Quasi-aligned carbon nanotubes synthesised from waste engine oil

• Waste engine oil (WEO) is used as a starting material for quasi-aligned CNTs production via thermal chemical vapour deposition (TCVD).
• The characterisation results showed that the quasi-aligned CNTs produced from WEO were comparable to those produced from conventional carbon sources.
• The quasi-aligned CNTs synthesised from WEO presented a potential for field emission application.
• This work offers a new, cheap, abundant and easily available source with high carbon content for CNTs production.

Quasi-aligned carbon nanotubes (CNTs) were successfully synthesised for the first time using waste engine oil (WEO) as the carbon source via thermal chemical vapour deposition (TCVD). The high carbon content of WEO was believed to promote the growth of the quasi-aligned CNTs. The synthesis process was performed at precursor and synthesis temperatures of 500 and 750 °C, respectively, with a ferrocene catalyst concentration of 17.99 wt%. Typical characterisation methods were employed to examine the CNTs: electron microscopy, energy dispersive X-Ray, X-ray diffraction and micro-Raman spectroscopy. The ability of CNT samples to emit electrons was also investigated by field electron emission (FEE) analysis. Electron microscopy and micro-Raman analysis revealed a dense mixture of quasi-aligned single- and multi-walled CNTs with a moderate ID/IG ratio of 0.90. The overall diameters of the CNTs ranged from 18.0 to 29.8 nm, with the diameters of the single-walled CNTs estimated to be between 0.6 and 1.1 nm. The FEE results showed that the quasi-aligned CNTs synthesised from WEO exhibited reasonable turn-on and threshold fields of 4.1 and 7.2 V μm−1, which corresponded to current densities of 0.1 and 1.0 μA cm−2, respectively. This study highlights WEO as a new, cheap, abundant and easily available carbon source for quasi-aligned CNTs production with a potential application in electron emission devices.

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