Formation of Carbon Nanotubes from Carbon-Rich Fly Ash: Growth Parameters and Mechanism

Abstract

Fly ash is a byproduct, generated due to the use of heavy oil or coal as a fuel in power plants. Recently, carbon rich fly ash is found to have ideal compositions as a catalyst and precursor for carbon nanotubes (CNTs) growth by the chemical vapor deposition method. The existing methods have a limitation on producing CNTs in a large scale. In this work the parameters effecting the growth of CNTs of fly ash were investigate. These include temperature, gas pressure, growth time and gas flow rate. The produced samples were characterized by different techniques. Consistent results is demonstrated in terms of CNTs uniformity, conversion, and lengths as produced under optimized values. The optimum values provide multiwalls CNTs with diameters in the 20-40nm range. Raman spectrum shows G and D bands (the G/D intensity ratio ~ 1.4). The as-grown CNTs displayed peaks of sp 2 and sp 3 carbons in the XPS spectrum with intensity ratio 7.5 eV.Two small bands are also observed at 288.2 and 290.5 eV, which could be assigned to -COO group and π-π* transition carbon. A proposed mechanism for CNTs growth is also presented. The goal of this method is to develop a large scale production of CNTs using fly ash for various applications.

Preparation of carbon nanofibers/tubes using waste tyres pyrolysis oil and coal fly ash derived catalyst

“…These values are consistent with reports where coal fly ash was used as support for synthesis of CNMs. [42,44] In this case, the authors reported I G /I D ratios of 1.35 and 1.4 when acetylene was used for CNMs synthesis at 750 ºC. In that study, the results had indicated that the materials had a high degree of wall graphitization suggesting good quality CNTs.…”

“…[25,26,42] If the intensity ratio of G and the D peaks (I G /I D ) is high, it indicates the degree of wall graphitization which gives quality CNTs/CNFs with low defects and high crystallinity. [42,44,54] In this study, the D band peaks of all materials are more prominent except for Mag-Cethy which suggested that the obtained CNMs consist of defects, however more graphitic due to the higher intensity ratios. The I G /I D intensity ratios of the CNMs grown on CFA using both ethylene and pyrolysis oil vapour are the same with the value of 1.18, as indicated in Table 2.…”

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

“…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). 14 However, to date the synthesis of heteroatom-doped (i.e.…”

Carbon nanotubes of oil fly ash as lubricant additives for different base oils and their tribology performance

“…13 This solid waste carbon rich material is not yet tried to be utilized as a source for nanostructures production. Salah and his group 11,12 showed the conversion of this y ash into CNTs and utilized them for different applications. Further, they reported that pure carbon content in the oil y ash is high, which has been extensively evaluated for the conversion into nanostructures and utilized for variety of applications.…”

“…It has been reported that this important nanomaterial can be produced using the chemical vapor deposition (CVD) method by utilizing oil y ash as a catalyst and co-precursor in the same time. 11,12 This ash is available in huge quantities as a solid waste and has a good amount of unburned carbon, which is more than 80%. 13 This solid waste carbon rich material is not yet tried to be utilized as a source for nanostructures production.…”