The effect of nickel content of composite catalysts synthesized by hydrothermal method on the preparation of carbon nanotubes

Multiwall carbon nanotubes were synthesized by pyrolysis of acetylene using the catalyst of Ni(OH)2/SiO2 composite powder, which is prepared by hydrothermal method using Ni(NO3)2·6H2O and (C2H5O)4SiO4 as the main precursor materials. Our study shows that: in a specific limits of the ratio of silicon to nickel (1:2–1:14), with increasing of nickel content, the diameter and crystallization degree of Ni(OH)2/SiO2 composite powder increase, while the activeness first improves and then falls. The output and purity of carbon nanotubes prepared by them first increase and then decrease, and the range of the pipe diameter of carbon nanotubes first shrinks and then expands. When the ratio of silicon to nickel in the catalyst is 1:12, the purity degree of carbon nanotubes is the highest, the pipe diameter is small and even, which is 25 nm mostly, and the output of carbon nanotubes is also the largest (each gram catalyst makes 3.5 g carbon nanotubes including catalyst).