Optical and hydrophilic properties of nanostructure Cu loaded brookite TiO 2 thin film Akbar Eshaghi a, ⁎, Ameneh Eshaghi b a Faculty of Materials Science and Engineering, Maleke Ashtar University of Technology, Shahinshahr, Isfahan, Iran b Sari Branch, Islamic Azad University, Sari, Iran abstract article info Article history: Received 18 January 2011 Received in revised form 17 August 2011 Accepted 17 August 2011 Available online 23 August 2011 Keywords: Titanium dioxide Surface modification Hydrophilicity Copper Sol–gel deposition Copper loaded TiO 2 brookite thin films were deposited on glass substrates using the dip-coating method. The crys- talline structure of the films was characterized by X-ray diffraction analysis. X-ray photoelectron spectroscopy was used to evaluate the properties of the film surfaces. The transmittance spectra of the films were obtained by the Shimadzu multi-purpose spectrophotometer. The water contact angle on the film surfaces during irradiation and storage in a dark place was measured by a contact angle analyzer. The results indicate that Cu loading did not affect the transmittance spectra, whereas it had a significant effect on the hydrophilicity of the TiO 2 film surface. Crown Copyright © 2011 Published by Elsevier B.V. All rights reserved. 1. Introduction Titanium dioxide (TiO 2 ) thin films are desirable for their optical, elec- trical and chemical properties. TiO 2 exists in three crystalline structures: rutile (tetragonal), anatase (tetragonal) and brookite (orthorhombic). Rutile is a stable form, whereas anatase and brookite are metastable and are readily transformed to rutile when heated [1]. The photocatalytic property of TiO 2 is known to be more effective with anatase phase than rutile phase but studies on TiO 2 with brookite phase as a photocatalyst have been uncommon because it is relatively hard to manufacture arti- ficially [2]. Masahiro [3] reported that brookite phase TiO 2 may function as a more effective photocatalyst than anatase phase under weak light or in the area of visible rays. Shibata et al. [4] indicated that brookite phase TiO 2 thin film shows high photoinduced hydrophilicity and high photocatalytic activity compared with rutile and anatase. Howev- er, TiO 2 thin films become superhydrophilic only under UV irradiation. To shorten the time required for making TiO 2 thin films superhydrophi- lic and to make them remain superhydrophilic in a dark place, various metals and oxides have been used as a dopant to produce surface de- fects and photocatalytic properties for the degradation of organic pol- lutants [5]. Several papers have reported that metal doping could work as a recombination center for electron–hole pairs and decrease the photocatalytic activity [6]. Recently, it has been reported that sur- face modification of TiO 2 , such as metal loading, is effective in inhibiting the recombination of photogenerated electron–hole pairs by increasing the charge separation and improving the photoreactivity of TiO 2 [7]. Among the metals loaded to improve the photocatalytic activity of TiO 2 , copper is the most desirable due to its low cost. Hashimoto et al. [8] reported that Cu-loaded TiO 2 rutile has higher photocatalytic activi- ty than that of unmodified TiO 2 for the oxidative decomposition of 2-propanol. However, the photoreactivity of Cu loaded brookite TiO 2 thin film has not been investigated yet. In the present study, the optical and photo induced super-hydrophilicity of Cu loaded brookite TiO 2 thin films on glass substrates were investigated. 2. Experimental method First, the loading of Cu onto TiO 2 brookite was performed as follow. An aqueous solution of Cu.2H 2 O (1.53 × 10 −4 mol) was dispersed in 15 g of TiO 2 brookite sol solution (NTB-1, Showa Titanium). The suspension solution was stirred magnetically at 80–90 °C for 1 h. Then, the volume of the solution was increased to 100 ml using deionized water. Before coating, the fluorine tin oxide coated glass sub- strates were cleaned carefully with detergent and then washed with deionized water. The TiO 2 and Cu loaded TiO 2 brookite thin films (0.126 at.% Cu) were deposited on the glass substrates by a dip coating method and withdrawn at a speed of 5.33 cm/min. Then, the films were dried at 120 °C for 3 h. The thickness of the thin films was increased by repeating the cycle of withdrawing to drying. This procedure was carried out six times. The total film thickness was estimated to be ~450 nm. The structure of the film samples was analyzed by X-ray diffraction analysis (XRD; Philips powder diffractometer, Ni-filter, Cu K α radia- tion λ = 1.5406 Å). The surface chemical composition of the film samples was analyzed by X-ray photoelectron spectroscopy (XPS; Thin Solid Films 520 (2011) 1053–1056 ⁎ Corresponding author. Tel.: + 98 0312 5225041; fax: + 98 0312 5228530. E-mail address: eshaghi.akbar@gmail.com (A. Eshaghi). 0040-6090/$ – see front matter. Crown Copyright © 2011 Published by Elsevier B.V. All rights reserved. doi:10.1016/j.tsf.2011.08.055 Contents lists available at SciVerse ScienceDirect Thin Solid Films journal homepage: www.elsevier.com/locate/tsf