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 TiO2 is not well understood. The photocatalytic elimination of Bacillus atrophaeus was examined under different calcination temperatures, dip-coating speeds, and ratios of TiO2, SiO2, and Ag to identify optimal production conditions for the production of TiO2- and/or TiO2/Ag-coated glass for surface disinfection. Photocatalytic disinfection of pure TiO2 or TiO2 plus Ag nanoparticles was dependent primarily on the calcination temperature. The antibacterial activity of TiO2 films was optimal with a high dip-coating speed and high calcination temperature (600 degrees C). Maximal bacterial inactivation using TiO2/Ag-coated glass was also observed following high-speed dip coating but with a low calcination temperature (250 degrees C). Scanning electron microscopy (SEM) showed that the Ag nanoparticles combined together at a high calcination temperature, leading to decreased antibacterial activity of TiO2/Ag films due to a smaller surface area of Ag nanoparticles. The presence of Ag enhanced the photocatalytic inactivation rate of TiO2, producing a more pronounced effect with increasing levels of catalyst loading.