Microwave purification of multi-wall carbon nanotubes in gas phase

•A novel technique to purify Multi-Walled Carbon Nanotubes (MWNTs)•Impurities are removed effectively by microwave purification in gas phase.•The best microwave purify technology for MWNTs is obtained from experiments.•The purification mechanism of microwave heating method in gas phase is discussed.•The microwave purification method is proved to be fast, efficient and economical.

It is a known fact that Multi-Walled Carbon Nanotubes (MWNTs) is one of the best reinforcement in conventional composites. However, impurities (like amorphous carbon blacks, graphite scraps, and catalyst particles) are generated inevitably when MWNTs are prepared. These impurities could affect the excellent properties of MWNTs as a reinforcing phase. In this paper, MWNTs were purified by microwave purification method using their excellent microwave absorbing properties. The simple purification process in the gas phase was expected to remove impurities effectively. Raman spectroscopy (Raman), X-ray Diffraction (XRD), Atomic Fluorescence Spectroscopy (AFS), Specific Surface Area (SSA), Thermogravimetric Analysis (TGA), Scanning Electron Microscopy (SEM) and Transmission Electron Microscopy (TEM) suggest that impurities are removed efficiently after microwave heating and simple acid pickling. The optimal purification result is obtained when MWNTs are microwave heated at 500 °C for 20 min, the morphology and structure remain intact. At last, the mechanism of purification is discussed.

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