Applied Catalysis B: Environmental 101 (2011) 504–514 Contents lists available at ScienceDirect Applied Catalysis B: Environmental journal homepage: www.elsevier.com/locate/apcatb Preparation and characterization of monometallic (Au) and bimetallic (Ag/Au) modified-titania photocatalysts activated by visible light Anna Zieli ´ nska-Jurek a , Ewa Kowalska b,d , Janusz W. Sobczak c , Wojciech Lisowski c , Bunsho Ohtani b , Adriana Zaleska a,∗ a Department of Chemical Technology, Faculty of Chemistry, Gdansk University of Technology, 80-952 Gdansk, Poland b Catalysis Research Center, Hokkaido University, Sapporo 001-0021, Japan c Laboratory of Electron Spectroscopies, Institute of Physical Chemistry, Polish Academy of Sciences, 01-224 Warsaw, Poland d Institute of Inorganic Chemistry, Friedrich-Alexander University of Erlangen-Nuremberg, 91-058 Erlangen, Germany article info Article history: Received 20 July 2010 Received in revised form 13 October 2010 Accepted 19 October 2010 Available online 23 October 2010 Keywords: Au nanoparticles Bimetallic (Ag/Au) nanoparticles Modified-TiO2 abstract The Au-TiO 2 and Ag/Au-TiO 2 nanoparticles have been prepared using a water-in-oil microemulsion system of water/AOT/cyclohexane and water/Triton X-100/cyclohexane. The obtained photocatalysts were subsequently characterized by a BET method, DRS spectroscopy, X-ray photoelectron emission spectroscopy (XPS), scanning transmission electron microscopy (STEM) and X-ray powder diffraction analysis (XRD). For gold-doped titanium (IV) oxide nanoparticles the effect of reducing agent and sta- bilizer on gold particles size and photocatalytic activity were observed. The effect of crystalline form of TiO 2 and gold nanoparticles size on photocatalytic activity of Au-TiO 2 and Ag/Au-TiO 2 in visible light were also investigated. The photocatalytic activity of noble metals modified-TiO 2 powders under visible light irradiation was estimated by measuring the decomposition rate of phenol in an aqueous solu- tion. The best photocatalytic activity revealed samples with large gold particles (∼90 nm) deposited on small titania nanoparticles. It was also found that the bimetallic samples (Ag/Au-TiO 2 ) showed a higher photodegradation rate in visible region than monometallic photocatalysts. © 2010 Elsevier B.V. All rights reserved. 1. Introduction TiO 2 -mediated photocatalytic oxidation and reduction offer potentially an environmental friendly and cheap method for removing pollutants from gas and liquid streams and solar-to chemical energy conversion via water splitting (H 2 generation) and CO 2 reduction into light hydrocarbons. Nevertheless, due to large band gap of pure TiO 2 (from 3.0 to 3.2 eV depending on the crys- tal structure) it could be activated only by UV irradiation, limiting the utilization of sunlight as an irradiation source in photocatalytic reactions. To improve the efficiency of solar-driven photocataly- sis a few approaches were proposed such as metal and nonmetal modification [1,2]. Noble-metal nanoparticles have often been used to extend the absorption properties from the ultraviolet to visible region and to enhance the photocatalytic activity of titanium(IV) oxide [3–7]. Silver and gold nanoparticles possess ability to absorb visible light, due to localized surface plasmon resonance (LSPR). Lee et al. [8] have investigated the effect of AgNO 3 content on the physical properties of Ag-TiO 2 nanoparticles and their impacts on the photocatalytic activity in degradation process of p-nitrophenol. ∗ Corresponding author. Tel.: +48 58 3472437; fax: +48 58 3472065. E-mail address: azal@chem.pg.gda.pl (A. Zaleska). It was found that the photocatalytic activity of Ag-TiO 2 nanoparti- cles was about 60% higher than that of the pure titanium (IV) oxide [8]. Bamwenda et al. [9] compared the photocatalytic activity of Au-TiO 2 and Pt-TiO 2 nanoparticles in a process of hydrogen gen- eration. The maximum hydrogen production yield was observed for platinum- and gold-modified titanium (IV) oxide nanoparti- cles containing 0.3–1 wt% and 1–2 wt% of noble metal, respectively [9]. Sonawane et al. [10] reported the preparation method of gold-modified titanium (IV) oxide nanoparticles highly active in visible region. They found that after 1h of irradiation in pres- ence of TiO 2 16.6% of phenol was degraded, whereas 33% and 43% was degraded using 1% Au-TiO 2 and 2% Au-TiO 2 , respectively. For complete decomposition of phenol 3.5 h of irradiation of Au-TiO 2 photocatalyst containing 2% of Au was required [10]. The activity of Au-TiO 2 photocatalysts strongly depends on the preparation method and mainly on the gold nanoparticles size and shape [11]. Gold nanoparticles less than 5 nm in size are very active catalysts [12]. Large gold nanoparticles supported on metal oxide or carbon with diameter of about 50 nm and more exhibit photocat- alytic activity for hydrogen production, environmental pollution control, low-temperature catalytic combustion and reduction of nitrogen oxides [9,13,14]. In the present study, we have reported a novel preparation method and characteristics of photocatalysts obtained by gold 0926-3373/$ – see front matter © 2010 Elsevier B.V. All rights reserved. doi:10.1016/j.apcatb.2010.10.022