Carbon Allotropes And Its Nanostructures Carbon is the building block of organic matter, and can be found in different forms.

Carbon is around us and in us Carbon, C, 6th Element in Periodic Table Main Isotope of Carbon has 6 Protons, 6 Electrons, 6 Neutrons. Makes up 20% of our bodies Important Building block (atom) of Nano Structures

Carbon has multiple bonding capabilities Carbon can have single bonds (Sp), double bonds (Sp2) and triple bonds (Sp3) Sp1 Sp2 Sp3

Carbon Nano Structures are made of many Sp2 bonds Different than Sigma bonds (Sp3)-Single Bonds (as in CH4) Pi bonds (Sp2)-Double Bonds Trigonal Planar Geometry

Allotropes of Carbon An allotrope is a variant of a substance consisting of only one type of atom. Diamond graphite (many layers of graphene) Fullerenes (buckyballs) Carbon Nanotubes (CNTs)

Closer Look at some of the Allotropes of Carbon

Diamond Diamond has a three-dimensional network structure in which each carbon is singly-bonded to four others with sp3 hybridization. Diamond is a covalent network solid each carbon covalently bonded to 4 others. Diamonds are the hardest substance known. 2

Graphene Graphene is a form of carbon. Not only the thinnest ever but also the strongest. As a conductor of electricity it performs as well as copper. As a conductor of heat it outperforms all other known materials. It is almost completely transparent, yet so dense

Graphite Graphite has a layered structure, in which the carbon atoms in each layer bond to three other carbons with sp2 orbitals. 2

Carbon Nanotubes (CNTs) Carbon nanotubes are formed by a layer of hexagonally-arranged carbon atoms rolled into a cylinder - usually have half buckyballs on one or both ends Electrons are localised internally, and some can move along the length of the tube by ballistic transport Carbon nanotube diameter ~ 1nm Carbon nanotube length can be a million times greater than its width Nanotubes can be - single-walled (d = 1-2 nm), or - multi-walled (d = 5-80 nm).

Fullerenes (Buckyballs) The fullerenes are a family of molecules with a closed cage of carbon atoms arranged in pentagons and hexagons. Each carbon is sp2 hybridized. 2

Structure Dictates  Function The Shape of the Molecules determine their strenght and and other physical properties The properties of the nano structures such as thermal and electrical conductivity depend on the flow of free electrons For instance the Sea of electrons causes most metals to act both as electrical and thermal conductors. However, some non-metallic materials are practical electrical conductors without being good thermal conductors.

Properties of Carbon Allotropes ++++++ + no +++++ Conducts electricity ++++ Buckyballs Carbon Nanotubes +++ Not known Diamond ++ Graphite Coal Conducts heat Tensile strength Hardness Allotrope NB buckyballs can be effective conductors if ‘doped’ with other elements. 13

Time Line of Discoveries "The trials of new carbon," Nature, January 5, 2011, pp. 14-16.

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