Bamboo-shaped carbon nanotubes generated by methane thermal decomposition using Ni nanoparticles synthesized in water-oil emulsions

Ni nanoparticles were synthesized using two water-in-oil emulsions formulated with different surfactants and using n-heptane as the organic phase and aqueous nickel acetate as the catalytic metallic precursor. Characterization by transmission electron microscopy showed that the Ni nanoparticles have diameters ranging from 3 to 12 nm, and that the surface is lightly oxidized. The decomposition of diluted methane catalyzed by the as-prepared Ni nanoparticles was studied in a thermogravimetric analyzer (TGA), operated in the 25–930 °C range. The weight gains measured during the analysis showed that the Ni nanoparticles decomposed methane above 480 °C, producing similar g.C/g.cat ratios (6–7) at the end of the tests. High resolution transmission electron microscopy (HRTEM) confirmed that the carbons collected at 930 °C were bamboo-shaped carbon nanotubes (BSCNTs) with well defined conical compartments. The average outside diameter of the tubes was between 30 and 60 nm.