Identification and spectral properties of PAHs in carbonaceous material produced by laser pyrolysis

Carbonaceous materials have been prepared by laser-induced pyrolysis of a mixture of hydrocarbons (C₂H₂, C₂H₄, and benzene) under different conditions. We have investigated the soluble and insoluble part of the condensed carbon powders with several techniques, such as UV/VIS and IR spectroscopy, mass spectroscopy, gas chromatography combined with mass and IR spectrometry and high-performance liquid chromatography (HPLC) in order to obtain information on the total content and composition of the extracted soluble part and on the influence of the soluble component on the spectroscopic properties of the condensed carbon nanopowder. It has been found that the extract contains more than 64 different polycyclic aromatic hydrocarbons (PAHs). The most abundant PAH molecules are those containing 3–5 rings. The total amount of aromatic soluble components depends on the temperature in the condensation zone whereas the ratio between high- and low-mass PAHs is influenced by both, the temperature and the precursor gases. IR spectroscopic investigations of the extract have shown partial hydrogenation of PAHs leading to the formation of CH₂ groups, at the edge of PAH molecules. The IR spectral properties of the carbonaceous materials and of the PAHs are influenced by the adsorption process.