[Show abstract][Hide abstract] ABSTRACT: Multi-Walled Carbon Nanotubes (MWCNTs) have promising properties that make them potentially useful in a wide variety of applications. The decoration of MWCNTs by metallic or semiconducting nanoparticles aims to intensify some of their properties, in particular thermal and electrical conductivity. Fluidized Bed Chemical Vapour Deposition (FBCVD) is an efficient process to uniformly coat powders by various materials. The coating by SnO 2 , Fe and Si nanoparticles of MWCNTs (Graphistrength ®) tangled in balls of 360 microns in mean diameter using the FBCVD process has been studied. The influence of some deposition parameters with and without oxidative pre-treatment is analysed on the nucleation and growth of nanoparticles. The various results obtained indicate that the intrinsic surface reactivity of MWCNTs is high enough for CVD precursors involving the formation of highly reactive unsaturated species such as silylene SiH 2 formed from silane SiH 4 pyrolysis in the case of Si deposition. But it must be enhanced for less reactive CVD precursors such as tin tetrachloride SnCl 4 which needs the presence of oxygen-containing groups at the nanotube surface to allow Sn nucleation. So, provided the reactivity of the powder surface and that of the CVD precursors are well tuned, the FBCVD process can uniformly coat the outer surface of MWCNTs by metallic or semiconducting nanoparticles.
Full-text · Article · Nov 2015 · Powder and particle
[Show abstract][Hide abstract] ABSTRACT: Reduction of carbon nanohorn (CNH) aggregates by potassium naphthalenide resulted in their dismantling and individualization. Furthermore, the reduced CNHs were functionalized by addition of electrophiles.
Full-text · Article · Feb 2015 · Chemical Communications
[Show abstract][Hide abstract] ABSTRACT: Ancient Jian wares are famous for their lustrous black glaze that exhibits unique colored patterns. Some striking examples include the brownish colored "Hare's Fur" (HF) strips and the silvery "Oil Spot" (OS) patterns. Herein, we investigated the glaze surface of HF and OS samples using a variety of characterization methods. Contrary to the commonly accepted theory, we identified the presence of ε-Fe2O3, a rare metastable polymorph of Fe2O3 with unique magnetic properties, in both HF and OS samples. We found that surface crystals of OS samples are up to several micrometers in size and exclusively made of ε-Fe2O3. Interestingly, these ε-Fe2O3 crystals on the OS sample surface are organized in a periodic two dimensional fashion. These results shed new lights on the actual mechanisms and kinetics of polymorphous transitions of Fe2O3. Deciphering technologies behind the fabrication of ancient Jian wares can thus potentially help researchers improve the ε-Fe2O3 synthesis.
Full-text · Article · May 2014 · Scientific Reports
[Show abstract][Hide abstract] ABSTRACT: The coefficient of thermal expansion (CTE) of peapod-derived double-walled carbon nanotubes and their host empty single-walled carbon nanotubes (SWCNTs) was determined using Raman spectroscopy. This was performed by measuring the dependence of Raman band frequency of the nanotubes in epoxy resin matrix composites and considering the effects of both the strain and temperature on the Raman bands. Both types of nanotubes show positive thermal expansion at room temperature of around +2 × 10−5 K−1, and the CTE of the SWCNTs was unaffected by the introduction of the inner wall nanotubes. It was also demonstrated that the temperature-induced Raman band shifts can be used to determine both the CTE and glass transition temperature of the matrix polymers.
No preview · Article · Feb 2014 · Applied Physics Letters
[Show abstract][Hide abstract] ABSTRACT: Multi-walled carbon nanotubes Graphistrength® were decorated with silicon by Fluidized Bed Chemical Vapor Deposition. The ability to fluidize of these nanotubes forming ball-shaped jumbles of several hundreds of microns in diameter and that of the final CNT-Si balls was first studied. These balls reveal to fluidize with characteristics of Geldart's group A particles, i.e. without bubbles and with high bed expansion. Coating experiments from silane SiH4 were performed at 500 °C in the 30–60 wt.% range of silicon deposited. SEM and TEM imaging reveals that the nanotubes are coated by silicon nanoparticles uniformly distributed from the periphery to the center of the balls for the whole conditions tested. On-line acquisition of key process parameters evolution shows that the material remains fluidizable, even for large proportions of silicon deposited. The Sauter diameter and the tapped, untapped and skeleton densities of balls increase with the percentage of silicon deposited, whereas their specific surface area decreases due to the progressive filling of the pores by the deposit. This composite material is a promising candidate as anode to replace graphite in lithium-ion batteries.
No preview · Article · Dec 2013 · Chemical Engineering Research and Design
[Show abstract][Hide abstract] ABSTRACT: Single-walled carbon nanotubes (SWCNTs) were produced by an electric arc process in a low-pressure chamber with vertical electrodes using heterogeneous graphite anodes containing nickel and yttrium catalysts. The influence of the chamber volume (18, 25 and 60 L) and graphite grain size (1 and 100 µm) of the anode on the resulting products was analysed. This was correlated with the physical properties of the plasma as studied by optical emission spectroscopy and with the temperature of the gaseous atmosphere surrounding the plasma as measured using thermocouples. Nanotube yield and purity were evaluated from high-resolution transmission electron microscopy. Results showed a strong influence of the heterogeneous anode grain size. It was found that the optimal synthesis conditions correspond to an arc chamber volume of 25 L and a graphite grain size of 1 µm. In that case the plasma temperature and the carbon over nickel concentration ratio in the plasma differ notably from those observed under the other synthesis conditions. It was also found that a slower temperature rise of the gaseous atmosphere surrounding the plasma and a higher anode erosion rate are associated with a higher SWCNT yield. These results were interpreted considering the vapour–liquid–solid nanotube formation model.
No preview · Article · Aug 2012 · Journal of Physics D Applied Physics
[Show abstract][Hide abstract] ABSTRACT: We investigate the low-temperature electron transport through C 60 peapods, which are carbon nanotubes encapsulating C60 fullerenes. We find that the temperature dependence of the Coulomb blockade oscillations in peapod quantum dots deviates from conventional Breit-Wigner behavior, showing signatures of the Franck-Condon blockade of conductance. This indicates the presence of a coupling between electronic states and vibrational excitations. Unlike for suspended empty nanotubes, these are not intrinsic vibrational modes of the tube but mechanical vibrations of the encapsulated fullerenes that affect the electronic transport. Fullerene peapods thus emerge as a new class of nanoelectromechanical systems.
Preview · Article · Nov 2011 · Acta Physica Polonica Series a
[Show abstract][Hide abstract] ABSTRACT: Silicon was deposited on balls of entangled multi-walled carbon nanotubes (CNT) with a mean diameter of several hundreds of microns, by Fluidized Bed Chemical Vapor Deposition from silane (SiH4). The weight total percentage of deposited silicon was between 30 and 70%, to test their efficacy in Li-ion battery anodes. TEM and SEM imaging revealed that silicon deposits were of the form of nanoparticles uniformly dispersed on the whole CNT surface. The diameter of these nanoparticles increases with the deposited silicon percentage from 18 to 36 nm whereas their density remains constant at 5 10(22) nanoparticles/g of CNT. This indicates a low affinity of chemical species born from silane pyrolysis with the CNT surface for nucleation. The increase of the silicon nanoparticles diameter leads to the decrease of the specific surface area and the porous volume of the balls, probably due to the filling of the pores of the CNT network by silicon. A slight increase of the mean diameter of the balls was observed for the two highest silicon percentages, certainly due to the ability of the CNT network to be deformed under the mechanical stress induced by the silicon nanoparticles growth.
No preview · Article · Sep 2011 · Journal of Nanoscience and Nanotechnology
[Show abstract][Hide abstract] ABSTRACT: Fullerene peapods, which are carbon nanotubes encapsulating fullerene molecules, can offer enhanced functionality with respect to empty nanotubes. Their prospective applications include, for example, data storage devices, single-electron transistors and spin-qubit arrays for quantum computing. However, the present incomplete understanding of how a nanotube is affected by entrapped fullerenes is an obstacle for peapods to reach their full potential in nanoscale electronic applications. In this paper, we investigate the effect of C(60) fullerenes on low-temperature electron transport through peapod quantum dots. Compared with empty nanotubes, we find an abnormal temperature dependence of Coulomb blockade oscillations, indicating the presence of a nanoelectromechanical coupling between electronic states of the nanotube and mechanical vibrations of fullerenes. This provides a method to detect the C(60) presence and to probe the interplay between electrical and mechanical excitations in peapods, which thus emerge as a new class of nanoelectromechanical systems.
[Show abstract][Hide abstract] ABSTRACT: X-ray diffraction studies comparing the transformation of C60 and C70 peapods into double walled carbon nanotubes are presented. The structures of the as-formed DWCNTs are strikingly similar, showing that they are not dependent on the nature of the fullerene precursor. High temperature X-ray diffraction measurements of C70 peapods below the coalescence temperature show that confined C70 molecules in large tubes undergo an orientational transition to free rotations. Fast re-orientations of C70 molecules allow cyclo-addition between adjacent fullerenes to form, in good agreement with the mechanism of coalescence proposed in the literature for C60 molecules.
[Show abstract][Hide abstract] ABSTRACT: Carbon multi-walled nanotubes (MWCNTs) may have several dangerous effects on different cell systems, but the mechanisms responsible for their cytotoxicity are not well known yet. At present, very little is known about the electrical interactions between nanomaterials and cells. We aimed to verify whether MWCNT electrical properties could affect the so called “charge-sensitive” cell parameters, interacting with cellular electrical activity. Human macrophages were challenged with two fully characterised MWCNT samples, one tested as-prepared (MWCNT), the other one purified (by annealing at 2400 °C) and better electro-conductive (a-MWCNT). Our findings show that a-MWCNTs are less cytotoxic but possess a higher inflammatory potential, as compared to MWCNTs. Moreover, only annealed and better conductive MWCNTs affect significantly the mitochondrial membrane polarity, the intracellular pH and the reorganisation of cytoskeleton actin filaments, cell functions strictly dependent on electro-chemical mechanisms. Based on our results, there is evidence for electro-chemical interactions taking place between cell membranes and electro-conductive MWCNTs. Such a specific behaviour could have wide-range applications in the biomedical field, not only concerning those cellular systems (neuronal and bone cells) sensitive to electrical stimuli, but also other cell systems.
[Show abstract][Hide abstract] ABSTRACT: The effect of stress transfer within double-walled carbon nanotubes upon their ability to reinforce composites has been reported. The level to which stress can be transferred between the different layers or walls in multiwalled carbon nanotubes (MWNT) is of profound significance for their ability to reinforce a matrix. The double multiwalled carbon nanotubes (DWNT) samples were prepared starting from commercial SWNT materials prepared via the electric-arc method (NANOCARBLAB). It has been found that the stress transfer from the outer to the inner walls in DWNT in composites is poor, such that the inner walls are virtually unstressed during both tensile and compressive deformation. The implication of this finding is that the effective Young's Modulus MWNT in composites will be relatively low. The pressurization involves only the hydrostatic component of the stress tensor, which deforms both the inner and outer walls equally.
No preview · Article · Sep 2009 · Advanced Materials
[Show abstract][Hide abstract] ABSTRACT: The average structure of double-walled carbon nanotube DWCNT samples can be determined by x-ray diffraction XRD. We present a formalism that allows XRD patterns of DWCNTs to be simulated and we give researchers the tools needed to perform these calculations themselves. Simulations of XRD patterns within this formalism are compared to experimental data obtained on two different DWCNT samples, produced by chemical vapor deposition or by peapod conversion i.e., high-temperature peapod annealing. For each sample, we are able to determine structural aspects such as the number of walls, the diameter distribution of inner and outer tubes, the intertube spacing, and the bundled structure.
[Show abstract][Hide abstract] ABSTRACT: Adsorption properties of gram-scale samples of different kind of arc discharge nanotubes were studied, namely: (A) raw collaret collected on the cathode, (B) raw soots collected on the lateral reactor wall, (C) thermally treated soot, and (D) thermally then chemically treated soot. The morphology, structure, and composition of these materials were characterized by SEM, TEM, TGA, and BET. In addition, hydrogen adsorption isotherms were recorded experimentally for A, B, and D samples over the pressure range of 0 to 55 bar at ambient temperature. Our experiments indicated a maximum-yet weak-hydrogen storage at room temperature of approximately 0.13 H2 wt% for the purified product (D).
No preview · Article · Nov 2007 · Journal of Nanoscience and Nanotechnology
[Show abstract][Hide abstract] ABSTRACT: The question of how the texture and structure of carbon nanofilaments (CNTs) are determined during growth is addressed via their preparation using the vapour phase method over Ni–Cu–Mg–Al catalysts. The CNTs formed and the related catalyst particles were investigated by high resolution transmission electron microscopy, electron diffraction, and X-ray energy dispersive spectroscopy. The nanofilament features were found to directly relate to the catalyst particle size and morphologies, which in turn depend on both the Ni/Cu ratio in the Ni–Cu alloy that forms the catalyst particles and the route by which they were prepared. The extent and orientation of graphenes within the carbon nanofilaments were found to be controlled by the extent of the related catalyst crystal faces and the angle value between the latter. It is proposed that energetics of graphenes, basically involving the ratio of the edge over the core carbon atoms, the energetic cost of heterocycles (pentagon), and that of the stress induced by the strain at graphene bending sites, determine whether the carbon nanofilaments would actually grow as nanotubes (i.e., hollow) with the dual “herringbone–bamboo” texture, or as nanofibres (i.e., not hollow) with either the “herringbone” texture or the platelet texture. Only the latter allowed the genuine graphite (3D periodicity) structure to develop, while the other nanofilament types could merely adopt the turbostratic structure. Meanwhile, it was demonstrated that the herringbone nanotubes and nanofibres here prepared are of “cup-stack” rather than “single helix” type.
Full-text · Article · Oct 2007 · Journal of Materials Chemistry
[Show abstract][Hide abstract] ABSTRACT: As-produced carbon nanotubes often contain a fraction of impurities such as metal catalysts, inorganic supports, and carbon by-products. These impurities can be partially removed by using acidic dissolution. The resulting nanotube materials have to be dried to form a powder. The processability of nanotubes subjected to regular (thermal vaporisation) drying is particularly difficult because capillary forces pack and stick the nanotubes irreversibly, which limits their dispersability in polymeric matrices or solvents. We show that this dramatic limitation can be circumvented by using freeze-drying instead of regular-drying during nanotube purification process. In this case, the nanotubes are trapped in frozen water which is then sublimated. As a result the final powder is significantly less compact and, more important, the nanotubes can be easily dispersed with no apparent aggregates, thereby greatly enhancing their processability, e.g., they can be used to make homogeneous composites and fibers. Results from coagulation spinning from water-based dispersions of regularly-dried and freeze-dried nanotubes are compared. We also show that freeze-dried materials, in contrast to regularly-dried materials, can be dissolved in organic polar solvents using alkali-doped nanotubes. High resolution TEM and XRD analysis demonstrate that the nanotube structure and quality are not affected at the nanoscale by freeze-drying treatments.
No preview · Article · Sep 2007 · Journal of Nanoscience and Nanotechnology
[Show abstract][Hide abstract] ABSTRACT: We studied structural changes in C60 and C70 peapods —i.e. C60 and C70 chains inserted inside single-walled carbon nanotubes— when submitted to high pressure and temperature conditions. X-ray diffraction experiments showed that while C60 molecules polymerize inside nanotubes at pressures and temperatures consistent with polymerization in bulk C60 phases, no polymerization is observed in C70 peapods, even at pressures and temperatures above the threshold for polymerization in bulk C70. Tubular confinement in the nanotube container prevents the monomers to rearrange in the way needed for polymerization. This result testifies for the strong influence of confinement on the behaviour of C70.
Full-text · Article · Aug 2007 · EPL (Europhysics Letters)
[Show abstract][Hide abstract] ABSTRACT: Encapsulated C70 molecules packed in single-walled carbon nanotubes display different orientations depending on the nanotube radius. We present x-ray scattering data obtained on a powder of nanotubes filled with C70 molecules. Analytical expressions for calculating the diffraction diagram taking into account fullerene orientations are developed. The comparison between calculations and experiments allows us to conclude that the change from the lying to standing orientation—corresponding to the molecule long axis parallel and perpendicular to the tube axis, respectively—takes place when nanotubes reach a diameter of about 1.42 nm. Energy calculations are performed using a Lennard-Jones (6-12) potential, leading to a calculated reorientation diameter in good agreement with that determined experimentally.
No preview · Article · Jan 2007 · Physical Review B
[Show abstract][Hide abstract] ABSTRACT: The authors have studied electrical transport properties of individual C <sub>60</sub> fullerene peapods, i.e., single-wall carbon nanotubes encapsulating C <sub>60</sub> molecules. Their measurements indicated power lawlike temperature dependencies of linear conductance similar to those for empty nanotubes. At temperatures below 30 K , peapod devices behaved as highly regular individual quantum dots showing regular Coulomb blockade oscillations. Signatures of Kondo physics appeared at the lowest measurement temperature of 315 mK .
No preview · Article · Jan 2007 · Applied Physics Letters