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

The adsorption of O-2 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 O-2 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 O-2. The results show that the adsorption energy of O-2 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 O-2 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 pi(2p)* 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. (C) 2010 Elsevier B.V. All rights reserved.