Effect of purification methods on the quality and morphology of plastic wastes derived carbon nanotubes

Abstract

Recent innovative research efforts on the usage of plastic wastes as a cheap carbon source for carbon nanotubes (CNTs) production has emerged as a low-cost and sustainable means of producing CNTs. Although, plastic waste derived CNTs are rarely used in some purity-sensitive and high-alignment needed applications due to the poor quality CNTs resulting from the abundance of impurities such as non-crystalline amorphous carbon, metallic nanoparticles and other impurities. Therefore, purification is a crucial issue to be addressed in order to fully harness all potential applications of CNTs derived from waste plastic materials. Here, the effect of employing different purification methods on the morphology and purity of waste plastic derived CNTs were investigated. CNTs was synthesized using waste polypropylene plastic as carbon feedstock via single-stage catalytic chemical vapour deposition technique (CVD). As-produced CNTs were purified using liquid phase oxidation (chemical oxidation in nitric acid), gas phase oxidation in air and a combination of both liquid and gas phase oxidation method. The obtained purified CNTs were characterized for morphology, purity, surface functional groups and crystallinity using Transmission Electron Microscopy (TEM), Raman Spectroscopy, Fourier transform infrared spectroscopy (FTIR), and X-ray powder diffraction (XRD), respectively. Results obtained showed that a combination of both liquid and gas phase oxidation purification technique resulted in purer and better quality CNTs while chemical treatment present more structurally defective CNTs compared to other investigated treatment methods. This study confirms that the choice of purification techniques influences the morphology and quality of plastic derived CNTs.