Microwave chemical vapor deposition synthesis of carbon nanotubes from carbon dioxide and acetylene using nickel, cobalt and molybdenum catalysts

Carbon nanotubes (CNTs) are tube-like allotropes of carbon with a nanometer-size diameter and up to centimeters long. Because of its properties, it became the most intensively studied material. CNTs have amazing range of applications but these applications had a limited success in the marketplace mainly because of the processing issues. There is a need for continuous study for the methods used and factors that will result to consistent high quality and high yield CNTs. Therefore, this study focused on the determination of the effects of using different types of catalyst and substrate to CNTs grown. The experiment was performed based from full factorial design with 27 runs. From this, input parameters such as type of catalyst (Ni, Co and Mo), substrate (Fe, Si wafer and alumina) and ratio of CO2 to C2H2 (40/60, 50/50 and 60/40) were investigated to determine the effects on the responses such as weight of CNTs produced, yield and carbon source conversion. There diameters were also measured through scanning electron microscope (SEM). CNTs were successfully grown by MCVD process at temperatures 400 0C to 900 0C for 10 min reaction time. The highest weight of CNTs produced was using Ni, Fe and CO2/C2H2:40/60 producing 32.0 mg of CNTs. Highest yield of CNTs produced was using Ni, Fe and CO2/C2H2:50/50 producing 79.43%. For carbon source conversion, Ni, Si wafer, CO2/C2H2:60/40 combination was the highest having 77.18% conversion. From the results, Ni was the best substrate and Si wafer was the most suitable substrate for CNT growth. For the analysis of gases, CO2 was successfully converted up to 33.85% to 82.49%. Plasma, high temperature and presence of coreactants (C2H2 and H2) supported conversion as characterized by changes in Gibbs energy and extent of reactions. Moreover, unreacted CO2, C2H2 and N2 were found at the effluent gas. There were also small amounts of carbon monoxide (CO) detected on some runs