4.4 - Graphene & Fullerenes

Graphene

• Graphene is a single layer of graphite, just one atom thick, making it a two-dimensional form of carbon.
• Within the layer, each carbon atom is joined to three neighbours by strong covalent bonds in a repeating pattern of hexagons.

Properties

• Very strong and light - Held together by strong covalent bonds throughout the sheet.
• Transparent - Being one atom thick allows light to pass straight through.
• Excellent conductor of electricity and heat - each carbon atom has one delocalised electron free to move across the whole sheet.

Uses

• Composite materials - Reinforces other materials to improve strength without adding much weight.
• Electronics - Its thinness and high conductivity make it valuable in miniature circuits.
• Batteries and solar cells - Used in batteries to make them lighter and faster to recharge, and in solar cells, where it lets light through and conducts electricity.

Fullerenes - Buckminsterfullerene and nanotubes

• Fullerenes are molecules of carbon atoms with hollow shapes - spherical cages or hollow tubes.
• Most rings are hexagons, but fullerenes also contain rings of five (pentagons) or seven carbon atoms that curve the sheet into closed structures.

Structure

• Unlike diamond and graphite, fullerenes are discrete molecules, not giant covalent structures.
• Strong covalent bonds hold the atoms together within each molecule, but only weak intermolecular forces hold separate molecules to one another.

Buckminsterfullerene (C₆₀)

• A hollow spherical molecule with the formula C₆₀, made of twenty hexagons and twelve pentagons.
• Slippery with a lower melting point than diamond or graphite, because only the weak intermolecular forces between molecules need to be overcome.
• Poor conductor of electricity because delocalised electrons cannot move between separate molecules.

Carbon nanotubes

• Cylindrical fullerenes with a very high length-to-diameter ratio.
• High tensile strength - They resist snapping when stretched because of their network of strong covalent bonds.
• Good conductors of electricity and heat, as delocalised electrons move freely along the tube.

Uses

• Drug delivery - Hollow spheres can cage drug molecules and deliver them to specific parts of the body.
• Lubricants - Spherical fullerenes roll easily between surfaces.
• Catalysts - A large surface area provides many sites for reactions.
• Reinforcing materials and electronics - Nanotubes' high tensile strength and conductivity make them ideal for high-tech composite materials and miniature circuits.