Abstract: The binary colloid (Ni(OH)₂/SiO₂) was prepared by using Ni(NO₃)₂(6H₂O) and (C₂H₅O)₄SiO₄ as starting materials. Then a part of the
colloid was dried in open air and the other part was used to form NiO/SiO₂ composite powders at hydrothermal conditions. Carbon
nanotubes (CNTs) were systhesized respectively by using these two kinds of powders as catalysts,with acetylene as the source of carbon.
The phase and morphology of the both catalysts and the morphology, output and yield of the two kinds of CNTs were compared by using XRD and
TEM. The results show that the catalyst powders synthesized by the hydrothermal method, compared with those synthesized in open air, are with smaller diameters
(10～20nm), better dispersion and have stronger catalytic activities, so that the pure CNTs with smaller tube diameters of
10～16nm can be obtained at a high yield. The differences of the carbon nanotubes prepared by using the catalysts synthesized by the
hydrothermal method at different temperatures were also studied.

Key words: hydrothermal method, dry method at atmosphere, carbon nanotube, catalytic py- rolysis