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

Abstract

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.Effective disinfection procedures are central to the safety of public water systems, not only for drinking and sanitation but also industrially, since biofouling is a commonplace and serious problem. Three of the most common methods of water or surface sterilization are chlorination, ozonation, and ultraviolet irradiation (3, 21). However, the reaction of chlorine with natural organic matter in water forms disinfection by-products, such as haloacetic acids and trihalomethanes (e.g., chloroform), that may be harmful to human health.Bacillus atrophaeus was used as a biological indicator to monitor sterilization processes and development of biosafety methods (10,28,35). B. atrophaeus has two forms, vegetative cell and spore. The spores of the various Bacillus species are 5 to 50 times more resistant to UV radiation than are the corresponding growing cells, and mechanisms receiving the damage by UV radiation are different between the vegetative cells and spores (29). The spore is a model for contamination of the microorganism from the environment, and vegetative cells are a model for growing bacteria. We used B. atrophaeus as the model microorganism for sterilization processes and focused on the vegetative cells as a model for growing bacteria.Advanced oxidation processes are seen as promising alternatives to traditional methods of disinfection. Several compounds have been investigated as potential photocatalytic materials for use in water purification, including

Sterilization effect of UV light on <I>Bacillus</I> spores using TiO2 films depends on wavelength

“…Inactivation was compared between the two forms of the bacteria. For vegetative cells, photocatalytic (TiO2 or TiO2/Ag films) inactivation of Bacillus were 4 to 9 fold (B. atrophaeus) and 1.2 to 1.4 fold (B. brevis) higher than when UVA exposure alone (normal glass) was used, which was consistent with previous observations (14)(15)(16)(17)20). In contrast, spores were resistant to UVA only exposure and photocatalytic inactivation.…”

“…Moreover, the ability of TiO2 to inactivate Bacillus spores was not markedly different in the presence of Ag. Although Ag itself has no killing activity (15), silver doping enhances electron-hole separation in TiO2, the visible light excitation of TiO2 and, by extension, the photocatalytic inactivation of microorganisms (29). It is speculated that Ag enhances the oxidative ability of TiO2 photocatalytic action (30).…”

“…Many studies have shown that activation of TiO2 and TiO2 with Ag photocatalysts with ultraviolet A (UVA) light is a highly effective process for complete inactivation of bacterial vegetative cells of Gram-negative (Escherichia coli) and Gram-positive (Staphylococcus aureus, Bacillus atrophaeus) bacteria (14)(15)(16)(17). The photocatalytic effect is reportedly dependent on the wavelength of light (18).…”

Exploring Antibacterial Activity and Bacterial-Mediated Allotropic Transition of Differentially Coated Selenium Nanoparticles

“…Specifically, the toxicological potential of silica NPs has been associated to their crystalline properties . AgNPs have also been reported to have better antibacterial properties in the crystalline state. , From an environmental point of view, Se nanocrystals exhibit excellent settling properties which facilitate their immobilization and recovery . Not only crystallinity but also the size, shape, surface charge, etc.…”

Effect of titania addition on adhesion of silver colloids to glass substrate

“…Titania and silver had been used together in various applications (16)(17)(18)(19)(20)(21), especially as photocatalyst. Here titania was the dominant component and silver provided some synergistic effect.…”