Synergistic surface plasmon resonance and S-scheme charge migration in oxygen vacancy rich TiO₂/Bi₁₉Br₃S₂₇/Bi nanostructures enabling outstanding photocatalytic degradation of pollutants

Background Dye and pharmaceutical pollution in water bodies poses a serious worldwide challenge, endangering both aquatic ecosystems and human health because of their durability, harmful effects, and potential to cause cancer, making urgent intervention. Methods In this study, plasmonic TiO_2-X/Bi₁₉Br₃S₂₇/Bi photocatalysts were successfully formulated through a two-step hydrothermal method using sodium borohydride as a reducing agent. The synthesized photocatalyst exhibited greatly improved photocatalytic performance in the degradation of various pollutants, including azithromycin (AZM), tetracycline hydrochloride (TCH), and cephalexin (CPN), and three dyes, including methyl orange (MO), methylene blue (MB), and rhodamine B (RhB). Key improvements are superior redox efficiency resulting from the highly negative conduction potential of Bi₁₉Br₃S₂₇, improved visible-light response induced by bismuth nanoparticles and defects formed in TiO₂ (abbreviated as TiO_2-x), efficient separation rate and photoinduced charge carrier transport, creation of active sites and species, development of S-scheme mechanism between the photocatalyst counterparts, and quantum size of the synthesized photocatalysts. Significant findings The impact of Bi₁₉Br₃S₂₇ nanoparticles (5, 10, and 20 wt%) on the performance of TiO_2-X was investigated to determine the optimal photocatalyst composition. The highest photocatalytic degradation of TCH was achieved by the TiO_2-X/Bi₁₉Br₃S₂₇ (10 %) nanocomposite (98 % in 180 min). The optimized TiO_2-X/Bi₁₉Br₃S₂₇/Bi-2 nanocomposite achieved a TCH degradation rate of 99.7 % within 60 min with a reaction rate constant of 1002 × 10^‒4 min^‒1, which was 4.81 times of TiO_2-X/Bi₁₉Br₃S₂₇ (10 %), 16.6 folds of Bi₁₉Br₃S₂₇, 14.6 times of TiO_2, and 4.41 as high as TiO_2-x under the identical conditions. The TiO_2-X/Bi₁₉Br₃S₂₇/Bi-2 nanocomposite exhibited stability across four reuse cycles, while its compatibility with biological systems was shown by successful lentil seed growth in the treated solution. This work introduces an innovative nanocomposite designed for the degradation of dyes and the elimination of antibiotics with usability in plant irrigation applications.