Kinetics and mechanism insights into the photodegradation of tetracycline hydrochloride and ofloxacin mixed antibiotics with the flower-like BiOCl/TiO2 heterojunction

Antibiotic pollutants have been constantly detected in the water environment. Photocatalytic degradation of antibiotics is one of the important ways of non-biological degradation. Due to the diversity and complexity of antibiotics, it is of great significance to study the interaction and degradation pathways of mixed antibiotics. In this paper, particular emphasis was given to the kinetics and mechanism of mixed antibiotics (tetracycline hydrochloride and ofloxacin) at different pH values and concentration ratio by using the flowerlike BiOCl/TiO2 as photocatalyst. The results showed that there was a tendency of selective degradation in the degradation process of the mixed antibiotics: TC (tetracycline hydrochloride) was preferentially degraded under alkaline conditions. This may be the ionization degree of TC is stronger than that of OFLX (ofloxacin) under alkaline conditions, generating more ionic state of TC, which are easily oxidized by OH. And, because of the difference in ionization intensity, the initial concentration of OFLX in mixtures ranged from 0 to 0.2 improved the degradation rate of TC from 0.1208 min(-1) to 0.2932 min(-1). Moreover, the degradation intermediates of antibiotics were analyzed by HPLC-MS and the degradation mechanism was obtained. It indicated that the main pathways of degradation did not affect each other in mixed antibiotics system. And the intermediates facilitated the development of C. vulgaris. This paper provides a useful reference for the study and degradation of water environmental systems containing various organic pollution.