Air oxidation of carbon soot generated by laser ablation

Abstract

Carbon soot was generated by laser ablation under oxygen-free and regulated-temperature conditions at 300 K and 1500 K. The soot was significantly oxidised by being exposed to air in darkness. The degree of oxidation was determined to be 0.038±0.012 and 0.093±0.009 for the high temperature (HT) soot and the low temperature (LT) soot, respectively, on the basis of elemental analysis, XPS and Karl-Fischer titration. Water physically absorbs on the soot in proportion to the degree of oxidation. TG, TPD and 13C-NMR revealed that there were at least 2 kinds of oxidised states. One of them mainly contributes to CO and CO2 emissions at 420–970 K, while another contributes to CO emission above 770 K. The former is a dominant oxide in the LT soot. On the basis of FT-IR and 13C-NMR spectra, carbonyl groups were confirmed to be one of the major oxidised species in the soot. FT-IR and acid-base titration revealed that the LT soot adsorbed more CO2 than the HT soot did. The adsorbed CO2 contributes to the acidic property of the soot. The soot is paramagnetic as well as conductive. C1s and Auger photoelectron spectra of the soot were neither graphite-like nor diamond-like. The air oxidation is discussed in relation to unique structures and formation mechanisms of the soot.