Co-sputtered boron-doped titanium dioxide films as photocatalysts

• B-TiO2 films by co-sputtering of Ti and TiB2 in a plasma of Ar and O2 gases.
• Three B species — [BO3], [Ti2BO2] and B2O3, identified in the B-TiO2 films.
• [BO3] and [Ti2BO2] red-shift absorption and promote visible-light activity.
• Nano-porous B-TiO2 films by annealing and evaporation of B2O3 component.
• Nano-porous B-TiO2 films with residual B2O3 improve the UV light activity.

Boron-doped titanium dioxide (B-TiO2) films were deposited by reactive magnetron co-sputtering from metallic titanium (Ti) and titanium diboride (TiB2) targets in Ar/O2 plasma. The films were characterized by X-ray diffraction (XRD), Scanning electron microscopy (SEM), X-ray photoelectron spectroscopy (XPS), and Ultraviolet–visible (UV–vis) spectroscopy. The photocatalytic activities of the samples were evaluated for degradation of methylene blue (MB) under UV and visible light irradiation. By changing the TiB2 target power, various boron amount and species are formed in the as-deposited and the annealed films. Therein, the [BO3] as well as [Ti2BO2] species would redshift the UV–visible absorption edge and improve the visible light activity of TiO2. Most of the B-species could be oxidized into B2O3 phase and evaporated in the annealed films. This introduced porosity into the films and apparently promoted the UV-light photocatalytic activity. The remaining B2O3 phase itself has no direct effect on the photocatalytic activities, but in couple with TiO2 they can reduce the recombination rate of the photogenerated carriers, and hence improve the photocatalytic activities of the annealed B-TiO2 films.