Enhanced visible light photocatalytic degradation of oxytetracycline hydrochloride using heterojunction BiOBr/TiO2 composites

Type II heterojunction photocatalysts were fabricated by compositing BiOBr with TiO 2 , with samples labeled BiOBr/TiO 2 -1 to BiOBr/TiO 2 -5 (the number denotes the mass of TiO 2 in mg used during synthesis). Among these, BiOBr/TiO 2 -2 (containing 100 mg TiO 2 ) exhibited optimal visible-light photocatalytic performance for oxytetracycline hydrochloride (OTC) degradation, achieving 94.38 % removal within 60 min. High-resolution transmission electron microscopy (HRTEM) confirmed successful composite formation through the observation of dual lattice spacings (0.28 nm for BiOBr (1   1   0) and 0.35 nm for TiO 2 ). This composite displayed a superior degradation rate constant of 0.04757 min −1 , exceeding those of pristine BiOBr and TiO 2 by factors of 2 and 14, respectively. The enhanced activity was attributed to effective charge separation enabled by the Type II heterojunction structure. Radical trapping experiments combined with electron paramagnetic resonance (EPR) analysis identified photogenerated holes (h + ) and superoxide radicals (•O 2 − ) as the dominant reactive species. HPLC–MS analysis revealed degradation intermediates, and toxicity assessment predicted progressive detoxification during the process. This study demonstrated that BiOBr/TiO 2 -2 is a stable and efficient photocatalyst with significant potential for antibiotic wastewater treatment.