Advanced characterization of soot precursors via excitation emission matrices fluorescence spectroscopy and molecular modeling

• Published in: Carbon (New York) 2024-09, Vol.228, p.119355, Article 119355
• Main Authors: Elias, J., Labarrière, L., Faccinetto, A., Moncomble, A., Cornard, J.-P., Mercier, X.
• Format: Article
• Language: English
• Subjects: Chemical Physics; Chemical Sciences; DFT calculations; Engineering Sciences; Excitation-emission matrix; Laser induced fluorescence; or physical chemistry; Physics; Polycyclic aromatic hydrocarbons; Resonance-stabilized radicals; Soot inception; Theoretical and
• ISSN: 0008-6223
• DOI: 10.1016/j.carbon.2024.119355

Particulate emissions generated from combustion processes of hydrocarbon fuels (soot) have become a significant environmental issue with implications for both human health and climate change. However, soot particles also offer exciting possibilities in the field of carbonaceous nanomaterials which have found applications in optoelectronics, bioimaging, drug delivery, and photocatalysis. This study aims to investigate the species implicated in the initial steps of soot particle formation characterized by the transformation of gaseous precursors, like polycyclic aromatic hydrocarbons (PAHs), into soot particles in the condensed phase. While PAHs have been long known to be soot precursors, recent researches suggest that resonance-stabilized radical (RSR) aromatic compounds may play a substantial role in this process. To shed light on this process, we conducted a series of experiments in a laminar diffusion sooting flame in controlled laboratory conditions, notably by implementing the excitation-emission matrix (EEM) method to study the optical properties of soot precursors. This innovative approach provides critical insights into the involvement of various kinds of aromatic species during the early steps of soot formation. In parallel with the experimental work, theoretical calculations were carried out to determine the spectral features of PAHs, PAH dimers, and resonance-stabilized PAH radicals. These calculations support the interpretation of the fluorescence EEM and assist the identification of species at the origin of soot inception. These findings contribute to a deeper understanding of the interplay between PAHs and persistent radicals, particularly at the onset of soot formation within flames. [Display omitted] •Implementation of an innovative optical method to characterize soot precursors.•New insights into various aromatic species characterizing soot precursors in flames.•Bridging the gap between gaseous precursors and solid soot in the inception stage.•Theoretical calculations to interpret spectra and identify key species initiating soot formation.