• Rodrigues, Ana

Abstract

<jats:title>Abstract</jats:title><jats:p>Perovskites BaTiO<jats:sub>3</jats:sub>, La<jats:sub>0.1</jats:sub>Ba<jats:sub>0.9</jats:sub>TiO<jats:sub>3</jats:sub> and BaFeO<jats:sub>3</jats:sub> were prepared by different methods and utilized as photo-catalytic material for the degradation of the AO7 dye, with visible light. The toxicity of the treated solutions and the toxicity of perovskite powders that remained in suspension after centrifuged was assessed.</jats:p><jats:p>Different catalytic properties were found by changing synthesis methods, annealing conditions, temperature of assay, initial concentration of pollutant and amount of perovskite in suspension. BaTiO<jats:sub>3</jats:sub> was prepared by ceramic or complex polymerization methods. This perovskite presents cubic structure, and the preparation method do not seem to have any influence on the unit cell parameter. On the other hand, annealing temperature has a marked influence on the time needed to attain good crystallinity. In the case of BaFeO<jats:sub>3</jats:sub> prepared by the ceramic method, for low annealing temperature there is the formation of tetragonal phase, which changes to hexagonal with the increase in annealing temperature, being a Ba<jats:sub>2</jats:sub>Fe<jats:sub>2</jats:sub>O<jats:sub>5</jats:sub> monoclinic phase involved in this phase transition.</jats:p><jats:p>Regarding AO7 photocatalytic degradation, the best results, with almost complete colour removal, were obtained with BaFeO<jats:sub>3</jats:sub> (97%), prepared by ceramic method, and with BaTiO<jats:sub>3</jats:sub> (78%), prepared by polymer complex method. Toxicity assays towards <jats:italic>Daphnia magna</jats:italic> were performed with AO7 25 ppm aqueous solution samples, collected in the centrifuged suspensions of the photocatalytic assays, performed with different perovskites, and samples collected in centrifuged suspensions of perovskite powders. In general, there is no increase in toxicity when compared to the toxicity of an AO7 25 ppm aqueous solution. Only in the photodegradation assay with BaFeO<jats:sub>3</jats:sub> a clear increase in toxicity was observed, indicating that toxic by-products are being formed.</jats:p>

Topics

• perovskite
• impedance spectroscopy
• polymer
• phase
• phase transition
• annealing
• toxicity
• crystallinity