Visible Light Driven Degradation of Tetracycline Hydrochloride in the Presence of Ruthenium Photosensitizer

Abstract

A ruthenium (II) photosensitizer, [Ru(bpy)₂(phen)][PF₆]₂ (RuPS), was synthesized and its structure was confirmed by UV–Vis and ¹H NMR spectroscopy. Under visible light, RuPS could efficiently promote the degradation of tetracycline hydrochloride (TC·HCl) in the presence of oxygen (O₂). Its degradation rate could reach 94.6% in 5 h under 20°C, 50 mW/cm² of radiation intensity, 20 mg/L of TC·HCl, 5 mg/L of RuPS, and pH 10.0. Its degradation pathways were complex and involved both direct and indirect photolysis. For both pathways, the degradation rate of TC increased with the increase of pH value. In acidic environment, the degradation of TC mainly depended on the sensitization of photosensitizer. Under alkaline conditions, the photodegradation of TC itself played a major role as well. For the indirect photolysis, it involved the oxidative degradation of exited TC (TC*) by triplet oxygen (³O₂) and the oxidative degradation of TC by singlet oxygen (¹O₂). ¹O₂ was mainly generated by RuPS under light. In conclusion, aerobic photodegradation under alkaline conditions was a feasible and convenient method to remove TC from water.