Purification) ND Soot contains non-diamond carbons, such as graphite and amorphous carbon (25–85 wt%), and metal impurities (1–10 wt%) mainly caused by the detonation chamber. Therefore, it is essential to remove these species to obtain high purity NDs for their actual applications. Furthermore, concerning the industrial aspects, the production of ND with controlled- and high- sp3/sp2 carbon ratio is very important for meeting market demands arising from a variety customers in various applications. For example, the ND in biomedical imaging applications may require an extremely high purity because non-diamond carbon causes unwanted sp2 background fluorescence. However, lubricants may need a proper amount of both ND and graphite because graphite exhibits lubricating properties. In addition, applications in the supercapacitor or supporting materials of catalyst (e.g. polymer electrolyte membrane fuel cells) may require sufficient electrical conductivity, which can be induced by graphite layers such as carbon onions. The control of sp3/sp2 carbon ratio appears to be a promising approach for these applications.