Flame synthesis of Ni-catalyzed nanofibers

Flame synthesis of Ni-catalyzed nanofibers is illustrated. Ni nanoparticles are formed by thermal decomposition of a nebulized Ni nitrate solution entrained into a reactive fuel mixture. Although at the earliest stages of growth, the Ni nanoparticles are sufficiently small to catalyze single-wall nanotubes (SWNTs), only the larger particles appear catalytically active yielding only nanofibers. Using different reactive gas mixtures consisting of CO or C₂H₂ or their combination, Ni nanoparticles exhibited a high preferential reactivity towards C₂H₂ to form nanofibers. These results are interpreted as a result of CO enhancing the dissociative adsorption of C₂H₂ through electronic charge donation mediated by the Ni nanoparticle and physically protecting active sites against blockage by aromatic molecules.