Synthesis of carbon nanotubes by chemical vapor deposition on iron nanoparticles synthesized from oxide precursors

MORALES MENDOZA N.; MARCOS FELISBERTO; LEANDRO SACCO; ROBERTO CANDAL; GERARDO H. RUBIOLO; SILVIA GOYANES

Carbon Nanotubes: Synthesis and Properties

Nova Publishers

Lugar: NewYork; Año: 2012; p. 365 - 400

The goal of this Chapter is to discuss the synthesis of carbon nanotubes by CVD using as catalyst iron nanoparticles obtained from iron oxides precursors, focused on the possibilities of synthesis with high yields and on substrates with large areas. The possibilities of sol-gel methods for generation of porous matrices of SiO2 and Al2O3 with iron nanoparticles included are reported and the advantage of aluminum matrix with respect to silica matrix is discussed. The influence of the effect of the drying-gelification temperature of the sol on the carbon yielding and conversion, as well as the influence of the partial pressure of carbon gas feedstock in the characteristics of the CNTs were discussed. The advantage of using aluminum matrix with respect to the silica matrix is that the resulting material after the synthesis, without purification, is a hybrid consisting of MWCNT with hercynite nanoparticles attached to their walls. In the case of silica matrix, purifications steps after the CVD synthesis are necessary to remove amorphous carbon and others by products of the reactions. Advanced oxidation techniques (AOTS) are newly an interesting alternatives for the controlled oxidation of CNT. With these techniques, controlling the degree of oxidation of CNT is easy, environmentally friendly and allows inducing the formation of carboxylic groups, -OH or both, depending on the selected AOT. Iron nanoparticles can also be synthesized on different substrates by using solutions of iron salts. Also, sold iron oxide nanoparticles disperse in an adequate solvent can be deposited on conductive substrates or semiconductors using an appropriate technique. Both methods allow the deposition of nanoparticles on large areas allowing the growth of carbon nanotubes over large areas. Besides, by both methods it is possible to control the density of catalyst on the substrate and then synthesize vertically aligned carbon nanotubes (VA-CNTs). Finally, the possibilities of synthesis using metal substrates where the catalytic sites are generated directly on the substrate surface without any previous catalytic deposition method was discussed