1472 Catal. Sci. Technol., 2012, 2, 1472–1479 This journal is c The Royal Society of Chemistry 2012 Cite this: Catal. Sci. Technol., 2012, 2, 1472–1479 Photocatalyst activation by intrinsic stimulation in TiO 2 –BaTiO 3 Sarmiza E. Stanca,* Robert Mu¨ller, Matthias Urban, Andrea Csaki, Frank Froehlich, Christoph Krafft, Ju¨rgen Popp and Wolfgang Fritzsche* Received 20th March 2012, Accepted 29th March 2012 DOI: 10.1039/c2cy20169k We report a nanoparticulate composite TiO 2 –BaTiO 3 film which exhibits an increased antibacterial photocatalytic activity under visible light. The pure BaTiO 3 , TiO 2 or their mixture do not attain a significant photocatalytic capacity under visible light. However, when these oxides are simultaneously synthesized under controlled conditions the resulting crystals exhibit a high catalytic effect. The effect of this material on microorganism lysis is studied and the mechanisms for the observed damage are investigated. Attenuated total reflection Fourier transform infrared spectroscopy provides the evidence of chemical changes (formation of carbonyl and carboxylic groups) in the cell membranes under visible light by TiO 2 –BaTiO 3 but not by TiO 2 . Cyclic voltammetry demonstrates that peroxidation occurs in the absence of UV light and in the presence of TiO 2 –BaTiO 3 but not in the presence of TiO 2 alone. Atomic force microscopy reveals the morphological changes of the cells in this process. 1. Introduction Antibacterial surface coating is an efficient way to suppress microbial infections. Often a coating based on TiO 2 is utilized because its photocatalysis has been demonstrated to be a competent mechanism for bacteria and fungi peroxidation. 1–8 Upon insufficient illumination the antibacterial photocatalytic ability of TiO 2 is inhibited. 1 Therefore, TiO 2 catalytic activity was improved by its combination with silver, 9–11 silver oxide, 12 apatite 13,14 or carbon nanotubes. 15 These efforts showed only modest progress, because they have different mode of actions and thereby complicating the applicability. Here, as an alternative, we report a nanoparticulate composite TiO 2 –BaTiO 3 film whose antibacterial photocatalytic activity is improved under visible light. The pure BaTiO 3 , TiO 2 or their simple mixture do not show a significant photocatalytic effect under visible light. However, when these oxides are simultaneously synthesized under controlled conditions (see Section 2.1) a high catalytic effect is observed for the resulting crystals under visible light; this effect is studied on the bacterial strain Staphylococcus aureus (see Section 3.3). A particular energy level structure in this composite enables electron flow by using lower energy photons that can excite the electrons from the valence to the conduction band. 16,17 The photoexcited catalyst transfers electrons and energy into a ground state molecule, thereby generating a sensitized photoreaction. 1,11 The efficiency of this reaction can be amplified by enlarging the catalyst surface. 18–21 This leads to the light concentration in subwavelength volumes and, consequently, the generated energy transfer can be coupled with the electron oscillators of the nanoparticles surface. They are essentially implicated in electron exchange for energy transfer. 1,20 2. Materials and methods All chemicals were purchased from Sigma-Aldrich (Taufkirchen, Germany, puriss p.a.), except where otherwise mentioned. 2.1. Particle synthesis TiO 2 –BaTiO 3 particles were prepared by an adapted glass crystallization method. 22 A glass of composition 50BaO– 25B 2 O 3 –25TiO 2 (mol%) was melted in air at E1400 1C in a Pt-crucible. The raw materials were: BaCO 3 ,H 3 BO 3 and TiO 2 . The melt was quenched between two rotating steel rollers with a quenching rate on the order of 10 4 Ks À1 to obtain amorphous flakes. The flakes were heat treated at 480 1C for one hour to achieve the crystallization of particles in the matrix. The powder was isolated by dissolving the complete matrix with hot diluted acetic acid and afterwards rinsed with water and dried. This annealing temperature led partly to the formation of a mixture of BaTiO 3 and TiO 2 . The sample had a predominant fraction (E75%) of very fine TiO 2 -particles (anatase crystallite size o 10 nm) and a minor fraction of large BaTiO 3 -particles (crystallite size: ca. 100 nm). A specific surface area of the powder of approximately 260 m 2 g À1 was measured by a Brunauer - Emmett - Teller (BET) method using the physical adsorption of gas molecules on a solid surface. Although in our non-annealed quenched and cooled glass titanium oxide could not be detected by X-ray diffraction (XRD) we cannot exclude a small amount of TiO 2 -seeds. Institute of Photonic Technology, Albert-Einstein-Straße 9, 07745 Jena, Germany. E-mail: sarmiza.stanca@ipht-jena.de, wolfgang.fritzsche@ipht-jena.de Catalysis Science & Technology Dynamic Article Links www.rsc.org/catalysis PAPER