Solar-driven water treatment has attracted increasing attention as energy transition and environmental remediation continue to advance. In this study, a series of La3+-doped Bi3NbO7 photocatalysts were prepared by a one-step hydrothermal method, and their visible-light activity was evaluated using tetracycline hydrochloride (TC) as the target pollutant. La3+ incorporation altered the crystal growth, morphology, and electronic structure of Bi3NbO7. The original agglomerated polyhedral particles were converted into interwoven two-dimensional nanosheets, together with local lattice distortion, increased oxygen-vacancy content, and changes in the band structure. Among these, 9%La-BNO exhibited the best photocatalytic activity, achieving a TC removal rate of 95.7% within 90 min, with a degradation rate 4.58 times that of pure Bi3NbO7. Further analysis combining LC–MS, molecular electrostatic potential, and Fukui function theoretical calculations identified the potential reaction sites for TC and inferred its degradation pathway. This study elucidates the mechanism by which La3+-induced synergistic restructuring of morphology, lattice, and electronic structure enhances the photocatalytic performance of Bi3NbO7.
