Synthesis of nonstoichiometric NiO nanocatalysts and growth of bamboo-like carbon nanotubes

The growth behavior of carbon nanotubes from NiO nanoparticles was investigated in terms of vacancy concentration and nanostructure. The NiO nanoparticles were prepared using anhydrous ethanol as a solvent to lower hydroxyl groups, compared to distilled water. The Ni vacancies in NiO via less hydrolysis were confirmed by lattice expansion and the increased mean oxidation state of Ni³⁺ through X-ray absorption spectroscopy. The increased Ni³⁺ ratio determined from the photoelectron spectrum and ferromagnetism implied a high concentration of Ni vacancies on the surface. Nonstoichiometric NiO exhibited a small particle size of 10.13 nm and a narrow size distribution. For the growth of CNTs, the NiO nanocatalysts with vacancies resulted in thinner CNTs. The internal structures of the CNTs obtained from the defective particles were grown into bamboo-like CNTs, identifying the variation in the carbon diffusion path.