with global water scarcity. However, the trade-off between ion selectivity and water permeability is a serious obstacle to desalination. Herein, we introduce an effective strategy to enhance the desalination performance of the membrane. A series of molecular dynamics simulations manifest that an additional lateral electric field significantly promotes ion rejection in carbon nanotubes (CNTs) under the drive of longitudinal pressure. Specifically, with the increase in the electric field, the ion flux shows a deep linear decay, while the water flux decreases only slightly, resulting in a linear increase in ion rejection. The energy barriers of ions around the CNT inlet are obtained by calculating the potentials of mean force to explain enhanced ion rejection. The lateral electric field uniformly raises the energy barriers of ions by pushing them away from the CNT inlet, corresponding to the enhanced ion velocity in the field direction. Furthermore, with the increase in CNT diameter, there is a significant increase in the flux of both ions and water; however, the lateral electric field can also obviously enhance the ion rejection in wider CNTs. Consequently, the enhancement of ion rejection by lateral electric fields should be universal for different CNT diameters, which opens a new avenue for selective permeation and may have broad implications for desalination devices with large pore sizes.

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Section: Resultsmentioning

confidence: 78%

Section: ■ Results and Discussionmentioning

confidence: 97%

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Enhanced Ion Rejection in Carbon Nanotubes by a Lateral Electric Field

Zhang

2022

Langmuir

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“…The pore size requires high precision, approaching the size of or smaller than the hydrated ions to endow membranes with high selectivity. As a representative salt solution of sodium chloride, the diameters of hydrated Na + and Cl – are ∼0.65 and ∼0.77 nm, respectively. , Nevertheless, a precisely controlled defect or pore size of <1 nm on large-area monolayer membranes is extremely challenging, ,, which prevents such materials from being practically utilized in industry.…”

mentioning

confidence: 99%

Beyond the Pore Size Limitation of a Nanoporous Graphene Monolayer Membrane for Water Desalination Assisted by an External Electric Field

Gao

Wang

et al. 2021

J. Phys. Chem. Lett.

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One efficient strategy for addressing the global water shortage is advanced membrane separation, which depends on the precise pore size being close to the hydrated ion size and other surface properties like charge and polarity. However, it is very difficult to fabricate uniform pores with diameters of <1 nm on monolayer membranes. By applying an electric field (bias voltage) perpendicular to the direction of the pressure difference, herein we demonstrate for the first time that a monolayer nanoporous graphene membrane with pores much larger than hydrated ions exhibits high salt rejection and allows a high rate of water transport. This theoretical proposal goes beyond the pore size limitation and shows promise for the design of high-performance reverse osmosis membranes.

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“…Moreover, MD simulations show that the transport selectivity of K + and Na + ions in CNTs under pressure reverses compared with that under the electric field. [ 36 ] But the steric confinement of CNTs often limits the permeability of ion transport, hindering the potential performance in ion separation with combined pressure and electric fields.…”

Section: Introductionmentioning

confidence: 99%

A New Strategy for Highly Efficient Separation between Monovalent Cations by Applying Opposite‐Oriented Pressure and Electric Fields

Zhang

Lin

Shen

et al. 2022

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Biological ion channels exhibit excellent ion selectivity, but it has been challenging to design their artificial counterparts, especially for highly efficient separation of similar ions. Here, a new strategy to achieve high selectivity between alkali metal ions with artificial nanostructures is reported. Molecular dynamics (MD) simulations and experiments are combined to study the transportation of monovalent cations through graphene oxide (GO) nanoslits by applying pressure or/and electric fields. It is found that the ionic transport selectivity under the pressure driving reverses compared with that under the electric field driving. Moreover, MD simulations show that different monovalent cations can be separated with unprecedentedly high selectivity by applying opposite‐oriented pressure and electric fields. This highly efficient separation originates from two distinctive ionic transporting modes, that is, hydration shells drive ions under pressure, but drag ions under the electric field. Hence, ions with different hydration strengths can be efficiently separated by tuning the net mobility induced by the two types of driving forces when the selected ions are kept moving while the other ones are immobilized. And nanoconfinement is confirmed to enhance the separation efficacy. This discovery paves a new avenue for separating similar ions without elaborately designing biomimetic nanostructures.

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Selectivity of ion transport in narrow carbon nanotubes depends on the driving force due to drag or drive nature of their active hydration shells

Cited by 20 publications

References 54 publications

Enhanced Ion Rejection in Carbon Nanotubes by a Lateral Electric Field

Enhanced Ion Rejection in Carbon Nanotubes by a Lateral Electric Field

Beyond the Pore Size Limitation of a Nanoporous Graphene Monolayer Membrane for Water Desalination Assisted by an External Electric Field

A New Strategy for Highly Efficient Separation between Monovalent Cations by Applying Opposite‐Oriented Pressure and Electric Fields

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