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Carbon nanotubes (CNTs) are ideal structures for use as reinforcement fibres in composite materials, due to their extraordinary mechanical properties, in particular high Youngrsquos modulus (Esim1 TPa). Usually the high value of E is taken as granted for all types of carbon CNTs. Here we demonstrate that multi-walled carbon nanotubes (MWCNTs) produced by catalytic chemical vapour deposition (CCVD) have low moduli (E

The cutting and functionalization of carbon nanotubes is described, applying a single-step ball-mill based process. Very short carbon nanotubes bearing primary amine functions were produced, characterized and incorporated in polymeric membranes. The gas separation performance of the composite membranes was tested.

An efficient synthesis of the marine metabolite 3-bromoverongiaquinol (1) and the first total synthesis of 5-monobromocavernicolin (2), both isolated from the marine sponge Aplysina cavernicola, have been described based on the 1,2 addition of the lithium enolate of N,O-bistrimethylsilylacetamide (BSA, 4) to 1,4-benzoquinone (3). Bromination and purification of the crude product on silica gel chromatography provided 3-bromoverongiaquinol (1) in 50% overall yield. Under alkaline conditions, the crude product of the bromination reaction was converted to 5-monobromocavernicolin (2) in 20% yield which was also obtained in 13% yield (25% yield based on recovered starting material) from 3-bromoverongiaquinol (1).

Cu (I) phenyl acetylide was used as a source of copper to achieve a homogeneous distribution of Cu2O nanocrystals (10–80 nm) decorated on multiwalled carbon nanotubes (MWCNTs) having an average diameter of 10 nm. Pristine MWCNTs were first oxygen-functionalized by treating them with a mixture of concentrated (H2SO4/HNO3 : 3/1) acids and the products were characterized by X-ray powder diffraction, transmission and scanning electron microscopy, energy dispersive X-ray analysis, X-ray photoelectron spectroscopy and thermogravimetric analysis. An easy, efficient and one-step impregnation method was followed to produce copper-containing nanoparticles on the MWCNTs. The copper-treated MWCNTs dried at room temperature were seen to be well decorated by copper-containing nanoparticles on their outer surface. The MWCNTs were then heat-treated at 400 °C in a nitrogen atmosphere to produce a homogeneous distribution of cuprous oxide nanocrystals on their surface. By varying the ratio of copper to oxygen-functionalized MWCNTs, Cu2O nanocrystals decorated on MWCNTs with different copper content can be obtained.

Carbon nanotubes (CNT) are very promising nano-objects due to their exceptional properties. However, their tendency to form bundles as well as their insolubility in common solvents makes them difficult to handle. The main way to solve the problem is chemical or physical CNTs functionalisations, with all the problems inherent to the methods. In this contribution, we present a new approach that allows predicting the solubility of carbon nanotubes in many solvents but also predicting the most appropriate solvents to use for given samples of CNTs. Solubilisation and dispersion being directly connected, the present approach of solubilisation proves also to be efficient in dispersing the CNTs bundles. This contribution is a first step toward the control of carbon nanotube's dispersion in polymers and their homogenous functionalisation. Moreover, we also report here a new method, based on solvents, to separate carbon nanotubes by size, the use of mixture of non-solvents in order to obtain good solvents and the use of mixture of good solvents to obtain higher solubility. The use of mixture of good solvents allowed us to obtain high solubility, up to three times higher then that reported in literature. We have also measured and analysed the solubility of some functionalised carbon nanotubes.

Multi-walled carbon nanotubes functionalized with F3C-(CF2)5-(CH2)2-SiCl3, a molecule bearing a fluorinated terminal group is found to favor the carbon nanotubes dispersion in three perfluoropolyether fluids (Galden SV70, Fomblin Y25 and Fomblin YR1800). The stability of the suspension appears to be related to the perfluoropolyether viscosity. With respect to time, Fomblin YR1800, the more viscous fluid, leads to the most stable solutions, followed in order by Fomblin Y25 and Galden SV70. In general the smallest particles stay in suspensions. Stability extending over more than one year is observed in the case of Fomblin YR1800.

MCM-22 or MCM-49 zeolites were directly prepared using NaOH or KOH as mineralizing agents. The initial batch composition was 30SiO 2 – v Al(OH) 3 – x NaOH(or x KOH)– y HMI– z H 2 O, with v = 1, 1.5, 2, 3; x = 2.7, 5.4, 9, 10.5, 12, 15, 18; y = 10.6, 15; z = 1050, 1200, 1350; HMI = hexamethyleneimine. The products were obtained by hydrothermal synthesis at 150 °C in stirring conditions. For HMI/Na ratio greater than 2 MCM-22(P) is formed, while for a lower HMI/Na ratio MCM-49 is formed. In presence of K + ions only MCM-22(P) could be obtained. In addition, the Al content of the MCM-22(P) samples is much lower (ca. 10 mol%) than those obtained with Na + ions (ca. 20 mol%). The MCM-22(P) zeolites prepared in presence of Na + ions are formed much faster than those prepared in presence of K + ions. The formation of MCM-22(P) is more difficult with increasing Al-content in the gel. The 27 Al NMR spectra show two lines at 55.5 ppm and 49.9 ppm. Both are due to framework tetrahedral species. No extraframework octahedral species were detected in any of the samples. The 29 Si NMR spectra could be decomposed using eight crystallographically different sites.

Carbon nanotubes containing non-hexagonal rings have been computer generated and relaxed by minimization of the energy using the conjugate–gradient method. Then the powder diffraction patterns have been computed and converted to a real-space representation by the Fourier transform, yielding pair correlation functions which are compared with the pulsed neutrons experimental data for the single-wall carbon nanotubes produced by catalytic chemical vapour deposition. Effects of defective graphene cylinders on the interatomic distances and the resulting structures are discussed. The obtained results are also discussed in relation to previously reported paracrystalline behaviour of the nearest-neighbours distance fluctuations.

The statistical distribution of a large number of helically coiled carbon nanotubes was analyzed in a cross-correlated way in their geometrical configuration space defined by diameter and pitch. Stability islands were identified, in which the number of coils exceeds about 15–10 times the value corresponding to a uniform distribution. When comparing our data with data from literature, a good agreement is found. The statistical findings are interpreted as indirect evidence that the geometric configuration of coiled carbon nanotubes is rather decided by the atomic structure of carbon layers building up the coils than by the external parameters which on the other hand may induce the particular conditions under which coiling occurs. The possible effect of impurities like N and S on the incorporation of non-hexagonal rings and tubular growth is pointed out.

In this paper we demonstrate the functionalization of single-walled carbon nanotubes prepared by chemical vapor deposition. The chosen functionalization agents were alkyl-halides such as trifluoromethane (TFM) and trichloromethane (TCM); or double bond containing alkyl-halides as tetrachloroethylene (TCE) and hexafluoropropene (HFP) that can easily form radicals. Functionalization of samples was carried out under mild conditions, by ball milling of nanotubes in an atmosphere of functionalization agent, at room temperature. For the sake of comparison, chlorination was also performed by chlorine gas. In this process the cleavage of nanotube C–C bonds results in active sites, which can activate molecules in gas phase or adsorbed on the surface of carbon nanotubes. Halogenated samples were characterized by means of particle induced γ-ray emission, transmission electron microscopy, thermogravimetry, and X-ray photoelectron spectroscopy. We concluded that this method gives functionalized single-walled carbon nanotubes in the range of 0.3–3.5 wt.% of fluorine and 5.5–17.5 wt.% of chlorine.

Multiwall carbon nanotubes containing carbon–zeolite composite materials have been obtained by ethylene catalytic chemical vapor deposition (CCVD) on Co-modified beta zeolite powder. High carbon selectivity to nanotubes was achieved. The combined physical characterisation through several techniques, such as TEM, HRTEM, SEM, XRD, N2 adsorption–desorption, allows to determine the geometric characteristics of nanotubes and their dependence of catalyst and synthesis conditions.

Carbon nanotubes were synthesised within the pores of an alumina membrane. The membrane had 200 nm diameter pores and 60 microm thickness, and ethylene was used as carbon source. Membrane dissolution by HF results in a bundle of parallel open tubes, aligned without macroscopic defects. The external diameter of the tubes is uniform and there is no evidence of any amorphous carbon. Wall thickness control was obtained by varying the reaction time, length by the thickness of alumina membrane, and external tube diameter by the membrane pore size. Scanning (SEM) and transmission (TEM) electron microscopy, atomic force microscopy (AFM), X-ray diffraction, thermogravimetric analysis (TG) and surface area evaluation by nitrogen adsorption were used for the characterization of membrane and nanotubes.

After adsorption on a silicon substrate, coiled multiwalled nanotubes retain a 3D structure with sections of freely suspended windings. Electrical gold contacts attached to the nanotubes turn out to be sensitive to vibrations (i.e., the contacts reveal a piezoresistive-like response). When exciting the nanotube windings either electrically or acoustically, the fundamental resonances (ranging from 100 to 400 MHz) can be detected. The resonators are sensitive to mass changes as small as a few tens of attograms.

In this paper, the chemical functionalization of multi-walled carbon nanotubes by a fluorinated trichlorosilane ((tridecafluoro-1,1,2,2-tetrahydrooctyl)trichlorosilane) is investigated. The chlorosilane has been shown to react with carboxylic acid moieties, created by an oxidative process on the nanotube walls, as well as with alcohol groups obtained by a reductive reaction of these previous oxidized nanotubes. The derivatizations were directly confirmed by x-ray photoelectron spectroscopy and thermogravimetry analyses. Little difference in the functionalization was observed for the oxidized or reduced nanotubes. However, the amount of grafted silane seems to be slightly more important when the silanization is carried out with reduced nanotubes.

This paper reports on structural characterisation of single and multi-wall carbon nanotubes, synthesised by catalytic decomposition of methane and acetylene, by wide-angle pulsed neutron scattering, extended up to a maximum scattering vector of Qmax=60 A−1. The intensity data were converted to real space via the Fourier transform yielding the radial distribution functions (RDFs) with the resolution of approximately 0.1 A. The structural parameters defining the interatomic distances, their standard deviations and the coordination numbers have been derived from the experimental data by a curve-fitting method based on a least-squares algorithm. The nearest-neighbour carbon–carbon distance 1.41 A is practically the same as that of graphite and clearly shorter than the value of 1.44 A found for fullerenes. The results provide experimental evidence for the hexagonal structure within a single tubule and turbostratic stacking of successive tubules. The derived RDFs can be fitted using a model based on a hexagonal network with disorder increasing with square root of the interatomic distance.

We introduce a method for atomic force microscopy (AFM)-based detection of mechanical resonances in helix-shaped multi-walled carbon nanotubes. After deposition on an oxidized silicon substrate, the three-dimensional structure of suspended nanotubes, which bridges an artificially created step on the surface, can be visualized using AFM operating in the non-contact mode. The suspended coiled nanotubes are resonantly excited, in situ, at the fundamental frequency by an ultrasonic transducer connected to the substrate. When the AFM tip is positioned above the coiled nanotube, the cantilever is unable to follow the fast nanotube oscillations. Nevertheless, an oscillation amplitude-dependent signal is generated due to the non-linear force-to-distance dependence. Measurement of the mechanical resonances of the helix-shaped carbon nanotubes can be used to quantitatively determine their elastic properties. Assuming that a coiled nanotube can be modeled as a suspended helix-shaped uniformly thin elastic beam, the obtained resonance frequency is consistent with a Young’s modulus of 0.17±0.05 TPa.

Zeolite synthesis was performed from low water containing initial gels. The batch composition was: aM2O–bNa2O–bAl2O3–150SiO2–2bTAABr–490H2O with M=Li, Na, K; TAA is tetramethyl, tetraethyl and tetrabutyl-ammonium; 2.25⩽a⩽8.82 and 1.87⩽b⩽30. Self-bonded pellets of high mechanical resistance of mordenite and ZSM-11 were obtained from two systems: the first one did not contain any organic cations, while the second one was made in presence of tetrabutylammonium bromide. The other systems led either to nonpelleted mordenite, ZSM-5 or sodalite.

Multiwall carbon nanotubes are produced by decomposition of acetylene at 600 degreesC on metal catalysts supported on NaY zeolite. The support and the metal are eliminated by dissolving them in aqueous hydrofluoric acid (HF). Two methods were used to eliminate the pyrolitic carbon: oxidation in air at 500 degreesC and oxidation by potassium permanganate in acidic solution at 70 degreesC. The progress and efficacy of the purification methods are verified by TEM. The properties of the purified multiwalled carbon nanotubes are probed using C-13 and Xe-129 NMR spectroscopy under continuous-flow optical-pumping conditions. Xenon is shown to penetrate the interior of the nanotubes. A distribution of inner tube diameters gives rise to chemical shift dispersion. When the temperature is lowered, an increasing fraction of xenon resides inside the nanotubes and is not capable of exchanging with xenon in the interparticle space. In the case of the permanganate-oxidized sample, rapid xenon relaxation is attributed to interaction with residual MnO2 nanoparticles in the interior of the tubes.

The role of NH + 4 , Na + , K + and Cs + cations was investigated in the synthesis of ZSM-5 using fluoride as mineralizing agent. The amounts of aluminum and alkali cations were varied in gels of initial composition 10SiO 2 – x MF– y Al(OH) 3 –1.25TPABr–330H 2 O with M=NH 4 , Na, K and Cs, x =9, 15 and 24, y =0.16, 0.5 and 1.0 and TPABr=tetrapropylammonium bromide. The potassium-containing system is the most effective one with respect to incorporation of aluminum into the zeolite framework, while the ammonium-containing system is the least effective one. Crystallization patterns and crystal morphologies are strongly influenced by the nature of the fluoride salt added to the reaction mixture. The kinetic data show that the cations not only influence the reaction rates by their electrostatic interaction, but also due to their specific interaction with the fluoride anion in various siliceous and aluminosiliceous complexes.

We describe a new and inexpensive method of purifying C 60 by fractional crystallization in 1, 3-diphenylacetone. After three steps, 99.5% pure C 60 was obtained with a global yield of 69%. This method is simpler and could be cheaper than any other method presently used. Furthermore, the purity of C 60 fullerene can be increased up to 99.99% by adsorption of the residual C 70 fullerene on charcoal. The temperature dependence of the solubility of C 60 and C 70 in 1, 3-diphenylacetone was studied and a maximum of solubility was observed at 136 °C for C 60 and at 41 °C for C 70 . This peculiar solubility behaviour is discussed in the light of possible aggregation of C 60 and C 70 molecules in the solution phase.

In this work, a method for differentiation of gasoline according to its geographical origin is presented. Comprehensive two-dimensional gas chromatography-flame ionization detection (GC×GC-FID) combined with multivariate analysis was used to differentiate Brazilian and Venezuelan gasoline samples. Pattern recognition of the GC×GC-FID chromatograms was performed by parallel factor analysis (PARAFAC) and it was successfully applied for the differentiation of these gasoline samples. Eluates with medium to high volatility, both aliphatic and aromatic, were responsible for this differentiation, based on the inspection of the score and loading graphs generated by PARAFAC. Neste trabalho, um método para a diferenciação de gasolinas de acordo com a sua origem geográfica é proposto. Cromatografia gasosa bidimensional abrangente com detecção por ionização em chama (GC×GC-FID) em conjunto com a análise multivariada foi utilizada para diferenciar amostras de gasolina brasileira de amostras oriundas da Venezuela. A análise de fatores paralelos (PARAFAC) foi utilizada no reconhecimento de padrões dos cromatogramas GC×GC-FID e foi aplicada com êxito na diferenciação das amostras de gasolina. Através da análise dos gráficos de escores e pesos gerados pela análise PARAFAC, foi possível determinar que eluatos de média a alta volatilidade, tanto alifáticos quanto aromáticos, foram responsáveis por essa diferenciação.

The catalytic production of carbon nanotubes was investigated using various iron catalysts. Catalyst samples were made by different preparation methods in order to improve both the quality and the quantity of as-prepared carbon nanotubes. The catalysts were tested in the decomposition of different hydrocarbons in the temperature range 650-800 degrees C using either fixed bed flow or fluidized bed reactor. The quality of the products was characterized by means of transmission electron microscopy. By using Fe/silica, the highest activity ever observed in catalytic nanotube formation can be reached. Copyright (C) 1996 Elsevier Science Ltd

The impact of Cl-2 addition on the fullerene formation in acetylene/oxygen/argon flat flames burning at low pressure was investigated. The quantities of C-60 and C-70 in the soot were determined by HPLC after extraction with toluene. Negative ion mass spectra were measured using chemical ionization by means of a CH4/N2O mixture. The chlorine containing species were identified by means of a precursor ion mass spectrum. The addition of 25% of Cl-2 led to a dramatic increase of fullerene formation; soot containing 7.7% of (C-60+C-70) was deposited in the combustion chamber. The mass spectra showed signals at the masses of C10H2, C11H8 and C12H10 for soot formed in flames with and without chlorine addition while peaks corresponding to the polycyclic aromatic hydrocarbons (PAH) C18H10, C22H12 and C24H12 could be observed only without chlorine addition. A positive role of thermally and photochemically unstable chlorinated intermediate species is suggested for the increase of fullerene formation. Copyright (C) 1996 Elsevier Science Ltd

Carbon nanotubules were produced in a large amount by catalytic decomposition of acetylene in the presence of various supported transition metal catalysts. The influence of different parameters such as the nature of the support, the size of active metal particles and the reaction conditions on the formation of nanotubules was studied. The process was optimized towards the production of nanotubules having the same diameters as the fullerene tubules obtained from the arc-discharge method. The separation of tubules from the substrate, their purification and opening were also investigated.

The connection of two straight chiral or achiral cylindrical carbon nanotube sections of approximately the same diameters connecting at a “knee” angle of π 5 is described. Such knees are based on the insertion in the plane of the knee of diametrically opposed pentagonal and heptagonal rings in the hexagonal network. Relationships are also established between the nanotubes and their concentric graphitic layers. A growth mechanism leading to perfect carbon tubules and tubule connections on a catalyst particle at a molecular level is described. The mechanism suggested explains the formation of curved nanotubes, tori or coils involving the heptagon-pentagon construction of Dunlap.

This paper presents the fundamental principles, instrumentation and selected applications of comprehensive two-dimensional gas chromatography (GC × GC). In this technique, introduced in 1991, two capillary columns are coupled and proper modulating interfaces continuously collect the eluate from the first column, transferring it to the second column. The result is a geometric increment in the chromatographic resolution, ensuring separation of extremely complex mixtures in time periods shorter or comparable to those of analysis using conventional gas chromatography and with better detectabilities and sensitivities.

International audience; An adherent polymer film based on a composite of polyacrylonitrile/multiwall carbon nanotubes (PAN/MWNTs) have been elaborated on a copper substrate. The first layer is an electrografted PAN brush on which of a subsequent layer of PAN/carbon nanotubes composite has been deposited by simple dipping from solution in dimethylformamide (DMF). MWNTs have been previously chemically functionalized with 3-cyanopropyltrichlorosilane to promote de-bundling and homogeneous dispersion of the carbon nanotubes in the composite.

Phenyl ethyl alcohol was used for fast and stable dispersion of carbon nanotubes. This solvent, more effective than ethanol and toluene, allows easy dispersion of carbon nanotubes for TEM characterization. For TEM grids prepared at high dilution, it is possible to observe each tube separately. Applying that solvent, it was possible to measure the length, the diameter and the solubility of different carbon nanotubes samples.

Experimental studies of carbon nanotubes (CNTs) obtained through different synthesis routes show considerable variability in their mechanical properties. The strongest CNTs obtained so far had a high Young's modulus of 1 TPa but could only be produced in gram scale quantities. The synthesis by catalytic chemical vapor deposition, a method that holds the greatest potential for large-scale production, gives CNTs with a high defect density. This leads to low Young's modulus values below 100 GPa for multiwall CNTs. Here we performed direct measurements of the mechanical properties of catalytically grown CNTs with only a few walls and find a Young's modulus of 1 TPa. This high value is confirmed for CNTs grown under two different growth conditions where the synthesis parameters such as the hydrocarbon source, catalyst material, and the synthesis temperature were varied. The results indicate that the observed difference in the Young's modulus for the catalytically grown CNTs with high and low numbers of walls is probably related to the growth mechanism of CNT.

The vibratory mill is used to decrease the single-wall carbon nanotubes (SWNTs) length and to increase their specific surface area. Electron microscopy, Raman spectroscopy, X-ray diffraction and BET measurements indicated that the optimum time of treatment seems to be 2 h. After that, the SWNTs quality decreases, with a complete disruption of the tubular structure leading to multi-layered polyaromatic carbon materials observed after 50 h.

International audience; An original image analysis method is presented to characterize multi-walled carbon nanotubes from transmission electron microscopy images. The analysis is performed in three steps: (i) image preprocessing in order to isolate the nanotubes from the background, (ii) image segmentation, aiming at keeping only the measurable sections of nanotubes, and finally (iii) tube characteristics measurement. The measurement is based on a Lambert-like electron absorption law and is performed on the original gray level image itself. Two geometrical and one physical characteristics are determined for each tube, namely, its outer and inner radius and a linear electron absorption coefficient. The method is illustrated by comparing a pristine and an annealed carbon nanotube samples. The compaction of the tube walls during annealing is shown to result from a lowering of the external radius while the inner radius is left unchanged.

Intermolecular carbon nanotube junctions were formed through amide linkage of amino functionalized multiwall carbon nanotubes and [Ru (dcbpy)(bpy)2](PF6)2, an inorganic metal complex. Nanotube interconnects were visualized using atomic force microscopy. Absorption and emission spectroscopy showed significant changes between starting products and the resulting ruthenium nanotube complex, indicative of successful chemical modification.

Catalytic synthesis and some characterization of multi- and single-wall carbon nanotubes are presented. Supported transition-metal catalysts were prepared by different methods and were tested in the production of nanotubes by decomposition of hydrocarbons at 700 degrees C, using a fixed-bed flow reactor. The quantities of deposited carbon were measured and the quality of the nanotubes was characterized by means of transmission electron microscopy and scanning tunneling microscopy. The inner and outer diameters of the nanotubes were also measured and the diameter distribution histograms were established. The multi-wall straight and coiled nanotubes were found to be quite regular with an average inner (outer) diameter of 4-7 nm (15-25 nm) and with lengths up to 50 mu m. The walls contain concentric cylindrical graphene sheets separated by the graphitic interlayer distance. The single-wall nanotubes were found as bundles of hundreds of aligned straight 1-nm-diameter nanotubes with lengths up to 1-mu m. The influence of various parameters such as the method of catalyst preparation, the nature and the pore size of the support, the nature of the metal, the quantity of catalyst active particles, and the reaction conditions on the nanotubes formation were studied. The numbers and dimensions of the catalyst active particles dispersed on the support were found to be of importance in regulating the shape of the produced nanotubes. Following these results, a model of growth mechanism was suggested for the nanotubes obtained by this method.

Discrete image-potential states (ISs) are revealed at double-walled carbon nanotubes by means of scanning tunneling microscopy (STM) and scanning tunneling spectroscopy (STS) in the distance-voltage z(V) spectroscopy mode. The nanotubes are supported by flat Au(111) substrates. Due to the high sensitivity of the hot IS electrons to local variations of the surface potential, they can be considered as a sensitive probe to investigate interactions with the supporting substrate and impurities or defects at the nanotube surface. ISs provide information on the local electronic structure as well as on the electron dynamics at supported nanotubes.

Multiwalled carbon nanotubes, covalently functionalised with chlorinated polypropylene, were used as the filler material in polymer nanotube composites. Both polystyrene and poly(vinyl chloride) were used as the polymer matrix. The functionalised nanotubes could be stably dispersed in tetrahydrofuran allowing the preparation of composites by solution processing. Close to a twofold increase in both modulus and strength were measured at nanotube loading levels of less than 1 vol%. Reinforcement values of dY/dVf = 115 ± 34 GPa and dY/dVf = 304 ± 90 GPa were observed for polystyrene and poly(vinyl chloride) based composites respectively. The high levels of reinforcement are due to the superior dispersion and stress transfer as evidenced by SEM images of the fracture surfaces. These properties can both be attributed to the presence of the functional groups.