Rutile nanostructures: Synthesis, characterization and potential application in photocatalytic processes

Abstract

Titanium dioxide is one of the most studied semiconductors because of its wide range of potential technological applications including pigments, cosmetics, photovoltaic cells and catalysis. TiO2 has three most commonly encountered crystalline polymorphs: anatase, brookite and rutile. The possible application of TiO2 critically depends on crystalline structure, size and shape of the particles. Rutile has the highest density and refractive index and is widely employed in pigments and cosmetic industry. TiO2 is transparent in the visible light region; its band gap is 3.0 eV for rutile and 3.2 eV for anatase crystalline phase. By doping or sensitization, it is possible to improve the optical activity of TiO2 and to move its absorption threshold into the visible light region. The subject of this chapter is different rutile nanostructures of pure and Fe3+-doped titania which were synthesized by co-precipitation in acidic aqueous solution. Obtained materials were characterized by structural (XRD), morphological (TEM and HRTEM), optical (UV/vis absorption, reflection, and photoluminescence), and analytical (XPS and ICP-OES) techniques. Also, photo-catalytic activity measurements were performed, using photo-degradation of specific herbicides as model systems. Applied synthetic procedure resulted in formation of flower like agglomerates of 200-400 nm in diameter. Agglomerates represent assembly of nano-rods consisted of ''chains'' of spherical particles, 5-7 nm in diameter, most likely interconnected through the so-called oriented attachment or grain-rotation induced-grain coalescence (GRIGC) process. The presence of dopant iron ions didn't distract morphology of rutile nano-particles, nor agglomerates, but significantly changed optical properties of titania compared to pure material. The photoluminescence of pure and Fe-doped rutile nano-particles is characterized with several well-resolved peaks extending in the visible spectral region. Photon energy up-conversion from rutile TiO2 nano-particles was also observed at low excitation intensities. The energy of up-converted photoluminescence spans the range of emission of normal photoluminescence. The explanation of photon energy up-conversion involves mid-gap energy levels originating from oxygen vacancies. © 2012 Nova Scicence Publishers, Inc. All rights reserved.