The effect of a high-power microwave magnetic field on carbon nanotube (CNT) thread is investigated. The thread produced by dry spinning of the CNTs synthesized by a floating catalyst CVD method was treated with a magnetic field in the microwave system operating at a fixed 2.45 GHz frequency. The study of the structure and elemental composition of the pristine CNT thread and the CNT threads subjected to a 1.3 kW microwave magnetic field is provided. An explanation of the paramagnetic behavior of CNT threads and an analysis of the interaction of threads with microwave radiation are presented.

Electrochemical recharging behavior of a binder-free flexible carbon nanotube cloth (CNTC) material in respect to aqueous supercapacitor applications is reported. To provide high enough pseudocapacitance, the surface of CNTC was exposed to wet oxidative functionalization by a KMnO4 treatment in an acidic medium. We report the effect of a KMnO4 to CNT molar ratio on capacitance, electrical resistivity and specific surface area of the CNTC material. The change in the composition of oxygen-containing interfacial functional groups attached to the carbon surface is also investigated by X-ray photoelectron spectroscopy and temperature-programmed desorp-tion methods. For the most oxidized CNTC sample the capacitance of ca. 71 F g-1 (29 mu F cm-2 BET) in 0.5 M H2SO4 (slightly decreasing with a scan rate up to 100 mV s-1) with the retention of ca. 99% during 30,000 recharging cycles as well as specific resistivity of ca. 31 mu ohm m are achieved. Finally, two flexible symmetric supercapacitor prototypes based on a 38% H2SO4 solution and operating at 1.3 or 1.5 V were assembled from the freestanding and graphite foil supported functionalized CNTC electrodes, respectively. For the former device, the volumetric capacitance of ca. 22 F cm-3, power density of ca. 10 kW l- 1 and energy density of ca. 3 Wh l- 1 (per total volume of both electrodes) are demonstrated. The issues of the long-term stability and self-discharge behavior of assembled prototypes are also considered. Reported results allow us to consider the functionalized CNTC ma-terial as a promising electrode material for flexible aqueous supercapacitors.

Catalytic synthesis of carbon nanotubes (CNT) produces numerous various byproducts such as soot, graphite platelets, catalyst nanoparticles, etc. Identification of the byproduct formation mechanisms would help develop routes to more selective synthesis of better carbon-based materials. This work reports on the identification of the formation zone and conditions for rather unusual closed multishell carbon nanocapsules in a reactor for float-catalysis synthesis of longer CNT. Structural investigation of the formed nanocapsule material along with computational fluid dynamics (CFD) simulations of the reactor suggested a nanocapsule formation mechanism, in which CNT embryos are suppressed in growth by the in-reactor turbulence. By means of TEM and FFT investigation, it is found that differently oriented single crystals of γ–Fe2O3, which do not have clear connections with each other, determine a spherical surface. The carbon atoms that seep through these joints do not form crystalline graphite layers. The resulting additional product in the form of graphene-coated (γ–Fe/Fe3C)/γ–Fe2O3 nanoparticles can be a lightweight and effective microwave absorber.

Electrochemical cyclic recharging of a binder-free flexible carbon material in respect to supercapacitor applications is reported. To provide high enough and stable pseudocapacitance, the surface of carbon nanotube cloth (CNTC) was exposed to dry oxidative functionalization by annealing in air at 460 °C. We report the effect of annealing time (0.5–3 h) on capacitance, electrical resistivity and specific surface area. CNTC annealed for 1 h demonstrated the best results: the capacitance of ca. 42 F g−1 in 0.5 M H2SO4 (slightly decreasing with a scan rate up to 1000 mV s−1) and specific resistivity of 20 µΩ m. For CNTC demonstrating these characteristics, the specific surface area was 342 m2 g−1, comprising almost from mesopores. Capacitance retention of 99.1% during 30,000 recharging cycles was observed. Finally, a flexible symmetric supercapacitor operating at 1 V was assembled from the freestanding (unsupported) CNTC electrodes to test their performance in a device prototype. Coulombic efficiency was close to 100% at high enough current densities. Our observations allow to consider air-oxidized CNTC as a promising electrode material for flexible supercapacitors.

Carbon fibers (CF) were formed from carbon nanotube-doped isotropic petroleum pitch. Ultra-long (the length of a single filament is more than 10,000 nm) double-walled carbon nanotubes (DWCNT) were used for doping in concentrations from 0.1 to 1.0 wt.%. The produced CF were investigated both in pristine and graphitized form. Physical properties (electrical resistivity, thermal conductivity coefficient), as well as X-ray diffraction (XRD) analysis and Raman spectroscopy of obtained DWCNT-doped CF were investigated. The influence of DWCNT concentration on the properties is nonlinear due to the influence on the CF molding mode and heterogeneity of the DWCNT distribution in the filament body. An increase in the DWCNT concentration, on the one hand, causes an enhancement in the thermal conductivity coefficient, and a decrease in the electrical resistivity of the fibers, on the other hand, it leads to local inhomogeneities formation in the material structure («gas bubbles»), as well as distortions of the CF outer surface. An increase in the DWCNT concentration also leads to an increase in CF average diameter and hollow filaments formation. This feature is paving the way to the development of novel technological methods to control CF properties and morphology, especially to feasible hollow CF composites manufacture.

Epoxy nanocomposites with float catalysis-produced CNT felt as a filler were prepared. Parameters such as the curing process, glass transition of epoxynanocomposites, structure and morphology of CNT felt, initial epoxy composition, and epoxy nanocomposites were investigated. The influence of CNT felt on curing process in epoxy nanocomposites with different amounts of curing agent was determined. An exothermic reaction between the curing agent and the surface of CNTs was established. It was found that the structure of epoxy nanocomposites has a high degree of heterogeneity: the presence of fiber-like structures and individualized CNTs is observed together with the regions that are typical for CNTs that are fabricated via a catalytic chemical vapor deposition (CVD). Based on the studies performed, it is possible to predict the production of epoxy nanocomposites with outstanding mechanical and thermophysical properties. In particular, the uncured compositions already obtained in this work can be used for the manufacture of electrically conductive glass and carbon fiber reinforced plastics and functional coatings.

The paper reports the synthesis of carbon nanotubes from ethanol over group VIII (Fe, Co, Ni) catalysts derived from corresponding metallocenes. Several unexpected cooperative effects are reported, which are never observed in the case of individual metallocenes such as the commonly used ferrocene catalyst Fe(C5H5)2. The formation of very long (up to several µm) straight monocrystal metal kernels inside the carbon nanotubes was the most interesting effect. The use of trimetal catalysts (Fe1-x-yCoxNiy)(C5H5)2 resulted in the sharp increase in the yield of carbon nanotubes. The electrical conductivity of the produced nanotubes is determined by the nature of the catalyst. The variation of individual metals in the Ni-Co-Fe leads to a drop of the electrical resistivity of nanotube samples by the order of magnitude, i.e., from 1.0 × 10−3 to 1.1 × 10−5 Ω∙m. A controlled change in the electrophysical properties of the nanotubes can make it possible to expand their use as fillers in composites, photothermal and tunable magnetic nanomaterials with pre-designed electrical conductivity and other electromagnetic properties.

The impurity level in carbon nanotubes is considered as a key factor for future applications, in particular electrochemical devices. The longer carbon nanotubes produced by proprietary continuous technique are reported to be investigated in both pristine and purified forms. The influemce of purirification on properties and especially supercapacitor application are significant. In particular, the electrochemical capacity jumps twice as a result of purification.

Longer carbon nanotubes (CNT) are synthesized in a scaled-up reactor with harvesting into big spools. The synthesis rig is capable of producing CNT cotton in spools or piles in kilogram amounts. The product was studied by electron microscopy, Raman spectroscopy and thermal analysis. It was shown that depending on the synthesis conditions the resulting cotton maybe dominated either by longer double-wall CNT or by short CNT combined with non-CNT carbon. In conclusion this successful scale-up development paves the way for the development of CNT-based fibers and composites.

The effect of an electron beam on nanoparticles of two Fe carbide catalysts inside a carbon nanofiber was investigated in a transmission electron microscope. Electron beam exposure does not result in significant changes for cementite (θ-Fe3C). However, for Hägg carbide nanoparticles (χ-Fe5C2), explosive decay is observed after exposure for 5–10 s. This produces small particles of cementite and γ-Fe, each covered with a multilayer carbon shell, and significantly modifies the carbon-fiber structure. It is considered that the decomposition of Hägg carbide is mostly due to the damage induced by high-energy electron collisions with the crystal lattice, accompanied by the heating of the particle and by mechanical stress provided by the carbon layers of the nanofiber.