Persulfate assisted photocatalytic degradation of tetracycline by bismuth titanate under visible light irradiation

Abstract

Tetracycline is a commonly used broad-spectrum antibiotic that can prevent and cure bacterial infections. However, incompletely metabolized tetracycline molecules discharged by organisms into the aquatic environment show ecological toxicity. Therefore, it is highly desirable to degrade tetracycline in aqueous environments. A combination of photocatalysis and persulfate (PS) based advanced oxidation processes is considered to be an effective approach for the degradation of tetracycline. Herein, Bi₂Ti₂O₇ (BTO) was synthesized via a simple hydrothermal method and a BTO/PS system was constructed to degrade tetracycline. The structure, optical properties, composition, and morphology were investigated via various characterization techniques. The experimental results implied that BTO/PS exhibits enhanced degradation activity in comparison to pure BTO and PS. A removal efficiency of 88.2% can be achieved using a BTO/PS system at a tetracycline concentration of 25 mg L⁻¹ under visible light within 150 min. The possible degradation pathway of tetracycline in the BTO/PS system is discussed. In addition, the electronic band structure was studied and trapping experiments and photoelectrochemical measurements were carried out. The results indicated that holes and superoxide radicals are the main active species, while sulfate radicals and hydroxyl radicals play a secondary role in the degradation process. The role of PS in the BTO/PS system can be ascribed to an increase in active radicals and the inhibition of carrier recombination. Finally, the probable mechanism of tetracycline degradation in the BTO/PS system was conjectured.