Growth and characterization of carbon nanotubes over CoFe₂O₄-MgO catalysts at different temperatures

Abstract

A novel approach for synthesizing carbon nanotubes (CNTs) via chemical vapor deposition (CVD) technique has been elucidated. CNTs are catalytically grown on the CoFe₂O₄-MgO nano-catalyst at various growth temperatures (700 °C, 800 °C, 900 °C) to clarify the effect of temperature and to achieve the optimum CNT growth temperature. The structural properties of the catalyst and CNTs were studied with thermal analysis (TGA), X-ray diffraction (XRD), FTIR spectroscopy (IR), Raman spectroscopy, and High Resolution Transmission Electron Microscope (HRTEM). X-ray diffraction is used to study changes in the crystal structure of the CoFe₂O₄+MgO nano-catalyst. The obtained data ratifies the formation of MWCNTs over the nanocatalyst. The intensity of the main peak of CNTs decreases as well as the yield with increasing the growth temperature. The two main Raman modes, G band and the D band, can be identified in the spectra multi-walled carbon nanotubes .The lowest I_D/I_G ratio is obtained at the highest growth temperature. HRTEM images show that the growth temperature has a significant parameter on CNT quality. The average diameters of grown CNTs are 42, 32 and 16 nm for growth temperatures of 700 ̊C, 800 ̊C and 900 ̊C, respectively. The inner and outer diameters of MWCNTs become thinner and the quality of the tubes is enhanced with increasing the growth temperature. Additionally, it can be concluded from the temperature study that the balance between decomposition of acetylene gas and diffusion rate of manufactured carbon atoms in CoFe₂O₄-MgO catalyst nanoparticles occurs at the optimal growth temperature of 900 °C.

Keywords:

• Carbon nanotube
• cobalt ferrite
• chemical vapor deposition (CVD)
• different growth temperatures