Editorial Feature

How are Carbon Nanotubes Made from Graphene?

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Carbon atoms form the basis of both graphene and carbon nanotubes. Graphene is the basic structural element that forms all other carbon allotropes, including carbon nanotubes, charcoal, graphite, and fullerenes.

Carbon nanotubes are important because of their various applications in field emission, energy storage, biomedicine, industrial catalysts, adhesives, thermal materials and also due to their impressive properties of being both strong and incredibly lightweight, as well as being excellent conductors of heat and electricity.

To form a carbon nanotube, the basic form of carbon and graphene is manipulated to form thin sheets that are rolled into cylinders. The sheets of graphene used to make the nanotubes are 2D due to graphene being one atom thick, this gives the nanotubes some of their special properties.

Similarities Between Graphene and Carbon Nanotubes

Graphene and carbon nanotubes have similar properties which make them very interesting to researchers from numerous industries. They are often both considered for use in the same applications, and as a result, scientists are now looking into combining graphene with carbon nanotubes in order to use them to make electronic products, sensors, batteries and more.

There are some differences between the substances, graphene as has been discussed, is 2D, whereas although they are constructed from graphene, carbon nanotubes are considered to be one dimensional. The two also have different semiconducting properties. Single-walled carbon nanotubes have metallic or semiconducting properties, with a bandgap between zero to around 2 eV. However, attempting to use graphene as a semiconductor is problematic, because it has a zero bandgap.

In addition, working with carbon nanotubes is often seen as more difficult than working with graphene because it is challenging to position and connect them.

Production of Carbon Nanotubes

The production of carbon nanotubes is simple in theory. A sheet of graphene of one atom in thickness is rolled into a tube. This creates a single-walled carbon nanotube. Other than this, layers of these graphene sheets can be rolled in order to create multi-walled carbon nanotubes, which have slightly different properties. Scientists have developed ways to create carbon nanotubes in varying diameters and lengths so that they can use them with the specific properties they require for different applications.

Currently, there are three main methods for producing carbon nanotubes, these are known as arc discharge, laser ablation of graphite, and chemical vapor deposition (CVD). Arc discharge and laser ablation of graphite are two methods that start with graphite which is then combusted, producing a gas from which the carbon nanotubes are developed.

The most widely used method for producing carbon nanotubes is CVD, which is able to produce the nanotubes in greater quantities, at a lower cost, under conditions that are simpler to manage. The method involves combining a metal catalyst with carbon-containing reaction gases and as a result, the carbon nanotubes are formed on the catalyst within a furnace.

Purification Stage

All production methods of carbon nanotubes require a purification process to improve the purity of the created nanotubes. Metal encapsulated nanoparticles, metal particles, and amorphous carbon can contaminate the nanotubes, making them lower in purity, causing structural defects and therefore modifying the nanotubes’ physicochemical properties. For this reason, a purification step is essential once the tubes have been formed. Purification can take the form of acid treatment or ultrasound performed at the end of the process.

Given the growing applications for carbon nanotubes, we can expect developments in the processes for making them too. Scientists are requiring larger volumes of pure samples for both research and commercial applications, this may drive the innovation of new and better production methods.

Source

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Sarah Moore

Written by

Sarah Moore

After studying Psychology and then Neuroscience, Sarah quickly found her enjoyment for researching and writing research papers; turning to a passion to connect ideas with people through writing.

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