Photocatalytic Mechanism of Action of Apatite-Coated Ag/Agbr/Tio2 on Phenol and Escherichia Coli and Bacillus Subtilis Bacteria Under Various Conditions

Abstract

Multi-component photocatalysts based on apatite-coated Ag/AgBr/TiO2 were prepared by the deposition method. The effects of various kinds of apatites, with hydroxyl and fluoro substituents, on photocatalytic activity were investigated. The antibacterial processes in the dark, and under visible light, on two types of bacteria indicate that the multi-composites can inhibit the growth of bacteria by two different mechanisms. TEM images and optical microscopic data demonstrate that by attaching the nanosize catalyst to the outer membrane of the cell, the bacteria could not derive nourishment from surrounding media, i.e. this component acts as bacteria-stal ic. The median ism for deactivation of bacteria in the dark can be related to the linkage between the phosphate group of the composite and the outer membrane of the cell. The photocatalytic destruction of bacteria under visible I ight indicates that attachment of the catalysts to the outer wall of the cell causes them to destroy effectively the cell wall and inner membrane by various reactive species such as OH, O2 - and 1O2. Thus this effect increases the photoactivity more than two-fold. Oxidation of phenol was also achieved under visible light- and UVA- irradiation using apatite-coated Ag/AgBr/TiO2 powders. Under UVA illumination, the ‘OH produced from the hole of the TiO2 valence band is responsible for the photodegradation of phenol, while under visible light, AgBr acts as the photoactive component of the catalyst, that can not produce’ OH and oxidize the phenol.