Oxygen Defects and Photocatalytic Activity of Bi2O3/TiO2 Nanotube-Based Catalysts

The development of efficient photocatalysts for the degradation of persistent organic pollutants in wastewater remains an important challenge. In this work, Bi2O3/TiO2 heterostructured catalysts with nanotubular morphology were successfully synthesized through a hydrothermal method followed by wet impregnation, and their photocatalytic activity was evaluated for methyl orange (MO) degradation under UV irradiation. Structural, morphological, surface feature, and optical properties were systematically investigated by XRD, Raman, FTIR, XPS, SEM, HRTEM-EDS, N2 physisorption, and UV–Vis DRS analyses. Rietveld refinement confirmed the existence of oxygen defects in bismuth oxides and their concentration increased with bismuth content. The incorporation of defective Bi2O3 with TiO2 nanotubes induced bandgap narrowing and interfacial electronic interactions. Among the synthesized Bi2O3/TiO2 materials, BTI500-20 exhibited the highest photocatalytic activity, achieving complete MO removal with the highest apparent kinetic constant. Reactive species trapping experiments indicated that photogenerated holes and hydroxyl radicals were the main oxidative species involved in the degradation process. High-performance liquid chromatography (HPLC) analysis revealed the progressive degradation pathway of MO through azo bond cleavage, formation of aromatic intermediates, and subsequent generation of low-molecular-weight oxidation products. The enhanced photocatalytic performance was attributed to the defective structure and synergistic effect of the Bi2O3/TiO2 heterojunction, which promoted interfacial charge separation and facilitated the generation of reactive oxidative species.