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Carbon nanostructures represent a revolution in science and hold the potential for a large range of applications because of their interesting electrical, mechanical, and optical properties. Multiwall carbon nanotubes and carbon nanofibers of herringbone formation were grown by chemical vapor deposition on different catalysts from a number of hydrocarbon sources. After the total or particle removal of the catalyst system, the carbon nanostructures were analyzed for hydrogen uptake. Six samples of nanofibers grown on a Pd-based catalyst system (with a surface area of 425-455 m2/g) were controlled oxidized in air, such that they had different ratios of Pd/C varying from 0.05 to 0.9 mole ratio. The hydrogen uptake experiments were performed volumetrically in a Sievert-type installation and showed that the quantity of desorbed hydrogen (for pressure intervals ranging from 1 to 100 bars) by the carbon nanostructures free of any metal catalyst particles was between 0.04 and 0.33% by weight. For the samples of nanofibers that contained Pd in various Pd/C ratios, palladium revealed catalytic properties and supplied atomic hydrogen at the Pd/C interface by dissociating the H2 molecules. The results show a direct correlation between the Pd/C ratio and the quantity of hydrogen absorbed by these samples. A saturation value of about 1.5 wt.% was reached for a high ratio of about 1:1 of Pd/C. The multiwall carbon nanotubes grown on a Fe:Co:CaCO3 catalytic system and purified by acid cleaning and air oxidation showed a hydrogen uptake value of 0.1 to 0.2 wt.%. [ABSTRACT FROM AUTHOR]

Carbon nanofibers, with diameters between 80 and 290 nm and specific area of 242 m 2 g -1 , have been prepared by the catalytic chemical vapor deposition method. After preparation, the powder was mixed with silicon oil in order to create a paste electrode. The electrochemical behavior of this type of electrode was investigated by cyclic voltammetry, using a solution of 10 -3 M ferrocenecarboxylic acid as mediator. The redox process is quasi-reversible, and it involves the transfer of electrons between Fe(II) and Fe(III). The same mediator was used for the construction of a second-generation glucose biosensor. The mediator was co-immobilized with the enzyme in the carbon nanofibers paste. The sensor linearly responded to glucose, in the concentration range of 1.7 to 7 mM. A time of around 30 seconds was required to reach 95% of the maximum steady-state current. Also, the oxidation of calf thymus DNA at the carbon nanofiber paste electrode was investigated by differential pulse voltammetry (DPV). A clear signal, due to guanine oxidation, was obtained in the case of single-stranded DNA. [ABSTRACT FROM AUTHOR]

The catalytic chemical vapor deposition (CCVD) method in which the outer furnace is replaced by the high frequency induction heating (IH) has been used for synthesis of carbon nanostructures. Using different catalysts, various types of carbon nanofibers were obtained, with the absence of the catalyst particles at their tip as a common characteristic. The IH mode combined with the CCVD method seems attractive for the synthesis of carbon nanostructures, allowing a significant decrease of energy consumption and of the overall reaction time as compared with the heating mode with outer furnace. [Copyright &y& Elsevier]

Abstract: Catalytic chemical vapor deposition was used to grow multi-walled carbon nanotubes on a Fe:Co:CaCO3 catalyst from acetylene. The influent and effluent gases were analyzed by gas chromatography and mass spectrometry at different time intervals during the nanotubes growth process in order to better understand and optimize the overall reaction. A large number of byproducts were identified and it was found that the number and the level for some of the carbon byproducts significantly increased over time. The CaCO3 catalytic support thermally decomposed into CaO and CO2 resulting in a mixture of two catalysts for growing the nanotubes, which were found to have outer diameters belonging to two main groups 8–35nm and 40–60nm, respectively. [Copyright &y& Elsevier]