Role of oxygenated surface functional groups on the reactivity of soot particles: An experimental study

The oxidative reactivity of soot particles depends on several factors such as the elemental composition, the ratio of aliphatic to aromatic carbons, the curvature of graphene layers in soot, and the graphitic or amorphous character of soot. While several studies have highlighted the high reactivity of soot due to the presence of oxygenated groups on it, some studies conclude that the presence of oxygenated groups on soot may not affect its reactivity. In this work, to be able to exclusively study the effect of oxygenated functional groups on soot and its reactivity, a model compound, graphite, is first partially oxidized through a simplified Torr method using KMnO₄ as an oxidizing agent to introduce oxygenated groups on it. The concentration of oxidizing agent is controlled to ensure the formation of partially-oxidized-graphite-oxides (POGO) without any significant changes in the structural characteristics so as to determine only the effect of oxygenated groups on oxidation. The POGO materials are then characterized using various techniques such as XRD for crystallite size, FTIR and EDX for oxygenated functional groups, SEM for surface morphological changes, and TGA for their weight-loss profiles during combustion in air. The results indicate a reduction in the activation energy for oxidation with the addition of oxygenated groups on the model soots (POGO), though, after the loss of such groups during oxidation, the activation energies of all the models were close to each other. This indicates that oxygenated groups on soot surface may enhance soot reactivity at low conversion level, but may not have a long-lasting effect on soot oxidation to affect its overall reactivity.