Aromatic structure of carbonaceous materials and soot inferred by spectroscopic analysis

UV-visible spectroscopy provides an extremely powerful methodology to investigate molecular structures of high molecular weight aromatic materials, not amenable to be characterized by analytical techniques as gas-chromatography, mass spectrometry, etc. However, the interpretation of UV-visible spectroscopic data relative to complex mixtures is extremely difficult and, when the technique is applied to solid samples, could lead to questionable results. In this work a very polar and powerful solvent as N-methyl-pirrolidinone (NMP) was utilized to dissolve and/or to get stable suspensions of soot and carbon-rich solid materials, allowing their analysis by means of UV-visible absorption spectroscopy. This technique was preliminarily applied to commercially carbon-rich aromatic compounds as pure polycyclic aromatic hydrocarbons, aromatic oils, polyacenaphthylene, naphthalene pitch, carbon soot, carbon nanotubes, carbon black. The spectroscopic data were compared with those relative to fuel oil asphaltenes and combustion products as soot and condensed species collected in a fuel-rich ethylene flame. Meaningful information about the aromatic moieties of these materials was deduced from UV-visible absorption analysis and evidence on the aromatization process involved in the mechanism of soot inception and growth were obtained.