Simulations of Unusual Properties of Water Inside Carbon Nanotubes

Nakamura, Yoshimichi; Ohno, Takahisa

doi:10.5772/36246

Cited by 3 publications

(4 citation statements)

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“…There is no compelling proof that the alteration of surface material can modify the structure and dynamics of confined water and hence water transport. , Whether the observed structure of confined water is peculiar to carbon materials is however yet to be investigated. The observed structuring of confined water is seen to be diameter dependent and is independent of water model. ,, Studies of Nakamura et al demonstrated that depending on CNT diameter size, all the water models commonly show the peculiar behavior during confinement. It was shown that the impact of water model on unusual behavior of confined water is quite significant for CNT diameter range of ∼1.1–1.2 nm, beyond that no considerable change due to differential water models was noticed.…”

Section: Introductionmentioning

confidence: 90%

“…The observed structuring of confined water is seen to be diameter dependent and is independent of water model. 41,58,59 Studies of Nakamura et al 58 demonstrated that depending on CNT diameter size, all the water models commonly show the peculiar behavior during confinement. It was shown that the impact of water model on unusual behavior of confined water is quite significant for CNT diameter range of ∼1.1−1.2 nm, beyond that no considerable change due to differential water models was noticed.…”

Section: Introductionmentioning

confidence: 99%

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Uniqueness of Nanoscale Confinement for Fast Water Transport: Effect of Nanotube Diameter and Hydrophobicity

Sahu,

Ali

2023

J. Phys. Chem. B

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Inspired by the enhanced water permeability of carbon nanotubes (CNTs), molecular dynamics simulations were performed to investigate the transport behavior through nanotubes made of boron nitride (BNNT), silicon carbide (SiC), and silicon nitride (SiN) alongside carbon nanotubes (which have different hydrophobic attributes) considering their implication for reverse osmosis (RO) membranes under different practical environments. According to our findings, not only do CNTs but also other kinds of nanotubes exhibit transition anomalies with increasing diameter. Utilizing the robust twophase thermodynamic (2PT) methods, the current examinations shed light on thermodynamic origin of favorable water filling of these nanotubes. The results show that regardless of the nanotube material, the filling of water inside small nanopores (d < 10 Å) as well as within pores of diameter larger than 15 Å will always be favored by the entropy of filling. However, the entropic preference for filling nanotubes with a diameter of 10−15 Å depends on the constituent material. In particular, the enhancement in total entropy of confined water was mainly due to the increased rotational freedom of confined water molecules. The thermodynamic origin of water transport was correlated with the structural and fluidic behavior of water inside these nanotubes. The observed data for density, flow, structure correlation functions, water−water coordination, tetrahedral order parameter, hydrogen bonds, and density of states functions quantitatively support the observed entropy behavior. Of critical importance is that the present study demonstrates the effectiveness of RO filtration using nanotubes of boron nitride rather than carbon. Furthermore, it was found that one should avoid the use of silicon nanotubes unless filtration needs to be performed under harsh environments where nanotube of other materials cannot survive. Specifically, the results show that both the structural and dynamic properties of water confined in BNNTs are similar to those of CNT's, and for SiNT it is similar as SiC. Our results show that besides the nanotube material, the chirality index of the nanotube also plays a significant role in determining the structure, dynamics and thermodynamics of confined water molecules

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Section: Introductionmentioning

confidence: 90%

Section: Introductionmentioning

confidence: 99%

Uniqueness of Nanoscale Confinement for Fast Water Transport: Effect of Nanotube Diameter and Hydrophobicity

Sahu,

Ali

2023

J. Phys. Chem. B

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“…Though the observed freezing of water inside nanotubes is perceived to be diameter-dependent, it has been found to be independent of the water model. 68,69 The earlier studies by Nakamura et al 69 demonstrated that, in general, all of the water models show freezing behavior under confinement inside nanotubes with critical diameters of ∼1.1−1.2 nm; however, the precise structure of frozen water may vary depending on the water model. The detailed study on the effect of the water model can be referred from the earlier studies by Mejri et al 68 and others.…”

Section: Acs Appliedmentioning

confidence: 99%

Studies on Continuum Breakdown and Water Transport Behavior of Nanotubes for Water Purification: Impact of Temperature, Nanotube Material, and Diameter

Sahu,

Ali

2024

ACS Appl. Nano Mater.

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The present studies shed light on the continuum breakdown of water confined in nanotubes of different materials and diameters. The structure and hydrodynamics of water confined in nanotubes of carbon (CNT), boron nitride (BNNT), silicon carbide (SiC), and silicon nitride (SiNT) of different chirality indices were analyzed to examine the potential nanomembrane material for water purification. According to our findings of the contact angle with water, BNNTs are more hydrophobic than CNTs, and silica nanotubes are hydrophilic. The higher permeability of water was observed through CNTs and BNNTs in comparison to silica nanotubes. Nearly flat velocity profiles indicated continuum breakdown at the nanoscale. Also, the trend for viscosity and diffusion coefficient did not follow the Stokes−Einstein relation, indicating continuum breakdown. The results demonstrated the connectivity of microscopic diffusion with the macroscopic permeation flux, which might be important information for the theoretical investigation of the suitable operational regime in reverse osmosis. Essentially, the continuum breakdown due to freezing of water was seen to be diminished with an increase in temperature. The results showed characteristic changes in the density profile, diffusion coefficient, velocity autocorrelation functions, density of state functions, and thermodynamic entropic components (evaluated using the two-phase thermodynamic method) of permeating water molecules. Importantly, our results reflect that the continuum breakdown observed for water confined in smaller nanotubes is true only at temperatures below 400 K due to the ice-like dense structure of water molecules. Once the entering water molecules can gain energy to compensate for the loss of H bonds, the conventional fluid dynamics relations can be well applied to estimate the hydrodynamics of confined water.

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“…Apart from the aforementioned temporal variation of water intercalation, there is also a spatial component to the wetting process of CNTs. The hydrophobic nature of the CNT wall causes water to first fill the center of the tube and only then (as the water density increases) it starts filling the near-wall region [ 115 ]. This is the exact opposite to the filling process of water in hydrophilic materials, such as MCM-41 [ 116 , 117 ].…”

Section: Intercalation Of Water In Cntsmentioning

confidence: 99%

Current Understanding of Water Properties inside Carbon Nanotubes

Chatzichristos

Hassan

2022

Nanomaterials

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Confined water inside carbon nanotubes (CNTs) has attracted a lot of attention in recent years, amassing as a result a very large number of dedicated studies, both theoretical and experimental. This exceptional scientific interest can be understood in terms of the exotic properties of nanoconfined water, as well as the vast array of possible applications of CNTs in a wide range of fields stretching from geology to medicine and biology. This review presents an overreaching narrative of the properties of water in CNTs, based mostly on results from systematic nuclear magnetic resonance (NMR) and molecular dynamics (MD) studies, which together allow the untangling and explanation of many seemingly contradictory results present in the literature. Further, we identify still-debatable issues and open problems, as well as avenues for future studies, both theoretical and experimental.

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Simulations of Unusual Properties of Water Inside Carbon Nanotubes

Cited by 3 publications

References 46 publications

Uniqueness of Nanoscale Confinement for Fast Water Transport: Effect of Nanotube Diameter and Hydrophobicity

Uniqueness of Nanoscale Confinement for Fast Water Transport: Effect of Nanotube Diameter and Hydrophobicity

Studies on Continuum Breakdown and Water Transport Behavior of Nanotubes for Water Purification: Impact of Temperature, Nanotube Material, and Diameter

Current Understanding of Water Properties inside Carbon Nanotubes

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