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

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 x 10(7) 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.