Highly efficient hydroxyapatite/TiO2 composites covered by silver halides as E. colidisinfectant under visible light and dark media

Abstract

TiO₂-based photocatalysts are seen as the most common agents for the photodegradation of bacteria. In this study, AgCl/TiO₂, hydroxyapatite(Hp)/AgCl/TiO₂, AgI/TiO₂, and Hp/AgI/TiO₂ were prepared by the deposition–precipitation method on P25 TiO₂ nanoparticles and were characterized by XRD, SEM, FT-IR, EDX and BET methods. The prepared composites showed high efficiency for the inactivation of Escherichia coli (E. coli) bacteria under visible light and in dark media with different catalyst amounts of 12 and 24 mg, respectively. In less than 30 min, AgI/TiO₂, prepared by the combination of cationic surfactant and PVPI₂, disinfected 1 × 10⁷ colony-forming units of E. coli completely. However, AgCl/TiO₂ was not stable under the same conditions. Hp was added to AgCl/TiO₂ and AgI/TiO₂ to extend the antibacterial effect to dark media. Hp/AgCl/TiO₂ showed desirable disinfection capabilities under visible light irradiations that function in less than 30 min. During the time interval when the inactivation was complete, the photocatalytic activity of Hp/AgCl/TiO₂ under visible light was maintained effectively without the destruction of AgCl. Hp/AgCl/TiO₂ and Hp/AgI/TiO₂ were found to prevent bacteria from growing during 3 h in the dark. The antibacterial properties of Hp composites in dark environments are mainly due to the strong linkage between Hp and the cell wall which limits the nourishment of bacteria, while under visible light, in addition to the photocatalytic process, the sense-shoot phenomena and the adsorption effects can be accepted.