Additional effects of silver nanoparticles on bactericidal efficiency depend on calcination temperature and dip-coating speed.

There is an increasing interest in the application of photocatalytic properties for disinfection of surfaces, air, and water. Titanium dioxide is widely used as a photocatalyst, and the addition of silver reportedly enhances its bactericidal action. However, the synergy of silver nanoparticles and TiO(2) is not well understood. The photocatalytic elimination of Bacillus atrophaeus was examined under different calcination temperatures, dip-coating speeds, and ratios of TiO(2), SiO(2), and Ag to identify optimal production conditions for the production of TiO(2)- and/or TiO(2)/Ag-coated glass for surface disinfection. Photocatalytic disinfection of pure TiO(2) or TiO(2) plus Ag nanoparticles was dependent primarily on the calcination temperature. The antibacterial activity of TiO(2) films was optimal with a high dip-coating speed and high calcination temperature (600°C). Maximal bacterial inactivation using TiO(2)/Ag-coated glass was also observed following high-speed dip coating but with a low calcination temperature (250°C). Scanning electron microscopy (SEM) showed that the Ag nanoparticles combined together at a high calcination temperature, leading to decreased antibacterial activity of TiO(2)/Ag films due to a smaller surface area of Ag nanoparticles. The presence of Ag enhanced the photocatalytic inactivation rate of TiO(2), producing a more pronounced effect with increasing levels of catalyst loading.

Sterilization effect of UV light on Bacillus spores using TiO(2) films depends on wavelength.

UV light and photocatalysts such as titanium dioxide (TiO(2)) and silver (Ag) are useful for disinfection of water and surfaces. However, the effect of UV wavelength on photocatalytic disinfection of spores is not well understood. Inactivation of Bacillus spores has been examined using different UV wavelengths and TiO(2) or TiO(2)/Ag composite materials. The level of UVA disinfection of Bacillus anthracis and Bacillus brevis vegetative cells increased with the presence of the TiO(2) and Ag photocatalysts, but had little effect on their spores. B. brevis spores were slightly more sensitive to UVB and UVC than the spores of B. atrophaeus. Photocatalytic sterilization against spores was strongest in UVC and UVB and weakest in UVA. The rate of inactivation of Bacillus spores was significantly increased by the presence of TiO(2), but was not markedly different from that induced by the presence of Ag. Therefore, TiO(2)/Ag plus UVA can be used for the sterilization of vegetative cells, while TiO(2) and UVC are effective against spores.