Effect of hydrocarbons precursors on the formation of carbon nanotubes in chemical vapor deposition
ABSTRACT High-temperature decomposition of hydrocarbons may lead to the formation of carbon deposits. However in our present studies, we found that the morphology of carbon deposits over MgO supported Fe catalyst during chemical vapor deposition (CVD) process was closely related to the thermodynamic properties and chemical structures of hydrocarbon precursors. Six kinds of hydrocarbons (methane, hexane, cyclohexane, benzene, naphthalene and anthracene) were used as carbon precursors in this study. Methane which has a pretty simple composition and is more chemically stable was favorable for the formation of high-purity single walled carbon nanotubes (SWNTs). For high-molecular weight hydrocarbons, it was found that the chemical structures rather than thermodynamic properties of carbon precursors would play an important role in nanotube formation. Specifically, the CVD processes of aromatic molecules such as benzene, naphthalene and anthracene inclined to the growth of SWNTs. While the cases of aliphatic and cyclic hydrocarbon molecules seemed a little more complicated. Based on different pyrolytic behaviors of carbon precursors and formation mechanism of SWNTs and multi-walled carbon nanotubes (MWNTs), a possible explanation of the difference in CVD products was also proposed.
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ABSTRACT: The semiconductivity of carbon nanotubes has been investigated by the luminescence measurement. The nanotubes were characterized by scanning electron microscopy and X-ray diffraction. Carbon nanotubes can luminesce under laser irradiation. Using the photoluminescence measurements the emission spectrum is very wide near the infrared emission range, with a major peak at 1.3 eV. According to the temperature dependence of the photoluminescence and the thermal photoluminescence experiments, the luminescence of carbon nanotubes comes from the center of the energy trap of a defect. In view of this result, it is suggested that the technique of thermal stimulated luminescence provides a simple alternative method to obtain the energy levels in carbon nanotubes systems.Proceedings of the Institution of Mechanical Engineers Part N Journal of Nanoengineering and Nanosystems 12/2011; 225(4):145-147.
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ABSTRACT: The commonly used batch-wise chemical vapor deposition (CVD) system has a low production rate for carbon nanotubes (CNTs) and it is cost ineffective from the economic point of view. In this research, a new horizontally oriented rotary reactor system that enables a continuous production of CNTs was designed and built. The experimental findings show that the rate of carbon deposition by using the rotary reactor was approximately 130 g/h and about 3 kg/day. The carbon content of the carbon deposits as determined from thermogravimetric analysis was 81.7% and carbon yield 446.4%. The as-produced carbon deposits were composed mainly of multiwalled CNTs with a diameter distribution of 12.8 ± 4.2 nm (mean diameter ±standard deviation).Chemical Engineering Communications 01/2012; 199(5):600-607. · 1.05 Impact Factor
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ABSTRACT: Polysaccharide nanocrystals, such as rod-like cellulose nanocrystals and chitin whiskers and platelet-like starch nanocrystals, were incorporated into alginate-based nanocomposite microspheres with the aim of enhancing mechanical strength and regulating drug release behavior. The structures and properties of the sols and the resultant nanocomposite microspheres were characterized by rheological testing, Fourier transform infrared spectroscopy (FT-IR), X-ray diffraction (XRD) and scanning electron microscopy (SEM). The presence of polysaccharide nanocrystals increased the stability of the crosslinked network structure, and the nanocomposite microspheres consequently exhibited prominent sustained release profiles, as demonstrated by inhibited diffusion of theophylline. Furthermore, based on the drug release results, the release kinetics and transport mechanisms were analyzed and discussed.Colloids and surfaces B: Biointerfaces 03/2011; 85(2):270-9. · 3.55 Impact Factor