Water adsorption on oxidized single atomic vacancies present at the surface of small carbonaceous nanoparticles modeling soot.

Quantum calculations are used to study the interaction of water molecules with carbonaceous clusters containing one single carbon atom vacancy. This is a simple but realistic way to model the active surfaces found in soot emitted by aircrafts. Prior to water adsorption, the atomic vacancy is oxidised by an approaching oxygen molecule, which is also likely to occur behind planes. The results of the calculations show that this oxidation process results in the formation of one ketone-like site and one epoxide-like site around the atomic vacancy. These sites may act as nucleation centers for water molecules, which are, however, physisorbed on the oxidized surface, leading to very weak charge transfer with the surface. Although less attractive for water than, for instance, a carboxyl-like site, the ketone-like site can also participate in the hydrophilic behavior of soot primary particles. In contrast, the epoxide-like site formed around the vacancy shows a very low affinity for water molecules.