Raman spectroscopy for characterization of soot and other carbonaceous materials

Abstract: Raman spectroscopy is well known as a method that can be used to study the structural characteristics of carbon materials such as soot and carbon black. In this work, a Raman spectroscopy setup was used to record spectra of various carbonaceous samples under different experimental conditions. The wave-number range of interest was from 900 to 3300 cm-1, which includes the first and second order Raman peaks of carbonaceous materials. In addition to the Raman spectral features a fluorescence background was observed, which could be related to organic compounds including polycyclic aromatic hydrocarbons. The recorded spectra were analyzed using different deconvolution protocols to identify contributions from various spectral features relating to soot nanostructure. These deconvolution protocols were compared in terms of goodness-of-fit parameters. Furthermore, the influence of the laser radiation on spectral features was studied. Thus, the intensity variation of Raman and fluorescence signal were measured as function of laser power and exposure time, and the depolarization ratio for the primary peaks were estimated. The effects of heating the soot were studied from room temperature to 800 C in air to obtain information regarding soot oxidation. The study has shown that Raman spectroscopy is a useful technique for structural characterization of soot and carbon black via their vibrational modes. Also, it was shown that care must be taken in experimental planning since parameters such as laser intensity and ambient conditions may influence the resulting data.