Single-walled carbon nanotubes synthesized by chemical vapor deposition of C2H2 over an Al2O3 supported mixture of Fe, Mo, Co catalysts (original) (raw)
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Nanotechnology, 2004
The effect of organic additives, including citric acid, PEG (2000) and PEG (200), on the yield and quality of single-wall carbon nanotubes (SWNTs) synthesized by a Fe-Mo catalyst dispersed on an alumina matrix prepared by the sol-gel process in assisted chemical vapour deposition (CVD) has been investigated by transmission electron microscopy (TEM), thermo-gravimetric analysis (TGA) and Raman spectroscopy. Different morphologies of catalyst including big flakes, spherical particles and porous supporting materials were obtained using citric acid, PEG (2000) and PEG (200) as dispersant, respectively. SWNT yields of 10 wt%, 16 wt% and 33 wt% were obtained using citric acid, PEG (2000) and PEG (200) as the dispersants, respectively, which implies that the PEG (200) is the most effective at improving the yield of SWNTs due to the effect of additives on the specific surface area of the catalyst. The as-grown SWNTs are mostly in large bundles with diameters of 0.5-2 nm, but in some cases, isolated tubes with much larger diameters can also be found. Finally a preliminary explanation for the increased SWNT yield using PEG (200) is presented.
Bundled single-walled carbon nanotubes (SWCNTs) together with multi-walled carbon nanotubes (MWCNTs) were directly grown on a water-soluble support catalyst that was prepared via sublimation of ferrocene on sodium chloride. The synthesis of nanotubes was carried out at a growth temperature of 700 1C in a combined methane and nitrogen environment of 1:1 volumetric ratio at a total flowrate of 80 ml/min for 1 h in a vertical reactor. Characterization techniques such as scanning electron microscope, transmission electron microscope, thermogravimetric analysis, and Raman spectroscopy were employed to study the carbon deposits. Transmission electron microscope shows the presence of SWCNTs with an average diameter of ca. 1.18 nm on the catalyst. The radial breathing mode (RBM) of Raman for shifts below 350 cm À 1 further confirmed the presence of SWCNTs and the diameters were calculated to be 0.93, 1.36, 1.5 and 1.85 nm.
Synthesis of Single-Walled Carbon Nanotubes on Alumina and Alumina-based Supports by CCVD
The raw materials, condition and the method of preparing the support play an important role in the growth of high quality single-walled carbon nanotubes. These effects have been studied in the catalytic chemical vapor deposition (CCVD) growth of SWNTs on Alumina or Alumina-Silica as a support and iron as a supported catalyst. Tetraethyl Orthosilicate (TEOS) with Alumina were used for support preparation. The supports were prepared at low temperature(less than 90˚C) by chemical method. Methane as a carbon source at 800-1000 ˚C was used for the SWNTs synthesis. Alumina-based supports, supported catalysts and SWNT samples have been characterized by TEM, SEM and XRD.
Synthesis of Multi-Walled Carbon Nanotubes by Fluidized-Bed Chemical Vapor Deposition over Co/Al2O3
Journal of Chemical Engineering of Japan, 2014
Synthesis of multi-walled carbon nanotubes (MWCNTs) was accomplished by catalytic chemical vapor deposition of ethylene over Co/Al 2 O 3 in a uidized-bed. The reaction temperature and ethylene concentration, as the molar percentage (mol%), were both found to be crucial factors determining the solid carbon conversion level and selectivity of MWCNT formation, but had no signi cant e ect on the size distribution of the obtained MWCNTs. Amorphous carbon and carbon nano bers (CNFs) were the main products obtained at a reaction temperature of 550°C. Amorphous carbon was also formed when using ethylene at a high concentration (62.5 mol%), which possibly deactivated the catalyst. Increasing the reaction temperature from 550 to 650°C resulted in better graphitized MWCNTs. The average diameters of the synthesized MWCNTs were in the range of 7-8 nm independent of the reaction temperature or ethylene concentration. The selectivity of alkane production decreased considerably at reaction temperatures above 675°C, resulting in a higher productivity of MWCNTs. The activation energy for MWCNT formation was found to be 65.3 kJ/mol, which matched well with that previously reported for carbon di usion in liquid cobalt.
Nano, 2009
SWCNTs are important materials in manufacturing advanced devices like field effect transistor and field emitters. Fe 2 O 3 /MgO catalyst was developed to grow SWCNTs and was used in chemical vapor deposition (CVD) of methane. The catalyst was prepared by mixing iron powder (Fe 2 O 3 ) with MgO at the prescribed stoichiometry ratio. The findings show that SWCNTs in bundle form were grown over the catalyst. Most of the observed bundles are broad with each bundle constitutes more than 20 individual SWCNTs. Raman analysis indicates that these nanotubes possessed highly graphitized structure. Comparing with other catalyst preparation methods, this approach creates better efficiency in the synthesis and reproducibility of SWCNTs in the methane CVD.
Journal of Nanoparticle Research, 2009
The effect of Fe and Ni catalysts on the synthesis of carbon nanotubes (CNTs) using atmospheric pressure chemical vapor deposition (APCVD) was investigated. Field emission scanning electron microscopy (FESEM) analysis suggests that the samples grow through a tip growth mechanism. High-resolution transmission electron microscopy (HRTEM) measurements show multiwalled carbon nanotubes (MWCNTs) with bamboo structure for Ni catalyst while iron filled straight tubes were obtained with the Fe catalyst. The X-ray diffraction (XRD) pattern indicates that nanotubes are graphitic in nature and there is no trace of carbide phases in both the cases. Low frequency Raman analysis of the bamboo-like and filled CNTs confirms the presence of radial breathing modes (RBM). The degree of graphitization of CNTs synthesized from Fe catalyst is higher than that from Ni catalyst as demonstrated by the high frequency Raman analysis. Simple models for the growth of bamboo-like and tubular catalyst filled nanotubes are proposed.
Formation of Single-Walled Carbon Nanotubes via Reduced-Pressure Thermal Chemical Vapor Deposition
Journal of Physical Chemistry B, 2003
We report the growth of carbon nanotubes (CNTs) via reduced-pressure chemical vapor deposition (CVD), using a gas mixture of methane/hydrogen and iron/molybdenum catalyst supported by alumina nanoparticles. The CNTs are either single-walled or double-walled as characterized by transmission electron microscopy. Investigation of various growth parameters indicates that CNT growth is limited by the gas supply when CVD is performed in the temperature range of 750-900°C, whereas the limiting factor for growth at 700°C is the rate of carbon diffusion through the catalyst particles. The density of CNTs changes with CVD pressure as well as gas flow rates when growth is limited by gas supply. We also use a single-step lithographic approach to form catalyst islands on top of patterned electrodes and to selectively grow CNTs bridging neighboring electrodes. The process yields both semiconducting and metallic CNTs as characterized by current-voltage measurements.
Carbon, 2011
A simple method is described to synthesize carbon nanotubes (CNTs) by the thermal decomposition of toluene at 750°C over a thin catalyst film deposited on Al powder. This method allows the bulk metal surface to act as both the catalyst and support for CNT growth. The catalyst film on Al was prepared from an ethanol solution of iron nitrate. Under the growth conditions, iron nitrate formed an amorphous iron oxide layer that transform into crystalline Fe 2 O 3 , which was further reduced to Fe 3 O 4 and Fe 3 C. It is believed that the growth of CNTs took place on iron carbide nanoparticles that were formed from FeO. The characterization of CNTs was mainly carried out by powder X-ray diffraction and scanning electron microscopy, X-ray fluorescence and thermogravimatric analysis. The CNTs were found to be highly dispersed in Al powder. This composite powder could be further used for the fabrication of Al matrix composites using powder metallurgy process in which the powder were first cold pressed at 500-550 MPa followed by sintering at 620°C for 2 h under a vacuum of 10 -2 torr. The mechanical properties of the sintered composites were measured using a microhardness tester and a Universal testing Instron machine.