Available at www.sciencedirect.com journal homepage: www.elsevier.com/locate/watres Preparation, stabilization and characterization of TiO 2 on thin polyethylene films (LDPE). Photocatalytic applications Yu Zhiyong a,f , E. Mielczarski b , J. Mielczarski b , D. Laub c , Ph. Buffat c , U. Klehm d , P. Albers d , K. Lee e , A. Kulik e , L. Kiwi-Minsker a , A. Renken a , J. Kiwi a,Ã a Institute of Chemical Sciences and Engineering, LGRC, Station 6, EPFL, 1015 Lausanne, Switzerland b INPL/CNRS, UMR 7569 LEM, 15 av du Charmois, 54501 Vandoeuvre les Nancy, France c Interdepartmental Institute of Electron Microscopy (CIME), Station 12, EPFL, 1015 Lausanne, Switzerland d AQura GmbH Industriepark Wolfgang, Rodenbacher Chaussee 4, D-63457 Hanau, Germany e Institute of Physics of Complex Matter, Station 9, EPFL, 1015 Lausanne, Switzerland f Department of Chemistry, Renmin University of China, 100872 Beijing, China article info Article history: Received 7 July 2006 Received in revised form 1 November 2006 Accepted 14 November 2006 Keywords: Photodiscoloration Polyethylene low-density films Orange II Electron microscopy X-ray photoelectron spectroscopy abstract An innovative way to fix preformed nanocrystalline TiO 2 on low-density polyethylene film (LDPE-TiO 2 ) is presented. The LDPE-TiO 2 film was able to mediate the complete photodiscoloration of Orange II using about seven times less catalyst than a TiO 2 suspension and proceeded with a photonic efficiency of 0.02. The catalyst shows photostability over long operational periods during the photodiscoloration of the azo dye Orange II. The LDPE-TiO 2 catalyst leads to full dye discoloration under simulated solar light but only to a 30% TOC reduction since long-lived intermediates generated in solution seem to preclude full mineralization of the dye. Physical insight is provided into the mechanism of stabilization of the LDPE-TiO 2 composite during the photocatalytic process by X-ray photoelectron spectroscopy (XPS). The adherence of TiO 2 on LDPE is investigated by electron microscopy (EM) and atomic force microscopy (AFM). The thickness of the TiO 2 film is seen to vary between 1.25 and 1.69 mm for an unused LDPE-TiO 2 film and between 1.31 and 1.50 mm for a sample irradiated 10 h during Orange II discoloration pointing out to a higher compactness of the TiO 2 film after the photocatalysis. & 2006 Elsevier Ltd. All rights reserved. 1. Introduction In the field of environmental chemistry, semiconductor mediated photocatalysis has been the focus of recent attention since it aims at the destruction of contaminants in water under mild conditions. The objective in this field is to find innovative low cost processes that can use sunlight as the source of irradiation (Oppenlaender, 2003; Mills and Lee, 1997). Suspensions of TiO 2 as photocatalysts present two major drawbacks: (a) the separation of TiO 2 after the treatment, and (b) the low quantum efficiency of these processes. Suitable supports for TiO 2 have been reported recently such as: Nafion (Fernandez et al., 1999), Raschig rings (Bozzi et al., 2004), polyethylene-maleic anhydride copolymer (Dhananjeyan et al., 2001) and synthetic fabrics (Bozzi et al., 2005). Suitable thin film supports should present four properties: (a) withstand reactive oxidative radicals attack during light, (b) maintain adequate long-term catalytic stability, (c) preclude TiO 2 leach- ing during the light irradiation, and (d) allow photocatalytic reaction to proceed with an acceptable kinetics. The photo- catalyst presented in this work shows these properties suitable for reuse during long-term reactor operation. ARTICLE IN PRESS 0043-1354/$ - see front matter & 2006 Elsevier Ltd. All rights reserved. doi:10.1016/j.watres.2006.11.020 Ã Corresponding author. Tel.: +41 021 693 3621; fax: +41 021 693 4111. E-mail address: john.kiwi@epfl.ch (J. Kiwi). WATER RESEARCH 41 (2007) 862– 874