Synthesis of Ni@SiO₂ Nanotube Particles in a Water-in-Oil Microemulsion Template

SiO 2 nanotubes containing Ni nanoparticles were synthesized in a template nonionic surfactant water-in-oil (w/o) microemulsion, and were characterized by bright-field TEM. The highly defined cylindrical nanotube cavities had a uniform diameter of 12–13 nm; however cavity lengths were shown to be strongly dependent on aging time before silica precursor addition, hydrazine concentration, and synthesis temperature. Depending on synthesis conditions, Ni@SiO 2 (i.e., core@shell) nanotubes attained lengths up to 2 μm. A hypothesis is advanced that gas phases form and remain entrained in reverse-micelles, effecting both their elongation and also the exclusion of agglomerating silica species to outer micellar regions, thereby causing cavity formation. SiO 2 shell thicknesses could be controlled in the range of 5.1 to 12.4 nm by simple variation of the amount of silica precursor used. Furthermore, H 2 chemisorption measurements demonstrated 14–15% Ni dispersions, and N 2 physisorption analyses showed intraparticle pores on the order of 1 nm. These results confirm the accessibility of active metal sites via diffusion through the porous silica shells. Therefore the reported Ni@SiO 2 materials make an interesting addition to the developing class of M 1 @M 2 O x yolk–shell catalytic materials.