Lasting antibacterial activities of Ag-TiO2/Ag/a-TiO2 nanocomposite thin film photocatalysts under solar light irradiation

Photodegradation of Escherichia coli bacteria in presence of Ag-TiO2/Ag/a-TiO2 nanocomposite film with an effective storage of silver nanoparticles was investigated in the visible and the solar light irradiations. The nanocomposite film was synthesized by sol-gel deposition of 30 nm Ag-TiO2 layer oil similar to 200 nm anatase(a-)TiO2 film previously doped by silver nanoparticles. Both Ag/a-TiO2 and Ag-TiO2/Ag/a-TiO2 films were transparent with a SPR absorption band at 412 nm. Depth profile X-ray photoelectron spectroscopy showed metallic silver nanoparticles with diameter of 30 rim and fcc crystalline structure were self-accumulated on the film surface at depth of 5 nm of the TiO2 layer and also at the interface of the Ag-TiO2 and a-TiO2 films (at depth of 30 nm). Both OH- bounds and H2O contents were concentrated oil the film surface and at the interface, as a profit in releasing more ionic (not metallic) Silver nanoparticles. Antibacterial activity of the nanocomposite film against E. coli bacteria was 5.1 times stronger than activity of the a-TiO2, in dark. Photo-antibacterial activity of the nanocomposite film exposed by the solar light was measured 1.35 and 6.90 times better than activity of the Ag/a-TiO2 and a-TiO2, respectively. The main mechanism for silver ion releasing was inter-diffusion of water and silver nanoparticles through pores of the TiO2 layer. Durability of the nanocomposite film was at least 11 times higher than the Ag/a-TiO2 film. Therefore, the Ag-TiO2/Ag/a-TiO2 Photocatalyst can be nominated as one of the effective and long-lasting antibacterial nanocomposite materials. (C) 2009 Elsevier Inc. All rights reserved.