Spectroscopic Studies of Oxidized Soots

Abstract

Vibrational spectroscopy, ESCA, and C-13 CP/MAS NMR provide a detailed picture of the structure, and therefore reactivity, of the products of the reactions of soot with various oxidants. Reactions such as soot-NO2/N2O4, soot-O3, and soot-SO2, at atmospheric and sub-atmospheric pressures, and at different temperatures, have been studied. The reaction between NO2/N2O4 and n-hexane soot is rapid near room temperature, yielding several surface species, including C-NO2, C-ONO, and C-N-NO2. These functionalities have been confirmed through reaction with 15NO2 and N−18O2. The oxidation of SO2 in soot-SO2 systems yields ionic sulfate, confirmed by isotopic substitution, and requires the presence of water vapor and oxygen. The presence of simulated solar radiation in the same system results in the formation of both ionic and covalent sulfate species. The spectroscopic measurements show carboxyl surface species formed during the soot-ozone reaction. The use of FT-IR, ESCA, and C-13 CP/MAS NMR has yielded consistent results for these carbonaceous particulates in each reaction, but the vibrational spectroscopy is easily the most definitive with such systems.