Solvothermal preparation of TiO 2 /saponite nanocomposites and photocatalytic activity Athanasia Nikolopoulou a , Dimitris Papoulis a,b, ⁎, Sridhar Komarneni b , Panagiota Tsolis-Katagas a , Dionisios Panagiotaras c , George H. Kacandes d , Peilin Zhang e , Shu Yin e , Tsugio Sato e a Department of Geology, University of Patras, 26504, Patras, Greece b Department of Crop and Soil Sciences and Materials Research Institute, The Pennsylvania State University, University Park, PA 16802, USA c Department of Mechanical Engineering, Technological Educational Institute of Patras, 26334, Patras, Greece d Geohellas S.A., Athens, Greece e Institute of Multidisciplinary Research for Advanced Materials, Tohoku University, Sendai 980-8577, Japan abstract article info Article history: Received 11 June 2009 Received in revised form 16 September 2009 Accepted 21 September 2009 Available online 30 September 2009 Keywords: Saponite Titania Nanocomposite Solvothermal preparation Photocatalytic activity A saponite-rich clay sample from western Macedonia, Greece was used for the preparation of TiO 2 –saponite nanocomposites by solvothermal reaction of a mixture of water and ethanol as the solvent, hexamethylene tetramine as the precipitant and titanium trichloride as the TiO 2 precursor. Phase composition was determined by X-ray diffraction (XRD) and particle morphology and elemental content was characterized by scanning electron microscopy and energy dispersive spectroscopy (SEM–EDS). These samples were also characterized by attenuated total reflection using Fourier transform infrared spectroscopy (ATR–FTIR). Particle-size analysis was carried out using dynamic light scattering method (DLS) and specific surface area and pore-size distribution analyses using BET N 2 adsorption–desorption isotherms. The composite photocatalysts showed a mesoporous structure with the distribution of pore diameters centered at 3.8 and at 5.7–9.8 nm, with high specific surface areas. The photocatalytic activities of titania–saponite nanocomposites in decomposing NOx gas were measured as a function of two different TiCl 3 –saponite ratios. TiO 2 :saponite with a mass ratio of 0.2:1 (Ti-Sap1) showed the highest photocatalytic activity because of its relatively large specific surface area and higher TiO 2 content. Both the TiO 2 –saponite nanocomposites showed higher photocatalytic activity than the standard titania (Degussa P25) based on TiO 2 content because the titania was well dispersed on saponite. © 2009 Elsevier B.V. All rights reserved. 1. Introduction Titanium dioxide (TiO 2 ) has proven to be the best photocatalyst for widespread environmental applications such as the degradation of oil spills and the decomposition of many organic pollutants in water and air (Nishimoto et al., 1985; Hoffmann et al., 1995; Michael et al., 1995; Fujishima et al., 2000a,b; Martínez-Ortiz et al., 2003). Persistent organic pollutants could be degraded and mineralized to harmless inorganic substances using photocatalysis. Because nanosized TiO 2 powder easily agglomerates into larger particles leading to reduced catalytic activity, stabilization of the nanosized TiO 2 in pillared clays improved the photocatalytic activity (Ooka et al., 2004; Sun et al., 2006a,b). The use of acidic sol precursors (pH < 1.8) to prepare pillared clays generally yield amorphous or poorly crystalline TiO 2 (Liu et al., 2009) and such phases may lead to a reduction in photocatalytic activity when compared to anatase (Kun et al., 2006). TiO 2 pillared clays have potential uses as adsorbents, catalysts and catalyst supports due to their mesoporous structure and large specific surface area (Occelli, 1986; Sterte, 1986; Yamanaka, et al., 1987; Figueras, 1988; Kikuchi and Matsuda, 1988; Malla, et al., 1989; Horio et al., 1991; Bernier et al., 1991; Komarneni, 1992; Khalfallah et al., 1994; Yamanaka and Makita, 1995). In TiO 2 pillared clays, most of the TiO 2 nanosized particles intercalate between the interlayer spaces of the clay mineral and only a minor fraction of TiO 2 particles seem to be present on the external surfaces of aggregated clay mineral particles (Ooka et al., 1999). Therefore, the TiO 2 pillared clay is expected to show a high photocatalytic activity (Liu et al., 2007; Ooka et al., 1999). Montmorillonite is the common and most widely used smectite (Ilisz et al., 2003). However, saponite has received an increasing attention in the last several years, particularly for the preparation of catalysts (Trujillano et al., 2009). This increasing attention is based on special properties of this clay mineral and specifically because its charge is located in the tetrahedral sheet originated by Al substitution for Si. This tetrahedral charge location has a strong influence on its acidity (Lambert and Poncelet, 1997). In addition, saponite has a noticeably higher thermal stability than montmorillonite, particularly when pillared samples are compared (Chevalier et al., 1992). Applied Clay Science 46 (2009) 363–368 ⁎ Corresponding author. Department of Geology, University of Patras, 26504, Patras, Greece. E-mail address: Papoulis@upatras.gr (D. Papoulis). 0169-1317/$ – see front matter © 2009 Elsevier B.V. All rights reserved. doi:10.1016/j.clay.2009.09.007 Contents lists available at ScienceDirect Applied Clay Science journal homepage: www.elsevier.com/locate/clay