Abstract
Abstract Perovskites BaTiO3, La0.1Ba0.9TiO3 and BaFeO3 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. Different catalytic properties were found by changing synthesis methods, annealing conditions, temperature of assay, initial concentration of pollutant and amount of perovskite in suspension. BaTiO3 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 BaFeO3 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 Ba2Fe2O5 monoclinic phase involved in this phase transition. Regarding AO7 photocatalytic degradation, the best results, with almost complete colour removal, were obtained with BaFeO3 (97%), prepared by ceramic method, and with BaTiO3 (78%), prepared by polymer complex method. Toxicity assays towards Daphnia magna 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 BaFeO3 a clear increase in toxicity was observed, indicating that toxic by-products are being formed.
Highlights
Photocatalysis is an important process for environmental applications, in particular when the photocatalytic materials are activated by a clean energy, such as visible or solar light
The introduction of La (10%) in the BaTiO3 structure, to obtain La0,1Ba0,9FeTiO3, did not change the cubic structure, nor the cell parameter. These results show the importance of the annealing temperature on the time needed to attain good crystallinity
LaxBa(1−x)FeyTi(1−y)O3 perovskites may be efficient photocatalytic materials for environmental applications activated by visible light
Summary
Photocatalysis is an important process for environmental applications, in particular when the photocatalytic materials are activated by a clean energy, such as visible or solar light. Perovskites are a class of compounds presenting the general formula ABX3, where A is an alkali or alkaline earth metal or a member of the lanthanides’ family, B is a transition metal, X is an anion, frequently an oxygen ion Their structures offer a rich opportunity for designing novel compounds based on A and B site occupancy, giving rise to a wide range of material systems with unique properties [1]. Due to their structure, perovskite oxides can accommodate about 90% of the Periodic Table metal elements, which may partially or fully occupy the A and/or B positions without destroying the matrix structure, but giving them different catalytic properties [2].
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