Narrow Nanotubes Research Articles

Magnetic skyrmions in cylindrical ferromagnetic nanostructures with chiral interactions

We study the geometrical conditions for stabilizing magnetic skyrmions in cylindrical nanostrips and nanotubes of ferromagnetic materials with chiral interactions. We obtain the low-temperature equilibrium state of the system implementing a simulation annealing technique for a classical spin Hamiltonian with competing isotropic exchange and chiral interactions, radial anisotropy and an external field. We address the impact of surface curvature on the formation, the shape and the size of magnetic skyrmions. We demonstrate that the evolution of the skyrmion phase with the curvature is controlled by the competition between two characteristic lengths, namely the curvature radius, $R$ (geometrical length) and the skyrmion radius, $R_{sk}$ (physical length). In narrow nanotubes ($R<R_{sk}$) the skyrmion phase evolves to a stripe phase, while in wide nanotubes ($R>R_{sk}$) a mixed skyrmion-stripe phase emerges. Most interestingly, the mixed phase is characterized by spatially separated skyrmions from stripes owing to the direction of the applied field relative to the surface normal. In the stability regime ($R \gtrsim R_{sk}$) skyrmions remain circular and preserve their size as a consequence of their topological protection. Zero-field skyrmions are shown to be stable on curved nanoelements with free boundaries within the same stability region ($R\gtrsim R_{sk}$). The experimental and technological perspectives from the stability of skyrmions on cylindrical surfaces are discussed.

Boron nitride nanotubes as containers for targeted drug delivery of doxorubicin

Using molecular dynamics simulations, the adsorption and diffusion of doxorubicin drug molecules in boron nitride nanotubes are investigated. The interaction between doxorubicin and the nanotube is governed by van der Waals attraction. We find strong adsorption of doxorubicin to the wall for narrow nanotubes (radius of 9 Å). For larger radii (12 and 15 Å), the adsorption energy decreases, while the diffusion coefficient of doxorubicin increases. It does, however, not reach the values of pure water, as adsorption events still hinder the doxorubicin mobility. It is concluded that nanotubes wider than around 4 nm diameter can serve as efficient drug containers for targeted drug delivery of doxorubicin in cancer chemotherapy.

Reverse Translocation of Nucleotides through a Carbon Nanotube.

We report molecular dynamics (MD) simulations of the reverse translocation of single nucleotides through a narrow carbon nanotube (CNT), with a diameter of 1.36 nm, immersed in a 1 M KCl electrolyte solution under an applied electric field along the tube axis. We observe ion selectivity by the narrow CNT, which leads to a high flow of K+ ions, in contrast to a negligible and opposing current of Cl- ions. The K+ ions, driven by the electric field, force a negatively charged single nucleotide into the narrow CNT where it is trapped by the incoming K+ ions and water molecules, and the nucleotide is driven in the same direction as the K+ ions. This illustrates a novel mechanism of nucleotide reverse translocation that is controlled by ion selectivity. An increase in the CNT diameter to 2.71 nm or an increase in nucleotide chain length both lead to translocation in the normal direction of the applied field. The reverse translocation rate of single nucleotides is correlated to the ionic current of K+ ions in the narrow tube, unlike translocation in the normal direction in the wider tube.

Changing the Phosphorus Allotrope from a Square Columnar Structure to a Planar Zigzag Nanoribbon by Increasing the Diameter of Carbon Nanotube Nanoreactors.

Elemental phosphorus nanostructures are notorious for a large number of allotropes, which limits their usefulness as semiconductors. To limit this structural diversity, we synthesize selectively quasi-1D phosphorus nanostructures inside carbon nanotubes (CNTs) that act both as stable templates and nanoreactors. Whereas zigzag phosphorus nanoribbons form preferably in CNTs with an inner diameter exceeding 1.4 nm, a previously unknown square columnar structure of phosphorus is observed to form inside narrower nanotubes. Our findings are supported by electron microscopy and Raman spectroscopy observations as well as ab initio density functional theory calculations. Our computational results suggest that square columnar structures form preferably in CNTs with an inner diameter around 1.0 nm, whereas black phosphorus nanoribbons form preferably inside CNTs with a 4.1 nm inner diameter, with zigzag nanoribbons energetically favored over armchair nanoribbons. Our theoretical predictions agree with the experimental findings.

Entropy deepens loading chemical potentials of small alcohols by narrow carbon nanotubes

Small alcohol confinement within narrow carbon nanotubes has been extensively and systematically studied via rigorous free-energy calculations. Employing molecular dynamics simulations, thermodynamic integration and thermodynamic cycling, the loading process of methanol and ethanol from aqueous solution into (6,6), (7,7) and (8,8) single-walled carbon nanotubes was computed and decomposed into its entropic and energetic terms. For all tubes and alcohols, loading is favoured from infinite dilution in water; for the same alcohol, wider tubes allow for the formation of a collective dipole which is cooperative in terms of electrostatics and reduce the rotational freedom of the loaded particles; narrow tubes only permit the formation of dipole-dipole dimers instead, with a (rotational) entropic gain that compensates for the loss of long-range dipole-dipole interactions. The latter renders deeper loading chemical potentials for narrower tubes when partitioning small alcohols from aqueous solution and it is a clear example of an entropy-energy compensation phenomenon.

Enhanced wettability of long narrow carbon nanotubes in a double-walled hetero-structure: unraveling the effects of a boron nitride nanotube as the exterior.

Studying the structure and dynamics of nano-confined water inside carbon nanotubes has consistently attracted the wide-spread interest of researchers. In the present work, molecular dynamics simulations indicated internal nonwetting behavior for the central region of the long and narrow single-wall carbon nanotube (5,5) (SWNT) and showed that continuous single-file water molecules are not formed through it. Unlike the SWNT, by adding boron nitride nanotubes (6,6) as an outer wall to the SWNT, a continuously long single-file water chain is formed through the double-walled carbon and boron nitride hetero-nanotube (DWHNT) and thorough internal wetting of the DWHNT is observed. The position and the number of water molecules, electrostatic potential heatmap of the nanotube's wall, free energy profile of nano-confined water, and number of hydrogen bonds between them confirmed the aforementioned results and complete internal wetting of the DWHNT. After using the boron nitride nanotube (6,6) as the outer wall, an homogeneous electrostatic potential distribution in the DWHNT and increase in the hydrophilic characteristics of the nano-channel wall are observed, bringing about gradual trapping of more water molecules through it. Finally, water molecules occupied the central region of the DWHNT and a thorough single-file water chain is formed inside the nano-channel. Water dipole orientation inside the DWHNT and their radial distribution function asserted the occurrence of the liquid-solid quasi-phase transition of single-file water molecules confined inside the long and narrow carbon nanotube (5,5) under ambient conditions.

Electronic and Magnetic Properties of Iron Clusters Encapsulated in Carbon Nanotubes

We have made theoretical study of the electronic and magnetic properties of iron clusters encapsulated in carbon nanotubes using density functional theory. We have considered cluster encapsulated inside finite pieces of single wall zigzag nanotubes of indices (11,0) and (10,0). Finite zigzag nanotubes have a peculiar magnetic structure, the ground state is an antiferromagnetic spin singlet S=0. The local spin polarization oscillates along the direction of the nanotubes axis and is small, except at the two ends of the edges of the nanotubes. We have studied the encapsulation of iron atoms and small Fen clusters n = 2,4,8 in a short (10,0) tube. By the constraints imposed by the cylindrical geometry of a narrow nanotubes, we have considered the encapsulation of an isomer of F12 with an elongated structure. We have also considered the encapsulation of the lowest energy, icosahedral structure of Fe12. The free elongated Fe12 isomer presented a strong ferromagnetic spin coupling giving rise to a large magnetic moment. The distortion in the density of state of the iron cluster is much smaller preserving the strong ferromagnetic character. There is some p-d hybridization between the nanotubes and the cluster states, mainly around the Fermilevel. The loweswt unoccupied molecular orbital of the pristine zigzag nanotubes becomes partially occupied due to charge transfer from the cluster to the nanotubes. We have analysed the interplay between the singular magnetic properties of the finite zigzag nanotubes and the large magnetization of the encapsulated iron clusters. The calculations indicated that the magnetism is confined within the iron aggregates, with small reduction of the magnetic moment per atom with respect to the free iron clusters. The magnetic moment per atom result enhanced with respect to those of bulk iron, due to the reduced coordination of the metal atoms. The obtained results were found in good agreement with previously obtained results.

Effect of nano-confinement on the structure and properties of water clusters: An ab initio study

An ab initio investigation on water clusters confined to armchair carbon nanotubes (CNT) with varying diameters has been performed using the density functional theory-based calculations. Different parameters have been investigated including structure, hydrogen bonding pattern and vibrational spectra of water-CNT complexes. Our results reveal that one-dimensional water chain parallel to CNT axis is formed in narrow nanotubes CNT(4,4) and CNT(5,5), whereas in CNT(6,6), zigzag structure is observed. An increase in the CNT diameter results in more symmetric structures similar to the gas phase. The vibrational analysis shows a redshift in stretching frequency of the hydrogen bond assisted O–H in CNT(6,6) due to the reduction in O—O separation whereas a significant blue shift in stretching frequency mode is observed in highly confined CNT(4,4) and CNT(5,5). It implies that the hydrogen bond strength between water molecules is strongest in CNT(6,6). It is also observed that water cluster tends to be near CNT wall due to H···π interaction between water molecule and the π-electron cloud of CNT. An inverse relation between the electronic charge transfer (from CNT to water) and the diameter is also established. This study demonstrates that the degree of confinement is extremely important in deciding the properties of confined water molecules. The structure and hydrogen bonding properties of the water clusters under nano-confined regime is investigated and the results reveal that the intramolecular charge separation for each water molecule increases under confinement and irrespective of the number of water molecules, the highest tube-water interaction energy is achieved in CNT(5,5) (diameter~7 A). The important finding is that the degree of confinement (diameter of carbon nanotube) is extremely important in deciding the properties of confined water molecules.

Anomalous changes of intermolecular distance in aqueous electrolytes in narrow pores of carbon nanotubes

Structures of NaCl and LiCl aqueous solutions in pores of carbon nanotubes with diameter 1 and 2 nm were evaluated by using X-ray diffraction and molecular dynamics simulations. Water intermolecular distances in carbon nanotubes with 1 and 2 nm pore diameters were more elongated and shortened than bulk water, respectively. Those were results of weakened and strengthened hydrogen bonds. The structures of aqueous solutions in carbon nanotubes were considerably different from water despite tiny amounts of ions in the pores. The nearest neighbour distances in aqueous solutions were rarely changed from that in water system in 1 nm carbon nanotubes pore, while those were longer than water in 2 nm carbon nanotubes pore. On the other hand, the second nearest neighbour distances in aqueous solutions in 1 and 2 nm pore diameter carbon nanotubes were both decreased from those in water in carbon nanotubes. Significant hydration formation and cleavage of hydrogen bonds were thus observed in 2 nm carbon nanotubes pore, because the elongated nearest neighbour and shortened second nearest neighbour distances were observed. Anomalous feature of the unchanged nearest neighbour and shortened second neighbour distances in 1 nm carbon nanotubes pore is the result that water intermolecular distance was much longer than bulk and hydrogen bonds were thus severely separated. Ions might play dominant role to connect hydrogen bonds and of course form hydration shell. Those anomalous structure changes from water to aqueous solution were observed only in extremely narrow carbon nanotubes.

First-Principles Evaluation of the Morphology of WS2 Nanotubes for Application as Visible-Light-Driven Water-Splitting Photocatalysts.

One-dimensional tungsten disulfide (WS2) single-walled nanotubes (NTs) with either achiral, i.e., armchair (n, n) and zigzag-type (n, 0), or chiral (2n, n) configuration with diameters dNT > 1.9 nm have been found to be suitable for photocatalytic applications, since their band gaps correspond to the frequency range of visible light between red and violet (1.5 eV < Δεgap < 2.6 eV). We have simulated the electronic structure of nanotubes with diameters up to 12.0 nm. The calculated top of the valence band and the bottom of the conduction band (εVB and εCB, respectively) have been properly aligned relatively to the oxidation (εO2/H2O) and reduction (εH2/H2O) potentials of water. Very narrow nanotubes (0.5 < dNT < 1.9 nm) are unsuitable for water splitting because the condition εVB < εO2/H2O < εH2/H2O < εCB does not hold. For nanotubes with dNT > 1.9 nm, the condition εVB < εO2/H2O < εH2/H2O < εCB is fulfilled. The values of εVB and εCB have been found to depend only on the diameter and not on the chirality index of the nanotube. The reported structural and electronic properties have been obtained from either hybrid density functional theory and Hartree–Fock linear combination of atomic orbitals calculations (using the HSE06 functional) or the linear augmented cylindrical waves density functional theory method. In addition to single-walled NTs, we have investigated a number of achiral double-walled (m, m)@(n, n) and (m, 0)@(n, 0) as well as triple-walled (l, l)@(m, m)@(n, n) and (l, 0)@(m, 0)@(n, 0) nanotubes. All multiwalled nanotubes show a common dependence of their band gap on the diameter of the inner nanotube, independent of chirality index and number of walls. This behavior of WS2 NTs allows the exploitation of the entire range of the visible spectrum by suitably tuning the band gap.

Spectroscopy of a rotating hydrogen molecule in carbon nanotubes.

A first-principles study of the spectroscopy of a single hydrogen molecule rotating inside and outside of carbon nanotubes is presented. Density functional theory (DFT)-based symmetry-adapted perturbation theory (SAPT) is applied to analyze the influence of the rotation in the dispersionless and dispersion energy contributions to the adsorbate-nanotube interaction. A potential model for the H2-nanotube interaction is proposed and applied to derive the molecular energy levels of the rotating hydrogen molecule. The SAPT-based analysis shows that a subtle balance between the dispersionless and dispersion contributions is key in determining the angular dependence of the H2-nanotube interaction, which is strongly influenced by the diameter of the carbon nanotubes. As a consequence, the structure of molecular energy levels is very different in wide and narrow nanotubes with the diameter above and below 1 nanometer, respectively. Strong anisotropy effects lead to a rather constrained rotation of molecular hydrogen inside narrow nanotubes.

Tuning the magnetic properties of beryllium chains.

In this work we explore the effect of confining beryllium chains inside carbon nanotubes. Linear Ben systems are characterized by two states originating from the presence of edge orbitals localized at the chain extremities. The two spins occupying these orbitals are, in the gas phase, antiferromagnetically coupled, with the magnetic coupling J decaying exponentially as a function of increasing length of the chain. When inserted into narrow carbon nanotubes, the linear geometry is found to be more stable than the more compact cluster conformation favored for the isolated case: the lack of space inside the cavity prevents the chain from folding. Most importantly, the presence of the surrounding nanotube not only preserves the linear structure of Ben, but affects its magnetic properties too. In particular it was found that the magnetic coupling between the ground and the first excited state can be modulated according to the nanotube diameter as well as the chain length, and our calculations suggest a possible direct relationship between these parameters and J. This behavior can be exploited to engineer a composite Ben@CNT system with the magnetic coupling tuned by construction, with interesting potential applications.

Confinement effect of carbon nanotubes on the chain mobility of conjugated polymer poly(9,9-dioctylfluorenyl-2,7-diyl)

The conjugated polymer polyflourene has been well studied for its strong blue light emission ability and high quantum efficiency behavior. It has wide applications for light emitting diodes, sensors as well as photo-detectors. Therein the &lt;inline-formula&gt;&lt;tex-math id="Z-20181210033236-1"&gt;\begin{document}$ \beta $\end{document}&lt;/tex-math&gt;&lt;alternatives&gt;&lt;graphic xmlns:xlink="http://www.w3.org/1999/xlink" xlink:href="20182008lilingdong_Z-20181210033236-1.jpg"/&gt;&lt;graphic xmlns:xlink="http://www.w3.org/1999/xlink" xlink:href="20182008lilingdong_Z-20181210033236-1.png"/&gt;&lt;/alternatives&gt;&lt;/inline-formula&gt; conformation of PFO crystals is more attractive due to its longer conjugation length, higher carrier mobility and better luminous efficiency. Therefore it is great essential to control the formation and stability of &lt;inline-formula&gt;&lt;tex-math id="Z-20181210033236-2"&gt;\begin{document}$ \beta $\end{document}&lt;/tex-math&gt;&lt;alternatives&gt;&lt;graphic xmlns:xlink="http://www.w3.org/1999/xlink" xlink:href="20182008lilingdong_Z-20181210033236-2.jpg"/&gt;&lt;graphic xmlns:xlink="http://www.w3.org/1999/xlink" xlink:href="20182008lilingdong_Z-20181210033236-2.png"/&gt;&lt;/alternatives&gt;&lt;/inline-formula&gt; conformation of PFO crystals to develop new kind of photo-electronic devices. As is known, polymeric materials confined in a nanometer-sized space often exhibit unique properties compared with their bulk state, such as abnormal chain mobility, molecular assembly and phase transition behavior. These factors are of great significance to develop new kind of material and applications. Generally the confined condition includes quantum dot (zero-dimensional, 0D), nanowire or nanotube (1D), ultrathin film (2D) and nanoparticle (3D). In this paper, we design a unique 1D nanoconfined environment based on vertically aligned carbon nanotube (CNT) array structure. An ultra-high CNT density is achieved through a solvent-induced contraction process. The adjacent narrow carbon nanotube gap thus forms a quasi-1 confined nano-space with the tunable size ranging from 5 to 50 nm. Then we infiltrate the conjugated polymer poly(9,9-dioctylfluorene-2,7-diyl) (PFO) into those nano-gaps of carbon nanotube arrays through a solvent evaporation method to obtain the PFO infilled CNT array composite film. It is found that the chain mobility of PFO molecules in such a 1D nano-confined space of carbon nanotubes is significantly suppressed compared with the scenario of the spin-coated PFO film. The transition speed between different crystal forms of PFO declines greatly, which meanwhile improves the thermal stability of the &lt;inline-formula&gt;&lt;tex-math id="Z-20181210033236-3"&gt;\begin{document}$ \beta $\end{document}&lt;/tex-math&gt;&lt;alternatives&gt;&lt;graphic xmlns:xlink="http://www.w3.org/1999/xlink" xlink:href="20182008lilingdong_Z-20181210033236-3.jpg"/&gt;&lt;graphic xmlns:xlink="http://www.w3.org/1999/xlink" xlink:href="20182008lilingdong_Z-20181210033236-3.png"/&gt;&lt;/alternatives&gt;&lt;/inline-formula&gt; conformation of PFO crystal. Additionally, the aligned carbon nanotubes have great effects on the orientation and distribution of PFO chains. The PFO crystals are confirmed to grow preferentially along the longitudinal direction of CNT array, which is potential to grow PFO crystals with high quality and excellent performance. Thus, such a PFO/CNT array composite film can have great potential to prepare PFO photovoltaic devices with excellent luminescent properties and high stability in the future.

Soliton-like propagation of dipole reorientation in confined single-file water chains

Water molecules confined in a narrow nanotube channel orient themselves into a uniformly ordered single-file chain. Here, we report by means of comprehensive molecular dynamics simulations and soliton-model-based theoretical analysis that the reorientation (i.e., rotation) of a single water molecule in this dipole chain, triggered for example by an external charge, can induce successive reorientation of the rest of the water molecules, which propagates in a soliton-like manner. The resulting local potential energy peak separating the reoriented and the pending reorientation subsections moves with an unweakened peak intensity at a constant velocity in the ambient environment, and particularly, can penetrate or make a turn through a crossed nanotube junction. The propagation velocity depends on the strength of the external charge, in agreement with our sine-Gordon soliton-based theoretical analysis. We further show that this unidirectional propagation originates from the partially inhibited fluctuation in dipole orientation of reoriented water with respect to that of original ones. These findings may be helpful in the development of high-efficiency information transmitting, processing and storage devices and the understanding of functioning of biological water channels.

Ab initio modelling of molecular hydrogen rotation in the outside of carbon nanotubes

ABSTRACTA first-principle modelling of hydrogen molecular rotation in the outside of carbon nanotubes is presented. Density functional theory (DFT)-based symmetry-adapted perturbation theory (SAPT) is first applied to analyse the influence of the rotation on the dispersion and dispersionless H-nanotube interaction for both sub- and nanometer-sized tubes. An adsorbate three-dimensional wave-function treatment is then applied to calculate the molecular energy levels of the rotating hydrogen molecule. As a key difference with the H located inside the tubes, the SAPT-based analysis indicates a marked influence of a nanotube curvature-induced dipole on the angular-dependent balance of exchange-repulsion, electrostatic, and dispersion contributions for narrow nanotubes. As a result, the landscape of molecular energy levels depends strongly on the diameter of the porous material. In addition, an effective one-dimensional model is proposed to account for the nuclear motion, reproducing full-dimensional approach within less than 1%.

Geometry-diversified Coulomb excitations in trilayer AAB stacking graphene

The lower-symmetry trilayer AAB-stacked graphene exhibits rich electronic properties and thus diverse Coulomb excitations. Three pairs of unusual valence and conduction bands create nine available interband excitations for the undoped case, in which the imaginary (real) part of the polarizability shows 1D square root asymmetric peaks and 2D shoulder structures (pairs of antisymmetric peaks and logarithm type symmetric peaks). Moreover, the low frequency acoustic plasmon, being revealed as a prominent peak in the energy loss spectrum, can survive in a narrow gap system with the large-density-of-states from the valence band. This type of plasmon mode is similar to that in a narrow gap carbon nanotube. However, the decisive mechanism governing this plasmon is the intraband conduction state excitations. Its frequency, intensity and critical momentum exhibit a non-monotonic dependence on the Fermi energy. The well-defined electron-hole excitation boundaries and the higher frequency optical plasmons are transformed by varying the Fermi energy. There remain substantial differences between the electronic properties of trilayer AAB, ABC, AAA and ABA graphene stackings.

Water in Narrow Carbon Nanotubes: Roughness Promoted Diffusion Transition

Diffusion of single-file water confined in carbon nanotubes (CNT) has been studied extensively via molecular dynamics simulations in the literature. However, very often, the simulation results do not provide a satisfactory insight to the fundamental mechanism, failing to explain the experimental trend. Sometimes, simulation results are even contradictory to each other. In this work, we first summarize factors that affect the diffusion calculation of single-file water confined in narrow CNTs. In particular, we investigate how the roughness of the CNT model affects diffusion properties of the confined water. A transition of ballistic to Fickian diffusion shall be observable when water is confined in (6, 6) CNTs with roughness. Our simulation results also reveal the single-file diffusion mechanism of confined water when the CNT has significant roughness. This is because the single-file water molecules confined in smooth CNTs move in a collective way, while the motion becomes random in CNTs with roughness. In...

Shrinkable Nanotubes for Duplex Formation of Short Nucleotides.

Molecular monolayer nanotubes produced by self-assembly of an amphiphile modified with a 2-nitrobenzyl group as a photoresponsive unit are able to encapsulate dinucleotides via electrostatic attraction. Upon photoirradiation, the 18 nm inner diameter of the nanotubes shrinks to less than 2 nm as a result of photochemical cleavage of the 2-nitrobenzyl group in the amphiphile. This shrinking of the nanotube channels leads to a propulsive release of the dinucleotides into the bulk solution and simultaneously accelerates formation of the dinucleotide duplexes. The larger nanotube channels without photoirradiation merely release each dinucleotide into the bulk solution, indicating that the squeezing via transportation in the narrow nanotube channels is necessary for duplex formation. In addition to the size effect, water with a lower polarity confined within the narrow nanotube channels helps to stabilize the energetically unfavorable hydrogen-bonded base pair between the dinucleotides. This system should enable researchers to perform biological reactions that occur only in specific environments and conditions in living organisms.

High Interfacial Barriers at Narrow Carbon Nanotube-Water Interfaces.

Water displays anomalous fast diffusion in narrow carbon nanotubes (CNTs), a behavior that has been reproduced in both experimental and simulation studies. However, little is reported on the effect of bulk water-CNT interfaces, which is critical to exploiting the fast transport of water across narrow carbon nanotubes in actual applications. Using molecular dynamics simulations, we investigate here the effect of such interfaces on the transport of water across arm-chair CNTs of different diameters. Our results demonstrate that diffusion of water is significantly retarded in narrow CNTs due to bulk regions near the pore entrance. The slowdown of dynamics can be attributed to the presence of large energy barriers at bulk water-CNT interfaces. The presence of such intense barriers at the bulk-CNT interface arises due to the entropy contrast between the bulk and confined regions, with water molecules undergoing high translational and rotational entropy gain on entering from the bulk to the CNT interior. The intensity of such energy barriers decreases with increase in CNT diameter. These results are very important for emerging technological applications of CNTs and other nanoscale materials, such as in nanofluidics, water purification, nanofiltration, and desalination, as well as for biological transport processes.

Thermoresponsive PEG-Coated Nanotubes as Chiral Selectors of Amino Acids and Peptides.

A series of nanotubes with a dense layer of short poly(ethylene glycol) (PEG) chains on the inner surface are prepared by means of a coassembly process using glycolipids and PEG derivatives. Dehydration of the PEG chains by heating increases the hydrophobicity of the nanotube channel and fluorescent-dye-labeled amino acids are extracted from bulk solution. Rehydration of the PEG chains by cooling results in back-extraction of the amino acids into the bulk solution. Because of the supramolecular chirality of the nanotubes, amino acid enantiomers can be separated in the back-extraction procedure, which is detectable with the naked eye as a change in fluorescence as the amino acids are released from the nanotubes. The efficiency and selectivity of the chiral separation are enhanced by tuning the chemical features and inner diameter of the nanotube channels. For example, compared with wide nanotube channels (8 nm), narrow nanotube channels (4 nm) provide more effective electrostatic attraction and hydrogen bond interaction environments for the transporting amino acids. Introduction of branched alkyl chains to the inner surface of the nanotubes enables chiral separation of peptides containing hydrophobic amino acids. The system described here provides a simple, quick, and on-site chiral separation in biological and medical fields.