Sputtered bismuth oxide thin films as a potential photocatalytic material

• Synthesis of Bi2O3 films by magnetron sputtering with different crystalline structures.
• Photodiscoloration of methyl orange was achieved by all samples at acidic environments.
• The highest reaction rate was achieved by the cubic-delta phase (δ-Bi2O3).
• The photoluminescence results showed that δ-Bi2O3 has fewer recombination centers due to defects.
• The point of zero charge was larger for the δ-Bi2O3 in comparison to the other samples.

Bismuth oxide (Bi2O3) thin films were deposited using a magnetron sputtering system under different conditions of power (radio frequency) and substrate temperature. The film structural characterization was done using X-ray diffraction, where it was demonstrated that films presenting different crystalline phases were obtained; cubic delta-Bi2O3 and a mixture of α- and β-Bi2O3 in different proportions. Three of these films were selected to compare their photocatalytic activity by measuring the percentage of photodiscoloration of 1 × 10−6 M of methyl orange (MO, C14H4N3SO3Na) using UV light; moreover, the effect of the pH of the solution on the photodiscoloration was also investigated. The results indicated that the films were only active under acidic pH and that the cubic delta phase was the most efficient. The optical properties were also evaluated by ellipsometric spectroscopy and the results were compared to the optical transmittance spectroscopy. In order to gain understanding about the effect of the pH and the structure, the point of zero charge and the photoluminescence of the three samples were also obtained. Furthermore, the photocatalytic activity of the sample presenting the best results was evaluated using higher concentration of the MO dye, but also using indigo carmine dye and both UV and blue lights.

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