Photocatalytic discoloration of methyl orange dye by δ-Bi2O3 thin films

Cubic delta bismuth oxide (δ-Bi2O3) thin films were deposited on glass substrates using magnetron sputtering onto Corning glass slides with different roughness. The efficiency of the Bi2O3 films as a photocatalytic semiconductor for the discoloration of dyes was tested by using methyl orange (MO) solutions as the probe under UV, sunlight and white light. Moreover, the effect of the substrate roughness, as a parameter to enhance the active surface area, was also evaluated. The results indicated that similar discoloration percentages (98% in 180 min) were obtained for the three illumination ranges for surfaces with average roughness below 1.5 μm. The discoloration reaction rate was significantly higher when the UV light was used in comparison to visible and sunlight. In order to appreciate the significance of these results, the photodiscoloration efficiency of the optimized δ-Bi2O3 films was compared to TiO2 films deposited by magnetron sputtering and TiO2-P25 Degussa particles. The outcomes showed better color removal of the dye when using the rough Bi2O3 thin films in comparison to both TiO2 materials, suggesting that δ-Bi2O3 films are a rather promising photocatalytic material. Moreover, the photoinduced wettability change of the films was measured showing that δ-Bi2O3 films present a photoinduced hydrophilicity, similarly to TiO2