Tuning electronic structure and photocatalytic properties by Ag incorporated on (001) surface of anatase TiO2

The incorporation of Ag on (0 0 1) surface of anatase TiO2 has been systematically investigated by means of density functional theory to understand the Ag effects on the electronic structure and photocatalytic properties in Ag/TiO2 composites. Several possible adsorptional, substitutional and interstitial sites with two different Ag concentrations at surface and subsurface layers are examined. Our results about stability of various Ag-incorporated (0 0 1) surfaces indicate that the adsorption site is favorable neglect of the oxygen conditions and the substitution site becomes more stable under the oxygen-rich condition, but it becomes difficult to incorporate Ag onto the surface with high concentration, especially for substitution sites in the limited range of oxygen chemical potential. The adsorption of Ag introduces gap states near or below the conduction band minimum (CBM) and the Fermi level locates near or in the conduction band, which can act as photo-generated electron trap centers and inhibit the recombination of electron-hole pairs. The electron transitions from the impurity level to the level above the Fermi level may be responsible for the small visible light absorption peak in experiment. Substitution Ag introduces some localized gap states, while the Fermi level is pinned near the top of valence band, and the impurity states can trap the hole to suppress the recombination of photo-generated carriers. For the interstitial Ag in surface, the Fermi level locates at the bottom of conduction band, and the partial occupied states may also act as electron trap centers which can improve the photocatalytic efficiency. (C) 2012 Elsevier B.V. All rights reserved.