Comparison of photocatalytic activities of various dye-modified TiO2 thin films under visible light

Owing to the large band gap energy of 3.2eV, pure TiO2 film operates as an efficient photocatalyst under UV light irradiation and exhibits no photocatalytic activity under the visible spectral region. UV is only about 3% of the light existing in the solar spectrum. Currently, the red-shift in the band gap energy induced by dye-modified TiO2 film is one of the most popular and economic processes for improving the drawback in TiO2 photocatalyst. Therefore, we assess the photocatalytic efficiency of dye-modified TiO2 thin film using various dye molecules such as Eosin Y, Safranine O and tris-2, 2′-bipyridyl dichlororuthenium (II) hexahydrate (Rubpy) using the sol–gel process under visible light (λ > 400 nm). These results showed that TiO2 thin film modified with Safranine O dye had the best photodegrading efficiency under visible light irradiation. The photocatalytic inactivation of Safranine O and Eosin Y dye-modified TiO2 thin films against phytopathogenic bacteria including Enterobacter cloacae SM1 and Erwinia carotovora subsp. carotovora 3 which cause severe soft/basal rot disease in vegetable crops in Taiwan were all more than 90% after irradiation with visible light for 60min. The evidence suggests that the dye-modified TiO2 thin film under visible light irradiation has potential for plant protection applications in hydroponic systems.