Selective and high-yield synthesis of higher fullerenes

Fullerenes have been prepared by de are synthesis with graphite (anode) rods containing light elements such as B, Si, or Al in a series of concentrations. Furthermore, the influence of mixing N-2(g) with He(g) on the yield of higher fullerenes has been addressed, For each type of experiment, the relative fullerene yields are obtained from the relative peak areas in surface analysis by laser ionization-mass spectrometry (SALI-MS) spectra and the absolute yield of C-60 and C-70 from calibrated HPLC; the relative yields in SALI-MS represent closely the nascent distribution in the primary soots. We determine the approximate absolute yields of higher fullerenes, for which extinction coefficients are not yet available for HPLC analysis, by scaling the absolute C-60 and C-70 yields with the relative concentrations from SALI-MS. The most prominent increased higher fullerene yield was obtained with a 1% B-doped graphite rod with a 2:100 volume mixture of Nz(g):He(g); the absolute yield of C-60 was reduced from 8.85% to 2.75%, and the yield of higher fullerenes such as C-78 and C-84 was increased by a factor of 2 over the pure C, pure He(g) case. We conclude that using a B-doped graphite rod and mixing in small amounts of Nz(g) into He(g) enhances both the absolute and relative yields of higher fullerenes.