Natural Laterite as a Catalyst Source for the Growth of Carbon Nanotubes and Nanospheres

Carbon nanotubes (CNTs), the closest structure to ideal one-dimensional (1D) conductors, have stimulated substantial interest in the last decades for many applications in the field of nanotechnology. Unfortunately, the high cost of efficient metal catalysts limits the large-scale exploitation of carbon nanomaterials' synthesis processed by chemical vapor deposition (CVD). However, minor or even trace amounts of metal or metal oxides in the ideal form to be used as catalysts can be easily found in almost all-natural materials. Herein, we report on the synthesis of carbon nanotubes and nanospheres obtained via CVD from a natural laterite, as a catalyst source. The synthesized nanostructures were carefully analyzed by X-ray diffraction (XRD), environmental scanning electron microscopy (ESEM), high-resolution transmission electron microscopy (HR-TEM), micro-Raman spectroscopy, and thermogravimetric analysis (TGA). In particular, we investigated and discussed the structural properties of the catalyst nanoparticles and of the produced carbon nanomaterials as well as the influence of temperature on the activity of the laterite based catalyst. At 700 °C, mainly CNTs grew, whereas at 800 °C carbon nanospheres start to form and they become clearly visible in the form of continuous networks of spheroidal structures in the samples grown at 900 °C. The obtained yields indicate that it could be possible to scale up the synthesis of CNTs to be used in technological applications, starting from natural mineral oxide sources.