Double-walled Nanotubes Research Articles

Structural and Electronic Properties of Double-Walled Black Phosphorene Nanotubes: A Density Functional Theory Study

The exploration of new low-dimensional systems based on phosphorus atoms is an area of intensive research because of their properties. We use first-principles total energy calculations to investigate the stability and the geometrical and electronic properties of double-walled black phosphorene nanotubes (DWβPNTs). We are dealing with a material that has not been synthesized yet. Therefore, it is important to know if it is stable, so it could be obtained experimentally. To do this, we have calculated the formation energy for several DWβPNTs. The results show that DWβPNTs are more stable than the SWβPNTs. Moreover, some of the systems are even more stable than a black phosphorene monolayer. Also, it is found that for the most stable DWβPNTs, the distance between the two concentric SWβPNTs is similar to the distance between layers of black phosphorus. As a consequence, very small DWβPNTs, in which this distance is not maintained, are not stable. The band gaps of DWβPNTs are smaller than the band gaps of thei...

Study of the stability and interwall distance of (6,0)@(n,0) double-walled silicon carbide nanotubes by the vdW-DFT method

In this work, the stability and electronic structure of zigzag double-walled silicon carbide nanotubes (DWSiCNTs) (6,0)@(n,0) (with n=11-17) were investigated by using ab initio Van der Waals density functional. By calculating the formation energy and the binding energy of each double walled nanotube, the best interwall distance for the outer nanotube was indicated. The results revealed that (13,0) nanotube could be the best external nanotube for the (6,0) internal nanotube with 3.53 Ainterwall distance to make (6,0)@(13,0) DWSiCNT. The structural calculations also revealed that all studied silicon carbide nanotubes were semiconductors and their energy gap decreased from the single one to the double-walled one. Moreover, with raising the nanotube diameter, the energy gap increased, such that at the most stable double-walled nanotube, its value was about 0.216 eV.

Finite element investigation of the elastic modulus of concentric boron nitride and carbon multi-walled nanotubes

The finite element method is used here to study the elastic properties of concentric boron nitride and carbon multi-walled nanotubes. Beam and spring elements are, respectively, employed to model the covalent bonds between atoms and nonbonding van der Waals interactions between atoms located on different walls. The double-walled and triple-walled nanotubes with different arrangements of boron nitride and carbon nanotubes are considered. It is shown that the elastic modulus of the concentric multi-walled BN and C nanotubes increases by increasing the ratio of nanotube length to its diameter (aspect ratio). In addition, the effect of aspect ratio on the elastic modulus of the armchair nanotubes is larger than that on the elastic modulus of the armchair nanotubes. Comparing the elastic modulus of the double-walled and triple-walled nanotubes, it is observed that the effect of number of walls on the elastic modulus of the concentric boron nitride and carbon multi-walled nanotube is negligible.

Dependence of electronic structures of multi-walled boron nitride nanotubes on layer numbers

By using first-principle calculations based on density functional theory, the electronic structures of multi-walled armchair and zigzag boron nitride nanotubes (BNNTs) are investigated. Band shifts between the two layers of the double-walled nanotubes narrow their band gaps and form significant coupling. With the increase of the layer number of the multi-walled BNNTs, the similarity of the electronic structures for the two outer layers is enhanced obviously and the influence of band shift is weakened. Electronic structures of the BNNTs formed with more than three layers are not sensitive to their layer numbers. These results are meaningful for the application researches of BNNTs.

Mechanical properties of defective double-walled boron nitride nanotubes for radiation shielding applications: A computational study

Radiation shielding is of great importance because of the wide-spread use of nuclear radiation in various applications, such as power generation, space industries, nuclear medicine, etc. Current research focuses on developing materials with high shielding efficiency and robust mechanical properties. Boron nitride nanotubes (BNNTs) make good candidate materials for space radiation shielding applications. They are usually mixed with polymer composites to boost their mechanical properties and increase their shielding capability. Shielding can be further enhanced by adding hydrogen to the BNNT lattice, where it binds to atomic sites, or resides in vacancies. These vacancy defects can degrade the mechanical properties of the shielding materials, making them unsuitable for industrial prolonged use. In this work, we study the effect of vacancies on the mechanical properties of double-walled BNNTs (DWBNNTs). Using density functional theory, we calculate Young’s modulus of defective DWBNNTs having up to 4 divacancies, in two configurations, armchair and zigzag. We find that defective armchair DWBNNTs suffer a decrease of 5–25% of their Young’s moduli, while zigzag DWBNNTs show a lesser decrease of 3–15%, relative to the defect-free DWBNNTs. In addition, the divacancies cause a length contraction in the armchair case, and an ellipsoidal deformation for the zigzag one. Our findings are important for predicting of the tolerance of DWBNNTs to space radiation environment.

Comparison of photoelectrochemical performance of anodic single- and double-walled TiO2 nanotube layers

In this work, the photoelectrochemical response of single-walled (SW) and double-walled (DW) TiO2 nanotube (TNT) layers is presented. TNT layers were grown on Ti substrates by anodization in two different ethylene glycol-based electrolytes to obtain ~5 and ~15 μm thick TNT layers. The inner shell of the TNT was quantitatively removed via a mild pre-annealing followed by a selective chemical etching treatment in piranha solution. All TNT layers were investigated for their photoelectrochemical response in the ultraviolet and near visible spectral range. Significantly enhanced photocurrent densities were revealed for the SW-TNT layers. This is ascribed to improved charge carrier separation along the tube walls due to the lack of the C- and F-rich inner shell removed by etching.

Observation of Vibronic-Coupling-Mediated Energy Transfer in Light-Harvesting Nanotubes Stabilized in a Solid-State Matrix.

Ultrafast vibrational spectroscopy is employed to obtain real-time structural information on energy transport in double-walled light-harvesting nanotubes at room temperature, stabilized in a host matrix to mimic the rigid scaffolds of natural light-harvesting systems. We observe evidence of a low-frequency vibrational mode at 315 cm-1, which transfers excitons from the outer wall of the nanotubes to a crossing point through which energy transfer to the inner wall can occur. This mode is furthermore absent in solution phase. Importantly, the coherence of this mode is not transferred to the inner wall upon energy transfer and is only present on the outer wall's excited-state energy surface, highlighting that complete energy transfer between the outer and inner walls does not take place. Isolation of the individual walls of the nanotubes provides evidence that this mode corresponds to a supramolecular motion of the nanotubes. Our results emphasize the importance of the solid-state environment in modulating vibronic coupling and directing energy transfer in molecular light-harvesting systems.

Band engineering of double-wall Mo-based hybrid nanotubes**Project supported by the National Key Research and Development Program of China (Grant No. 2016YFA0202300), the National Natural Science Foundation of China (Grant No. 61390501), the National Basic Research Program of China (Grant No. 2013CBA01600), Strategic Priority Research Program (B) of Chinese Academy of Sciences (Grant Nos. XDPB0601 and XDPB08-1), the CAS Pioneer Hundred

Hybrid transition-metal dichalcogenides (TMDs) with different chalcogens on each side (X-TM-Y) have attracted attention because of their unique properties. Nanotubes based on hybrid TMD materials have advantages in flexibility over conventional TMD nanotubes. Here we predict the wide band gap tunability of hybrid TMD double-wall nanotubes (DWNTs) from metal to semiconductor. Using density-function theory (DFT) with HSE06 hybrid functional, we find that the electronic property of X-Mo-Y DWNTs (X = O and S, inside a tube; Y = S and Se, outside a tube) depends both on electronegativity difference and diameter difference. If there is no difference in electron negativity between inner atoms (X) of outer tube and outer atoms (Y) of inner tube, the band gap of DWNTs is the same as that of the inner one. If there is a significant electronegativity difference, the electronic property of the DWNTs ranges from metallic to semiconducting, depending on the diameter differences. Our results provide alternative ways for the band gap engineering of TMD nanotubes.

Probing of polymer to carbon nanotube surface interactions within highly aligned electrospun nanofibers for advanced composites

By electrospinning poly(ethylene oxide) (PEO)-blended sodium dodecyl sulfate (SDS) functionalized carbon nanotube (CNT) solutions, we engineered single- and double-walled nanotubes into highly aligned arrays. CNT alignment was measured using electron microscopy and polarised Raman spectroscopy. Mechanical tensile testing demonstrates that a CNT loading of 3.9 wt% increases the ultimate tensile strength and ductility of our composites by over a factor of 3, and the Young's modulus by over a factor of 4, to ∼260 MPa. Transmission electron microscopy (TEM) reveals how the aligned nanotubes provide a solid structure, preventing polymer chains from slipping, as well as polymer crystallisation structures such as ‘shish-kebabs’ forming, which are responsible for the improved mechanical properties of the composite. Differential scanning calorimetry (DSC) and small angle X-ray scattering (SAXS) reveals micellar and hexagonal columnar structures along the axis of the fibers, some of which are associated with the presence of the CNT, where these hexagonal structures are associated with the SDS functionalization on the CNT surfaces. This work demonstrates the benefits of CNT alignment within composites, revealing the effectiveness of the electrospinning technique, which enables significantly improved functionality, increasing the utility of the composites for use in many different technological areas.

Computational study of the shift of the G band of double-walled carbon nanotubes due to interlayer interactions

The interactions between the layers of double-walled carbon nanotubes induce measurable shift of the G bands relative to the isolated layers. While experimental data on this shift in free-standing double-walled carbon nanotubes has been reported in the past several years, comprehensive theoretical description of the observed shift is still lacking. The prediction of this shift is important for supporting the assignment of the measured double-walled nanotubes to particular nanotube types. Here, we report a computational study of the G-band shift as a function of the semiconducting inner layer radius and interlayer separation. We find that with increasing interlayer separation, the G band shift decreases, passes through zero and becomes negative, and further increases in absolute value for the wide range of considered inner layer radii. The theoretical predictions are shown to agree with the available experimental data within the experimental uncertainty.

Scaled-up process for producing longer carbon nanotubes and carbon cotton by macro-spools

A scaled up process of the longer carbon nanotube synthesis is reported. The developed suspended-bed synthesis rig is capable of producing carbon nanotube cotton in spools or piles in kilogram amounts. A possibility to produce free-standing non-woven nanotube thin films is demonstrated. The embryonation and initial growth periods are recorded. The carbon nanotube cotton was investigated by electron microscopy (SEM/TEM), Raman spectroscopy and thermal analysis. It was shown that the material is dominated by double-walled nanotubes. Opportunities of combing, roving and spinning the carbon nanotube cotton are discussed. In conclusion this successful scale-up development paves the way for intensification of the development in macroscopic carbon nanotube-based fibers and composite materials.

Double-walled silicon nanotubes: an ab initio investigation

The synthesis of silicon nanotubes realized in the last decade demonstrates multi-walled tubular structures consisting of Si atoms in and the hybridizations. However, most of the theoretical models were elaborated taking as the starting point structures analogous to carbon nanotubes. These structures are unfavorable due to the natural tendency of the Si atoms to undergo . In this work, through ab initio simulations based on density functional theory, we investigated double-walled silicon nanotubes proposing layered tubes possessing most of the Si atoms in an hybridization, and with few atoms localized at the outer wall. The lowest-energy structures have metallic behavior. Furthermore, the possibility to tune the band structure with the application of a strain was demonstrated, inducing a metal-semiconductor transition. Thus, the behavior of silicon nanotubes differs significantly from carbon nanotubes, and the main source of the differences is the distortions in the lattice associated with the tendency of Si to make four chemical bonds.

Improved structural design of single- and double-wall MnCo2O4 nanotube cathodes for long-life Li-O2 batteries.

Developing a cathode material with a stable pore structure and efficient bifunctional activity toward oxygen electrochemistry is the key to achieve practical and high-performance Li-O2 batteries. Here, hierarchically porous MnCo2O4 nanotubes with single- or double-wall architecture are fabricated through a facile electrospinning technique, by adjusting the concentration of the electrospinning solution. The electrochemical measurements indicate that both types of nanotubes possess excellent catalytic abilities toward oxygen reduction and evolution reactions in alkaline aqueous or non-aqueous media. When used as air-electrode catalysts for Li-O2 batteries, both single- and double-wall MnCo2O4 nanotubes show significantly improved electrochemical performance. In particular, the novel double-wall MnCo2O4 nanotubes (DW-MCO-NT), with a high surface area and a large pore volume almost twice as big as the single-wall nanotubes, can offer numerous catalytically active sites as well as sufficient space to deposit discharge products. The DW-MCO-NT based Li-O2 batteries can deliver a maximum discharge capacity of 8100 mA h g-1, with a potential plateau at 2.77 V, and achieve an excellent cyclability over 278 cycles, under strict conditions of 1000 mA h g-1 at 400 mA g-1 within 2.6-4.3 V. Moreover, the XRD and SEM analyses show that the dominant discharge product with a particulate shape is crystal Li2O2 and is prone to being completely decomposed, endowing the MnCo2O4 nanotube-based Li-O2 battery with a long cycle life.

Modelling of adsorption and intercalation of hydrogen on/into tungsten disulphide multilayers and multiwall nanotubes.

Understanding the interaction of hydrogen with layered materials is crucial in the fields of sensors, catalysis, fuel cells and hydrogen storage, among others. Density functional theory, improved by the introduction of van der Waals dispersion forces, provides an efficient and practical workbench to investigate the interaction of molecular and atomic hydrogen with WS2 multilayers and nanotubes. We find that H2 physisorbs on the surface of those materials on top of W atoms, while atomic H chemisorbs on top of S atoms. In the case of nanotubes, the chemisorption strength is sensitive to the nanotube diameter. Diffusion of H2 on the surface of WS2 encounters quite small activation barriers whose magnitude helps to explain previous and new experimental results for the observed dependence of the hydrogen concentration with temperature. Intercalation of H2 between adjacent planar WS2 layers reveals an endothermic character. Intercalating H atoms is energetically favorable, but the intercalation energy does not compensate for the cost of dissociating the molecules. When H2 molecules are intercalated between the walls of a double wall nanotube, the rigid confinement induces the dissociation of the confined molecules. A remarkable result is that the presence of a full H2 monolayer adsorbed on top of the first WS2 layer of a WS2 multilayer system strongly facilitates the intercalation of H2 between WS2 layers underneath. This opens up an additional gate to intercalation processes.

Theoretical Studies on Magnetic Structures, Hysteresis Loops and Size Effects of a Pair of Frustrated Double-Walled Nanotubes

We propose a theoretical quantum model and derive a set of analytic formulas to study the physical properties of a pair of double-walled magnetic nanotubes. The Heisenberg exchange parameters between the two walls of the nanotubes are assumed to differ only in sign. Thus, in the absence of external magnetic field, our calculated macroscopic properties of this pair of nanotubes are almost precisely identical, exhibiting fascinating duality of the nanosystems and demonstrating the correctness of our theoretical model. The two spin systems are all frustrated, so that sudden changes in the macroscopic properties are observed around T M2 that is well below the transition temperature T M1. However, only the inner shell consisting of smaller A-type spins has been obviously affected. In the temperature range T M2 < T < T M1, this shell becomes semi-antiferromagnetic and its magnetization is considerably suppressed, whereas as temperature falls below T M2 the shell gradually restores its ferromagnetic nature. The longitudinal hysteresis behavior of such a double-waled nanotube is ferromagnetic-like below T M2, but antiferromagnetic-like in the temperature interval T M2 < T < T M1. Moreover, we find that the diameter of the nanotube has seemly no effects on its physical properties, whereas its length does affects the two temperatures slightly, and also its spin configuration at very low temperatures if the tube is sufficiently long. More importantly, the theoretical results presented in this paper can be precisely reproduced with the quantum computational method we develop in recent years, justifying the validity of the numerical approach once again.

Hysteresis loop behaviors of a decorated double-walled cubic nanotube

The effect of surface shell parameters on the hysteresis loop behaviors of a decorated Ising cubic nanotube, consisting of a ferromagnetic spin-12 core which is interacting ferrimagnetically with a ferromagnetic spin-1 surface shell, is investigated, in the present work, within the effective-field theory with correlations based on the probability distribution technique. We have found that these parameters have a strong effect on the shape and the number of hysteresis loops and also on the coercive field and remanent magnetization behaviors. Indeed, triple, quintuple, septuple and nonuple hysteresis loop patterns have also been observed.

Possibility of Improving Oscillation Performance of Double-Walled Nanotube Oscillators via Tuning Vacancy Defects

The oscillatory behaviors of an oscillator made from double-walled carbon nanotubes (DWCNTs) with vacancy defects were systematically investigated via molecular dynamics simulation method. We found that the vacancy defects change the off-axial rocking motion and the van der Waals potential, resulting in more energy dissipation. Unlike the case in the C60–nanotube oscillators (Song, et al., Phys. Lett. A. 373 2009, 1058-1061) that one vacancy can make the oscillators more stable, our study showed that the vacancies cannot improve the performance of DWCNT-based oscillators no matter where vacancy defects are located.

X-ray Crystallographic Structure of a Giant Double-Walled Peptide Nanotube Formed by a Macrocyclic β-Sheet Containing Aβ16–22

This paper describes the supramolecular assembly of a macrocyclic β-sheet containing residues 16-22 of the β-amyloid peptide, Aβ. X-ray crystallography reveals that the macrocyclic β-sheet assembles to form double-walled nanotubes, with an inner diameter of 7 nm and outer diameter of 11 nm. The inner wall is composed of an extended network of hydrogen-bonded dimers. The outer wall is composed of a separate extended network of β-barrel-like tetramers. These large peptide nanotubes pack into a hexagonal lattice that resembles a honeycomb. The complexity and size of the peptide nanotubes rivals some of the largest tubular biomolecular assemblies, such as GroEL and microtubules. These observations demonstrate that small amyloidogenic sequences can be used to build large nanostructures.

Synthesis and photoeletrochemical performance of AuAg@CdS double-walled nanotubes

Uniform CdS coated AuAg alloyed double-walled nanotubes were successfully fabricated by solvothermal process using Ag nanowires as the template. UV–vis-NIR extinction spectra revealed that the obtained double-walled nanotubes can present an enhanced light absorption ability compared with both pure AuAg alloyed nanotubes and CdS nanowires. Photocurrent and electrochemical impedance spectroscopy measurements indicated that such double-walled structure could significantly extend the lifetime of photo-generated carriers and increase the light-harvesting efficiency of CdS, due to the low charge transfer resistance and a high carrier transfer rate of the double-walled structure. The growth mechanism of such kind of nanotubes was also proposed.

Evolution of TiO2 Nanotubular Morphology Obtained in Ethylene Glycol/Glycerol Mixture and its Photoelectrochemical Performance

The evolution of TiO2 nanotubular morphology, synthesized in a mixture of fluorinated ethylene glycol and glycerol electrolyte, was studied as a function of the anodization time. The samples were characterized by FEG-SEM, XRD, XPS, UV-Vis and EIS. The formation of single-or double-walled TiO2 nanotube structure can be efficiently controlled by the anodization time. For anodization times less than 30 minutes, a compact oxide layer is formed, followed by double-walled nanotube formation up to 120 minutes and single-walled nanotubes up to 240 minutes. XPS analyses show that the samples obtained with short anodization time have a high carbon content and oxygenated surface species compared to the longer-time anodized sample; however, binding energy peaks for Ti 2p remained invariant. The performances of TiO2 nanotubular photoelectrodes were evaluated in photoelectrochemical water splitting where TiO2 nanotubes anodized for 120 minutes presented the best performance that was related to their optimal morphology and charge transportation.