TiO 2 nanoparticle layer formation on ceramic support, a statistical approach to control influential synthesis parameters Saba Habibi a , Shohreh Fatemi a, c, ⁎, Soheila Izadyar a , Tahereh Mousavand b a School of Chemical Engineering, University College of Engineering, University of Tehran, Enghelab Street, P.O.Box 11365-4563, Tehran, Iran b Department of Chemical Engineering, McGill University, 817 Sherbrooke Street, West Montréal, Québec H3A 2K6, Canada c School of Chemical Engineering, Oil and Gas Center of Excellence, University of Tehran, Enghlab Street, P.O.Box 11365-4563,Tehran, Iran abstract article info Article history: Received 12 April 2012 Received in revised form 29 May 2012 Accepted 2 June 2012 Available online 9 June 2012 Keywords: TiO 2 nanopowder TiO 2 thin film Synthesis parameters Photocatalytic degradation Volatile organic compounds TiO 2 nanoparticles were synthesized by sol–gel method and they were coated on alpha-alumina supports to form ultra fine layer of nanosized TiO 2 . The effect of synthesis parameters; molar ratio of surfactant/precur- sor, refluxing temperature and refluxing time, calcination temperature and time was simultaneously investi- gated on crystallite size, crystalline phase content, specific surface area and photocatalytic activity of the product, using a statistical approach. The powder samples were characterized using X-ray diffraction (XRD), scanning electron microscopy (SEM) and Brunauer–Emmett–Teller technique (BET). The results re- vealed positive effect of refluxing temperature on the crystallite size and crystallinity, while a negative effect was observed on the anatase phase content. The anatase phase content was enhanced by increasing the re- flux time. Increasing calcination temperature and calcination time resulted to the higher crystallite size and relative crystallinity but lower anatase phase content. Application of surfactant improved specific surface area and pore size of the crystals. The optimal synthesis conditions to achieve maximum content of anatase phase, surface area and minimum crystallite size were found to be equal molar ratio of surfactant/precursor, refluxing temperature of 60 °C, reflux time of 6 h, calcination temperature of 550 °C and calcination time of 2 h. The optimal gel product was applied for preparing TiO 2 thin films by spraying the gel content on the alpha-alumina support. The photocatalytic behavior of the coated films was examined in photocatalytic deg- radation of acetaldehyde in gas phase batch reactor under UV irradiation and a reduction of 61% was ob- served for only 0.01 g coated TiO 2 film on the ceramic support. © 2012 Elsevier B.V. All rights reserved. 1. Introduction Among the various numbers of photocatalysts, TiO 2 holds one of the most important places due to its high photocatalytic activity, either as powder or as coatings. The preferential use of TiO 2 in the photocatalytic degradation of volatile organic compounds (VOCs) is because it is rela- tively inexpensive, highly stable chemically, and the photogenerated holes are highly oxidizing [1,2]. In addition, photogenerated electrons are reducing enough to produce superoxide from dioxygen [3] thus; TiO 2 has gained much attention as the material of choice for environ- mental applications such as air purification [4], water treatment [5] and self-cleaning [6] recently. TiO 2 photocatalyst is used either as free- standing particulates or as a coating on a support. Using finely pow- dered TiO 2 particles suspended in contaminated water or gaseous medium, may prove useful but is rather commercially unavailable and may be costly. In addition, use of these nanosized particles in continuous medium is impossible because it may cause water and air pollution. Coated catalyst configurations, on the other hand, eliminate the need for catalyst filtration and centrifugation [7,8]. Previous studies have revealed that the physical and chemical characteristics, as well as the performance of nanostructured TiO 2 strongly depend on its crystal- line structure, morphology, and dimension [9–11]. It has been reported that the photocatalytic activity of TiO 2 highly depends on its crystallite size, surface area, crystalline structure and synthesis procedure [11,12]. Among different methods of synthesis, sol–gel is one of the most ap- propriate technologies. The interest in the use of sol–gel process is due to its good homogeneity, ease of composition control, low processing temperature, coating large areas, low equipment cost and good optical properties [13,14]. In particular, the sol–gel method is efficient in pro- ducing thin films on various supports. This method provides fine control of the physical and chemical properties of the TiO 2 crystalline phase and as a result improves its photocatalytic activity [15]. In addition, high- purity products can be synthesized at low temperatures and homoge- neous multi-component systems can be obtained by mixing precursor solutions, which allows for easy chemical doping of the materials pre- pared, and the activity of titanium dioxide powders and thin films high- ly depends on the synthesis procedure. Powder Technology 229 (2012) 51–60 ⁎ Corresponding author at: School of Chemical Engineering, University College of En- gineering, University of Tehran, Enghelab Street, P.O.Box 11365-4563, Tehran, Iran. Tel.: +98 21 61112229; fax: +98 21 66957784. E-mail address: shfatemi@ut.ac.ir (S. Fatemi). 0032-5910/$ – see front matter © 2012 Elsevier B.V. All rights reserved. doi:10.1016/j.powtec.2012.06.004 Contents lists available at SciVerse ScienceDirect Powder Technology journal homepage: www.elsevier.com/locate/powtec