Construction of a Visible Light-Driven LaFeO3/Bi4Ti3O12 Heterojunction Photocatalyst Towards Removal of Tetracycline in Aquatic Environment

A LaFeO3/Bi4Ti3O12 heterojunction photocatalyst composite was constructed for the removal of tetracycline (TC). The structure, morphology, and elemental composition of the composite were systematically characterized using tools such as XRD, SEM, and XPS. The results from characterization jointly verified the successful construction of a LaFeO3/Bi4Ti3O12 heterojunction. UV–vis DRS analysis further revealed a narrowing of the optical bandgap from 3.29 eV to 2.24 eV, which enhanced visible-light absorption. Characterization via XPS identified the presence of Fe2+/Fe3+ mixed valence states, while bismuth predominantly existed in the stable Bi3+ state. Under simulated sunlight (300 W xenon lamp) irradiation, the photocatalytic performance of LaFeO3/Bi4Ti3O12 was systematically evaluated. The results demonstrated that the LaFeO3/Bi4Ti3O12 composite achieved a removal efficiency of 95% for TC within 120 min, with a reaction rate constant of 0.023 min−1. The construction of heterojunction greatly increased not only the removal efficiency but also the reaction rate. For instance, the first-order reaction rate constants of LaFeO3/Bi4Ti3O12 were 3.8 and 4.7 times higher than those of pure LaFeO3 and Bi4Ti3O12. TC removal by the composite was affected by dosage, initial TC concentration, and pH of the water. The composite exhibited the best performance at a dosage of 1.6 g/L with a pH around 7–8 and an initial TC concentration less than 20 mg/L. Anions such as Cl− and NO3− had minimal impact on its photocatalytic activity, whereas H2PO4−, humic acid, showed inhibitory effects. Free radical trapping experiments further confirmed that holes (h+) and hydroxyl radicals (·OH) were the primary active species in the process.