Synergistic Charge Transfer-Enhanced Photocatalytic Degradation of Oxytetracycline and Cr(VI) Reduction Using Sm₂O₃/Ir@Bi₂O₃

In this present investigation, a Sm₂O₃/Ir@Bi₂O₃ ternary nanocomposite was fabricated using the hydrothermal method, and comprehensive physicochemical characterization was conducted to understand the morphology, crystal phase, optical behavior, and elemental composition. The prepared material was investigated for the degradation of oxytetracycline (OTC) and chromium(VI) reduction under UV–vis. irradiation. The Sm₂O₃/Ir@Bi₂O₃ composite displayed the highest photocatalytic activity toward OTC mineralization (95% in 55 min) and Cr(VI) reduction (91% in 45 min), surpassing standalone Sm₂O₃ and Bi₂O₃, due to the synergistic effect. These removal efficiencies correspond to rate constants of 0.073 min^–1 and 0.058 min^–1 for the degradation of the OTC and Cr(VI) reduction, respectively. These were 55 times and 40 times higher than the rates achieved using Sm₂O₃ as a catalyst for OTC and Cr(VI) detoxification, respectively. The influence of various reaction conditions, such as catalyst dosage, pollutant concentration, pH, and inorganic ions, was studied during both the OTC and Cr(VI) pollution mitigation. Coexisting anions greatly governed the Sm₂O₃/Ir@Bi₂O₃ photocatalytic performances. Reactive oxidative species trapping and EPR analyses revealed that the dominant reactive species follow the order HO^• > O₂^•– > h⁺ > e^– for OTC degradation and e^– > O₂^•– > h⁺ > HO^• for Cr(VI) reduction. The probable OTC degradation pathway involved both direct and indirect oxidation mechanisms, primarily decarboxylation, hydroxylation, and demethylation. This study demonstrated the successful development of a material with versatile photocatalytic properties. The high photocatalytic efficiency of the Sm₂O₃/Ir@Bi₂O₃ nanocomposite in degrading antibiotics and reducing toxic heavy metals demonstrates its potential as a practical solution for advanced wastewater treatment in pharmaceutical and industrial effluents.