Metal catalyst adsorption effects in the growth of carbon nanostructures on mesoporous material

Mesoporous silica films were used as host for metal-based (Me = Fe, Co, Ni) nanoparticles via wet impregnation at pH = 5. A hydrogen ion beam was used to reduce the metallic oxide and hydroxides, previously detected by X-ray photoelectron spectroscopy, in metals. Chemical vapor deposition processes at three different conditions varying the acetylene-nitrogen proportion were performed on the mesoporous films decorated by different metal-based nanoparticles. The grown carbon nanostructures were characterized by high-resolution transmission electron microscopy and scanning electron microscopy. The ability to grow carbon nanostructures decreases in the following order: Fe > Co > Ni. When pure acetylene is used, iron allows to form graphene sheets around the metal catalyst like carbon nanocapsules, whereas cobalt allows to form structures that seem to be carbon nanotubes. Nitrogen leads to control the size and shape of carbon nanocapsules for iron catalyst and avoid the growth of such carbon nanotube-like structures for cobalt catalyst.