La- and Ti-Doped Bismuth-Based Photocatalysts: Oxygen Vacancies and Bi ³⁺ /Bi ⁴⁺ Synergistically Enhance Double Type-Z Charge Transport for Improving Photocatalytic Performance

Bismuth-based photocatalysts synthesized via a solid-state method frequently exhibited challenges, including particle agglomeration, insufficient active sites, and sluggish charge carrier mobility. Element doping and heterostructure construction were regarded as effective methods to address these issues. In this study, La- and Ti-doped Bi₂SiO₅-BiOBr-Bi₂WO₆ (La-BSBW and Ti-BSBW) double type-Z heterojunction photocatalysts were successfully synthesized by solid-state methods and ion-exchange strategies. The doping of La and Ti induced the generation of abundant oxygen vacancies (V_O) and promoted the transformation of part of Bi³⁺ to Bi⁴⁺ to form Bi³⁺/Bi⁴⁺ redox centers. Their synergistic effect formed a "V_O-Bi³⁺/Bi⁴⁺" dynamic catalytic cycle, which not only shortened the photogenerated carrier migration path and reduced the electron transition energy barrier and interfacial resistance but also promoted the formation of double type-Z heterojunction to achieve efficient photogenerated carrier transport. In addition, on the basis of doping, the introduction of ultrasonic effects could provide a continuous driving force for the "V_O-Bi³⁺/Bi⁴⁺" dynamic catalytic cycle, significantly improving the migration efficiency of electrons (e^-)-holes (h⁺) and suppressing carrier recombination. Ultimately, under simulated sunlight and ultrasound, the degradation rates of La-BSBW and Ti-BSBW for rhodamine B (Rh B) reached 0.07465 and 0.08266 min^-1 respectively, which were 2.1 and 2.3 times that of undoped BSBW, demonstrating superior photocatalytic performance. Further, La-BSBW and Ti-BSBW both showed degradation efficiency exceeding 88% for TCH, CIP, and BPA, demonstrating significant broad-spectrum degradation capabilities. This study provided a simple and efficient modification strategy for developing highly efficient bismuth-based photocatalysts via the solid-phase method.