Sol-gel synthesis of antibacterial silver-doped silica powders from sodium silicate (water glass)

Tufan, Evrim Özdem
Sol-gel processing routes for the synthesis of antibacterial silver-doped silica (Ag-SiO2) powders from an inorganic precursor, sodium silicate (Na2SiO3, water glass), have been established. For the synthesis of SiO2 powders, two different processing approaches were used. In the first one (indirect synthesis), silver ions were incorporated into the immature wet silica gels obtained from sodium silicate by the exposure of the silica gels to aqueous silver nitrate (AgNO3) solutions. In the second one, silver was directly incorporated into the aqueous silica forming formulations during sol development. In the initial work, the effect of washing treatment on the sodium removal from the silicate by-products has been investigated for the indirect synthesis route. Then, for both routes, silver-doped silica (Ag- SiO2) powders were synthesized based on the results of washing treatment studies. The effect of silver incorporation amount on the silver formation efficiency during thermal maturing of silica network (200-800°C) was examined. The phase analysis of the powders was performed using x-ray diffraction (XRD). The antibacterial activity of the powders was determined against Staphylococcus aureus and Escherichia coli by disk diffusion method. Furthermore, the effect of synthesis route, the silver dopant amount ([AgNO3]/[Na2SiO3] ratio) and the calcination temperature on the structural properties and on the antibacterial activity of the powders were investigated. The time-dependent antibacterial performance was evaluated for the samples obtained from different processing routes and parameters. The investigations revealed that the silver-doped silica powders were much more effective against Staphylococcus aureus than Escherichia coli. In addition, a high level of antibacterial activity was observed especially for the powders obtained by indirect synthesis route with low silver dopant amount.