Photo-induced Superhydrophilicity on TiO 2 Thin Films Prepared by an Ionized Cluster Beam Deposition Method
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Photo-induced Superhydrophilicity on TiO2 Thin Films Prepared by an Ionized Cluster Beam Deposition Method Masato Takeuchi Æ Kenji Sakamoto Æ Koichiro Tsujimaru Æ Masakazu Anpo
Received: 15 January 2009 / Accepted: 15 March 2009 / Published online: 23 May 2009 Ó Springer Science+Business Media, LLC 2009
Abstract The photocatalytic reactivity and the surface wettability of highly transparent TiO2 thin films prepared by an ionized cluster beam deposition method were investigated, focusing on their surface morphologies, surface areas, and crystal phases. The As-prepared TiO2 thin films showed higher photocatalytic reactivity, greater roughness in surface morphology and a larger surface area than the films calcined at temperatures higher than 823 K. Furthermore, the As-prepared film exhibited efficient photoluminescence (PL) spectra at 77 K, showing prolonged lifetimes for the photo-formed electron–hole pairs. Detailed discussions on the interaction between the PL intensity and photocatalytic reactivity as well as the surface wettability have been carried out from the viewpoint of the physicochemical properties of the TiO2 thin films. Keywords Photo-induced superhydrophilicity TiO2 thin films Ionized cluster beam deposition method
1 Introduction The discovery of the photo-induced superhydrophilicity of TiO2 thin films in 1997 [1] has opened up various new possibilities for TiO2 photocatalysts to be applied in selfcleaning, anti-fogging, anti-bacterial and stain-proofing agents [2, 3]. TiO2 thin films have also been applied in electrodes for dye-sensitized solar cells, as known by the Gra¨tzel cell [4]. Also, to apply TiO2 photocatalysts for the
M. Takeuchi K. Sakamoto K. Tsujimaru M. Anpo (&) Department of Applied Chemistry, Graduate School of Engineering, Osaka Prefecture University, 1-1, Naka-ku, Gakuen-cho, Sakai, Osaka 599-8531, Japan e-mail: [email protected]
purification of toxic compounds in polluted water and air, the fixation of TiO2 powders as thin films or thick coatings onto various substrates without any dispersion or loss are also strongly desired. TiO2 thin films has mainly been prepared by wet processes such as the sol-gel, dip-coating, spin-coating and spray methods using coating solutions containing titanium alkoxide or TiO2 sol [2, 3]. In order to obtain the strong adhesion of the thin films onto the substrates, these wet preparation methods have necessitated a post-calcination process at high temperatures after the coating of the precursor solutions. In contrast, ion-engineering techniques classified as a dry process possess some potential advantages: (1) Since thin films are prepared in a high vacuum chamber, contamination with impurities can be prevented; (2) Since no organic solvents are used for the preparation of thin films, these methods are environmentally safe; (3) Thin films of high crystallinity and strong adhesion to the substrates can be easily prepared even without calcination at high temperatures; (4) The physical and chemical properties can be easily controlled. I
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