Synthesizing few-layer carbon materials from asphaltene by thermal treatment

Abstract

Few-layer carbon materials were synthesized from asphaltene by a top-down approach using a thermal treatment. Asphaltene was carbonized in a rotating quartz-tube furnace under inert atmosphere at a temperature range of 400–950 °C. The carbonization process converted asphaltene molecules into few-layer carbon materials by eliminating the alkyl side chains, exfoliating the aromatic layers (n), and expanding the aromatic sheet diameter (La). The elimination of the alkyl side chains was confirmed by the FTIR analysis; while the exfoliation of aromatic layers was verified by the XRD, Raman, and TEM analyses. The XRD, Raman, and TEM results also revealed an increase in the aromatic sheet diameter as the carbonization temperature increased, which would suggest secondary reactions in the aromatic core of asphaltene. The elemental analysis indicated insignificant changes in sulfur and nitrogen contents for all samples, indicative of the existence of these heteroatoms within the intact aromatic sheets. The density of defect in aromatic sheets was quantified by measuring the average distance between defects (LD), which showed an almost constant value (~13 Å). The consistent trends between the LD measurements and the sulfur and nitrogen contents would infer that the observed defects are mainly associated with the presence of heteroatoms in the aromatic layers.