Chapter 5 - Synthesis, Extraction, and Purification of Fullerenes

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This chapter describes the laboratory methods commonly used to synthesize, extract, and purify fullerenes. Fullerene molecules are formed in the laboratory from carbon-rich vapors which can be obtained in a variety of ways, e.g., resistive heating of carbon rods in a vacuum, ac or dc plasma discharge between carbon electrodes in He gas, laser ablation of carbon electrodes in He gas, and oxidative combustion of benzene/argon gas mixtures. Most methods for the production of large quantities of fullerenes simultaneously generate a mixture of stable fullerenes (C60, C70, …), impurity molecules such as polyaromatic hydrocarbons, and carbon-rich soot. Therefore, the synthesis of fullerenes must be followed by procedures to extract and separate fullerenes from these impurities according to mass, and for the higher fullerenes, separation according to specific isomeric forms may also be required. Fullerenes can be synthesized in the laboratory in a wide variety of ways, all involving the generation of a carbon-rich vapor or plasma. All current methods of fullerene synthesis produce primarily C60 and C70, and these molecules are now routinely isolated in gram quantities and are commercially available. Higher-mass fullerenes and endohedral complexes can also be made and isolated, albeit in substantially reduced amounts. At present the most efficient method of producing fullerenes involves an electric discharge between graphite electrodes in ∼200 torr of He gas. Fullerenes are embedded in the emitted carbon soot and must then be extracted and subsequently purified. A variation of the arc technique is used to synthesize graphene tubules. However, it appears that it will be difficult to extend the chemical methods now used to isolate particular fullerene isomers to separate the carbon tubules according to diameter and chiral angle.