Nanofibers and Nanotubes

These nanomaterials are also characterized by their extremely high aspect ratio. The aspect ratio is defined as the length of the major axis divided by the width or diameter of the minor axis. According to this definition, spheres have an aspect ratio of 1, while carbon nanotubes or nanofibers have an aspect raho ranging from 

Work carried out in the laboratory on the catalytic synthesis of carbon nanotubes using a mixture of C2H6 and H2 and a Fe/Al203 catalyst led to the synthesis of several grams of carbon nanotubes per gram of catalyst per hour [33]. The quartz reactor tube was rapidly filled with a black flufiy soUd after two hours of reaction indicating the extremely high activity of the catalyst to form carbon nanotubes (Fig. 7.2). 

High-magnification TEM images of the carbon nanotubes are presented in Fig. 7.3C and D. Close observation reveals that the tube wall has a relatively low crystal- 

TEM micrographs also reveal that some iron nanoparticles were located inside the carbon nanotubes. This is consistent with the proposed mechanism of reaction 

The porosity of the multi-walled carbon nanotubes was mainly mesoporous an inner hoUow channel with an average pore size ranging between 5 and 60 run and abrogated pores ranging from 20 to 100 nm. No micropores are found in these carbon nanomaterials, contrary to what is observed in activated charcoal where generaUy half or one-third of the specific surface area comprised a micropore network [6-10]. 

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The carbon-based nanofillers are mainly layered graphite, nanotube, and nanofibers. Graphite is an allotrope of carbon, the stmcture of which consists of graphene layers stacked along the c-axis in a staggered array [1], Figure 4.1 shows the layered structure of graphite flakes. 

Concerning the Fischer-Tropsch synthesis, carbon nanomaterials have already been successfully employed as catalyst support media on a laboratory scale. The main attention in literature has been paid so far to subjects such as the comparison of functionalization techniques,9-11 the influence of promoters on the catalytic performance,1 12 and the investigations of metal particle size effects7,8 as well as of metal-support interactions.14,15 However, research was focused on one nanomaterial type only in each of these studies. Yu et al.16 compared the performance of two different kinds of nanofibers (herringbones and platelets) in the Fischer-Tropsch synthesis. A direct comparison between nanotubes and nanofibers as catalyst support media has not yet been an issue of discussion in Fischer-Tropsch investigations. In addition, a comparison with commercially used FT catalysts has up to now not been published. 

Serp, P, Corrias, M., and Kalck, P. 2003. Carbon nanotubes and nanofibers in catalysis. Applied Catalysis A General 253 337-358. 

Shaffer M, Kinloch IA. Prospects for nanotube and nanofiber composites. Composites Science and Technology. 2004 Nov 64(15) 2281-2. 

A wide range of nanosfructured carbons has been discovered since fhe original discovery of carbon nanotubes (CNTs) by lijima in 1991. Carbon nanotubes and nanofibers are nanoscale cylinders of rolled up graphene sheets. 

Lee, K., Zhang, J., Wang, H., and Wilkinson, D. P. Progress in the synthesis of carbon nanotube- and nanofiber-supported Pt electrocatalysts for PEM fuel cell catalysis. Journal of Applied Electrochemistry 2006 36 507-522. 

Application of transmission electron microscopy (TEM) techniques on heterogeneous catalysis covers a wide range of solid catalysts, including supported metal particles, transition metal oxides, zeolites and carbon nanotubes and nanofibers etc. 

Hydrogen interaction with the carbon nanostructural materials (nanotubes, nanofibers, fullerenes C60 and C70 has been intensively studied over the last years. A developed surface of nanotubes and nanofibers induced a considerable applied interest aimed at hydrogen storage and reduced consumption of organic fuel in modem industry. For the academic studies, of interest is the nature of the hydrogen interaction with the carbon nanomaterials. 

High-Pressure Hydrogenated Single-Walled Carbon Nanotubes and Nanofibers... 

Four different aryldiazonium salts have been used to functionalize SWCNTs through electrochemical reduction. By XPS and Raman diffusion measurements, the growth of aryl chains on the sidewalls of the nanotubes was observed [178]. Electrically addressable biomolecular functionalization of SWCNT electrodes and vertically aligned carbon nanofiber electrodes with DNA was achieved by elec-trochemically addressing (reduction) of nitrophenyl substituted nanotubes and nanofibers. Subsequently, the resulting amino functions were covalently linked to DNA forming an array of DNA-CNT hybrid nanostructures (Scheme 1.28) [179],... 

Che, G., Lakshmi, B.B., Martin, C.R., and Fisher, E.R. Chemical vapor deposition based synthesis of carbon nanotubes and nanofibers using a template method. Chem. Mater. 10, 1998 260-267. 

Nanotubes and Nanofibers, Yury Gogotsi Carbon Nanomaterials, Yury Gogotsi... 

A.N. Redkin, L.V. Malyarevich, Preparation carbon nanotubes and nanofibers by method of ultraspeed heating ethanol vapors. Inorganic.material, 2003, T. 39. JVb 4. pp. 433-437. 

For large scale production of carbon nanotubes and nanofibers chemical vapor deposition (CVD) method is most effective. Acetylene, ethylene, propylene, methane, natural gas (consisting predominantly of propane), carbon monoxide were used as a source of carbon [ 1 -8] (in view of large number of publications on CNT synthesis these references are selected arbitrary). Ethylene and possibly propylene are most convenient carbon sources for mass synthesis of high quality multiwall CNT (MWNT). 

Besides the traditional markets for carbon, some novel applications for the carbon produced via methane decomposition are discussed in the literature. Kvaemer has initiated R D program to investigate the potential of novel grades of carbon black as a storage medium for hydrogen, and as a feedstock for the production of solar grade silicone.35 The production of carbon nanotubes and nanofibers via solar thermal decomposition of methane over supported Co and Ni catalysts, respectively, was also reported.36... 

Rakov, E.G. (2004) Pyrolytic synthesis of carbon nanotubes and nanofibers, Ros. Khim. J. XLY111(5), 12-19. 

Gogotsi Y (ed) (2006) Nanotubes and nanofibers. CRC Press, Boca Raton... 

Carbon nanotubes and nanofibers have lately attracted great attention in nanomedicine including their potential use as drug carriers, although there are also considerable concerns associated with their safety (Lange et al., 2003 Muller et al.,... 

In the future, nanotubes and nanofibers can be administered systemically, if the problem of their toxicity is addressed, for example, by appropriate polymer coating. In this respect, the continuous nanofibers are more likely to be used in implants or tissue engineering applications. 

Che G, Lakshmi B, Maifin C, Fisher E, Ruoff R (1998) Chemical vapor deposition based syntliesis of carbon nanotubes and nanofibers usmg a template metliod. Chem Mater 10 260—267. 

Nanocarbon materials have been obtained by different ways with three catalysts Ni, Co and Fe. The metal nanoparticles inside the nanotubes and nanofibers have both fee and bcc structure. Their orientations along the axis of the nanotube (or nanofiber) can be one of the following [100], [110], [111] and [112]. The shape of catalyst particles (fillings) and their twinning are considered as the result of deformation, caused by the action of surrounding graphene shells. 

At the beginning of the 2U century, it is thought that the improvement of the existing chemical industry will pass through the development of new kinds of catalysts to meet the latest environmental requirements. Since their discovery in 1991 [1], carbon nanotubes and nanofibers have received increasing interest in academic research and for several potential applications [2-4]. It has been reported by different authors that carbon nanofibers could be efficiently used as catalyst support for several catalytic reactions either in gas or in liquid phase [5-7], In both cases, the carbon nanofiber based catalysts always exhibited higher catalytic performances compared to those observed on equivalent conventional catalysts. 

A large variety of carbon materials can and have been used as catalyst supports. The most important are granular and powdered activated carbons and carbon blacks, but there is increasing interest in related materials, such as activated carbon fibers and cloths, nanotubes, and nanofibers [8]. A comprehensive review... 

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