4c. From fullerenes (buckyballs) to carbon nanotube structures

You should be able to explain the properties of these in terms of their structure, bonding and properties.

Know that fullerenes are molecules of carbon atoms with hollow shapes.

The structure of fullerenes is often based on hexagonal rings of carbon atoms but fullerenes may also contain rings with five or seven carbon atoms.

The first fullerene to be discovered was Buckminsterfullerene (a C₆₀ molecule of hexagonal and pentagonal rings) which has a spherical shape.

Carbon nanotubes are long cylindrical fullerenes with very high length to diameter ratios.

Again, their properties make them useful for nanotechnology, electronics and materials.

You should be able to recognise graphene and fullerenes from diagrams and descriptions of their bonding and structure and give examples of the uses of fullerenes, including carbon nanotubes.

FULLERENES

The first fullerene discovered was the C₆₀ molecule, named buckminsterfullerene.

It is hollow and the 'surface' is made up of 20 hexagons and 12 pentagons.

The pentagons are necessary so the surface can curve over to form a spherical molecule.

Other fullerenes are elongated to give the shape of a rugby ball.

Ultimately they can be made so elongated they form what are known as nanotubes - big molecules!

• FULLERENES: A 4th form of carbon (another allotrope of carbon) are fullerenes or 'bucky balls'!
  • They consists of a 3D connected arrangement of pentagonal, hexagonal or heptagonal rings like graphite. Alternating pentagonal rings of carbon atoms allow curvature of the spherical surface, in fact curved sufficiently to form their characteristic 'football' or 'rugby ball' shapes and elongated closed tubes.
  • Some fullerenes have rings of seven carbon atoms, again to allow curvature of the surface of the hollow sphere of the 'bucky ball'.
  • This means fullerenes are 'hollow' molecules in which other molecules can fit in.
• Buckminster Fullerene C₆₀ ,the first to be discovered, is shown on the right and the bonds form a pattern like a soccer ball.
  • Others are oval shaped like a rugby ball.
  • It is a black solid of needle-like crystals and is insoluble in water.
  • All of the fullerenes are hollow with the hexagonal and pentagonal rings of carbon atoms forming the surface.
  • These 'molecular size' fullerene particles behave quite differently to a bulk carbon materials like graphite or diamond.
• Fullerenes are NOT considered giant covalent structures - small ones, not tubular, are classed as simple covalent molecules.
• Fullerenes do dissolve in organic solvents giving coloured solutions (e.g. deep red in petrol hydrocarbon solvents, and although solid, their melting points are not that high because of weak intermolecular bonding attractive forces.
• Fullerene molecules have a large surface area - potential for industrial catalytic functions e.g. attach catalyst molecules to the surface of the fullerene molecule.
• Fullerene molecules may be used for drug delivery into the body, they can enclose or 'cage' another molecule e.g. of a medical formulation.
• Fullerenes are used as lubricants, the molecules readily slide over each other.
• Fullerenes can be part of a catalyst composite, catalysts can be attached to their large surface area.
• Fullerenes in the form of carbon nanotubes can be used for reinforcing composite materials, eg sports equipment like tennis rackets. More on nanotubes below.

A section of multi-layered graphite	One of the simplest 'buckyballs'  C60	A longer buckminsterfullerene which is 'rugby ball' or 'sausage' shaped, C72 etc.
A section of a carbon nanotube e.g. 6 x 100 nm, the ends would be like those of the 'sausage' above right. All images © doc brown

• NANOTUBES: Carbon based nanotubes are also fullerenes are also mentioned here to illustrate the different forms of carbon AND they can be made into continuous tubes to form very strong fibres of 'pipe like' molecules called 'nanotubes'.
  • Carbon nanotubes are basically long cylindrical fullerenes.
  • Carbon nanotubes have a high length to diameter ratio
  • Carbon nanotubes ...
    • have a very high tensile strength, strong when stretched,
    • very good electrical conductivity and a relatively high thermal conductivity i.e. good conductors of heat and electricity.
• Uses of carbon nanotubes – carbon nanotechnology – examples of nanochemistry
  • They can be used as semiconductors in electrical circuits.
  • They act as a component of industrial catalysts for certain reactions whose economic efficiency is of great importance (time = money in business!).
    • The catalyst can be attached to the nanotubes which have a huge surface are per mass of catalyst 'bed'.
    • Their large surface area combined with the catalyst ensure two rates of reaction factors work in harmony to increase the speed of an industrial reaction so making the process more efficient and more economic.
  • Carbon nanotube fibres are very strong and so they are used in 'composite materials' e.g. reinforcing graphite in carbon fibre tennis rackets.
    • This is partly due to carbon nanotubes have a high length to diameter ratio.
  • Carbon nanotubes or long fullerenes can 'cage' other molecules and can be used as a means of delivering drugs in controlled way to the body because the thin carbon nanotubes can penetrate cell walls.
  • Carbon nanotubes or fullerenes are an important additive in other oil based lubricants to enhance their performance.
    • Additives are added to lubricating oils to improve their effectiveness in reducing friction and as a chemical stabiliser eg to inhibit thermal degradation of the oil in high temperature situation, but I'm not sure what the function of carbon nanotubes is in this case? I suspect the reasons involve some complex physics of viscosity well beyond the scope of these notes!
  • More on nanotechnology including carbon nanotubes, nanoparticles - properties and uses
• I've written pages with more examples and more details on

  • General introduction to nanoscience and commonly used terms explained

  • NANOCHEMISTRY – an introduction and potential applications

  • NANOCHEMISTRY including fullerenes and CARBON NANOTUBES
  • SMART MATERIALS SCIENCE (alphabetical index at top of page)

  • More on From fullerenes & bucky balls to carbon nanotubes