The structure of fullerene black and the incorporation of C 60 investigated by 13C NMR

Abstract

13C NMR measurements were performed on different fullerene black materials in order to gain knowledge about the fullerene black structure, the incorporation of C 60 molecules in the fullerene black, the generation process of the fullerenes in the arc reactor, the influence of solvents and the amount of fullerenes not removable by solvents. Our results are consistent with the model that fullerene black is an amorphous carbon material containing a high amount of bent and spheroidal carbon fragments. The C 60 molecules are dispersed on the large fullerene black surface and rotate rapidly. A weak signal in the fullerene black at about 70 ppm could arise from polyynic carbon chains, one of the discussed intermediate compounds in the fullerene generation process. X-ray diffractometry shows that the treatment of the fullerene black raw material with tetrahydrofuran (THF) leads to structural relaxation and a rearrangement of carbon sheets. 13C NMR is rather insensitive to this modified texture of the fullerene black matrix indicating that the local carbon structure remains largely unchanged by solvent treatments. In the extracted fullerene black materials we did not find fullerene signals proving that the amount of possibly entrapped fullerenes is very small and that the conventional fullerene extraction with toluene can be regarded as complete.