GENERATION OF HIGHER FULLERENES IN FLAMES

The presence of fullerenes up to C-116 was observed in condensable mat erial from a benzene/oxygen flame. The flame material was Soxhlet-extr acted with toluene for 363 h, fractionationed by means of a silica-bas ed semipreparative HPLC column, and analyzed by HPLC coupled to a mass spectrometer via a heated nebulizer interface using a 2-(1-pyrenyl)et hylsilica stationary phase. UV-vis spectra were measured for C-60, C60 O, C-60. CH4, C-70, C70O, C-76, C-78, C-80, C-84, a C-84 adduct, C-86, C-88, C-90, C-92, C-94, C-96, C-98, C-1OO, C-102, and C-108. Isomers could be discerned for C-78, C-90, and C-94. A calibration using exter nal standards was performed for C-60, C-70, C-76, C-78, and C-84. For all other species the relative abundances were estimated based on HPLC peak integration results. Electric are soot was extracted under simil ar conditions and the quantification of fullerenes compared to the dat a obtained with flame-generated condensable material. Except for C-60 and C-76, the abundances were significantly higher in the case of flam e-generated condensable material. Also, striking differences between t he two fullerene production methods are seen in the relative abundance s of C-78 isomers. Considering the present results and the ease with w hich the experimental setup could be scaled up, flame-generated conden sable material represents an excellent starting material for the prepa rative isolation of higher fullerenes.