Self-accumulated Ag nanoparticles on mesoporous TiO2 thin film with high bactericidal activities

Antibacterial activity of sol–gel synthesized Ag–TiO2 nanocomposite layer (30 nm) deposited on rough anatase (a) TiO2 thin film (∼ 200 nm in thickness) was investigated against Escherichia coli bacteria, in dark and also in exposure to UV light. The nanocomposite thin films were transparent with a surface plasmon resonance absorption band at a wavelength of 410 nm. The metallic silver nanoparticles with an average diameter of 30 nm and fcc crystalline structure were self-accumulated on surface of a mesoporous and aqueous TiO2 layer with a capillary pore structure having a pore radius of 3.0 nm. By adding the silver nanoparticles in the TiO2 layer, recombination of the photoexcited electron–hole pairs in the (a)TiO2 thin film was delayed, while the pore structure was unchanged. Decrease in the recombination rate and accumulation of the silver nanoparticles on the film surface let the mesoporous Ag–TiO2/(a)TiO2 nanocomposite thin films have excellent antibacterial activity against E. coli bacteria. It was found that the relative rate of reduction of the viable bacteria in dark (in exposure to the UV light) for the Ag–TiO2/(a)TiO2 nanocomposite thin film was 3.2 × 10–2 min–1 (26 × 10–2 min–1) which was 4.6 (2.0) times greater than the corresponding value for the (a)TiO2 thin film. The behavior of silver ion release showed that the dominant mechanism of the release process in long time was based on water diffusion through the capillary mesoporous of the TiO2 layer, unlike the usual diffusion of water on the surface of silver-based bulk materials. Therefore, the synthesized Ag–TiO2/(a)TiO2 nanocomposite thin film can be utilized as a promising and effective bactericidal material in the future.