Effect of catalysts and precursors in the synthesis of carbon nanotubes by catalytic chemical vapour deposition

Abstract

Since the pioneering report of discovery of carbon nanotubes (CNTs) in 1991 by Iijima, scientists and researchers worldwide have carried out in depth investigations in this new family of carbon because of its myriad properties and potential applications. The synthesis of novel nanoscale material is the main target in current material science. This study investigates the effect of different types of cabon source and and catalyst on the type of CNTs formed via catalytic chemical vapour deposition (CCVD) method. Three types of carbon source i.e. acetylene, methane and ethanol were used for the synthesis of CNTs. The catalysts used in the synthesis of CNTs are monometallic, bimetallic and trimetallic derived from Fe, Co and Ni salts using wet impregnation method. The catalysts were characterized by scanning electron microscope (SEM) and energy-dispersive X-ray analysis (EDX). The analysis confirmed the presence of Fe, Co and Ni. The as-synthesized CNTs were characterized using SEM/field emission-scanning electron microscope (FE-SEM), EDX, Raman spectroscopy and transmission electron microscopy (TEM). This analysis also confirmed that all the prepared catalysts were active for the production of CNTs. SEM/FE-SEM analysis revealed different morphologies of CNTs were formed when different catalysts and carbon source were used. Raman spectra revealed that acetylene and methane precursor produced multi-walled carbon nanotubes (MWNTs) as indicated by the presence of G-band and D-band peaks. However, their structures were different depending on the catalysts used. Meanwhile, the presence of RBM peaks along with the G-band and D-band revealed that singlewalled carbon nanotubes (SWNTs) are produced using ethanol as the carbon source. TEM micrographs obtained confirmed that acetylene and methane produced MWNTs and ethanol produced SWNTs with diameter in the range of 14.74-34.59 nm, 10.19-37.61 nm and 0.96-2.52 nm, respectively. However, Fe/Al2O3 catalyst selectively produced double-walled carbon nanotubes (DWNTs) when ethanol was used as the carbon source. Generally, this research has been successful in producing various types of CNTs depending on the catalyst used and the carbon source selected