Ti4+-Induced Oxygen-Vacancy Engineering in BiFeO3 Photocatalysts Achieves Exceptional Cycling Stability for Congo Red Degradation

BiFeO 3 (BFO) is an attractive visible-light-active photocatalyst but suffers from a relatively wide band gap, rapid charge-carrier recombination and photocorrosion, which collectively result in poor cycling stability. Herein, we employ a B-site Ti 4+ single-doping strategy to construct a series of BiFe 1-x Ti x O 3 (x = 0, 0.05, 0.10, 0.15, 0.20) photocatalysts with enhanced durability. Ti 4+ incorporation improves the structural stability of the TiO 6 /FeO 6 octahedral framework and mitigates photocorrosion, while simultaneously creating oxygen-vacancy (OV)-related defect states that facilitate charge separation. The optimized composition, BiFe 0.90 Ti 0.10 O 3 (10% BFTO), achieves 99.98% degradation of Congo red (CR) within 120 min under visible-light irradiation in the presence of H 2 O 2 , which is 8.79% higher than that of pristine BFO. Remarkably, 10% BFTO retains 97.97% of its initial activity after 24 consecutive cycles, corresponding to only a 2.01% loss in performance and, to the best of our knowledge, representing one of the highest cycling stabilities reported for BFO-based photocatalysts in dye degradation. Combined microstructural, XPS, photoluminescence and UV–Vis diffuse reflectance analyses indicate that Ti 4+ mono-doping narrows the band gap to 1.86 eV, strengthens visible-light absorption and generates OV-related defect states that promote charge separation and reactive oxygen species (ROS) formation. This work provides a simple single-element doping paradigm for designing high-activity, ultrastable photocatalysts and offers a promising route toward practical photocatalytic applications.