The gram-scale synthesis of carbon onions

The combustion of naphthalene has been found to yield gram-scale quantities of carbon onions that are free of impurities and furthermore without the use of catalysts. X-ray diffraction (XRD) indicates that the interlayer spacing between concentric shells of the carbon onions is not uniform across the particle; rather it decreases from a graphite-like 0.34 nm and approaches a diamond-like 0.29 nm interlayer spacing towards the inner layers. The dispersion in the interlayer spacing is believed to result from differing external pressures exerted on the individual nanometer-sized graphitic membranes during formation of the onions. Electron microscopy techniques such as high-resolution transmission electron microscopy (HRTEM) and scanning electron microscopy demonstrate the extensive formation of carbon onions. The HRTEM indicates that the onions consist of 50–54 shells, found to be in good agreement with the XRD data.