Effect of calcination temperature on the antibacterial activity of TiO2/Ag nanocomposite

Abstract

TiO2/Ag nanocomposites were prepared by a sol-gel method from titanium (IV) isopropoxide and silver nitrate as raw materials followed by calcination at 350, 450, and 500 °C. The structures and morphologies of powders were fully studied by combination of x-ray diffraction (XRD) patterns, field emission scanning electron microscope (FE-SEM), and transmission electron microscope (TEM) images. The diffraction peaks of XRD patterns confirm the anatase structure of TiO2 which is applicable as an antibacterial agent. The calculation of TiO2 crystallite size based on Scherrer equation suggests that sizes are 6.6, 8.9, and 10.8 nm for calcination temperature 350, 450, and 500 °C respectively. The increase of TiO2 crystallite size can be attributed to thermal-dependent crystallite growth. The higher calcination temperature causes the rate of nucleation and the generation of the growth species more rapidly. The band-gap energies of 2.48, 2.36, and 2.19 eV were obtained for TiO2/Ag nanocomposites by calcination at temperature of 350, 450, and 500 °C respectively. The results indicate that the photoactivity of TiO2/Ag nanocomposites are feasible to active in visible light. Antibacterial activity was evaluated by using Escherichia coli (E. coli) and Staphylococcus aureus (S. aureus) as gram-negative and gram-positive bacteria respectively. TiO2/Ag nanocomposite calcinated at 350 °C is more active on the killing E. coli bacteria than TiO2/Ag nanocomposite calcinated at 500 °C for the same diluted concentration. On the other hand, the antibacterial activity of TiO2/Ag nanocomposite calcinated at 500 °C is higher than TiO2/Ag nanocomposite calcinated at 350 °C for the same diluted concentration. These results lead to the conclusion that the capability of TiO2/Ag nanocomposites in the killing bacteria depends on their structure and morphology which are affected by their calcination temperature.