Enhanced visible-light photodegradation of fluoroquinolone-based antibiotics and E. coli growth inhibition using Ag-TiO 2 nanoparticles.

Antibiotics in wastewater represent a growing and worrying menace for environmental and human health fostering the spread of antimicrobial resistance. Titanium dioxide (TiO 2 ) is a well-studied and well-performing photocatalyst for wastewater treatment. However, it presents drawbacks linked with the high energy needed for its activation and the fast electron-hole pair recombination. In this work, TiO 2 nanoparticles were decorated with Ag nanoparticles by a facile photochemical reduction method to obtain an increased photocatalytic response under visible light. Although similar materials have been reported, we advanced this field by performing a study of the photocatalytic mechanism for Ag-TiO 2 nanoparticles (Ag-TiO 2 NPs) under visible light taking in consideration also the rutile phase of the TiO 2 nanoparticles. Moreover, we examined the Ag-TiO 2 NPs photocatalytic performance against two antibiotics from the same family. The obtained Ag-TiO 2 NPs were fully characterised. The results showed that Ag NPs (average size: 23.9 ± 18.3 nm) were homogeneously dispersed on the TiO 2 surface and the photo-response of the Ag-TiO 2 NPs was greatly enhanced in the visible light region when compared to TiO 2 P25. Hence, the obtained Ag-TiO 2 NPs showed excellent photocatalytic degradation efficiency towards the two fluoroquinolone-based antibiotics ciprofloxacin (92%) and norfloxacin (94%) after 240 min of visible light irradiation, demonstrating a possible application of these particles in wastewater treatment. In addition, it was also proved that, after five Ag-TiO 2 NPs re-utilisations in consecutive ciprofloxacin photodegradation reactions, only a photocatalytic efficiency drop of 8% was observed. Scavengers experiments demonstrated that the photocatalytic mechanism of ciprofloxacin degradation in the presence of Ag-TiO 2 NPs is mainly driven by holes and ˙OH radicals, and that the rutile phase in the system plays a crucial role. Finally, Ag-TiO 2 NPs showed also antibacterial activity towards Escherichia coli ( E. coli ) opening the avenue for a possible use of this material in hospital wastewater treatment.