Efficient Photocatalytic Degradation of Tetracycline Over a Novel Dual Z-Scheme Bi2O3/ZnTiO3–SrTiO3 Composite Photocatalyst

Tetracycline (TC) is a broad-spectrum antibiotic, and its introduction into the environment is known to cause serious water pollution issues and can result in the evolution of drug-resistant genes and superbugs. In this study, a new ZnTiO3–SrTiO3 double perovskite composite photocatalyst, synthesized using a simple molten salt method, was found to exhibit excellent performance in the photocatalytic degradation of TC in an aqueous solution under visible-light photoirradiation at λ = 420 nm. Individually, ZnTiO3 and SrTiO3 were identified as being inactive in the same reaction. However, the addition of Bi2O3 to the ZnTiO3–SrTiO3 composite (Bi2O3/ZnTiO3–SrTiO3) formed a dual-Z-scheme heterojunction, achieving 87.1% photocatalytic degradation rate of TC within 60 min. The obtained reaction rate constant (k = 0.03052 min–1) was 9.5 and 1.62 times higher than those achieved using the individual SrTiO3 (k = 0.00321 min–1) and ZnTiO3–SrTiO3 (k = 0.01882 min–1) species, respectively. Furthermore, a potential degradation pathway and mechanism for TC degradation using the Bi2O3/ZnTiO3–SrTiO3 composite photocatalyst was proposed. Overall, this approach provides a cost-effective and efficient method for preparing dual Z-scheme heterojunction photocatalysts.