Fullerene Synthesis by Alteration of Coal and Shale by Simulated Lightning

A graptolitic shale, a metamorphosed black schist and a bituminous coal with different organic carbon content but without detectable amounts of fullerenes were subjected to high-energy electric impulses of current amplitudes comparable to those of natural lightning strikes that could lead to the formation of fulgurites. The search for fullerenes concentrated on rock surfaces altered during the impulse experiment using Fourier transform infrared spectroscopy (FTIR). Toluene-extractable materials from the altered zones were investigated by high-performance liquid chromatography (HPLC) and electron-impact ionization mass spectroscopy (EIMS). Powders from altered surfaces were also analyzed by laser desorption time-of-flight mass spectroscopy. Two of four characteristic C₆₀ FTIR peaks were only observed in one piece of black schist. As no C60 fullerene was detected by HPLC and EIMS in this modified sample, we find no evidence that electric impulse-induced fullerenes were present in any samples. We discuss how the physicochemical conditions in our lightning-strike simulation experiments could have contributed to failure to produce fullerenes in rocks that are rich in organic carbon. Our results underscore the apparent paucity of natural fullerenes induced by lightning strikes.