Origin of the Optimization of Photocatalytic Activities for Titanium Oxide Film Modified by an Oxidized Copper Layer

In this study, the surface photocatalytic activity of an anatase-titanium oxide (TiO_x) film was modified by a thin copper (Cu) layer with the subsequential oxidation annealing process. Through this simple annealing process, the photocatalytic activity of the TiO_x/Cu structure to decompose the methylene blue solution and inhibit the growth of <i>Escherichia coli</i>. could be optimized. With the help of a study on the conductive type required for the oxidation of a single Cu layer, an <i>n/p</i> nanocomposite heterojunction was realized, as this contact system anneals at temperatures of 350 °C and 450 °C. An extra electrical field at the contact interfaces that was be beneficial for separating the photo-generated electron-hole pairs (EHPs) under UV light irradiation was built. The built-in electrical field led to an increase in the structural photocatalytic activity. Moreover, as the <i>p</i>-type cuprous oxide (<i>p</i>-Cu₂O) structure oxidized by the annealed Cu layer could provide a high conduction band that is offset when in contact with the TiO_x film, the photogenerated EHPs on the TiO_x surface could be separated more effectively. Accordingly, the 350 °C-annealed sample, abundant in the nanocomposite TiO_x/Cu₂O heterojunction which could significantly retard the recombination of photo-generated carriers, corresponded to an increase of about 38% in the photocatalytic activity as compared with the single TiO_x film.