UV- and Visible-Light Photocatalytic Activity of Simultaneously Deposited and Doped Ag/Ag(I)-TiO2 Photocatalyst

Ag modification has been demonstrated to be an efficient strategy to improve the photocatalytic performance of TiO2 photocatalysts. However, the previous studies about the Ag modification are only restricted to the surface loading of metallic Ag or Ag(I) doping, investigations have seldom been focused on the simultaneously deposited and doped Ag/Ag(I)-TiO2 photocatalyst. In this study, Ag/Ag(I)-TiO2 photocatalyst was prepared by a facile impregnated method in combination with a calcination process (450 °C) and the photocatalytic activity was evaluated by the photocatalytic decomposition of methyl orange and phenol solutions under both UV- and visible-light irradiation, respectively. It was found that Ag(I) doping resulted in the formation of an isolated energy level of Ag 4d in the band gap of TiO2. On the basis of band-structure analysis of Ag/Ag(I)-TiO2 photocatalyst, a possible photocatalytic mechanism was proposed to account for the different UV- and visible-light photocatalytic activities. Under visible-light irradiation, the isolated energy level of Ag 4d contributes to the visible-light absorption while the surface metallic Ag promotes the effective separation of the following photogenerated electrons and holes in the Ag/Ag(I)-TiO2 nanoparticles, resulting in a higher visible-light photocatalytic activity than the one-component Ag-modified TiO2 (such as Ag(I)-TiO2 and Ag/TiO2). Under UV-light irradiation, the doping energy level of Ag(I) ions in the band gap of TiO2 acts as the recombination center of photogenerated electrons and holes, leading to a lower photocatalytic performance of Ag-doped TiO2 (such as Ag/Ag(I)-TiO2 and Ag(I)-TiO2) than the corresponding undoped photocatalysts (such as Ag/TiO2 and TiO2). Considering the well controllable preparation of various Ag-modified TiO2 (such as TiO2, Ag/TiO2, Ag(I)-TiO2, and Ag/Ag(I)-TiO2), this work may provide some insight into the smart design of novel and high-efficiency photocatalytic materials.