Structure of carbon onions and nanotubes formed by arc in liquids

Since carbon nanotubes and onions were discovered, many methods have been proposed for their production. For applications the main requirements are low capital cost, high purity of the produced material, simplicity of technique, and its potential for scale up. Recently a cathodic arc between two graphitic electrodes immersed in liquids has been demonstrated to be a simple method to produce carbon nanoparticles such as nanotubes and onions. In this paper high-resolution transmission electron microscopy is employed to examine the shape of the nanoparticles and the purity of the final material produced under various conditions. In this study we have used an arc discharge in two different liquids--liquid nitrogen and distilled water--and we have changed the grade of the carbon electrodes. The variety in structure, shape, and size of the produced particles is discussed in line with a model proposed to describe the physical process.