303 Influence of Manganese Oxides on the Optical Absorption and Photocatalytic Activities of Titanium Dioxide L. Kernazhitsky 1,* , V. Shymanovska 1 , T. Gavrilko 1 , V. Naumov 1 , T. Khalyavka 2 and V. Kshnyakin 3 1 Abstract. Nanocrystalline titanium–manganese mixed oxides (TMMO) with Mn content of 13–16 at. % were first synthesized by manganese hydroxide precipitation on anatase or rutile particles. UV–vis absorption spectra were investigated in 2.4–6.0 eV region and revealed that compared with pure TiO 2 the presence of manganese oxides results in an increase of the absorption intensity and significant red shift of the TMMO absorption edge. Photocatalytic activity of pure TiO 2 , Mn 2+ doped TiO 2 and TMMO during the photocatalytic decomposition of the safranine dye under UV irradiation was studied. A great improvement of photocatalytic activity is registered for Mn 2+ -doped TiO 2 (anatase and rutile), and rutile-based TMMO sample. Key words: titanium–manganese mixed oxides, optical properties, photocatalysis, safranine dye. I. INTRODUCTION The wide technological usage of TiO 2 for photo-catalysis, is impaired by its large band gap (3 eV for rutile and 3.2 eV for anatase), which requires UV irradiation. In order to improve the photoactivity as well as the response in the visible part of spectrum TiO 2 is doped by different admixtures: ions of transition metals, nitrogen, sulphur, and other [1]. Among them, the couple TiO 2 /MnO x seems to present interesting optical and photocatalytic properties. In the present work the optical and photocatalytic properties of the first synthesized titanium–manganese mixed oxides (TMMO) with different Mn contents (13– 16 at.%) were reported. II. EXPERIMENTAL The TMMO samples were synthesized by chemical precipitation of manganese hydroxide on pure polycrystalline TiO2 particles (rutile or anatase) with subsequent thermal treatment at different temperatures - 300, 850, 900 and 1000°C. According to XRD, EDS, XRF data, the synthesized TMMO materials are polydisperse compounds of different phase composition (Table 1). It is shown that the TMMO-1 anatase sample calcined at 850 o contain TiO 2 and Mn 2 O 3 oxides. At the same time, the high- temperature-treated TMMO-2 and TMMO-3 rutile (heated up to 900 and 1000 o ) contains also MnTiO 3 in their 1 Institute of Physics, National Academy of Sciences of Ukraine, Kyiv, Ukraine 2 Institute for Sorption and Problems of Endoecology, NAS of Ukraine, Kyiv, Ukraine 3 Sumy State University, Sumy, Ukraine * kern@iop.kiev.ua structure. The average crystallite sizes of TiO 2 , Mn 2 O 3 and MnTiO 3 phases in TMMO were determined from XRD line broadening using the Scherrer equation and appeared to be equal to 52-120, 36-45 and 33-40 nm for TMMO, correspondingly. For comparison, the samples of pure rutile and anatase, as well as rutile and anatase surface-doped TiO 2 by Mn 2+ cations by adsorption from MnCl 2 solutions, were synthesized and studied in parallel. Table 1. Chemical composition and parameters of the samples Sample T, °C Mn content, % at. Phase composition Phase content, % wt. Crystallite size, nm (Dhkl) Pure TiO2 An 300 0 Anatase 100 13.3 (101) Ru 300 0 Rutile 100 20.8 (110) Mn 2+ adsorption on TiO2 An/Mn 300 1.0 Anatase 100 15.4 (101) Ru/Mn 900 1.0 Anatase Rutile 10.2 89.8 70.8 (101) 40.3 (110) Mn hydroxide precipitation on anatase TMMO-1 850 13.4 Anatase Rutile Mn2O3 54.6 35.6 9.7 42.2 (101) 51.7 (110) 44.8 (222) Mn hydroxide precipitation on rutile TMMO-2 900 15.6 Rutile Mn2O3 MnTiO3 85.7 12.1 2.2 120.8 (110) 36.0 (222) 32.6 (104) TMMO-3 1000 13.4 Rutile MnTiO3 86.0 14.0 62.6 (110) 39.9 (104) The absorption spectra in the UV-vis range for pure TiO 2 (rutile and anatase) and TMMO were measured in 2.5- 6.0 eV range. The activity of TMMO and surface-doped TiO 2 /Mn 2+ in the reaction of safranine dye photocatalytic destruction under UV irradiation was studied. III. RESULTS AND DISCUSSION Experimental UV–vis absorption spectra for pure nanocrystalline TiO 2 powder (rutile or anatase) and TMMO samples measured in a photon energy range from 2 to 6 eV are shown in Fig. 1 and Fig. 2. The UV–vis absorption spectra have complicated character, but the main features are invariable for all samples. In the region from 2.5 to 3.0 eV a "tail" absorption of TiO 2 , caused by optical transitions between the states located above the top of the valence band (from 0 to 0.5 eV) and the bottom of the conduction band, are observed. These states can be associated with the bulk structure defects in TiO 2 and can be populated by the thermal excitation of electrons at room temperature from the valence band. It is supposed that a significant increase in the absorption for TMMO-2, 3 rutile by 4-5 times as compared with pure rutile (Fig. 1), is due to the superimposed broad