Degradation of ciprofloxacin in aqueous bismuth oxybromide (BiOBr) suspensions under visible light irradiation: A direct hole oxidation pathway

• BiOBr can be promising photocatalyst for the degradation of pharmaceutical pollutants under visible light irradiation.
• The predominant reaction site of ciprofloxacin was the piperazine moiety, while the quinolone rings remained intact.
• The oxidation of ciprofloxacin is dominant by the direct hole oxidation process.
• Ciprofloxacin is a good model to uncover the photodegradation mechanism for photocatalyst with low oxidation ability.

Ciprofloxacin (CIP) in natural waters has caused serious environmental problems because of its potent biological activity. In this study, the visible light-induced degradation of CIP was examined by using bismuth oxybromide (BiOBr) as photocatalyst. The flake-shape BiOBr was synthesized by hydrothermal method and characterized by X-ray powder diffraction, scanning electron microscopy and UV–vis diffuse reflectance spectroscopy. The degradation process was monitored by high performance liquid chromatography. The photodegraded intermediates were identified by high performance liquid chromatography–mass spectrometry and the degradation pathway was proposed on the basis of product analysis. It was found that, during the visible light induced degradation of CIP on BiOBr, the piperazine moiety of CIP was the predominant reaction sites, while the quinolone and cyclopropane rings remained essentially intact. The pH-dependence of reaction rates, product analysis and theoretical calculation pointed to a surface reaction mechanism that the CIP oxidation is dominant by the direct hole oxidation process, whereas OH, which is the common active species in the advance oxidation processes, is not effective in the visible light induced photocatalytic process on BiOBr. This study demonstrated that CIP is a good model substrate to uncover the photodegradation mechanism for photocatalyst whose valence band has moderate oxidation ability.

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