Visible-light-mediated Sr-Bi2O3 photocatalysis of tetracycline: Kinetics, mechanisms and toxicity assessment

• A novel nano materials Sr-doped β-Bi2O3 (Sr-Bi2O3) is successfully prepared.
• The degradation of TC follows the pseudo-first-order kinetics by Sr-Bi2O3.
• It is an effective and eco-friendly method to eliminate TC by Sr-Bi2O3.
• A photochemical degradation mechanism of TC is proposed.
• The intermediates formed by Sr-Bi2O3 photocatalysis have lower toxicity.

Photodegradation of tetracycline (TC) was investigated in aqueous solution by visible-light-driven photocatalyst Sr-doped β-Bi2O3 (Sr-Bi2O3) prepared via solvothermal synthesis. The decomposition of TC by Sr-Bi2O3 under visible light (λ > 420 nm) irradiation followed pseudo-first-order kinetics, and the removal ratio reached 91.2% after 120 min of irradiation. Sr-Bi2O3 photocatalysis is able to break the naphthol ring of TC which decomposes to m-cresol via dislodging hydroxyl group step by step by photogenerated electron. This mechanism was verified by electron spin resonance measurement, the addition of radical scavengers and the intermediate product analysis, indicating that the photogenerated electron acts as a reductant and can be the key to the degradation process. In contrast, in TiO2 photocatalysis the naphthol ring is broken via oxidation by hydroxyl radical, while in direct photolysis the ring remains intact. In addition, the toxicity of photodegradation products was analyzed by bioluminescence inhibition. After 120 min of irradiation by Sr-Bi2O3, the toxicity decreases by 90.6%, which is more substantial than direct photolysis (70%) and TiO2 photocatalysis (80%), indicating that the Sr-Bi2O3 photocatalysis is more eco-friendly than the other two methods.