Carbon onions including Fe3C were synthesized by the catalytic decomposition of acetylene at 400 °C using iron supported on sodium chloride as catalyst. The samples were examined by high resolution transmission electron microscopy, energy dispersive spectroscopy, and X-ray diffraction. The results show that carbon onions including Fe3C core with a structure of stacked graphitic fragments and diameters in the range 15-50 nm were obtained. When the product was further heat-treated under vacuum at 1100 °C, carbon onions with a clear concentric graphitic layer structure were obtained.
The reactions were carried out by decomposing acetylene at 1000 °C in a two-stage furnace system for 10 min. In the first furnace no catalyst was placed and an AAO template with the average diameter about 50 nm was placed in the second furnace whose temperature was designed to be 500 °C, 600 °C and 700 °C. The samples were characterized by scanning electron microscopy and high resolution transmission electron microscopy. The results show that carbon spheres with average diameter about 50 nm on the AAO template surface were obtained when the temperature of the second furnace was designed to be 700 °C. These carbon spheres are composed of unclosed graphene layers with an interlayer distance of 0.33–0.35 nm between the layers.
Synthesis reactions were carried out by chemical vapor deposition using iron catalyst supported on aluminum hydroxide at 400 °C and 420 °C, in the presence of argon as carrier gas and acetylene as carbon source. The aluminum hydroxide support was separated by refluxing the samples in 40% NaOH solution for 2 h and 36% HCl solution for 24 h, respectively. The samples were characterized by field-emission scanning electron microscopy, energy dispersive spectroscopy, high-resolution transmission electron microscopy and X-ray diffraction. The results show that carbon nanotubes were the main products at 420 °C, while large scale high purity nano onion-like fullerenes encapsulating Fe3C, with almost uniform sizes ranging from 10-50 nm, were obtained at the low temperature of 400 °C.
Well-aligned carbon nanotubes were synthesized in a horizontal furnace using acetylene as the carbon source and argon as the carrier gas through by AAO templates. To cut the upper parts of CNTs out of the template, the temperature of the furnace was first cooled to 350 °C under an argon atmosphere, and the temperature of 350 °C was remained for 5 min under an air atmosphere, then the furnace was cooled to room temperature in air. The as-prepared aligned CNTs were also carefully scratched from the substrate and some of them were placed on a copper grid for high resolution transmission electron microscopy (HRTEM) observations. The morphology of CNTs was examined by scanning electron microscopy (SEM). The results show that well-aligned carbon nanotubes were obtained and the carbon nanotubes on the surface of AAO templates were cut off successfully.
Nano-carbon materials were synthesized by decomposing acetylene at 400 °C using iron supported on alumina as catalyst. The catalysts contain about 0.3 and 5.2 wt% iron. The products were refluxed in concentrated HCl at 80°C for 36 h in order to remove the catalyst support. The samples were examined by transmission electron microscopy and X-ray diffraction. The results show that carbon onions surrounding Fe3C core were obtained using the catalyst containing 0.3 wt% iron and these carbon onions had a structure of stacked graphitic fragments, with diameters in the range 15-50 nm.
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