Short Nanotubes Research Articles

Strong shape-dependence of Morin transition in α-Fe2O3 single-crystalline nanostructures

Single-crystalline hematite (α-Fe2O3) nanorings (short nanotubes) and nanotubes were synthesized by a hydrothermal method. High-resolution transmission electron microscopy and selected-area electron diffraction confirm that the axial directions of both the nanorings and nanotubes are parallel to the crystalline c-axis. Intriguingly, the Morin transition occurs at about 210 K in the short nanotubes with a mean tube length of about 115 nm and a mean outer diameter of about 169 nm. However, it does not occur in the nanotubes with a mean tube length of about 317 nm and a mean outer diameter of about 148 nm. Detailed analysis of magnetization data, X-ray diffraction patterns, and room-temperature Mossbauer spectra demonstrates that this very strong shape-dependence of Morin transition is intrinsic to hematite. We explain this intriguing shape-dependence quantitatively, in terms of the opposite signs of the surface magnetic anisotropy constants of the surface planes parallel and perpendicular to the c-axis.

Thermophysical properties of Single Wall Carbon Nanotubes and its effect on exergy efficiency of a flat plate solar collector

In order to enhance thermal efficiency of a flat plate solar collector, the effects of thermo-physical properties of short Single Wall Carbon Nanotubes (SWCNTs) suspended in water was investigated in this study. Sodium dodecyl sulphate was used as a dispersant for preparing a stable nanofluid. Subsequently, the nanofluid was comprehensively characterized by particle size measurement and spectroscopic technique. Specific heat with the increase of particle loading and temperature was investigated. Thermal conductivity increment also showed a linear dependence on particle concentration and temperature. Viscosity of the nanofluids and water reduced with the increase of temperature and increased with the particle loading. Using improved thermo-physical properties of the nanofluid, the maximum energy and exergy efficiency of flat plate collector was enhanced up to 95.12% and 26.25% compared to water which was 42.07% and 8.77%, respectively. This low exergy efficiency shows that flat plate collectors still require substantial enhancement. To the authors’ knowledge, SWCNTs–H2O was used as the functioning fluid for the first time to investigate both the thermos-physical properties as well as the increase in thermal efficiency of a flat plate solar collector.

Polymers encapsulated in short single wall carbon nanotubes: pseudo-1D morphologies and induced chirality.

Molecular dynamics simulations are performed to investigate the stable morphologies of semi-flexible polymer chains within a single wall carbon nanotube (CNT). We characterize these morphologies with a variety of measures. Due to the different curvature inside the CNT to outside, there are increased numbers of polymer-CNT bead contacts for polymers which reside inside the CNT. A sufficiently long polymer chain first adsorbs on the exterior of the nanotube and subsequently moves inside the cavity of the nanotube. At equilibrium, the polymer configuration consists of a central stem surrounded by helically wrapped layers. Sections of the polymer outside the CNT have helical conformations (for CNTs of small radius) or circular arrangements (for CNTs of larger radius). Polymers encapsulated within the CNT have an increased chirality due to packing of the beads and this chirality is further enhanced for moderately stiff chains.

Peptide-induced affinity binding of carbonic anhydrase to carbon nanotubes.

Although affinity binding between short chain peptides and carbon nanotube (CNT) has been reported, little is known for the study of proteins with CNT recognition and specific binding capabilities. Herein, carbonic anhydrase (CA) was functionalized via protein fusion with a single-walled carbon nanotube (SWNTs)-binding peptide, thereby forming a bioactive protein with high affinity binding capability. TEM and AFM analyses showed that the fusion CA could firmly coat to SWNTs with a surface coverage over 51%, while the enzyme maintained its catalytic activity. Structural analysis revealed that slight conformation changes were induced as a result of the fusion; however, the affinity binding of CA to the hydrophobic surface of SWNTs restored the native structure of the protein, with the conformation of the SWNT-bound CA largely resembling that of the native parent enzyme. Interfacial interactions between the fusion CA and SWNT were further investigated with Raman spectrometry and microscopic analysis. The results suggested that such peptide-induced CNT-protein binding allows the development of bioactive hybrid materials with the native structures of the protein moieties largely undisrupted.

The Electronic Structure of Short Carbon Nanotubes: The Effects of Correlation

This paper presents atight bindingandab initiostudy of finite zig-zag nanotubes of various diameters and lengths. The vertical energy spectra of such nanotubes are presented, as well as their spin multiplicities. The calculations performed using thetight bindingapproach show the existence of quasi-degenerate orbitals located around the Fermi level, thus suggesting the importance of high-qualityab initiomethods, capable of a correct description of the nondynamical correlation. Such approaches (Complete Active Space SCF and Multireference Perturbation Theory calculations) were used in order to get accurate ground and nearest excited-state energies, along with the corresponding spin multiplicities.

Tailoring Industrial Scale CNT Production to Specialty Markets

AbstractThe vast majority of industrial scale Carbon Nanotube (CNT) production involves short nanotubes (< 100 microns) that appear as a powder. These products are typically utilized as minor components (usually less than 2%) in polymers where they may or may not impart marginal improvements in composite properties. At Nanocomp Technologies we produce large-format CNT material by floating catalyst chemical vapor deposition. This technique produces very long CNTs (> 1 mm) in the gas phase, where entanglement produces large format material of exceptional strength and electrical conductivity. By manipulating the physics and chemistry of the process, the format and properties of the material can be controlled. Post-production processing further enhances the desired material properties. In this way applications such as Armor, Wiring and Cables for aerospace, and Integrated Energy Storage can be realized.

Nearly exclusive growth of small diameter semiconducting single-wall carbon nanotubes from organic chemistry synthetic end-cap molecules.

The inability to synthesize single-wall carbon nanotubes (SWCNTs) possessing uniform electronic properties and chirality represents the major impediment to their widespread applications. Recently, there is growing interest to explore and synthesize well-defined carbon nanostructures, including fullerenes, short nanotubes, and sidewalls of nanotubes, aiming for controlled synthesis of SWCNTs. One noticeable advantage of such processes is that no metal catalysts are used, and the produced nanotubes will be free of metal contamination. Many of these methods, however, suffer shortcomings of either low yield or poor controllability of nanotube uniformity. Here, we report a brand new approach to achieve high-efficiency metal-free growth of nearly pure SWCNT semiconductors, as supported by extensive spectroscopic characterization, electrical transport measurements, and density functional theory calculations. Our strategy combines bottom-up organic chemistry synthesis with vapor phase epitaxy elongation. We identify a strong correlation between the electronic properties of SWCNTs and their diameters in nanotube growth. This study not only provides material platforms for electronic applications of semiconducting SWCNTs but also contributes to fundamental understanding of the growth mechanism and controlled synthesis of SWCNTs.

Channeling of protons through BN nanotubes

In this paper we study the angular and spatial distributions of protons channeled through boron–nitride (BN) nanotubes. The BN nanotubes have very similar structures like carbon nanotubes, but they are more thermally and chemically stable, and they also present good candidates for future channeling experiments. We present the angular and spatial distributions of MeV energy protons through the straight short (10,10) single-wall BN nanotubes (SWBNNs). They were generated by a computer simulation method Borka et al. (2011, 2012a,b). Also, the effect of focusing of channeled protons is observed. A possible application of the obtained results for characterization of BN nanotubes is discussed. Analysis of angular and spatial distributions could be used to provide detailed information on the projectile–target interaction potentials inside BN nanotubes. We also varied the proton incident angle and energy and demonstrate that we can get a significant rearrangement of the propagating protons within the BN nanotube. This investigation may be used for proton beam guiding, to locate atomic impurities in nanotubes as well as for creating nanosized proton beams to be used in materials science, biology and medicine.

Spin ordering in RKKY nanowires: Controllable phases inC13nanotubes

Detailed study of nuclear spin order in semiconducting ${}^{13}\mathrm{C}$ nanotubes reveals subtle interplay of the chemical potential, length, diameter, and chirality, resulting in the complex four-dimensional phase diagram of the helical ground states. Increase of the chemical potential causes abrupt transitions between different helical spin orderings of three regimes which are interpolated by a smooth change of helical angle within each regime: in the middle one the helimagnet is a deviation from the commensurate order and fully characterizes the geometry of the nanotube, while outside it the ground state is an incommensurate helical deviation from the ferromagnet. This behavior of the ${}^{13}\mathrm{C}$ nanotubes manifests the long-range of the RKKY interaction and quasi-one-dimensional geometry, thus being universal for all RKKY interaction governed nanowires. Short enough nanotubes are ferromagnetic; the critical length when frustration arises decreases with the chemical potential but increases with diameter and chiral angle. The results, verified numerically, show that with nanotubes of the different but realistic lengths, various scenarios of the helical order response to the gate voltage can be achieved.

TiO2 nanotube arrays for photocatalysis: Effects of crystallinity, local order, and electronic structure

To furnish insight into correlations of electronic and local structure and photoactivity, arrays of short and long TiO2 nanotubes were synthesized by electrochemical anodization of Ti foil, followed by thermal treatment in O2 (oxidizing), Ar (inert), and H2 (reducing) environments. The physical and electronic structures of these nanotubes were probed with x-ray diffraction, scanning electron microscopy, and synchrotron-based x-ray absorption spectroscopy, and correlated with their photocatalytic properties. The photocatalytic activity of the nanotubes was evaluated by monitoring the degradation of methyl orange under UV-VIS light irradiation. Results show that upon annealing at 350 °C all as-anodized amorphous TiO2 nanotube samples partially transform to the anatase structure, with variations in the degree of crystallinity and in the concentration of local defects near the nanotubes' surface (∼5 nm) depending on the annealing conditions. Degradation of methyl orange was not detectable for the as-anodized TiO2 nanotubes regardless of their length. However, the annealed long nanotubes demonstrated detectable catalytic activity, which was more significant with the H2-annealed nanotubes than with the Ar- and O2-annealed nanotube samples. This enhanced photocatalytic response of the H2-annealed long nanotubes relative to the other samples is positively correlated with the presence of a larger concentration of lattice defects (such as Ti3+ and anticipated oxygen vacancies) and a slightly lower degree of crystallinity near the nanotube surface. These physical and electronic structural attributes impact the efficacy of visible light absorption; moreover, the increased concentration of surface defects is postulated to promote the generation of hydroxyl radicals and thus accelerate the photodegradation of the methyl orange. The information obtained from this study provides unique insight into the role of the near-surface electronic and defect structure, crystal structure, and the local chemical environment on the photocatalytic activity and may be employed for tailoring the materials' properties for photocatalysis and other energy-related applications.

Mechanical properties of bulk carbon nanomaterials

Bulk carbon nanomaterials, which open prospects for the development of a new generation of supercapacitors, are actively investigated for recent years, but their mechanical properties and structure remain poorly understood. In connection with this fact, the influence of the hydrostatic and uniaxial compression on mechanical properties and structure of three bulk nanomaterials consisting of (i) bent graphene flakes, (ii) short carbon nanotubes, and (iii) fullerenes C240 are investigated by the molecular dynamics method. It is shown that the strength of the material and its stability to graphitization depend on its constituent structural units. At large degrees of deformation, the material consisting of bent graphene sheets has the highest strength, whereas at the material density lower than 2.5 g/cm3, the highest strength is observed in the nanomaterial consisting of fullerene molecules. The differences in mechanical properties of the materials under consideration are explained by their structural features.

Synthesis and characterization of FeCo/C hybrid nanofibers with high performance of microwave absorption

FeCo/C hybrid nanofibers (FeCo/C HNFs) with short multi-walled carbon nanotubes grown on the nanofiber surfaces have been prepared by electrospinning combined with stabilization and carbonization. The in-situ formed FeCo nanoparticles uniformly disperse along nanofibers and are encapsulated with ordered graphite layers. It is found that the as-prepared FeCo/C HNFs exhibit excellent microwave absorption performance with low density and small absorber thickness. Reflection loss exceeding −20dB can be obtained in a wide frequency range of 7.2–18GHz for the silicone composites containing only 5wt.% FeCo/C HNFs as filler by choosing an appropriate absorber thickness between 1.4 and 3.0mm, and the minimum reflection loss reaches −47.5dB at 16.6GHz for a 1.6mm absorber layer, indicating that the FeCo/C HNFs can be a promising candidate for lightweight, highly-efficient and stable microwave absorbing materials in X- and Ku-bands.

One-pot and Three-component Functionalization of Short Multi-walled Carbon Nanotubes with Isatoic Anhydride and Benzyl Amine and Their Effect on the MKN-45 and MCF7 Cancer Cells

The one-pot and three-component chemical functionalization of short acyl-chloride multi-walled carbon nanotubes (Sh-MWCNT-COCl) by isatoic anhydride and benzyl amine for producing 2-amino-N-benzylbenzamide (Sh-MWCNT-amide) and then by POCl3 to produce 3-benzylquinazolin-4(3H)-one (Sh-MWCNT-quinaz) has been investigated. The resulting materials were characterized with different techniques such as Fourier transform infrared spectroscopy, Raman spectroscopy, elemental analysis, thermogravimetric analysis, scanning electron microscopy, derivative thermogravimetric, steady-state fluorescence spectroscopy, solubility test, and cellular investigations. The functionalized nanotubes showed photo-electronic properties, which is due to the attachment of the function groups to them as proved by fluorescence spectroscopy. These functionalizations have been chosen due to active sites of NH and carbonyl groups in Sh-MWCNT-amide, which might be used as functional materials in future. The toxicity of the samples was evaluated with human gastric and breast cancer cells and killed cell numbers were measured by reduction of living cells with 3-(4,5-Dimethylthiazol-2-yl)-2,5-diphenyltetrazolium bromide (MTT). Cellular results showed high toxicity of modified Sh-MWCNTs on the gastric cancer cells compared with breast cells.

Controlled oxidative cutting of carbon nanotubes catalysed by silver nanoparticles

A systematic comparison of different methods for the cutting of carbon nanotubes has shown that oxidation catalysed by silver nanoparticles is a superior method for the efficient procurement of short carbon nanotubes with minimal introduction of sidewall damage. Complementary examination by microscopic and spectroscopic approaches indicates that the mean length of multi-walled carbon nanotubes synthesised by chemical vapour deposition can be reduced by a factor of five or more while preserving sidewall structure. We have demonstrated the versatility of this procedure by application to an array of hollow carbon nanostructures possessing a diverse range of structural characteristics, such as length, diameter, internal and external structures, with the extent of cutting seemingly related to the initial degree of structural imperfection in the nanotube.

Smart damping of fuzzy fiber reinforced composite plates using 1--3 piezoelectric composites

This article is concerned with the investigation of active constrained layer damping (ACLD) of smart laminated fuzzy fiber reinforced composite (FFRC) plates. The distinctive feature of the construction of this novel FFRC is that the uniformly spaced short carbon nanotubes (CNTs) are radially grown on the circumferential surfaces of carbon fibers. The effect of CNT waviness on the damping characteristics of the laminated FFRC plates is investigated when wavy CNTs are coplanar with either of the two mutually orthogonal planes. The constraining layer of the ACLD treatment is made of vertically/obliquely reinforced 1–3 piezoelectric composite material. A finite element model is developed for the laminated FFRC plates integrated with the patches of ACLD treatment. The effects of different boundary conditions of the FFRC plates and orientation angle of piezoelectric fibers on the damping characteristics of the laminated FFRC plates have also been investigated. Results reveal that if the plane of radially grown wavy CNTs on the circumferential surface of carbon fiber is coplanar with the plane of carbon fiber axis then the attenuation of amplitude of vibrations and the natural frequencies of the laminated FFRC plates are significantly improved over those of the FFRC containing straight CNTs or wavy CNTs being coplanar with the transverse plane of carbon fiber.

Mechanical properties of bulk carbon nanostructures: effect of loading and temperature.

Carbon-based bulk nanostructures are believed to entail certain advantages over their parent low-dimensional materials and are promising candidates for supercapacitors due to their unique properties such as extremely high specific surface area and high conductivity. Herein the mechanical and structural properties of four types of carbon nanopolymorph-based nanomaterials were calculated using molecular dynamics simulations. Bulk carbon nanostructures composed of structural units of bent graphene flakes, short carbon nanotubes, fullerenes and their mixture were considered. The effect of the loading scheme and temperature was studied and constitutive relationships describing the deformation of the materials were given. The simulation results revealed that the effect of the loading scheme significantly depends on the type of structural units, and was slightly affected by the temperature especially for high densities. The constitutive equations obtained in this work can be applied to describe the mechanical behavior of new bulk carbon nanostructures.

Use of whole genome expression analysis in the toxicity screening of nanoparticles

The use of nanoparticles (NPs) offers exciting new options in technical and medical applications provided they do not cause adverse cellular effects. Cellular effects of NPs depend on particle parameters and exposure conditions. In this study, whole genome expression arrays were employed to identify the influence of particle size, cytotoxicity, protein coating, and surface functionalization of polystyrene particles as model particles and for short carbon nanotubes (CNTs) as particles with potential interest in medical treatment. Another aim of the study was to find out whether screening by microarray would identify other or additional targets than commonly used cell-based assays for NP action. Whole genome expression analysis and assays for cell viability, interleukin secretion, oxidative stress, and apoptosis were employed. Similar to conventional assays, microarray data identified inflammation, oxidative stress, and apoptosis as affected by NP treatment. Application of lower particle doses and presence of protein decreased the total number of regulated genes but did not markedly influence the top regulated genes. Cellular effects of CNTs were small; only carboxyl-functionalized single-walled CNTs caused appreciable regulation of genes. It can be concluded that regulated functions correlated well with results in cell-based assays. Presence of protein mitigated cytotoxicity but did not cause a different pattern of regulated processes.

Cyclacenes and short zigzag nanotubes with alternanting Ge―C bonds: theoretical impacts of Ge on the ground state, strain, and band gap

[6]n Cyclacenes and short zigzag [6]n carbon nanotubes (n = 5–10) have unstable singlet open‐shell (Sos) ground states. We have boosted their stability by implementing altering Ge―C bonds that acquire Scs ground states with larger band gap (ΔELUMO–HOMO) at B3LYP and BPW91 levels of theory. Fascinatingly, homodesmic calculations indicated release of almost two folds of strain energy upon substitution of germanium for carbon. This may turn the green lights for synthesis of germanium–carbon cyclacenes and short zigzag nanotubes. Copyright © 2014 John Wiley & Sons, Ltd.

Mesoscale Simulations of Cylindrical Nanoparticle-Driven Assembly of Diblock Copolymers in Concentrated Solutions

Dissipative particle dynamics simulations have been performed to study the coassembly behavior of short carbon nanotubes and diblock copolymers in concentrated solutions by modeling nanotubes as cylindrical nanoparticles (CNPs). With varying the hydrophobic/hydrophilic ratio of the diblock copolymers (AmBn) at fixed concentration and fixed chain length (m + n = 15), the influence of the addition of CNPs on the lyotropic mesophases including micellar, hexagonal, and lamellar phases has been examined in detail, in comparison with the reference systems involving spherical nanoparticles (SNPs). The simulations reveal that the one-dimensional nature of CNPs plays an important role in determining the final coassembly superstructures. It is interesting to find that the addition of CNPs has significantly increased the stability of the hexagonal phase of coassemblies by inducing the phase transformations of the micellar-to-hexagonal in A3B12 solutions and the lamellar-to-hexagonal in A7B8 solutions, whereas the la...

Tube-like ternary α-Fe2O3@SnO2@Cu2O sandwich heterostructures: synthesis and enhanced photocatalytic properties.

Heterogeneous photocatalysis is of great interest for environmental remediation applications. However, fast recombination of photogenerated electron-hole pair and a low utilization rate of sunlight hinder the commercialization of currently available semiconductor photocatalysts. In this regard, we developed a unique ternary single core-double shell heterostructure that consists of α-Fe2O3@SnO2@Cu2O. This heterostructure exhibits a tube-like morphology possessing broad spectral response for the sunlight due to the combination of narrow bandgap and wide bandgap semiconductors forming a p-n heterojunction. To fabricate such a short nanotube (SNT), we used an anion-assisted hydrothermal route for deposition of α-Fe2O3, a seed-mediated deposition strategy for SnO2, and finally an aging process to deposit a Cu2O layer to complete the tube-like ternary α-Fe2O3@SnO2@Cu2O single core-double shell heterostructures. The morphology, composition, and photocatalytic properties of those ternary core-shell-shell heterostructures were characterized by various analytical techniques. These ternary heterostructures exhibited enhanced photocatalytic properties on the photodegradation of the organic dye of Rhodamine B (RhB) under simulated sunlight irradiation. The origin of enhanced photocatalytic activity is due to the synergistic effect of broad spectral response by combining narrow bandgap and wide bandgap semiconductors and, hence, an efficient charge separation of photogenerated electron-hole pairs facilitated through the p-n heterojunction. Furthermore, our unique structure provides an insight on the fabrication and controlled preparation of multilayer heterostructural photocatalysts that have intriguing properties.