Isotope fractionation in the synthesis of fullerenes

Abstract

The synthesis of fullerenes by the direct current (DC) carbon arc evaporation method produces a number of different carbon materials. This investigation has involved the structural characterisation of the materials and the study of their isotopic composition. The cathode deposit was a highly ordered graphite with the basal planes oriented in the axial direction of the graphite rod. Raman microprobe spectroscopy, X-ray powder diffraction, and temperature programmed combustion measurements also showed that the material was heterogeneous. The structural characterisation results were consistent with the deposit being formed at progressively lower heat-treatment temperatures with increasing deposition. The fullerene soot was a very heterogeneous material with a large surface area. Isotope composition studies showed that the raw fullerene soot, fullerene depleted soot (toluene extract), C 60, and C 70 were enriched in 13C relative to the graphite anode, whereas the cathode deposit was depleted in 13C. The measurements show that C 60 is richer in 13C compared with both C 70 and the toluene-extracted soot. The implications regarding the mechanisms for the formation of fullerenes are discussed.