Characteristics of carbon nanoparticles synthesized by a submerged arc in alcohols, alkanes, and aromatics.

Fullerene-related carbon nanostructures can be synthesized by an arc-in-liquid system as a cost-effective technique. In this work, we investigated the effects of additional carbon sources from liquid media that were alcohols (C(m)H(2m+1)OH, m = 1-8), alkanes (C(m)H(2m+2), m = 6-7), and aromatic compounds (C6H6-C(n)H(2n), n = 1-2) on the product structures and the yield of nanocarbon-rich deposits. It was found that carbon nanoparticles (CNPs) that included multi-walled carbon nanotubes (MW-CNTs) and multi-shelled carbon nanoparticles were produced at high concentrations in the hard deposit at the cathode tip formed by the arc in the alcohols and alkanes, similar to that in a water environment. Importantly, not only graphite electrodes but also these organic compounds played a role of a carbon source to produce CNPs that led to an approximately 8-100 times higher yield than the arc-in-water system. There was a tendency that the increase in alcohol concentration and carbon content in the organic molecules positively affected the yield and production rate of the CNPs. However, the selectivity of MW-CNTs was significantly reduced when aromatic compounds were used. Structural analyses by dynamic light scattering and Raman spectroscopy revealed the dependency of the hydrodynamic particle sizes of CNPs and their crystallinity on the liquid components. For a discussion on the reaction mechanism, optical emission spectra of the arc plasma were analyzed to estimate the arc temperature. In addition, liquid byproducts were analyzed by a UV-vis absorbance spectrometer.