Purification of Carbon Nano-Onions Fabricated by Arc Discharge

Soot containing carbon nano-onions was synthesized by traditional electric arc-discharge method with nickel powder as catalyst. After heating at 400 degrees C for 2 h, the arc discharged soot was soaked in hydrochloric acid solution 8 h, and then ultrasonically dispersed into sodium cholate solution. Such obtained dispersion was filtrated with a medium-speed filter paper, and the filtrate was further filtered with a 0.2 mu m polytetrafluoroethylene membrane to collect the purified carbon nano-onions. SEM (scanning electron microscope) and TEM (transmission electron microscope) observation showed that carbon nano-onions with hollow or nickel-encapsulated cavities were observed and they had a wide size distribution with an averaged diameter of 24.4 nm. XRD (X-ray diffraction) and Raman scattering investigations evidenced a high degree graphitization of such obtained carbon nano-onions. The XPS (X-ray photoemission spectroscopy) analysis, survey to surface chemistry, demonstrated that oxygen-containing and nitrogen-containing functional groups and the metal catalyst were removed from the surface of carbon nano-onions after purification.