The effect of CO2 on the CVD synthesis of carbon nanomaterials using fly ash as a catalyst

Abstract

The efficient use of fly ash is a worldwide issue due to its high production and harmful effects on the environment. In this work the synthesis of carbon nanomaterials (CNMs) via the chemical vapour deposition (CVD) method, using fly ash as a catalyst and CO₂ as an alternate carbon source, was investigated. Here CO₂ was employed in three different ways: (1) as a sole carbon source, (2) as an additive to C₂H₂ and (3) as a carbon source prior to the reaction of C₂H₂ with fly ash. SEM, TEM and laser Raman spectroscopy confirmed that CNMs were formed in all three cases. In the first case, when CO₂ was used as a sole carbon source, CNMs were formed in low yields with a considerable amount of amorphous carbon. However, in the second case when CO₂ was used as an additive to C₂H₂, a drastic increase in CNM formation was observed. In both cases optimal yields were observed at 600 °C. However in the third case, when CO₂ was used as a carbon source prior to the reaction with C₂H₂, uniform-sized nanofibers of the highest yields of all three cases were formed. Likewise these CNMs were found to be the most thermally stable. Hence this study has shown that the use of waste materials such as fly ash as a catalyst and CO₂ as a carbon source prior to the reaction with C₂H₂, results in a very simple and cost efficient process to make uniformally shaped, thermally stable CNMs.