pyrene (C16H10); and various carbon- containing gases, such as carbon monoxide (CO), methane (CH4), etc., are also used as the carbon source. Che et al. (1998) have shown that solid carbon nanofibers are formed by increasing the deposition time at 900 °C in a CVD unit when ethylene and pyrene were used as precursor [53]. The morphologies of the CNF synthesized from chemical precursors could be coiled or straight CNFs.
Figure 2.12 CNF synthesized from chemical precursors: (a) Ethanol and (b) Acetylene using CVD method in our lab.
Figure 2.13 Schematic illustration of CNF and CNT.
2.4.2 CNF Synthesized from Plant Parts or Plant Metabolites as Precursors
The CVD method is mostly used for the synthesis of CNF from plant parts (stem, leaf, seeds) or plant metabolites that are rich in carbon or hydrocarbons (oil, resins, latex). CNF synthesized from plant parts usually show unique structures that are similar to the carbon-based anatomy of that particular plant part (Figures 2.5, 2.8 and 2.9), whereas plant metabolites produce CNF having similarities with the structure of CNF produced when chemical precursors are used.
2.5 Concluding Remarks
In this chapter, carbon nanofibers (CNF) synthesized from plant parts and plant metabolites were investigated both scientifically and for practical applications. Apart from petroleum hydrocarbon-based precursors, natural precursors are accepted as an alternative to the synthesis of CNFs. In this chapter, factors for biogenic synthesis using the CVD system and the factors affecting it were touched upon. Yield of different unique morphologies of CNF that varied with precursors were presented. The impact of a wide range of temperatures on the quality and quantity of yield and effect of temperature on the performance of metal catalysts, such as deciding solubility of carbon, is believed to increase at higher temperatures, and the catalyst and catalyst support systems enhance the rate of growth of CNFs. The effect of carrier gas is not yet very conclusive. Hydrogen seems to have a marked influence on superior CNF synthesis. Despite numerous studies on CNFs being synthesized from natural precursors, there is still room for further understanding of the mechanism of CNF growth by CVD method. CNF composites are able to be applied as promising materials in many fields, such as electrical devices, electrode materials for batteries and supercapacitors, etc.
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