Purification of Carbon Nanotubes by Physical Method

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After 1991, we made clear that multiwalled carbon nanotubes could be prepared by DC arc evaporation of graphite rods in atmospheric gas as cathode deposit. When we used pure hydrogen gas as atmospheric gas, high quality multiwalled carbon nanotubes with less co-existing carbon nanoparticles could be obtained (1997). Thus, if co-existing carbon nanoparticles were less originally, it is easy to remove co-existing carbon nanoparticles and to purify. In fact, we could get purified maltiwalled carbon nanotubes irradiating the specimen in air (1998) by infrared radiation heater at 500ﾟC for 30min.When we evaporated the graphite electrode in pure hydrogen gas, we could get maltiwalled carbon nanotubes having extremely narrow inner tube of the diameter 1.Onm in the order. The inner tube was surrounded by graphene sheets of equal distance, 0.34nm, and with high crystalline. We can get X-ray diffraction patterns, Raman scattering, or electric conductivity of purified multiwalled carbon nanotubes (1998). Especially, we could fmd new peaks similar to breathing mode for siglewalled carbon nanotubes at low frequency region (180-500cm_<-1>), and strong new peaks near 1850 cm^<-1>, These purified multiwalled carbon nanotubes are expected to use as good electron source for field emission.