Investigating the Optical and Structural Properties of MiniCAST soot via UV-Vis-NIR Absorption Spectroscopy and Online Raman Spectroscopy

Sammanfattning

Soot, formed during incomplete combustion of hydrocarbons, is a challenging compound to study. It affects air quality, climate, and human health. Its structural and optical properties are not fully understood due to variations in particle size, structure, chemical composition, and degree of carbon hybridization. In this work, soot was generated using a MiniCAST 5201C soot generator, which produces various types of soot aerosols with different maturity levels. of varying maturity. Samples were collected at five operational points (OP1, OP3, OP5, OP6, and OP7), corresponding to decreasing soot maturity. UV–Vis–NIR absorption spectroscopy was employed to characterise optical properties, and both in flight and ex situ techniques were compared. Online Raman spectroscopy was also performed in a 90◦ scattering configuration with a horizontally polarised laser to suppress interfering ambient signals. The data, collected previously, was analysed in this study. From the absorption spectra, the optical band gap, an important parameter, was estimated using the Tauc approach. Tauc analysis revealed an increase in optical band gap from mature to immature soot. Systematic changes in Raman spectral features such as the increase of peak width and decrease of peak intensity ratio were observed with decreasing maturity, indicating variations in graphitic ordering and defect content. These findings show that combining absorption spectroscopy and Raman spectroscopy provides a comprehensive approach for probing the optical properties and nanostructure of soot across different maturity