Extraction of EMFs from Raw Soot

Sublimation is an efficient method to separate fullerene-related materials from other byproducts, such as carbon nanotubes and amorphous carbon [5]. This method can be scaled up easily and is solvent free, which is particularly suitable for industrial production. As discussed below, when sublimation is combined with other methods, some exciting results are obtained. 

It seems that chemists prefer solutions to solids. Solvent extraction is presently the most popular method for the isolation of EMFs from soot. Toluene, carbon disulfide, and xylene are popular solvents used to extract EMFs. The Soxhlet apparatus and ultrasonication technique [63] were applied to improve extraction efficiency. However, results show that nearly half of the EMFs remained in the extracted residue, which can be further processed using such solvents as pyridine and 1,2,4-trichlorobenzene (TCB). 

Extracts of different organic solvents normally contain the same soluble species empty fullerenes such as Ceo, C70, and Cs4 are dominant, whereas M Cs2 is always the most abundant EMF species and M2 Cso is normally the most abundant di-metallofullerene. Extraction of TNT cluster metallofullerenes is easier because of both the high production yield and the high solubility in common solvents. The general extraction process for TNT EMFs is the following the soot is first washed by acetone to eliminate hydrocarbon byproducts then the residue is subjected to solvent extraction with CS2 or xylene [68, 69]. 

3 Extraction of Insoluble EMFs by Reduction/Oxidation Methods 

Aniline was found to be effective to extract the Ceo-based EMFs, but some fullerene species other than M C6o can also be extracted because of complexation between aniline and the species [70], With the assistance of sublimation, semi-pure samples of Eu C6o and Dy C6o in aniline were obtained after high-performance liquid chromatography (HPLC) separation, and the electronic valences of Eu and Dy were determined, respectively, to be 4-2 and 4-3. 

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