Question

What are nanomaterials? Explain preparations of CNT’s by arc-discharge method.

Answer 1

In this review, we focus on the synthesis of multiwalled and single-walled carbon nanotubes (MWNTs and SWNTs, respectively) by an arc discharge method. MWNTs can be obtained in the cathode deposit of the dc arc discharge of pure graphite rods. Ambient gas plays an important role, and pure hydrogen gas is the best gas for obtaining high-crystallinity MWNTs. A thin innermost tube of less than 0.4 nm diameter and a carbon nanowire including a carbon chain can be produced by a hydrogen-ambient dc arc discharge method. The Raman spectra of MWNTs are important because radial breathing modes with frequencies higher than 300 cm –1 and a new Raman band near 1850 cm –1 appear. In the case of SWNT synthesis by an arc discharge method, the incorporation of catalytic metal particles in a graphite anode is necessary, and SWNTs are obtained as soot in an evaporation chamber. By an arc-plasma-jet method wherein two electrodes are placed at a sharp angle, the yield of soot including SWNTs is increased by decreasing the amount of cathode deposit. In particular, the arc evaporation of a graphite rod with a pure Fe catalyst in a gas mixture (hydrogen + inert gas) is effective for obtaining macroscopic SWNT nets. The purification of the SWNTs nets by heat and hydrochloric acid treatments is easy.