Carbon nanofibers considerations

In the early literature of DP with carbon supports, in particular of nickel hydroxide on carbon, nonuniform distribution of metals was observed [43]. With iron on carbon nanotnbes, the metal dispersion was quite low [44]. A detailed mechanistic consideration of DP with carbon was needed prior to successful application. This mechanistic study is described for Ni onto carbon nanofibers in the next section. 

Wang et al. [125] proved that the conductivity of PAN-based carbon nanofibers produced by electrospinning increases sharply with the pyrolysis temperature, and also increases considerably with pyrolysis time at lower pyrolysis temperatures. 

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. 

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.,... 

This step is the most important part of carbon fibers and nanofibers formation and has been attracted a lot of attentions [6, 14,20,]. It has been shown that thermal stabilization conditions have considerable effect on the properties of the resulting carbon fiber [14]. It is necessary to choose the optimum conditions of temperature, heating rate and oxidation duration. Studies showed that optimal stabilization conditions lead to high modulus carbon fibers. Too low temperatures lead to slow reactions and incomplete stabilization, whereas too high temperatures can fuse or even bum the fibers [6, 9]. 

The incorporation into PU foams of different types and concentrations of nanosized functional particles, both platelet-like such as nanoclays or graphene, fibrous-like such as carbon nanotubes and nanofibers, or even spherical-like such as nanosilica, has been shown to have a significant effect in the structure and physical properties of the resulting materials, considerably expanding the already wide range of possible applications of these lightweight materials. 

Compared with the traditional adsorbent such as activated carbon, zeolites, and silica gel, electrospun nanoflbers are good candidates for heavy metal ion adsorption due to its large surface area, tailored pore structure, good interconnectivity of pores, and potential to incorporate active chemistry or functionality on nanoscale [62,63]. Moreover, recycle is of great importance in the field of water treatment taking this aspect into consideration, the nanofiber-based adsorbents are more suitable compared with powdered nanoporous materials. 

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