Photocatalytic bactericidal activity of silver-sensitized titanium dioxide on Micrococcus lylae

Abstract

Under UV irradiation, titanium dioxide (TiO 2 ) exhibits a strong bactericidal activity through the generation of hydroxyl radicals (•OH). Silver (Ag) sensitization is an effective way to enhance photocatalytic activity of TiO 2 . In the present study, Micrococcus lylae was used as a model bacterium to compare the bactericidal activity of Agsensitized TiO 2 (in two different Ag/TiO 2 molar ratios) and pure TiO 2 (P25). When the concentration of photocatalysts was fixed on 0.2 mg/ml with 300 rpm stirring, no obvious difference observed among the three photocatalysts. However, the Ag-sensitized photocatalysts with higher Ag/TiO 2 ratio showed better bactericidal efficiency when their concentration decreased (0.1 mg/ml) or the stirring speed increased (380 rpm). The results indicated that optimizing the phosico-chemical conditions of reaction promoted the efficiency of photocatalyst. Moreover, transmission electron microscopy (TEM) was used to observe the sub-cellular structural changes of M. lylae during photocatalytic oxidation (PCO). According to the TEM images, the disruption of cell wall occurred at a relatively long time after the cell death. The cause of cell death was the destruction of plasma membrane induced by membrane permeable •OH. These results supported that both modification on photocatalyst properties and optimization on reaction conditions enhanced the bactericidal efficiency of PCO.

Additional Effects of Silver Nanoparticles on Bactericidal Efficiency Depend on Calcination Temperature and Dip-Coating Speed

“…The antibacterial effects of TiO 2 , either in suspension or immobilized, have been studied with respect to substrate support (e.g., glass and stainless steel) (2,12,25,37), the Ag/TiO 2 molar ratio (37), and the light source and wavelength (13,17,21,27). However, bactericidal effects are also affected by the condition of the glass coating, the photocatalyst ratio, and the sterilization process.…”

“…The deposition of metal elements into the TiO 2 matrix has been used to increase the efficiency of photocatalytic disinfection (12,37), resulting in an increase in the hole concentration and a decrease in band gap energy, which extends the range of the photoactive response to the visible light spectrum (36). Silver doping enhances electron hole separation in TiO 2 , the visible light excitation of TiO 2 , and by extension enhancement of the photocatalytic inactivation of microorganisms (30).…”