Visible-Light-Driven AO7 Photocatalytic Degradation and Toxicity Removal at Bi-Doped SrTiO₃

In this study, Bi-doped SrTiO₃ perovskites (Sr_1-xBi_xTiO₃, x = 0, 0.03, 0.05, 0.07 and 0.1) were synthesized using the solid-state method, characterized, and tested as photocatalysts in the degradation of the azo dye acid orange 7 (AO7) under visible light. The perovskites were successfully synthesized, and XRD data showed a predominant, well-crystallized phase, belonging to the cubic perovskite symmetry. For the doped samples, a minority phase, identified as bismuth titanate, was detected. All doped samples exhibited improved photocatalytic activity under visible light, on the degradation of AO7 (10 mg L^-1), when compared with the undoped SrTiO₃, with an increase in relative Abs_{484 nm} decay from 3.7% to ≥67.8% after 1 h, for a powder suspension of 0.2 g L^-1. The best photocatalytic activity was exhibited by the Sr_0.95Bi_0.05TiO₃ perovskite. Reusability studies showed no significant loss in photocatalytic activity under visible light. The final solutions showed no toxicity towards D. magna, proving the efficiency of Sr_0.95Bi_0.05TiO₃ as a visible-light-driven photocatalyst to degrade both the AO7 dye as well as its toxic by-products. A degradation mechanism is proposed.