Synthesis Of One-Dimensional Nanotube Arrays With Template-Based Method

Template-synthesis and applications of metal-doped carbon nanotubes have been extensively studied during the last decade. Their potential use is focus on heterogeneous catalysis, biosensor, environmental energy, microelectronics and so on. The conventional synthesis of metal-doped carbon nanotubes is to first synthesize carbon nanotubes within the pores of template, then place the formed nanotubes into metal solution. After calcination and alkaline treatment, metal-doped carbon nanotubes are obtained eventually. Obviously, this two-step method takes much time, and the reaction temperature is very high. Therefore, one of goals of this research is to synthesize metal-doped carbon nanotubes in only one reaction under low-temperature conditions. Corona discharge is efficient for the decomposition of methane. In-situ measurement of the gas temperature with IR thermal imaging is carried out during the synthesis of NiO-doped carbon nanotubes. The results show that the gas temperature of corona discharge is not higher than 250 ℃, so the carbon nanotubes can be synthesized under low-temperature conditions. In order to shorten the synthesis time, metal is firstly loaded into the alumina template. Then corona discharge enhanced chemical vapor deposition is executed, in which the formation of carbon nanotubes and the introduction of metal are carried out simultaneously. Besides iron-group metals, Pt, Cu. La and Zn are also loaded into carbon nanotubes. The iron-group metals are completely imbedded into the walls of carbon nanotubes, but it is only partially for the others. In-situ MS analysis, during the synthesis of NiO-doped carbon nanotubes, indicates that only ethylene and acetylene are found in the effluent gas. This confirms that the synthesis itself is also methane-coupling reaction. The combination of the two reactions can promote the utilization of carbon atoms and hydrogen atoms. In-situ OES analysis indicates that the main active massive particles in corona discharge are activated C atom, activated H atom, CH⁺ and radicals like CH and C2. With the discharge time, the intensity of C and C₂ spectra is quickly decreased. Therefore these species play an important role in the formation of carbon nanotubes. On the other hand, Ce(NO₃)₃ nanotubes are easily synthesized within the pores of template with simple incipient wetness impregnation after dried at 50℃. This is due to interaction between Ce³⁺ and alumina. If it is thermally treated at temperature more than 150 ?C, CeO2 nanotubes are obtained. The HRTEM observation shows that the CeO2 nanotubes are composed of many fine CeO2 nanoparticles, but their agglomeration makes sure the integrity of nanotubes. The XPS analysis indicates that CeAlO3, formed at high temperature between CeO2 and Al2O3, is observed at the outer surface, that is to say CeO2 nanoparticles are likely adsorbed onto the inner surface of template homogeneously.