Doc Brown's Chemistry Revision Notes  NANOCHEMISTRY - Nanoscience - Nanotechnology - Nanostructures

Part 4. From fullerenes & bucky balls to carbon nanotubes

Alphabetical keyword index for the nanoscience pages : Index of nanoscience pages : boron nitride * Buckminsterfullerenes-bucky balls * carbon nanotubes * fat nanoparticles * fluorographene * fullerenes * graphene * health and safety issues * liposomes * nanochemistry * nanomaterials * nanoparticles * nanoscale * nanoscience * nanosize-nanosized-particles * nanostructures * nanotechnology * nanotubes * problems in nanomaterial use * silver nanoparticles * safety issues * sunscreens-sunblockers * titanium dioxide

Part 4. Fullerenes and carbon nanotubes

• What are fullerenes? What is the formula and structure of Buckminsterfullerene? What are fullerenes used for? What is a 'bucky ball'? What is a nanotube?
• Apart from the carbon allotropes of diamond and graphite, a 3rd form of carbon exists as fullerenes or 'bucky balls'.
  • There is also amorphous carbon e.g. soot or charcoal, but this is mainly chemically modified impure graphite.
  • Allotropes are different atomic, molecular arrangements of the same element in the same physical state.
• They consist of hexagonal rings like graphite and alternating pentagonal carbon rings to allow curvature of the surface (see diagram further down). They are a sort of a hollow 'cage' shaped pure carbon molecule.
  • Fullerenes are NOT nanoparticles BUT they are smaller molecular versions equating to sections of the tiny molecular carbon tubes called carbon nanotubes, AND they are very interesting molecules in themselves and provide a way into studying carbon nanotubes in terms of their molecular structure and applications in nanotechnology.
• The carbon-carbon bonds in Buckminster Fullerene C₆₀ (shown on right) form a pattern like a soccer ball and is a brownish-reddish-magenta colour in organic solvents. It is a black? solid insoluble in water.
  • The name Buckminsterfullerene (fullerene-60), is derived from the American architect R. Buckminster Fuller who invented the geodesic dome design in building construction.
• Other typical fullerenes have formulae such as ...
  • C₂₈, C₃₂, C₅₀, C₇₀ (red in solution, rugby ball shape - US American football shape)
  • In these fullerenes the carbon atoms lie at vertices of a polyhedron with 12 pentagonal faces with a minimum of two hexagonal faces.
• They are NOT considered giant covalent structures and are classed as simple relatively small molecules, even those above C_n!
  • They do dissolve in organic solvents giving coloured solutions.
  • The colour depends on the solvent ranging from red to deep purple and violet.
  • They are the only soluble allotrope of carbon.
  • Although solid, their melting points are not that high.
• Uses of fullerenes
  • They have many chemical synthetic and pharmaceutical applications.

    • The may be use as vehicles to carry drugs into cells, the cage like fullerene molecules could contain a drug, and the combination can pass easily through the wall of a target cell.

  • Chemical derivatives of fullerenes have fascinating electrical and magnetic behaviour including superconductivity and ferromagnetism (nano nature?, beyond the scope of this page?)
  • C₆₀ is an optical limiter. When light is shone on it, a solution of fullerene-60 turns darker instantly and the more intense the light, the darker it gets, so the intensity of transmitted light is limited to a maximum value. This limiting light transmittance property can be used in the design of safety goggles in intense light situations e.g. people working with laser beams.
• Fullerenes are mentioned here to illustrate the different forms of carbon AND they can be formed into continuous tubes to give very strong fibres of 'pipe like' molecules called 'nanotubes'. These nanotube molecules-particles behave differently compared to bulk carbon materials like graphite and the much smaller fullerene molecules.
• What are Nanotubes? - What is the molecular structure of carbon nanotubes? (sometimes called 'buckytubes') and of what use are they in carbon nanotechnology?

  • Carbon nanotubes are one of the most intensively studied and characterised used nanomaterials, consisting of tiny cylinders of carbon, no wider than a strand of DNA with a wide range of properties of great use to materials scientists.

  • In other words, lots of varieties of carbon nanotubes, differing in size and atomic arrangement can have very different properties.

    • You can also fabricate multiple layered carbon nanotubes like an elongated 'Russian doll'!
      • These presumably would make a stronger material?

  • Uses of Carbon nanotubes

    • Nanotubes can be stronger than steel with only ¹/₆th the weight.

  • Some nanotubes are excellent insulators, semiconductors or conduct electricity as well as copper!

    • They can be used as semiconductors or 'miniature wires' in electrical circuits and of great use in miniature electronic circuitry in computers and other electronic devices.
  • 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'.
    • They large surface 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.
  • Nanotube fibres are very strong and so they are used in 'composite materials' e.g. reinforcing graphite in carbon fibre tennis rackets.
    • Note that pure graphite is a soft slippery solid with low physical strength.
    • Bundles of the nanotubes, processed into fibres, have very high tensile strength and can be much stronger than steel on a weight for weight basis.
  • Nanotubes 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 could be used to make tiny mechanical devices, molecular computers or extremely strong materials

  • The structure and properties of carbon nanotubes (see diagrams further down)
    • The main cylinder or tube is made only from carbon hexagons (essentially graphite layers curved into a 'molecular pipe').
    • However pentagons are needed to close the structure at the ends or form spherical or rugby football shaped molecules.
    • The nanotube molecule is held together by strong covalent carbon-carbon bonds which extends all along the nanotube or all round the smaller 'bucky ball' molecules as they are sometimes called.
    • Single or multiple-walled tubes, made from concentric nanotubes (i.e. one tube inside a larger nanotube), can be formed.
    • Note that graphite is soft and malleable.
    • The behaviour of electrons depends on the length of the tube, so some forms are excellent conductors and others
      are semiconductors. This is a typical nanoscale (quantum) effect, i.e. there are major differences between the properties of the bulk material the size-dependent properties on the nanoscale (silver is another good example).
• Diagrams of the molecular structure of buckminster fullerenes ('fullerenes') and nanotubes (graphite shown for comparison)

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

• Some further discussion on molecular structure

• One possible skeletal formula representation of a layer of graphite or a molecule of graphene (graphene described in next section) is shown above in Kekule style as in aromatic compounds.

  • The C-C bond length in graphite or graphene is 0.142 nm, midway between a single C-C carbon-carbon bond length of 0.154 nm and a double C=C carbon-carbon bond of 0.134 nm.

  • The carbon-carbon bond order in graphite/graphene is 1.33, which follows from 4 valency electrons overlapping from each carbon atom BUT each carbon atom forms three C-C bonds.

    • The bond order is 1.5 in benzene, the average of a carbon-carbon single bond (bond order 1) and carbon=carbon double bond (bond order 2), but there is a C-H bond too.

  • The C-C-C bond angle is exactly 120^o, what you would expect for the planar carbon hexagons.

  • In graphite the planar hexagonal ring layers of carbon atoms are 0.335 nm apart.

• How you get the curvature in the molecular shape of fullerenes and the ends of nanotubes. The C-C-C bond angles for a planar carbon pentagon will be ~108^o and for a planar carbon hexagon ~120^o.

• Note the analogous structure of carbon nanotubes and graphite layers or the graphene molecule.

  • Nanotubes are essentially a single layer of graphite (or a molecule of graphene) wrapped around to form an elongated tube-like molecule.

• An example of the versatility of carbon nanotubes based on two possible fabrications, giving subtle differences in molecular structure and properties is described below.

  • The two diagrams below illustrate a short section of long carbon nanotubes displaying the two principal symmetries of hexagonal carbon ring orientation with respect to the central axis of a carbon nanotube.

    • These two types of single walled nanotubes can be made by folding graphenes/graphite sheets in different directions (but at 90^o with respect to each form).

• etc. and etc.

  • In A the longest axis of the carbon hexagons is aligned at 90^o to the principal axis of the carbon nanotube.

    • A is sometimes referred to as the 'armchair' form and is electrically semiconducting and can be used as a semi-conductor transistor in microelectronic circuits.

  • In B the longest axis of the carbon hexagons is aligned in the same direction as the principal axis of the carbon nanotube.

    • B is sometimes called the zig-zag form and has metal like electrical conductivity and can be used in micro-circuitry i.e. the tiniest possible? electrical circuit dimensions.

• -

See also Covalent Bonding - macromolecules and giant covalent structures including diamond & graphite

WHERE NEXT?

INDEX NANOSCIENCE-NANOCHEMISTRY pages

Part 1. General introduction to nanoscience and commonly used terms explained

Part 2. NANOCHEMISTRY - an introduction and potential applications

Part 3. Uses of Nanoparticles of titanium(IV) oxide, fat and silver

Part 4. From fullerenes & bucky balls to carbon nanotubes

Part 5. Graphene and Fluorographene

Part 6. Cubic and hexagonal boron nitride BN

Part 7. Problems, issues and implications associated with using nanomaterials

see also INDEX SMART MATERIALS PAGES

Keywords: uses applications  bucky balls * carbon nanotubes * nanochemistry * nanomaterials * nanoparticles * nanoscale * nanoscience * carbon  nanotubes * Revising for KS4 Science IGCSE/O level/GCSE Chemistry Information Study Notes for revising for AQA GCSE Science, Edexcel 360Science/IGCSE Chemistry & OCR 21stC Science, OCR Gateway Science, CCEA/CEA GCSE science, WJEC science  (revise courses equal to US grades 9-10) Aid notes for GCE Advanced Subsidiary Level AS Advanced Level A2 IB Revise AQA OCR Edexcel Salters CIE, CCEA/CEA & WJEC advanced level courses for pre-university students (equal to US grade 11 and grade 12 and Honours/honors level courses)

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