Comparison of photocatalytic activities of various dye-modified TiO 2 thin films under visible light K.S. Yao a , T.C. Cheng a , S.J. Li b , L.Y. Yang b , K.C. Tzeng c , C.Y. Chang a, ⁎, Y. Ko d a Department of Life Science, Mingdao University, Taiwan b Institute of Materials and System Engineering, Mingdao University, Taiwan c National Chung-Hsing University, Taichung, Taiwan d Department of Post-Modern Agriculture, Mingdao University, Taiwan abstract article info Available online 12 August 2008 Keywords: Photocatalytic activity Dye-modified TiO2 thin film Visible light Owing to the large band gap energy of 3.2eV, pure TiO 2 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 TiO 2 film is one of the most popular and economic processes for improving the drawback in TiO 2 photocatalyst. Therefore, we assess the photocatalytic efficiency of dye-modified TiO 2 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 N 400 nm). These results showed that TiO 2 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 TiO 2 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 TiO 2 thin film under visible light irradiation has potential for plant protection applications in hydroponic systems. © 2008 Elsevier B.V. All rights reserved. 1. Introduction It is well-known that pure TiO 2 film operates as an efficient photocatalyst only under UV light irradiation. It exhibits no photo- catalytic activity under the visible spectral region because of its large band gap energy of 3.2eV. UV is, however, only approximately 3% of the light existing in the solar spectrum. In addition, artificial UV light use for photocatalytic purposes is expensive because of the additional powder supply. These factors limit the wide application of TiO 2 photocatalyst in various fields from the practical point of view [1]. To overcome these limitations, several research teams have attempted to induce a red-shift in the band gap energy by doping TiO 2 with various treatments such as transition metal ions [2,3] and organic dyes [4–8]. Dye molecules that act as sensitizers have attracted much attention since O'Regan and Grätzel applied it in solar cells [9]. Once dye sensitizers are absorbed onto the TiO 2 surface, they are excited by absorbing visible light and influencing electron injection into the TiO 2 photocatalyst conduction band. The photocatalytic processes were then followed through the charge transfer [5,10–12]. Presently the technique prepared using dye-modified TiO 2 film is one of the most Surface & Coatings Technology 203 (2008) 922–924 ⁎ Corresponding author. Tel.: +886 4 8876660x8313; fax: +886 4 8871774. E-mail address: cychang@mdu.edu.tw (C.Y. Chang). Fig. 1. Schematic diagram of photocatalytic experimental apparatus. 0257-8972/$ – see front matter © 2008 Elsevier B.V. All rights reserved. doi:10.1016/j.surfcoat.2008.08.006 Contents lists available at ScienceDirect Surface & Coatings Technology journal homepage: www.elsevier.com/locate/surfcoat