Effect of calcination on microstructure and antibacterial activity of silver-containing silica coatings

Silver nanoparticle containing silica coatings on soda-lime glass were prepared by the sol-gel process. The effect of thermal densification treatment at different temperatures in the range of 100-700 degrees C on microstructure and antibacterial properties of the coatings were examined. The structural characterization of the coatings was performed by using scanning electron microscope, X-ray diffraction, UV-visible and X-ray photoelectron spectroscopy (XPS), and atomic force microscope (AFM). The antibacterial activity of the coatings was determined against Staphylococcus aureus by disk diffusion method. The mechanisms for formation and distribution of silver nanoparticles in the silica matrix with respect to the calcination temperature are discussed, and the correlation between the microstructural properties and antibacterial activity is described. The investigations revealed that silver nanoparticles were mainly in the metallic state during thermal treatments. AFM and XPS examinations proved that silver accumulated on the surface diffuse into glass substrate at higher calcination temperatures. A high level of antibacterial activity was observed for the coatings calcined at 300 degrees C or lower temperatures allowing accommodation of silver on the surface of the coating. Silver diffusion into bulk via ion-exchange with sodium and calcium ions from glass substrate during calcination at higher temperatures (500 or 700 degrees C) resulted in apparent degradation in the antibacterial activity.