Degradation of Cd-yellow Paints: ab initio study of the adsorption of oxygen and water on {10.0} CdS surface

The cadmium yellow paints (CdS) used in impressionist and modernist paintings in early 1900s are undergoing several deterioration processes, including whitening and discoloration. A relevant effect produced at the surface of the paintings is the growth of discolored crusts, formed mainly by white globular hydrated cadmium sulfate (CdSO4*nH(2)O) and cadmium carbonate (CdCO3). Recent studies ascribe to an initial photo-oxidation process of CdS the input for the formation of such whitish compounds. In order to understand, at atomic level, the oxidation and hydration mechanisms of these whitish globules, we present the early stages of a theoretical study of the interaction between the hexagonal {10.0} surface of CdS and O-2 and H2O molecules to simulate the combined effects of exposure to air and humidity. For this purpose, we adopted a first principles method within the framework of the Density Functional Theory (DFT) in the Generalized Gradient Approximation (GGA-PBE) with the use of ultrasoft pseudopotentials.