DFT study of coadsorption of water and oxygen on galena (PbS) surface: An insight into the oxidation mechanism of galena

Graphical abstract: H₂O and O₂ molecules coadsorption on the PbS (100) surface. ΔE is the adsorption energy. - Highlights: • Single H₂O hardly interacts with the hydrophobic PbS surface. • The dissociation of both H₂O and O₂ molecules occur after coadsorption. • Coadsorption of H₂O and O₂ produces S=O^w radical and hydrogen peroxide. • Further adsorption of hydrogen peroxide on surface Pb atoms produces lead hydroxyl radicals. • Water molecule is involved in the oxidation of PbS surface. - Abstract: Oxidation of galena (PbS) is of crucial importance in environmental and geochemical processes. Hydrophobic nature of galena surface hinders the adsorption of water, which involves and determines the finally oxidative product of galena. In this work, DFT simulations of the adsorption of O₂ and H₂O on the hydrophobic galena surface have been performed. Results show that the isolated O₂ molecule is dissociated and adsorbed on the S atoms of galena surface, and the isolated H₂O molecule hardly interacts with the hydrophobic galena surface. However, the dissociation of both H₂O and O₂ molecules occur after coadsorption, and water molecule dissociates into O^w and H radicals, which then react with surface S atom and adsorbed O₂ molecule to form S=O^w radical and hydrogen peroxide, respectively. Further adsorption of hydrogen peroxide on surface Pb atoms produces lead hydroxyl radicals. This work could provide microscopic insight into the mechanism of galena oxidation.