Carbon Nanotubes Synthesis using Siliceous Breccia as a Catalyst Source

In this work, siliceous breccia, a natural rock composed essentially of SiO2 -quartz, has been employed as a catalyst for the synthesis of carbon nanotubes (CNTs) via chemical vapour deposition. The pristine powder was characterized by using X-ray diffraction, energy dispersive X-ray spectroscopy, and micro Raman spectroscopy. In addition to quartz, it contains dispersed micro-inclusions of iron oxide-hydroxides, goethite or hematite, that act as catalysts. The catalytic performance of this powder was evaluated for ethylene decomposition at 750 ºC, with and without H2 flux. Thermal oxidation stability and carbon yield were measured by means of thermogravimetric analysis. Structural and vibrational spectroscopy characterization of the resulting material was carried out by environmental scanning electron microscopy (ESEM) and micro Raman spectroscopy. ESEM images clearly show the effect of the H2 addition on the CNTs diameter size. It is inferred that the ethylene flux with hydrogen treatment removes amorphous carbon and results in an enhanced growth of nanotubes.