Author's personal copy Low temperature deposition and characterization of TiO 2 photocatalytic film through cold spray Guan-Jun Yang a, * , Chang-Jiu Li a , Feng Han a , Wen-Ya Li a , Akira Ohmori b a State Key Laboratory for Mechanical Behavior of Materials, Xi’an Jiaotong University, Xi’an, Shaanxi 710049, PR China b Joining and Welding Research Institute, Osaka University, 11-1 Mihogaoka, Ibaraki, Osaka 567-0047, Japan Received 7 August 2007; received in revised form 17 December 2007; accepted 17 December 2007 Available online 23 December 2007 Abstract Cold spray was employed as a novel low temperature approach to deposit titanium dioxide (TiO 2 ) photocatalytic film. The film microstructure was characterized using X-ray diffraction and scanning electron microscopy. The photocatalytic performance was examined through acetaldehyde degradation under ultraviolet illumination. Results showed that TiO 2 film was successfully deposited on substrate surface through cold spray. The film thickness reached up to 15 mm. The film presented a rough surface and porous structure. Owing to the low temperature of spray powder, no phase and particle size changes occurred to TiO 2 during deposition. It was found that the cold-sprayed TiO 2 film was active for photodegradation of acetaldehyde. # 2007 Elsevier B.V. All rights reserved. Keywords: Titanium oxide; Film; Photocatalysis; Cold spray 1. Introduction Titanium dioxide (TiO 2 ) is a promising photocatalyst owing to its potential applications to environmental purification, solar cells, sterilization, cancer therapy and antifogging films [1–5]. The immobilized TiO 2 photocatalysts in the form of films are practically of many advantages than that of powders [6]. Many coating processes were employed to deposit TiO 2 photocatalyst films. Those processes include two routes: (1) preparation from TiO 2 powders ready for use, e.g. the commercially available Degussa P25 titania powder, and (2) preparation of a photocatalyst in situ from a precursor [7,8]. As photocatalyst powders are deposited on an inert support, they are fixed on the support by some binders, such as glue and various solutions [6,9,10]. The adherence of the photocatalyst to the support is very important, since some catalyst particles may be detached from the support and enter the liquid phase if the adhesion of the photocatalyst to the support is not strong enough. Annealing treatment from 500 to 700 8C is often utilized to improve the adherence [6,9,10]. However, owing to the change of the surface microstructure of photocatalyst powders, the immobilization processing of photocatalyst powders at a high temperature generally deteriorates photo- catalytic activity. Therefore, it is of significant importance to retain the photocatalytic activity of feedstock in the film. On the other hand, since the photocatalysis takes place on the external and internal surface of photocatalyst particles, the microporous film presents higher photocatalytic performance owing to its larger surface area than compact film. Consequently, film with micro-porosity or nano-porosity is of essential interest. In this study, nanoporous TiO 2 film was deposited with TiO 2 powder through cold spray. The microstructure and photo- catalytic performance of the deposited film was examined. 2. Experimental 2.1. Materials TiO 2 powder in pure anatase crystalline structure was used as feedstock. The starting anatase powder (10–45 mm) was prepared through agglomerating ultra-fine primary particles www.elsevier.com/locate/apsusc Available online at www.sciencedirect.com Applied Surface Science 254 (2008) 3979–3982 * Corresponding author at: School of Materials Science and Engineering, Xi’an Jiaotong University, Xi’an, Shaanxi 710049, PR China. Tel.: +86 29 82660970; fax: +86 29 83237910. E-mail address: ygj@mail.xjtu.edu.cn (G.-J. Yang). 0169-4332/$ – see front matter # 2007 Elsevier B.V. All rights reserved. doi:10.1016/j.apsusc.2007.12.016