Applied Catalysis B: Environmental 147 (2014) 526–533 Contents lists available at ScienceDirect Applied Catalysis B: Environmental jo ur nal home p ag e: www.elsevier.com/locate/apcatb Three-phase nanocomposites of two nanoclays and TiO 2 : Synthesis, characterization and photacatalytic activities Dimitrios Papoulis a,∗ , Sridhar Komarneni b , Dionisios Panagiotaras c , Elias Stathatos d , Konstantinos C. Christoforidis e,f , Marcos Fernández-García e , Huihui Li g , Yin Shu g , Tsugio Sato g , Hiroaki Katsuki h a Department of Geology, University of Patras, 26504 Patras, Greece b Materials Research Institute, 205 Materials Research Laboratory, The Pennsylvania State University, University Park, PA 16802, USA c Laboratory of Chemistry, Department of Mechanical Engineering, Technological Educational Institute (TEI) of Western Greece, 26334 Patras, Greece d Department of Electrical Engineering, Technological Educational Institute (TEI) of Western Greece, 26334 Patras, Greece e Instituto de Catálisis y Petroleoquímica, CSIC, C/Marie Curie 2, 28049 Madrid, Spain f Department of Materials Science and Engineering and Chemical Engineering Universidad Carlos III de Madrid, Avenida de la Universidad 30, 28911 Leganés, Spain g Institute of Multidisciplinary Research for Advanced Materials, Tohoku University, Sendai 980-8577, Japan h Saga Ceramics Research Laboratory, 3037-7, Arita-machi, Saga 844-0022, Japan a r t i c l e i n f o Article history: Received 23 July 2013 Received in revised form 9 September 2013 Accepted 16 September 2013 Available online 25 September 2013 Keywords: Palygorskite Halloysite Nanocomposites Photocatalytic activity Clay minerals a b s t r a c t For the first time two different nanoclay minerals were combined with nanophase anatase for the syn- thesis of three-phase nanocomposites with improved photocatalytic properties. The novel halloysite (H) + palygorskite (Pal)–TiO 2 nanocomposites were prepared using palygorskite and halloysite from Greece. Three nanocomposites were synthesized using [Hal + Pal] to TiO 2 mass ratios of [10 + 20]:70, [15 + 15]:70 and [20 + 10]:70, respectively by depositing anatase form of TiO 2 on the clay surfaces using titanium isopropoxide as a precursor under hydrothermal treatment at 180 ◦ C. Phase composition, par- ticle morphology and physical properties of these three-phase nanocomposites were characterized by XRD, ATR–FTIR, SEM, TEM, DR-UV–Vis, N 2 -adsorption/desorption isotherms. The photocatalytic activ- ities of three-phase clay–titania nanocomposites in decomposing NO x gas and toluene vapor were determined. The three-phase clay–titania nanocomposites showed significantly higher photocatalytic activity in decomposing inorganic and organic pollutants compared to that of either palygorskite- or halloysite–TiO 2 nanocomposites under both UV- and visible-light irradiation. These studies led to a new class of clay-based nanocomposite materials with advanced photocatalytic properties. © 2013 Elsevier B.V. All rights reserved. 1. Introduction Ultra fine TiO 2 powders, especially in the form of anatase, have good catalytic activities because of their large specific surface areas as surfaces are where reactions take place [1]. Anatase has also been proven to be among the most suitable semiconductors for widespread environmental applications such as the decomposition of many air and organic pollutants [2–4]. An important drawback of anatase powders is that they easily agglomerate into larger par- ticles, resulting in an adverse effect on catalyst performance [1]. Many clay minerals have been used to synthesize nanocompos- ites with TiO 2 (especially anatase) to reduce anatase agglomeration ∗ Corresponding author. Tel.: +30 2610 997842; fax: +30 2610 997560. E-mail address: papoulis@upatras.gr (D. Papoulis). problem and to enhance the decomposition of organic and inor- ganic pollutants by photocatalytic degradation [4–6]. Intercalation of TiO 2 nanoparticles in the clay mineral structure allowed to obtain the high initial dispersion, prevented their aggregation and enhanced their photocatalytic activities [6–8]. Previous experi- ments (single clay nanocomposites) also showed that using clay minerals with microfibrous morphology increased TiO 2 photocat- alytic activity [9,10]. Recent studies revealed that dispersing the TiO 2 particles onto fibrous palygorskite [4,11] or tubular halloysite [12] surfaces under mild conditions is a promising method to obtain and maintain highly dispersed TiO 2 under reaction conditions. In this paper we describe the novel synthesis and characteri- zation of nanophase TiO 2 particles supported on a mixture of two different clay minerals with different morphologies, palygorskite (fibrous morphology) and halloysite (tubular morphology) in three different proportions, using a simplified method under mild 0926-3373/$ – see front matter © 2013 Elsevier B.V. All rights reserved. http://dx.doi.org/10.1016/j.apcatb.2013.09.025