Paper TF-WeE9
Synthesis and Characterization of TiO₂ and Bi₂O₃ Thin Films for Photocatalytic Applications

Wednesday, December 10, 2014, 8:20 pm, Room Makai

The magnetron sputtering technique was used to obtain bismuth oxide (Bi₂O₃) and titania (TiO₂) thin films. The films were characterized using X-ray diffraction (XRD), scanning electron microscopy (SEM), X-ray Photoelectron Spectroscopy (XPS) and contact angle measurements. The results indicated that the Bi₂O₃ thin films presented the cubic delta phase and the TiO₂ thin films showed a combination of rutile-anatase. The photocatalytic activity for both films was evaluated testing the degradation of methyl orange dye (C₁₄H₄N₃SO₃Na) under ultraviolet light and a solution of pH 3.5. The dye degradation and the kinetic of the reaction were estimated using the variation of the corresponding absorption band as a function of the irradiation time. The results pointed out that the photocatalytic activity was always larger for Bi₂O₃ films than for TiO₂ films. Moreover the activity was also larger for Bi₂O₃ in comparison to equivalent mass-amounts of TiO₂ powders (P25) under the same experimental conditions. However XPS tests showed that after a degradation cycle bismuth oxide transforms to Bismuth Oxychloride (BiOCl) due to the interaction with Cl ions from the HCl solution used to decrease the pH, and as a consequence the photocatalytic effect was reduced. After calculating and comparing the reaction kinetic constants for both oxide films, it is concluded that under UV light, the Bi₂O₃ reaction rate is three-fold larger than TiO₂ reaction rate constant. These results suggest that the Bi₂O₃ films are a new promising photocatalytic material for water treatment application. Moreover, studies of photoinduced changes in the wettability demonstrated a similar behavior between Bi₂O₃ and TiO₂ thin films.