Allotropes of Carbon – Fullerene

Carbon is an element with many allotropes, which means it has a similar chemical structure but different physical forms. The allotropes exist in two or more forms with distinct physical qualities but the same chemical properties. Fullerene is a crystalline allotropic form of carbon and is unadulterated. They lack dazzling edges or surface bonds which tend to attract atoms. R.E Smalley and R.F Curl collectively discovered it in 1985 and, for the discovery, won the Nobel Prize in 1996. One of the prominent fullerenes uses the development of carbon nanotubes. The article has all the necessary information you need to know about fullerene.

Structure of Fullerene

• The basic fullerene structure is a large spherical molecule C60 and is highly symmetrical. It is produced by heating graphite in an electric arc in an inert gas like argon or helium. This leads to the formation of a sooty material due to the condensation of small molecules.
• The sooty material formed consists of C60 with small quantities of C70 and other molecular traces. The C60 fullerene structure is known as buckminsterfullerene.
• It is easy to separate the fullerene from the soot by extraction with toluene or benzene followed by the chromatography process.
• The buckminsterfullerene has the shape of a saucer ball with 60 vertices and a carbon atom located at each vertex. It consists of 20 rings with six members and 12 rings with five members.

Properties of Fullerene 

• Fullerenes show variation in terms of behaviour and structure on temperature change. It is found that the structure fluctuates at high temperatures and hence converts to C70 form.
• Fullerenes are soluble in a range of organic solvents like toluene, chlorobenzene etc. It is easy to dissolve in many common solvents at room temperature.
• The structure of fullerene changes under different pressure has an ionisation enthalpy of 7.61 electron volts and electron affinity of 2.6 to 2.8 electron volts.
• It is a stable allotrope of carbon and is not reactive. It acts as an oxidising agent as it consists of an electron-accepting group.
• It has high superconductivity properties when crystallised with alkali or alkaline earth metals.
• Some fullerenes have inherent chirality due to the presence of D2 – symmetric. 

Different forms of fullerene 

• Buckyball clusters are completely closed fullerenes with an empirical formula of C60. It is the smallest of all the types, with pentagonal and hexagonal rings without two pentagons sharing an edge. It is naturally occurring.
• Carbon nanotubes are cylindrical, and the tubes range from less than a micrometre to several millimetres in length. These mostly have closed ends. It has macroscopic properties with high tensile strength electrical and heat conductivity, is highly ductile and has relative chemical inactivity.
• Carbon Mega tubes have diameters larger than nanotubes and have a variable wall thickness range. It helps transport various types of molecules in a range of different sizes.
• Hetero fullerenes and non-carbon fullerenes are synthetically developed where other elements replace some or all carbon atoms. Elements like boron, molybdenum etc., replace it. In the heterofullerenes, the carbon in the cage or tube structure is replaced by heteroatoms. In metallofullerene, a metal atom is trapped inside a fullerene cage.

Production of Fullerenes 

Fullerene-rich soot is used to produce fullerene, which involves sending a large electric current between two nearby graphite electrodes in the presence of an inert atmosphere. The sooty residue is produced by vaporising the carbon into plasma with the help of an electric arc. Combustion is an effective process that helps in fullerene production. The pyrolysis of aromatic hydrocarbons is another method for the production of soot. After production of the soot residue, fullerene is extracted with the help of organic solvent and separated with the help of chromatography.

Uses and applications of fullerenes 

There are various applications and fullerene uses, predominately used in the nanotechnology domain.

• Used in tumour research – It is extensively used in tumour research. HeLa cells are known to develop new photosensitisers with their increased ability to absorb cancer cells and trigger cell death. The aim is to prevent unwanted cell death. Functional fullerenes are absorbed by HeLa cells. Once cancer cells are absorbed, the C60 derivatives convert molecular oxygen into reactive oxygen that triggers apoptosis in HeLa cells and other cancer cells, minimising damage to surrounding tissues while undergoing treatment.
• It is used in medical technology as a light-activated antimicrobial agent. It is used across multiple biomedical applications like X-ray imaging contrast agents, photodynamic therapy, and drug and gene delivery. Buckminsterfullerene is largely used in drug delivery systems.
• Fullerene is used as a conductor of electricity, and it is a good absorbent for gases. 
• A dominant fullerene use is the making of carbon nanotubes based fabrics and fibres.

Conclusion

Fullerene is one of the naturally occurring and purest forms of carbon allotrope. Although it is of varying chemical composition, the most common one is called buckminsterfullerene with an empirical formula of C60. It is a crystalline allotrope of carbon with good heat and electricity conductor properties. Fullerene uses are predominant in the medical field, and its use in tumour research has helped bring several breakthroughs. The topics include all the information about fullerene, its structure, properties, and uses for comprehensive understanding.