A comparison of purification procedures for multi-walled carbon nanotubes produced by chemical vapour deposition

A comparison of three different purification procedures for multi-walled carbon nanotubes (MWCNTs) produced by chemical vapour deposition (CVD) has been presented. The methods involved gas-phase oxidation by calcination, liquid-phase oxidation by H2O2, hydrothermal treatment and acid refluxing in HCl. Sample purity was documented with the Raman spectroscopy, Transmission electron microscopy (TEM), Scanning electron microscopy (SEM) and thermo gravimetric analysis (TGA). The Raman spectroscopy, SEM and TEM results showed that the liquid phase oxidation-acid refluxing route successfully eliminated most of the impurities without damaging the nanotube structure. TGA analysis showed in increase in density of MWCNTs with better oxidation resistance after purification and the metal content was reduced from 23.8 wt% to 5.4 wt%.