Carbon nanofibres

So what are these new nanoscale fibrous materials The story of carbon nanofibres really started with the discovery of fullerenes in the early 1980s (Kroto et al., 1985) when it was found that new molecular structures could be synthesised at the nanoscale, which have fascinating and useful properties. By nanoscale we mean of the dimension of nanometres (Inm is 10 m). So we are talking about the sorts of units you need to describe the sizes of individual atoms/molecules. Carbon nanomaterials can be made by a variety of processes and can be examined under the electron microscope when their structure becomes apparent. 

Amorphous and graphitic carbon have been used as an absorbant for some materials for many years. Activated carbon has been available as a storage and filter medium 

Graphitic nanofibres are made by decomposing hydrocarbons or carbon monoxide over suitable catalysts. The catalyst influences the arrangement of the graphitic sheets 

Physical absorption on activated carbon is bicreased at low temperatures. Super activated carbons have been developed which can store up to 7 wt% hydrogen at pressures of 40 bar and temperatures of 165 K. 

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Bezemer G.L., Bitter J.H., Kuipers H.P.C.E., Oosterbeek H., Holewijn J.E., Xu X., Kapteijn F., van Dillon A.J., and de Jong K.P. 2006. Cobalt particle size effects in the Fischer-Tropsch reaction studied with carbon nanofibre supported catalysts. J. Am. Chem. Soc. 128 3956-64. 

As observed in Figure 3, the results obtained for carbon nanofibres and nanotubes (closed symbols) fit in the tendencies obtained for activated carbons, showing that hydrogen adsorption depends on the porosity of the sample and does not depend on its structure. 

S. Helveg, C. Lopez-Cartes, J. Sehested, P. Hansen, B. Clausen, J. Rostrup-Nielsen, F. Abild-Pedersen, and J. Norskov, Atomic-scale imaging of carbon nanofibre growtti. Nature 427,426-429 (2004). 

McKenzie JL, Waid MC, Shi R et al (2004) Decreased functions of astrocytes on carbon nanofibre materials. Biomaterials 25 1309-1317... 

Abstract. It was established that powdered Mg2NiHx is effective procatalyst of synthesis of carbon nanofibres. The maximal yield on soot is reached at 500°C, and an optimum ratio of gas components in a mixture for the maximal yield is C2H4 H2 Ar= 1 1.25 1.25. 

X-rays diffraction picture of washed sample 3 (Fig. 2c) contains intensive and wide asymmetrical peak corresponding to amorphous carbon and carbon nanofibres [6], set of Fe3C peaks and some weak peaks of y-Fe phase (Fig. 2c). 

During the synthesis, besides carbon nanofibers formation, a plenty of chemical transformations occurred in the catalyst incorporation of ions Fe in MgO lattice and Mg xFxO solid solution formation as well as Fe3C, y-Fe and iron-magnesium-graphite complex, being a transitional stratum between a metal particle and a carbon nanofibre formation. Were revealed inert (Mgi xFxO) and active, very fine particles of the catalyst (MgFe204) components which are involved in the process of carbon nanofibres formation. 

Tambov State Technical University (TSTU) in cooperation with research and industrial teams carries out research, design and manufacturing works for process equipment to obtain carbon nanofibres and nanotubes. 

Keywords carbon nanofibres, pyrolysis, x-ray diffraction, reaction kinetics... 

Carbon-based adsorbents such as activated carbons, carbon nanotubes, and carbon nanofibres have been the subject of intensive research over the past 15 years. The research on hydrogen storage in carbon materials was dominated by announcements of extraordinary high storage capacities in carbon nanostructures. 

Helveg S, Lopez-Cartes C, Sehested J, et al. Atomic-scale imaging of carbon nanofibre growth. Nature. 2004 427 426. 

It is well known that catalyst support plays an important role in the performance of the catalyst and the catalyst layer. The use of high surface area carbon materials, such as activated carbon, carbon nanofibres, and carbon nanotubes, as new electrode materials has received significant attention from fuel cell researchers. In particular, single-walled carbon nanotubes (SWCNTs) have unique electrical and electronic properties, wide electrochemical stability windows, and high surface areas. Using SWCNTs as support materials is expected to improve catalyst layer conductivity and charge transfer at the electrode surface for fuel cell oxidation and reduction reactions. Furthermore, these carbon nanotubes (CNTs) could also enhance electrocatalytic properties and reduce the necessary amount of precious metal catalysts, such as platinum. 

Hammer, N. et al.. Au- l i(), catalysts on carbon nanofibres prepared by deposition-precipitation and from colloid solutions, Catal. Today 123, 245, 2007. 

Kvande, I. et al.. Deposition of Au colloids on plasmachcmically modified carbon nanofibres. Carbon, 46, 759, 2008. 

On the other hand, the oxidative coupling reaction of CH4 in the presence of O2, even when performed in membrane type reactors,188 is mainly catalysed by metal oxides catalysts.185 Also, oligomerisation, aromatisa-tion, and the partial oxidation apply non-metallic heterogeneous catalysts (such as zeolites). The reader is therefore directed to some excellent reviews on these subjects.189,190 At this point, it is perhaps relevant to introduce the formation of carbon nanofibres or nanotubes from methane, these being catalysed by metal nanoparticles, but at this moment this is not considered as a Cl chemistry reaction. Again we direct the attention of the reader to some reviews on this type of process.191 192... 

However, the shapes of the carbon structures appear quite different on Pd-Ni bimetallic catalysts.43 For a Pd-Ni bimetallic catalyst with a Pd/(Pd + Ni) atomic ratio of 0.5, branched carbon nanofibres with a large variety of diameters ranging from 10 to 300 nm are developed, in contrast with the carbon nanofibres formed on supported nickel catalyst (Fig. 7.2). 

Figure 5. Effect of the Ni loading on carbon capacity of Ni-TLC samples at 773, 823 and 873K. A model has been proposed for interpreting the kinetic effects of the Ni crystal size concluding that both deactivation and growth rate of carbon nanofibres (CNF) depend upon several factors like carbide diffusion, flux area, particle thickness, and saturation concentration of CNF. On small Ni crystals the increased saturation concentration of CNF, which leads to a low driving force for carbon diffusion, causes a lowering of coking rate and a drastic deactivation (encapsulating carbon), whereas for large Ni particles the formation of surface...

Figure 5.8 Schematic representations of (a) buckminsterfullerene (b) carbon nanofibres (c) single- and multi-walled carbon nanotubes (d) metal-organic framework, MOF-177.

Kim, C. Electrochemical characterization of electrospun activated carbon nanofibres as an electrode in supercapacitors. J. Power Sources. 2005,142(1), 382-388. 

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