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 CO 2 as an alternate carbon source, was investigated. Here CO 2 was employed in three different ways: (1) as a sole carbon source, (2) as an additive to C 2 H 2 and (3) as a carbon source prior to the reaction of C 2 H 2 with fly ash. SEM, TEM and laser Raman spectroscopy confirmed that CNMs were formed in all three cases. In the first case, when CO 2 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 CO 2 was used as an additive to C 2 H 2 , a drastic increase in CNM formation was observed. In both cases optimal yields were observed at 600 C.However in the third case, when CO 2 was used as a carbon source prior to the reaction with C 2 H 2 , 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 CO 2 as a carbon source prior to the reaction with C 2 H 2 , results in a very simple and cost efficient process to make uniformally shaped, thermally stable CNMs.

Synthesis of zeolites Na-A and Na-X from tablet compressed and calcinated coal fly ash

“…Most zeolites are periodic framework compounds of aluminium silicates formed by interconnected SiO 4 and AlO 4 tetrahedrons [30]. Owing to the crystalline nature and the abundant AlO 4 sites, zeolites possess well-defined distribution of pore size and outstanding cation-exchange capacity, enabling extensive industrial applications as adsorbents [31][32][33][34], catalysts [35], catalyst supports [36,37] and cation-exchange materials [38][39][40][41][42]. Zeolites are conventionally synthesized with sodium silicate and aluminate through hydrothermal crystallization.…”

Recovery of waste gold for the synthesis of gold nanoparticles supported on radially aligned nanorutile: the growth of carbon nanomaterials

“…Detailed studies showed that both the diameter and the thickness distribution range increase drastically with increase in temperature. 30 This is because metal catalyst particles tend to sinter or agglomerate such that they catalyse the synthesis of thicker CNFs. This is coupled by temperature enhanced decomposition of C 2 H 2 and thus more carbon available for knitting the carbon matrix of the CNFs.…”

“…7,20,[24][25][26] furthermore, this study is a parametric study that reports on some of the factors that have been reported to inuence the growth of carbon nanomaterials using a CVD setup. [27][28][29][30][31]…”

Morphological and crystallinity differences in nitrogen-doped carbon nanotubes grown by chemical vapour deposition decomposition of melamine over coal fly ash

“…12 Likewise we have shown that the yields of CNFs could be enhanced by pre-treating CFA with CO 2 before the introduction of C 2 H 2 and H 2 . 13 Saudi Arabian and Japanese CFA have also been used to synthesize undoped CNTs. 14,15 Similarly, Salah et al have optimised the synthesis parameters (temperature, gas pressure, growth times, and gas ow rates for the decomposition of C 2 H 2 in the presence of H 2 ) for the growth of undoped MWCNTs on carbon rich CFA by low pressure chemical vapour deposition (LPCVD).…”