TiO 2 –MCM-41 for the photocatalytic abatement of NOx in gas phase M. Signoretto a, *, E. Ghedini a , V. Trevisan a , C.L. Bianchi b , M. Ongaro b , G. Cruciani c a Dipartimento di Chimica, Universita ` Ca ` Foscari, Consortium INSTM-RU of Venice, Calle Larga Santa Marta, 2137, 30123 Venice, Italy b Dipartimento di Chimica Fisica ed Elettrochimica, universita ` degli Studi di Milano, Consorzio INSTM_RU Milano, Via Golgi 19, 20133 Milan, Italy c Dipartimento di Scienze della Terra, Universita ` diFerrara, Via Saragat 1, I-44100 Ferrara, Italy 1. Introduction Titanium dioxide is one of the most common materials in everyday life. It has been widely used as white pigment in paints, cosmetics and foodstuffs and in recent years photocatalytic processes using TiO 2 have been applied to important problems of environmental interest like purification of water and air. TiO 2 is a semiconductor with a band gap energy E g = 3.2 eV (this value is that of the anatase form); when this material is irradiated with photons (e.g. sunlight) the electron–hole pair that is created may separate and the resulting charge carriers might migrate to the surface where they can react with adsorbed water and oxygen to produce radical species. These attack any adsorbed organic molecule and can lead to complete decomposition into CO 2 and H 2 O [1]. Compared with traditional advanced oxidation processes the technology of photocatalysis is known to have some advantages, such as ease of setup and operation at room temperatures, no need for post-processes, low consumption of energy and consequently low costs, high degradation efficiency in removing organic pollutants even at ultra low concentrations. For the realization of these practical applications, development of highly active photocatalysts is keenly desired. Based on the kinetic investigation of photocatalytic reactions, TiO 2 nanoparticles in the anatase crystal form having both high crystallinity and large surface area [2] must exhibit higher photocatalytic activity. This last property should increase the amount of surface-adsorbed substrate to enhance the capture of photogenerated electron and positive hole. The control of the final features of the oxide can be achieved by several approach among that: sol–gel synthesis [3], by employing surfactants [4,5] and more recently there has been increasing interest in introducing titanium into high surface area support materials. Good candidates for supports are mesostruc- tured silicas because of their high surface areas, ordered frame- works, and narrow pore size distribution [6–9]. Several approaches can be adopted for the synthesis of high area mesoporous silica/titania systems that can be divided in two classes: (i) introduction of TiO 2 during the formation of the silica material (one-pot synthesis) [10–12]. (ii) introduction of TiO 2 in a pre-synthesized silica support by applying post-synthesis methods: acid-catalysed sol–gel method, chemical solution deposition, multistep deposition [9–15]. The first approach permits an accurate control of the final properties of the titania/silica catalyst by varying the variables involved in the synthesis process but at the same time requests a careful control of the reactivity of the Ti- and Si-precursors that have to be adjusted to each other. This is the most critical step (very hard in some cases) of the synthesis process and the successfully realization of the final composite (TiO 2 /SiO 2 ) is strictly dependent to it. Post-modification is a more practical pathway for to obtain silica/titania catalysts but often does not permit an accurate control on the incorporation of the TiO 2 particles at the different Applied Catalysis B: Environmental xxx (2010) xxx–xxx ARTICLE INFO Article history: Received 4 November 2009 Received in revised form 9 December 2009 Accepted 17 December 2009 Available online xxx Keywords: Nanotitania Mesoporous silica NOx oxidation Photocatalysis ABSTRACT Nanotitania supported on mesoporous silica systems were synthesized by a reliable procedure based on an incipient wetness impregnation post-synthetic approach. Characterization by X-ray diffraction, N 2 physisorption, TEM, X-ray photoelectron spectroscopy, ICP has been carried out in order to investigate the chemical–physical properties of the catalysts with particular attention to the chemical nature of the titanium species. The photocatalytic activity of the samples was evaluated for the degradation of NOx in the gas phase. The influence of both the textural properties and the nature of titanium species on the photocatalytic activity is discussed. ß 2009 Elsevier B.V. All rights reserved. * Corresponding author. Tel.: +39 041 2348650; fax: +39 041 2348517. E-mail address: miky@unive.it (M. Signoretto). G Model APCATB-10946; No of Pages 7 Please cite this article in press as: M. Signoretto, et al., Appl. Catal. B: Environ. (2010), doi:10.1016/j.apcatb.2009.12.019 Contents lists available at ScienceDirect Applied Catalysis B: Environmental journal homepage: www.elsevier.com/locate/apcatb 0926-3373/$ – see front matter ß 2009 Elsevier B.V. All rights reserved. doi:10.1016/j.apcatb.2009.12.019