Answer:
There are several approaches to the commercial manufacture of carbon nanotubes. They include the arc discharge method, the laser-aided vaporization method and the chemical vapor deposition (CVD) method.
The arc discharge method has been accidentally discovered in 1991 when carbon nanotubes were found in the residue of an electrical arc discharge. The laser-aided vaporization method (commonly known as the laser ablation method) involves a graphite board that's enclosed within a high-temperature reactor chamber. A laser is then activated and the graphite board is consequently vaporized. All the while, a non-reactive gas is allowed to escape into the reactor chamber. The vapor inside the chamber is then allowed to cool and carbon nanotubes are formed in result.
The CVD method involves a substrate layer on which surface lie catalytic metal particles. The substrate is placed inside the reactor and heated while two types of gas are fed into the reactor. As the carbon-containing gas passes over the heated metal particles, pure carbon is separated from its base compound and carbon nanotubes are formed.