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Solid carbon nanofibers (CNFs), hollow CNFs, metal-filled carbon nanotubes (CNTs), and carbon onions were synthesized by chemical vapor deposition (CVD) using a novel Ni/Y catalyst supported on Cu at different reaction temperatures. XRD, TEM, and EDS analyses reveal that the structure of the catalyst changes with increasing reaction temperature. The evolution of Y doped in Ni directly influences the morphologies of the products. At relatively low temperature, Y is doped in Ni and causes CNF formation, and when the temperature is increased to above 650 °C, Y separates from Ni as yttria nanoparticles and carbon onions are synthesized. The catalyst evolution and carbon nanostructure growth mechanism are discussed in detail. [ABSTRACT FROM AUTHOR]

Abstract: Multi-walled carbon nanotubes (CNTs), which are with the diameter from 15 to 50 nm and length from several microns to several tens of microns, were synthesized over Ni/Al composite catalyst by CVD of methane at the temperature range of 723 K–923 K. The Ni content in the Ni/Al composite catalyst varied from 5 wt.% to 15 wt.%. As the synthesis temperature increased from 723 K to 923 K and the nickel content increased from 5 wt.% to 15 wt.%, the CNT yield increased by about 17 times. The purity of CNTs decreased and the diameter of CNTs increased with the increase of Ni content in the catalyst. The relative amount of crystalline graphite sheets increased progressively with the growth temperature and a higher degree of crystalline perfection could be achieved at 923 K. These results demonstrated that the growth rate, diameter, and crystallinity of CNTs can be controlled by varying the synthesis temperature and catalyst composition. [Copyright &y& Elsevier]

Abstract: Bamboo-shaped carbon nanotubes and carbon onions have been synthesized, respectively, by CVD using a novel Ni/Y/Cu catalyst at different reduction and reaction temperature (500–700°C). Characterization of the as-prepared catalyst and carbon nanoproducts are investigated by X-ray diffractometer (XRD), transmission electron microscopes (TEM) and X-ray energy dispersive spectrometer (EDS). The results show that yttria doped in nickel catalyst plays a key role in keeping the activity of the catalyst by resisting or postponing the interaction between copper and nickel. Along with the temperature increasing, the morphologies of the carbon products will be changed: carbon nanotubes at 500°C, carbon onions at 600 and 700°C. The growth mechanisms of CNTs and carbon onions are discussed in details. [Copyright &y& Elsevier]

Abstract: In this paper, carbon nanotubes (CNTs) are added in order to investigate their influence on the electronic conductivity of LiFePO4 cathode. CNTs/LiFePO4 composites are prepared by in-situ chemical vapor deposition method and the traditional mechanical mixture method respectively in order to investigate the influence of CNTs as an additive on the electrochemical performance of LiFePO4 cathode. The particle morphology and electrochemical performances of the CNTs/LiFePO4 composites are characterized and compared with commercial cathodes, LiFePO4 mixed with carbon black. The in-situ synthesized CNTs/LiFePO4 composite by chemical vapor deposition method maintains full retaining ratio after 100 cycles at 1C and 94.5% retention after 20 cycles at 10C, which precede the CNTs/LiFePO4 composite fabricated by the mechanical mixture method as well as the commercial cathode. The enhanced electrochemical performance is due to the excellent interface bonding between LiFePO4 and CNT in in-situ synthesized CNTs/LiFePO4 composites. The interface benefits the electronic conductivity of the composites, as well as the polarization reduction. [Copyright &y& Elsevier]

Abstract: It is well known that Fe, Co, Ni, and their alloy are the effective catalyst components in chemical vapor deposition growth of carbon nanotubes (CNTs), while Cu has low catalytic activity owing to its nearly zero carbon solubility. In this paper, a simple and effective approach was developed to synthesize multi-walled CNTs using unmodified Cu catalyst supported on Al matrix under a low temperature (600°C). The obtained CNTs with bamboo-like structure are mainly composed of well-crystallized graphite. It is found that the Al carrier plays a key role in the catalytic growth of CNTs, signifying a new way for low-temperature synthesis of multi-walled CNTs. [Copyright &y& Elsevier]

Abstract: Electrochemical hydrogen storage of multi-walled carbon nanotubes (MWCNTs) decorated by TiO2 nanoparticles (NPs) has been studied by the galvanostatic charge and discharge method. The TiO2 NPs are deposited on the surface of MWCNTs by sol–gel method. Structural and morphological characterizations have been carried out using XRD, SEM and TEM, respectively. TiO2 NPs can significantly enhance the discharge capacity of MWCNTs. The cyclic voltammograms analysis indicates that the electrical double layer contributes little to the discharge capacity of TiO2-decorated MWCNTs. The MWCNTs modified with a certain amount of TiO2 NPs have a discharge capacity of 540 mAh/g, corresponding to an electrochemical hydrogen storage capacity of about 2.02 wt%, which is quite interesting for the battery applications. The enhancement effect of TiO2 NPs on the discharge capacity of MWCNTs could be related to the increased effective area for the adsorption of hydrogen atoms in the presence of TiO2 NPs on MWCNTs and the preferable redox ability of TiO2 NPs. [Copyright &y& Elsevier]

Abstract: Well graphitized carbon nano-onions (CNOs) with large yield have been synthesized by the catalytic decomposition of methane over an unsupported Ni–Fe catalyst at 850°C. The unsupported Ni–Fe catalyst was prepared by a reduction-substitution method. In the Ni–Fe alloy particle, α-Fe(Ni) phase (kamacite) transforms to γ-Fe–Ni phase at the high temperature for hydrogen reduction and chemical vapor deposition. The synthesized CNOs contain either a Fe0.64Ni0.36 particle or a hollow core with thick graphitic layers and a polyhedral shape. Based on the characterization, we believe that the catalyst involved in the synthesis of carbon products is Fe–Ni–C austenite rather than the γ-Fe–Ni phase (Fe0.64Ni0.36). A growth mechanism for the CNOs is proposed. [ABSTRACT FROM AUTHOR]

Abstract: The B4C nanowires can be easily fabricated by employing an activated carbon, boron and Ni(NO3)2 whereas almost no B4C nanowires can be obtained if activated carbon is replaced by pure carbon. The analyses show that there are Si and Al impurities in the activated carbon, and both Si and Ni are critical to the growth of the B4C nanowires. Additionally, the yield of the B4C nanowires is greatly increased if the B4C nanowires are grown by the carbon nanotubes-confined method when Si is introduced. The mechanism of the Si enhanced growth of B4C nanowires is discussed. [Copyright &y& Elsevier]

Abstract: We investigated theoretically the adsorption of individual Mg atoms on single-walled carbon nanotubes (SWCNTs) by first-principles method within density functional theory in order to clarify the binding energies and the electronic structures of Mg atoms contact with SWCNTs. Our results suggest that the interaction of Mg atom adsorbed on pristine SWCNTs, which is normally very weak, can be enhanced upon functionalization of SWCNTs by B- or N-doping. Especially, the B-doping increases dramatically the binding energies of Mg-adsorbed on both armchair and zigzag SWCNTs. [Copyright &y& Elsevier]

Abstract: Fe(OH)3/Al with different Fe contents was prepared using a new deposition–precipitation reaction. Then mixed oxides were obtained by calcination of these precursors, and their catalytic activities were examined during synthesis of various carbon nanostructures. It was found that carbon nanotubes were synthesized using a Fe/Al2O3 catalyst with 10wt% Fe, while carbon coated metal nanoparticles resulted from Fe/Al2O3 catalyst with 15wt% Fe, but for the Fe/Al2O3 catalyst with 5wt% Fe, only amorphous carbon has been obtained. [Copyright &y& Elsevier]

Abstract: A facile method was proposed to use Ni/Al2O3 as a catalyst to produce metallic nickel filled carbon nanotubes. Multi-walled carbon nanotubes filled with long continuous nickel nanowire length were synthesized through chemical vapor deposition at low temperature (600°C). Furthermore, the multi-walled carbon nanotubes were well-graphitized nanotubes. The analysis of scanning electron microscopy, transmission electron microscopy, selected area electron diffraction and X-ray diffraction revealed that the metallic nickel nanowires encapsulated inside carbon nanotubes existed as a single crystalline with fcc structure. [Copyright &y& Elsevier]

Abstract: A mass of carbon-coated cobalt nanoparticles were successfully synthesized by chemical vapor deposition of methane over Co/Al catalyst at 650°C. The phases found in the as-prepared carbon-coated nanoparticles were fcc-Co. The diameter of these nanoparticles with 2–10nm carbon coating shell was in the range of 5–80nm. However, it is well-known that the Co nanoparticles are suitable for carbon nanotube synthesis, such as Co/Al2O3 and Co/SiO2 catalysts. Here, we speculated that the formation mechanism of carbon-coated cobalt nanoparticles might due to that the formation of carbon nanotubes was inhibited by the catalyst supporter of Al. Compared with Al2O3 and SiO2, Al possesses very low melting point (660°C), very high diffusion coefficient and thermal conductivity, thus the isotropic precipitation of carbon species on the surface of cobalt particles took place, favoring the formation of carbon-coated Co nanoparticles. [Copyright &y& Elsevier]

Abstract: A mass of carbon nanotubes with straight and short bodies was produced by chemical vapor deposition of methane over Ni/Al2O3. Scanning electron microscopy, transmission electron microscopy and thermogravimetric analysis were used to analyze the synthesized carbon nanotubes. The results showed that they were well-graphitized multi-walled nanotubes and had not tangled together. Their average length was several hundreds of nanometers, suitable for their use as a nanometer-scale material. [Copyright &y& Elsevier]

Abstract: Changes in the thermogravimetrically determined oxidation behaviors of CVD-grown multi-walled carbon nanotubes (MWNTs) over Ni/Al catalyst with different Ni content were examined. Catalyst type was found to have a measurable impact upon nanotube stability, suggesting differing levels of crystalline perfection in the resulting nanotubes. With increasing the Ni content in the Ni/Al catalyst, the CNTs obtained became less stable during heat treatment in air. Furthermore, high-resolution transmission electron microscopy was employed to investigate the defect sites of as-grown MWNTs. The results provide evidence showing that defect sites along the walls and at the ends of the raw MWNTs facilitate the thermal oxidative destruction of the nanotubes. [Copyright &y& Elsevier]

Abstract: Novel binary and triple carbon nanotubes (CNTs) with one common catalytic particle encapsulated have been synthesized using Ni/Cu/Al2O3 catalyst, which was produced by a sol–gel method. But when using Ni/Al2O3 as catalyst, a mass of common CNTs, that is, one CNT with one catalytic particle encapsulated, was obtained. The results showed that copper-element doping to the Ni/Al2O3 catalyst played a key role in the synthesis of CNTs, signifying a novel approach to modify the Ni/Al2O3 catalyst. Based on the transmission electron microscopy observations, a simple growth mechanism was developed to describe the growth of the binary or triple CNTs, which could be well explained by a diffusion segregation process. [Copyright &y& Elsevier]

Abstract: Straight carbon nanotubes, carbon onions and two kinds of herringbone carbon nanofibers have been synthesized over nickel supported on aluminum matrix by catalytic decomposition of methane. Nickel precipitated on the aluminum matrix was used as catalyst, which only had 5wt.% nickel. Through varying the production parameters such as the carrier gas, reaction temperature and reaction time, various morphologies of nanocarbons were obtained, which will be employed to reinforce aluminum matrix composites and thus the aluminum matrix composites obtained will have different potential applications. [Copyright &y& Elsevier]

Abstract: The initial stage growth of bamboo-shaped carbon nanotubes (CNTs) synthesized by catalytic decomposition of methane is investigated. A special experimental procedure has been developed to stop the process after short durations (0s to 3min). It has found that during the early stages (60s), carbon cluster-encapsulated nanoparticles are formed. With prolonging synthesis time (3min), some CNTs coexisted with carbon cluster-encapsulated nanoparticles are formed. HRTEM observations show that these CNTs display multi-walled and bamboo structure and the encapsulated catalytic particles are quasi-cone morphologies. At the same time, the catalytic particles only encapsulated with carbon clusters present quasi-sphere structures. For growth up to 60min, two kinds of bamboo mode structures are observed: conical, and cylindrical, which are developed by quasi-cone and quasi-sphere catalytic particles, respectively. Moreover, the early stage growth mode of the CNTs is predominantly of the base growth mode according to TEM observations. [Copyright &y& Elsevier]

Abstract: The possibility of using aluminum powder as transition metal catalyst carrier for CVD growth of carbon nanotubes (CNTs) has been investigated. The fabrication process of Ni/Al catalyst involved the production of binary colloid (Ni(OH)2/Al) by deposition–precipitation method, followed by calcination in N2 and reduction in H2. The nickel particles obtained were with uniform diameters. After the catalytic synthesis at 600°C a mass of well-graphitized multi-walled CNTs with the diameters in the 10–20nm range have been obtained, as evidenced by HRTEM. The operated catalytic particle encapsulated in CNT was nickel according to EDX analysis. However, when using pure nickel without aluminum as the catalyst, no CNTs have formed due to the agglomeration of Ni particles. Thus we speculated that the aluminum powder was responsible for the formation and the even dispersion of the nano-scale transition metal particles. [Copyright &y& Elsevier]

Abstract: Ni/Al catalysts with different Ni concentrations have been used successfully for the synthesis of carbon nanotubes and onions from methane by chemical vapor deposition. The catalyst nanoparticles were produced by a deposition–precipitation method, and the carbon products by the catalytic decomposition of methane at 600°C. Carbon nanotubes (CNTs) were formed in the presence of a Ni/Al composite catalyst containing 20wt.% nickel. The CNTs were multi-walled, 10–20nm in diameter and up to 15μm long. Hollow carbon onions were produced in the presence of a Ni/Al composite catalyst containing 80wt.% nickel. The carbon onions were from 5 to 50nm in diameter and consisted of several concentric carbon layers surrounding a hollow core. The mechanisms for the formation of both the CNTs and carbon onions were discussed on the basis of the experimental results. [Copyright &y& Elsevier]