A first-principle study of the effect of vacancy defects and impurities on the adsorption of O2 on sphalerite surfaces

The adsorption of O2 on a sphalerite surface with vacancies and impurities is investigated through first-principle calculations based on density functional theory (DFT). The calculated results show that O2 adsorption is unavailable on perfect sphalerite surfaces, while the presence of vacancies (e.g., Zn-vacancy and S-vacancy) and impurity atoms (such as Fe, Mn, Cu and Cd) energetically favors the adsorption of O2.The results show that the adsorption energy of O2 on a S-vacancy surface is −408.25 kJ/mol, which is stronger than that of a Zn-vacancy surface at −218.55 kJ/mol. For a Zn-vacancy surface, the O 2p orbital interacts strongly with the S 3p orbital, and electrons transfer from the S atom to the O atom, which results in the oxidation of S. For the S-vacancy, the O 2p orbital interacts strongly with the Zn 3d orbital, and electrons transfer from the Zn atom to the O atom, which results in the oxidation of Zn.The adsorption energies of O2 on the sphalerite surface with Fe, Mn, Cu and Cd impurities are −181.40 kJ/mol, −146.66 kJ/mol, −95.53 kJ/mol and −55.96 kJ/mol, respectively, which indicates that Fe-bearing sphalerite is easily oxidized, while Cd-bearing sphalerite is not easily oxidized. The oxygen molecule dissociates on Fe-, Mn- and Cd-bearing sphalerite surfaces, while oxygen does not dissociate on the Cu-bearing surface. The 3p orbital of S and the 3d   orbital of Fe, Mn and Cu atoms donate electrons to the antibonding orbital π2p∗ of the O atom, which enhances the bonding of oxygen with the sphalerite surface. However, the 4d orbital of the Cd atom donates fewer electrons, which weakens the bonding of oxygen with the surface.