A comparative study of the effect of magnesium oxide and calcium carbonate as support material in the synthesis of carbon nanotubes using the catalyst Fe/Co is presented. The synthesized carbon nanotubes were characterized with Raman spectroscopy, scanning electron spectroscopy (SEM), high-resolution transmission electron microscopy (HRTEM), X-ray diffraction spectroscopy (XRD), and energy dispersive spectroscopy (EDS). The morphology of the carbon nanotubes synthesized with magnesium oxide as support material gives rise to carbon nanotubes with consistent and well-defined structure unlike that synthesized with calcium carbonate. The
Synthesis of carbon nanotubes (CNTs) has been extensively investigated by a number of researchers, since the first observation in 1991 [
It is reported that the most effective catalysts for CCVD growth of CNTs are known to be iron (Fe), cobalt (Co), and Nickel (Ni) [
In this study, we report the effect of calcium carbonate and magnesium oxide as support materials in the synthesis of CNTs using Fe/Co catalysts by thermal CCVD of acetylene gas. The CNTs were grown on Fe/Co/CaCO3 and Fe/Co/MgO under the same conditions. The morphological features were investigated using transmission electron microscopy, scanning electron microscopy, X-ray diffraction, Raman spectroscopy, and energy dispersive spectroscopy.
Iron(III) nitrate, cobaltous nitrate, magnesium oxide, calcium carbonate, and concentrated hydrochloric acid 32% were obtained from Sigma-Aldrich South Africa and used directly without further purification. Catalytic chemical vapor deposition (CCVD) reactor was obtained from Elite Thermal Systems Limited, South Africa, Mass flow meter and PowerPod 400 multichannel power supply instrument were obtained from Teledyne Hastings Instruments, USA.
Iron(III) nitrate, cobaltous nitrate, and supporting materials were dissolved in 200 cm3 of distilled water in molar ratios of 2 : 1 : 2, respectively, in a beaker. The mixed dispersions were heated and evaporated with constant stirring until a paste was formed. The paste was then dried in an oven at 110°C for about 12 hours. The resulting solid material was calcined at 800°C for 5 hours.
Carbon nanotubes were prepared in a cylindrical CCVD reactor; 40 mm o.d
The morphological features of nanomaterials were analyzed by Raman spectroscopy, FE-SEM, HR-TEM, EDS, and XRD. The Raman spectra were obtained by a Raman spectroscope, Jobin-Yvon HR800 UV-VIS-NIR Raman spectrometer equipped with an Olympus BX 40 attachment. The excitation wavelength was 514.5 nm with an energy setting of 1.2 mV from a coherent Innova model 308 argon-ion laser. The Raman spectra were collected by means of back scattering geometry with an acquisition time of 50 seconds. The surface morphology and EDS measurements were recorded with a JEOL 7500F Field Emission scanning electron microscope. The HR-TEM images of the sample were obtained by a CM 200 electron microscope operated at 100 kV. Powder X-ray diffraction (PXRD) patterns were collected with a Bruker AXS D8 Advanced diffractometer operated at 45 kV and 40 mA with monochromated copper K
Raman spectra of nanomaterial synthesized with the catalyst Fe/Co supported on magnesium oxide (MgO) and calcium carbonate (CaCO3), respectively, are presented in Figure
Raman spectra of nanomaterial synthesized from Fe/Co on (a) magnesium oxide and (b) calcium carbonate as support material.
The scanning electron micrograph of the nanomaterial synthesized with the catalyst Fe/Co supported on magnesium oxide and calcium carbonate are presented in Figure
Scanning electron micrograph (SEM) of nanomaterial synthesized from (a) Fe/Co supported on magnesium oxide and (b) Fe/Co supported on calcium carbonate.
The HR-TEM micrograph of the nanomaterial synthesized with the catalyst Fe/Co with magnesium oxide and calcium carbonate supports are presented in Figure
High-resolution transmission electron micrograph (HR TEM) of nanomaterial synthesized from Fe/Co supported on magnesium oxide ((a)–(c)) and Fe/Co supported on calcium carbonate ((d)–(f)).
The energy dispersive spectroscopy (EDS) analysis of the as-prepared carbon nanomaterial formed in this synthesis using magnesium oxide and calcium carbonate as support material is presented in Figure
Quantitative analysis of elements and atoms obtained from energy dispersive spectroscopy of Fe/Co catalyst supported on magnesium oxide and calcium carbonate.
Element | Fe/Co/MgO | Fe/Co/CaCO3 | ||||
---|---|---|---|---|---|---|
Element (% weight) | Atom (%) | Peak height (au) | Element (% weight) | Atom (%) | Peak height (au) | |
Carbon (C) | 27.11 | 33.20 | 30326 | 27.15 | 33.25 | 25528 |
Oxygen (O) | 72.46 | 66.61 | 1598 | 72.49 | 66.64 | 626 |
Magnesium (Mg) | 0.22 | 0.13 | 892 | — | — | — |
Calcium | — | — | — | 0.17 | 0.06 | 296 |
Iron | 0.14 | 0.04 | 312 | 0.09 | 0.02 | 261 |
Cobalt | 0.07 | 0.02 | 312 | 0.10 | 0.03 | 261 |
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Total | 100 | 100 | 100 | 100 |
Energy dispersive spectroscopy (EDS) of nanomaterial synthesized from (a) Fe/Co supported on magnesium oxide and (b) Fe/Co supported on calcium carbonate.
The X-ray diffraction diffractograms of nanomaterial synthesized with the catalyst Fe/Co supported on magnesium oxide (MgO) and calcium carbonate (CaCO3) are presented in Figure
Peaks obtained from X-ray diffraction of Fe/Co catalyst supported on magnesium oxide and calcium carbonate.
Support | 2 Theta degrees ( |
|||
---|---|---|---|---|
MgO | 25.97 | 35.27 | 42.57 | 44.46 |
CaCO3 | 26.00 | 35.11 | 42.43 | 44.46 |
X-ray diffraction spectra (XRD) of nanomaterial synthesized from (a) Fe/Co supported on magnesium oxide and (b) Fe/Co supported on calcium carbonate.
Carbon nanotubes synthesized with the catalyst Fe/Co supported on magnesium oxide and calcium carbonate have been compared. The carbon nanotubes produced using magnesium oxide as support material show better consistency and size compared to the carbon nanotubes produced using calcium carbonate as support. Raman spectra of the as-prepared carbon nanotubes indicate the presence of higher amorphous material in the carbon nanotube prepared with calcium carbonate as support material compared to that prepared with magnesium oxide as observed in the high intensity of the
The authors declare that there is no conflict of interests regarding the publication of this paper.
This work was supported by a research grant from the Faculty of Applied and Computer Science Research and Publications Committee of Vaal University of Technology, Vanderbijlpark. The authors thank staff members of the CSIR Pretoria for microscopic analysis.