Photodegradation of tetracycline and formation of reactive oxygen species in aqueous tetracycline solution under simulated sunlight irradiation

The photochemical kinetics and mechanism of the antibiotic compound tetracycline (TC) was investigated in aqueous solution under simulated sunlight irradiation. The study of the electron spin resonance revealed that the singlet oxygen (1O2) was generated and the formation rate decreased with increasing pH in illuminated TC solution. Also, it was found that the H2O2 was produced and increased with increasing pH under the simulated sunlight irradiation. The results verified that TC could be sunlight excited and induced the formation of reactive oxygen species. Moreover, the contributions of oxidation reaction to photodegradation of TC were clarified by the role of different radical scavengers. The kinetic model elucidated the involvement of TC photoinduced singlet oxygen on the photodegradation of TC. It was verified that the photodegradation of TC was predominantly attributed to direct photolysis. The quantum yields of direct photolysis increases with increasing pH in the range of 6.0–9.0, varying from 3.4 × 10−4 to 1.1 × 10−2. The indirect photolysis of TC was carried out in the presence of nitrate, bicarbonate, ferric ions and humic acid (HA), respectively. The results verified that the photodegradation of tetracycline was not obviously affected by these photosensitizers except ferric ions, indicating that the direct photolysis of TC was predominant process.