Double-walled Carbon Nanotubes Research Articles

Rhodamine B Photodegradation in Aqueous Solutions Containing Nitrogen Doped TiO2 and Carbon Nanotubes Composites.

In this work, new results concerning the potential of mixtures based on nitrogen doped titanium dioxide (TiO2:N) and carbon nanotubes (CNTs) as possible catalyst candidates for the rhodamine B (RhB) UV photodegradation are reported. The RhB photodegradation was evaluated by UV–VIS absorption spectroscopy using samples of TiO2:N and CNTs of the type of single-walled carbon nanotubes (SWNTs), double-wall carbon nanotubes (DWNTs), multi-wall carbon nanotubes (MWNTs), and single-walled carbon nanotubes functionalized with carboxyl groups (SWNT-COOH) having various concentrations of CNTs. The best photocatalytic performance was obtained for sample containing TiO2:N and 2.5 wt.% SWNTs-COOH, when approx. 85% of dye removal was achieved after 300 min. of UV irradiation. The reaction kinetics of RhB aqueous solutions containing TiO2:N/CNT mixtures followed a complex first-order kinetic model. The TiO2:N/CNTs catalyst induced higher photodegradation efficiency of RhB than TiO2:N due to the presence of CNTs, which act as adsorbent and dispersing agent and capture the photogenerated electrons of TiO2:N hindering the electron–hole recombination.

Interlayer Interactions in 1D Van der Waals Moiré Superlattices.

Studying two‐dimensional (2D) van der Waals (vdW) moiré superlattices and their interlayer interactions have received surging attention after recent discoveries of many new phases of matter that are highly tunable. Different atomistic registry between layers forming the inner and outer nanotubes can also form one‐dimensional (1D) vdW moiré superlattices. In this review, experimental observations and theoretical perspectives related to interlayer interactions in 1D vdW moiré superlattices are summarized. The discussion focuses on double‐walled carbon nanotubes (DWNTs), a model 1D vdW moiré system, and the authors highlight the new optical features emerging from the non‐trivial strong interlayer coupling effect and the unique physics in 1D DWNTs. Future directions and questions in probing the intriguing physical phenomena in 1D vdW moiré superlattices such as, correlated physics in different 1D moiré systems beyond DWNTs are proposed and discussed.

The Host-Guest Complexes of Various Carbon Nanotubes (CNTs) and Boron Nitride Nanotubes (BNNTs) with Water at DFT Levels

We have investigated the various nanotube (NT)-water complexes as important host-guest complexes via the DFT method using B3LYP/6-31G* and M06/6-31G* levels of theory. These NTs include single-walled and double-walled carbon nanotubes (SWCNT and DWCNT, respectively). In addition, the boron nitride nanotube (BNNT) and tip-functionalized CNTs are also designed. All geometries turn out as minima on their energy surfaces. Calculated structural and thermodynamic parameters, along with atoms in molecules (AIM) and natural bond orbital (NBO) analyses, indicate that water inside the SWCNTs shows a higher interaction with NT where the nature of interactions is partially electrostatic-partially covalent. Therefore, the SWCNTs turn out as the best candidates for carrying and storage the water molecules.

Stability- and Crosstalk-Based Performance of Multi- and Double-walled Mixed CNT Bundles as Interconnect for Next-Generation Technology Nodes

The temperature-dependent modeling technique (in the temperature range of 200–500[Formula: see text]K) for a mixed class of carbon nanotube (CNT) bundle interconnects is proposed. The equivalent single conductor (ESC) transmission line models of multi-walled carbon nanotube (MWCNT) and double-walled carbon nanotube (DWCNT) are combined to develop multiple single conductor (MSC) model of mixed CNT interconnects. Various possible arrangements of densely packed MWCNT and DWCNT bundles (MDCB) are considered to form different types of mixed CNT bundle structures (MDCB-1, MDCB-2, MDCB-3 and MDCB-4). The integrated circuit emphasis simulation is performed and the performances of these mixed CNT bundle interconnects are investigated in terms of propagation delay (with and without crosstalk), power dissipation, power-delay product (PDP). Switching times, overshoot voltages and Nyquist plots are analyzed to check the stability of these mixed CNT structures for global interconnect length for 32-nm, 22-nm and 16-nm technology nodes. It is observed that the MDCB-1 structure yields the most promising result in all aspects for interconnect applications in the near future.

Rheological, electrical, and dynamic thermomechanical properties: Comparison between multiwall and double-wall carbon nanotubes in polylactide and polyamide 11

In this study, multiwall carbon nanotubes (MWCNTs) and double-wall carbon nanotubes (DWCNTs) have been dispersed in polylactide (PLA) and polyamide 11 (PA11) using an internal mixer. Rheological characterization confirmed the formation of carbon nanotube (CNT) networks in PLA and PA11 attributed to well-dispersed CNTs in the respective matrices. A lower rheological percolation threshold of PLA/MWCNT nanocomposites (less than 0.5 wt. %) compared to PA11/MWCNT nanocomposites (about 2 wt. %) confirmed the greater affinity of CNTs for PLA. The threshold for DWCNTs was below 0.5 wt. % in PLA and between 0.5 and 1 wt. % in PA11. PLA-based nanocomposites also showed higher electrical conductivity values compared to PA11-based nanocomposites. Nanocomposites containing DWCNTs exhibited higher electrical conductivities compared to those containing MWCNTs due to the higher aspect ratio of DWCNTs. Dynamic mechanical thermal analysis showed enhanced storage modulus values and reduced damping behavior with increasing content of CNTs for both polymers.

Impact of edge functionalization on electron field-emission characteristics of carbon nanotubes: A theoretical approach

A theoretical approach using first-principle calculations of the density of states (DOS) of functionalized carbon nanotubes (CNTs) is carried out to understand their enhanced electron field emission (FE) properties. The theoretical functionalization of CNTs is perceived using hydrogenation (H/O–H) and oxidation methods. In order to investigate the enhancement in the FE properties of functionalized CNTs, both single-walled carbon nanotubes (SWCNT) and double-walled carbon nanotubes (DWCNT) are studied. The work function is observed to be more decreased in case of zigzag SWCNT (φ = 3.32 for oxygenated SWCNT) as compared to others SWCNT. The dependence of DOS on zigzag/armchair edge functionalization has also been investigated to reveal the impact of DOS on FE. The observed results indicate that edge functionalization of CNTs leads to significant changes in the band structure, DOS, and work functions. The shifting of DOS away from the Fermi level and decrease in work function is evidenced owing to the reduction in the curvature effect of CNT. Also, due to enhanced DOS near the Fermi level, making them a better proposition for FE applications. Our calculations provide an in-depth insight into the functionalization mechanism to understand the enhanced FE properties from them.

Interference effects in one-dimensional moiré crystals

Interference effects in finite sections of one-dimensional moiré crystals are investigated using a Landauer-Büttiker formalism within the tight-binding approximation. We explain interlayer transport in double-wall carbon nanotubes and design a predictive model. Wave function interference is visible at the mesoscale: in the strong coupling regime, as a periodic modulation of quantum conductance and emergent localized states; in the localized-insulating regime, as a suppression of interlayer transport, and oscillations of the density of states. These results could be exploited to design quantum electronic devices.

Computationally Guided Design of Large-Diameter Carbon Nanotube Bundles for High-Strength Materials

Large-diameter carbon nanotubes (CNTs) synthesized by floating-catalyst chemical vapor deposition (FC-CVD) assemble into bundles and subsequently into aerogel networks from which yarns and sheets are mechanically drawn. The CNT bundles exhibit unique microstructures with collapsed CNT packing, not found in other types of CNT yarns. At the same time, the bundle structure is not homogeneous and the wide variability of CNT cross-sectional shapes reflects the bundling process. Transmission electron microscopy (TEM) images allow detailed quantification of CNT diameters, shapes, and number of walls. Molecular dynamics (MD) simulations of CNT assemblies are subsequently built to match the observed CNT shape characteristics and mass densities. Contrary to an established notion of an applied “buckling” pressure requirement for radial collapse, MD demonstrated that interacting large-diameter CNTs can collapse spontaneously, suggesting that collapse can occur during bundling. Computational explorations of this mechanism yield conditions for large double-walled CNTs (with a mean diameter around 7.8 nm) to assemble into phases with significantly increased packing efficiencies and Young’s moduli approaching 1 TPa. The results may play a guiding role in advancing FC-CVD aerogel synthesis and processing methods to yield yarn and sheets with larger densities and superior mechanical properties.

Large‐Diameter Carbon Nanotube Transparent Conductor Overcoming Performance–Yield Tradeoff

AbstractThe floating catalyst chemical vapor deposition (FCCVD) method for producing single‐walled carbon nanotubes (SWNTs) has demonstrated great potential in transparent conductive film (TCF) application. In FCCVD, reducing the concentration of carbon nanotubes (CNTs) is a well‐agreed method of improving the conductivity of SWNT TCF, achieved by producing thinner and longer CNT bundles. However, this method decreases the yield dramatically, which has persisted throughout the TCF development. Here, the production of large‐diameter double‐walled CNT (DWNT) TCFs via FCCVD is reported, which overcomes the tradeoff between performance and yield. These TCFs of DWNTs with an average diameter of ≈4 nm have a low sheet resistance of 35 Ω sq−1 at 90% transmittance. The conductivity here aligns with the best‐performing SWNT TCFs reported to date, showing a production yield greater than two orders of magnitude. The main factor contributing to the high performance and yield is considered to be the large tube diameter, which greatly improves the yield threshold of CNT bundling and leads to long tube length and unique junctions broadening. Moreover, the application of DWNT TCFs in perovskite solar cells exhibits a power conversion efficiency of 17.4%, which has not been reported yet in indium‐free CNT‐based solar cells.

Modes of Vibration of Single- and Double-Walled CNTs with an Attached Mass by a Non-local Shell Model

Modes of Vibration of Single- and Double-Walled CNTs with an Attached Mass by a Non-local Shell Model

Structural and electronic properties of double-walled [formula omitted]-graphyne nanotubes

The structural and electronic properties of double-walled α-graphyne nanotubes (α-DWGNTs) are investigated using a combination of computation and theoretical methods, including density functional theory. DWGNTs differ from conventional double-walled carbon nanotubes by the presence of carbon atoms featuring both sp and sp2 hybridizations, endowing DWGNTs with a set of desirable properties that could lead to a number of applications. Classical molecular dynamics (MD) and Born–Oppenheimer molecular dynamics (BOMD) simulations were performed to reveal the structural stability of these nanotubes at room temperature. Their dynamical stability was confirmed using tight-binding based phonons calculations. The high flexibility of the graphyne sheet and van der Waals interactions between the shells lead to strong deformations of the outer tube. Consequently, the electronic structure of the component single-walled tubes undergoes significant changes once cast into the double-walled geometries due to the coupling of electronic states from the inner wall with the outer tube. Such strong inter-wall hybridization can not only modulate the electronic band gap of semiconducting tubes, in comparison to their isolated single-walled counterparts, but can also affect the electronic properties of the double-walled systems. These behaviors open up possibilities of using such nanostructures in the design of electronic device applications.

Ultrasonication-induced extraction of inner shells from double-wall carbon nanotubes characterized via in situ spectroscopy after density gradient ultracentrifugation

Even though ultrasonication is considered to be an effective method to disperse carbon nanotubes (CNTs), its devastating effects on the nanotubes are often neglected. Here, even mild ultrasonication is found to rapidly extract the inner single-wall CNTs (SWCNTs) from the outer shells of the double-wall CNTs (DWCNTs). As-synthesized DWCNTs are gently solubilized in a surfactant solution, strictly avoiding any ultrasonication, followed by two consecutive density gradient ultracentrifugation (DGU) steps to obtain a purified colloidal solution of isolated DWCNTs. The latter is carefully selected based on in situ resonant Raman (RRS) and fluorescence (PL) spectroscopy, measured as a function of depth directly in the ultracentrifuge tube after DGU. These purified DWCNTs are ultrasonicated in successive time steps while intermittently probing the sample via RRS and PL spectroscopy. These results unravel the very fast increasing, yet saturating extraction mechanism that leads to the formation of fluorescing SWCNTs. A statistical high-resolution transmission electron microscopy study confirms the drastic increase in SWCNTs after ultrasonication, and evidences that ultrasonication forms SWCNTs from both the inner and outer shells of the DWCNTs. This study demonstrates how easily ultrasonication extracts SWCNTs from individually solubilized DWCNTs, unavoidably complicating any further spectroscopic studies on DWCNTs severely.

Nitrogen-doped graphene nanosheet-double-walled carbon nanotube hybrid nanostructures for high-performance supercapacitors

A hybrid nitrogen-doped graphene nanosheet-grafted double-walled carbon nanotube (NG-DWCNT) was synthesized by chemical vapor deposition (CVD). Double-walled carbon nanotube (DWCNT) was synthesized by floating catalytic CVD using ferrocene and thiophene dissolved in ethanol. NG was directly grafted onto the DWCNT bundles by thermal CVD using mixed ethanol-urea solution. The NG possess sharp-edged petal-like structure on one-dimensional DWCNT bundle. The NG-DWCNT showed the nitrogen content of approximately 1.93 at%. The NG-DWCNT hybrid nanostructures exhibited a higher specific capacitance of 563 F g−1 than that of the DWCNT and un-doped G-DWCNT. The improvement of capacitance value is attributed to the synergic effect of the nitrogen doping together with the sharp-edged petal-like structure of the NG. The facile technique by CVD method provides a promising approach for simple and low-cost technique to synthesize the NG-DWCNT hybrid nanostructures. A hybrid carbon nanostructure of NG-DWCNT has a potential application in electrochemical conversion and energy storage devices.

Carbon nanotubes as fillers for composites with enhanced thermal conductivity

Thermal conductivities of single- and double-wall carbon nanotubes in contact with foreign atoms on their surfaces are investigated by means of molecular dynamics simulations. Small amounts of atoms on the surfaces of single-wall nanotubes drastically reduce their thermal conductivity, while the conductivities of the inner walls of double-wall nanotubes which are only weakly coupled to the outer walls are retained even for large amounts of atoms on the surfaces. Based on the simulation results, an estimation for the conditions under which an enhancement of thermal conductivities can be expected is presented.

Molecular dynamics of axial interwall van der Waals force and mechanical vibration of double-walled carbon nanotubes

In the first part of this study, the axial interwall van der Waals (vdW) interaction forces of Double-Walled Carbon nanotubes (DWCNTs) are calculated using the Molecular Dynamics (MD) method. The axial vdW forces, including Leonard-Jones forces, are simulated for different chiralities to investigate the effects of the carbon atoms arrangement of DWCNTs on the axial interwall vdW forces using six pairs of DWCNTs. The results show the maximum axial vdW forces for the zigzag DWCNTs. In the second part of this study, the axial vibrations of DWCNTs are calculated considering the effects of axial interwall vdW forces. These forces are modeled by linear springs in which their stiffness values (force per unit length per unit of displacement) are approximated based on the vdW forces obtained in the first part of this study. The equations of motion are analytically derived and solved for DWCNTs. The natural frequencies of axial vibrations are validated by the classical model. Consideration of the axial interwall vdW forces of DWCNTs had considerable influence on the natural frequencies of axial vibration. This impact is intensified by enhancement of DWCNT length, especially in the first vibration mode (Up to 49%).

Moiré-Induced Vibrational Coupling in Double-Walled Carbon Nanotubes.

Moiré patterns are additional, long-range periodicities in twisted crystalline bilayers. They are known to fundamentally change the electronic states of the layers, but similar effects on their mechanical and vibrational properties have not been discussed so far. Here we show that the moiré potential shifts the radial breathing mode in double-walled carbon nanotubes (DWCNTs). The change in frequency is expected to be proportional to the shift in optical transition energies, which are induced by the moiré patterns. To verify our model, we performed resonance Raman scattering on purified and sorted semiconducting DWCNTs. We find that the radial breathing mode shifts up to 14 cm-1 higher in energy followed by displacement of optical transition energies of up to 200 meV to lower energies, in comparison to the single-walled tubes. We show how to identify the strong coupling condition in DWCNTs from their phonon frequencies and construct a Kataura plot to aid their future experimental assignment.

Linear and Helical Cesium Iodide Atomic Chains in Ultranarrow Single-Walled Carbon Nanotubes: Impact on Optical Properties.

One-dimensional (1D) atomic chains of CsI were previously reported in double-walled carbon nanotubes with ∼0.8 nm inner diameter. Here, we demonstrate that, while 1D CsI chains form within narrow ∼0.73 nm diameter single-walled carbon nanotubes (SWCNTs), wider SWCNT tubules (∼0.8-1.1 nm) promote the formation of helical chains of CsI 2 × 1 atoms in cross-section. These CsI helices create complementary oval distortions in encapsulating SWCNTs with highly strained helices formed from strained Cs2I2 parallelogram units in narrow tubes to lower strain Cs2I2 units in wider tubes. The observed structural changes and charge distribution were analyzed by density-functional theory and Bader analysis. CsI chains also produce conformation-selective changes to the electronic structure and optical properties of the encapsulating tubules. The observed defects are an interesting variation from defects commonly observed in alkali halides as these are normally associated with the Schottky and Frenkel type. The energetics of CsI 2 × 1 helix formation in SWCNTs suggests how these could be controllably formed.

Applicability and Limitations of Simplified Elastic Shell Theories for Vibration Modelling of Double-Walled Carbon Nanotubes

The applicability and limitations of simplified models of thin elastic circular cylindrical shells for linear vibrations of double-walled carbon nanotubes (DWCNTs) are considered. The simplified models, which are based on the assumptions of membrane and moment approximate thin-shell theories, are compared with the extended Sanders–Koiter shell theory. Actual discrete DWCNTs are modelled by means of couples of concentric equivalent continuous thin, circular cylindrical shells. Van der Waals interaction forces between the layers are taken into account by adopting He’s model. Simply supported and free–free boundary conditions are applied. The Rayleigh–Ritz method is considered to obtain approximate natural frequencies and mode shapes. Different aspect and thickness ratios, and numbers of waves along longitudinal and circumferential directions, are analysed. In the cases of axisymmetric and beam-like modes, it is proven that membrane shell theory, differently from moment shell theory, provides results with excellent agreement with the extended Sanders–Koiter shell theory. On the other hand, in the case of shell-like modes, it is found that both membrane and moment shell theories provide results reporting acceptable agreement with the extended Sanders–Koiter shell theory only for very limited ranges of geometries and wavenumbers. Conversely, for shell-like modes it is found that a newly developed, simplified shell model, based on the combination of membrane and semi-moment theories, provides results in satisfactory agreement with the extended Sanders–Koiter shell theory in all ranges.

Nanotube-Based 1D Heterostructures Coupled by van der Waals Forces.

1D van der Waals heterostructures based on carbon nanotube templates are raising a lot of excitement due to the possibility of creating new optical and electronic properties, by either confining molecules inside their hollow core or by adding layers on the outside of the nanotube. In contrast to their 2D analogs, where the number of layers, atomic type and relative orientation of the constituting layers are the main parameters defining physical properties, 1D heterostructures provide an additional degree of freedom, i.e., their specific diameter and chiral structure, for engineering their characteristics. The current state-of-the-art in synthesizing 1D heterostructures are discussed here, in particular focusing on their resulting optical properties, and details the vast parameter space that can be used to design heterostructures with custom-built properties that can be integrated into a large variety of applications. First, the effects of van der Waals coupling on the properties of the simplest and best-studied 1D heterostructure, namely a double-walled carbon nanotube, are described, and then heterostructures built from the inside and the outside are considered, which all use a nanotube as a template, and, finally, an outlook is provided for the future of this research field.

Propagation of waves with nonlocal effects for vibration response of armchair double-walled CNTs

In this paper, vibration characteristics of double-walled carbon nanotubes (CNTs) are studied based upon nonlocal elastic shell theory. The significance of small scale is being perceived by developing nonlocal Love shell model. The wave propagation approach has been utilized to frame the governing equations as eigen value system. The influence of nonlocal parameter subjected to diverse end supports has been overtly analyzed. An appropriate selection of material properties and nonlocal parameter has been considered. The influence of changing mechanical parameter Poisson's ratio has been investigated in detail. It is found that the frequencies decrease as nonlocal parameter increases and for the certain values of nonlocal parameter against range of Poisson ratio rise slowly with length double-walled CNTs. The dominance of boundary conditions via nonlocal parameter is shown graphically. The results generated furnish the evidence regarding applicability of nonlocal shell model and also verified by earlier published literature.