INVESTIGATION OF THIN SEMICONDUCTOR COATINGS AND THEIR ANTIMICROBIAL PROPERTIES
ABSTRACT Regular disinfection of surfaces is required in order to reduce the number of microorganisms, unable to transmit infections and maintaining the surfaces sterilized. For this purpose, antimicrobial thin film coatings on the various surfaces such as glass and ceramic surfaces, capable of killing harmful microorganisms are being investigated. Generally a semiconducting material which can be activated by UV light tends to exhibit a strong antimicrobial activity. With holes (h+) and hydroxyl radicals (OH*) generated in the valence band, electrons and the superoxide ions (O2-) generated in the conduction band, illuminated semiconductor photocatalysts can inactivate microorganisms by participating in a series of oxidation reactions leading to carbon dioxide. The aim of this current study was developing semiconductor coatings, increasing the photocatalytic activity of these coatings by metal doping, particularly palladium doping, and investigating the antimicrobial properties of these coatings. In this study, glass surfaces were coated with titanium dioxide (TiO2), tin dioxide (SnO2) and palladium doped TiO2 and SnO2 sol-gels. After achieving thin, dense and strong coatings, antimicrobial properties of the coatings were investigated by applying the indicator microorganisms directly onto the coated glasses. Different cell wall structure of microorganisms can strongly affect the photocatalytic efficiency of the coatings. Hence Escherichia coli as a Gr (-) bacteria, Staphylococcus aereus as Gr (+) bacteria, Saccharomyces cerevisiae as a yeast and Aspergilus niger spores were used in the experiments. Photocatalytic efficiency of TiO2 was better than SnO2 coatings. Palladium doping increased the antimicrobial activity of both coatings. The reduction efficiencies were found to decrease in the following order of E. coli [Gr (-)] > S. aereus [Gr (+)] > S.cerevisiae (yeast) > A. niger spores. The complexity and the density of the cell walls increased in the same order. As a result of this study, with the coating that shows the best photocatalytic activity, 98% of Escherichia coli, 87% of Staphylococcus aereus, 43% Saccharomyces cerevisiae were killed after 2 hours illumination.