Production of carbon nanotubes on bio-char at low temperature via microwave-assisted CVD using Ni catalyst

Microwave-assisted chemical vapor deposition (CVD) was employed for the synthesis of carbon nanotubes (CNTs) on pine nut shell (PNS) chars. The impact of reaction temperature, catalyst, carbon source, and the renewable carbon substrate on the synthesis of the CNTs were investigated. Microwave irradiation, the type of carbon source, and the presence of nickel catalyst were found to be the governing factors during the formation and growth of CNTs at low temperatures. 600 °C was found to be the optimum temperature for the formation of the CNTs. The high-resolution transmission electron microscope (HRTEM) results showed that the CNTs synthesized at 600 °C had a multiwall structure and a d-spacing of 0.34 nm. The diameter and length of CNTs were ~50 nm and 2600–3200 nm, respectively. Raman spectroscopy analysis revealed that a high degree of carbon order was achieved at 600 °C due to the formation of CNTs on the surface of bio-char. The formation and growth mechanisms of CNTs under microwave irradiation were proposed and discussed.