Photocatalytic antimicrobial and self-cleaning properties of titana-silica mixed oxide thin films

Korkmaz Erdural, Beril
In this study photocatalytic antibacterial and self-cleaning activities of TiO2-SiO2 thin films as a function of TiO2/SiO2 ratios were investigated. TiO2-SiO2 mixed oxides were synthesized by sol-gel method and coated over soda-lime glass plates by dip coating technique. Escherichia coli was used as a model microorganism for the photocatalytic antibacterial tests. Degradation rate of methylene blue (MB) molecules was used to characterize photocatalytic self-cleaning activities of thin film surfaces. The maximum antibacterial activity was achieved over 92 wt% SiO2 containing thin films. However, when the SiO2 content exceeds 92 wt%, photocatalytic antibacterial activity decreased considerably, which was explained by the dilution of TiO2 phase and inaccessibility of TiO2. Increase in photocatalytic antibacterial activity was attributed to increases in the relative surface area, roughness, hydroxyl (OH-) groups and bacterial adhesion. The favored bacterial adhesion enhanced direct contact of bacteria with TiO2 particles and surface reactive oxygen species. The highest initial decomposition rate of MB was obtained for 60 wt% SiO2 and the activity decreases as SiO2 concentration increases. The increase in photocatalytic activity by the SiO2 addition can be explained by the increase of the amount of MB per unit area of TiO2-SiO2 thin films. Different adsorption capability of thin films against MB molecule and E. coli cell was explained as the first reason why the antibacterial and self-cleaning activities reached their maximum values at different SiO2 ratios. The second reason could be related with the different control mechanisms of self-cleaning and antibacterial activities by different textural and surface properties.