Nano-crystalline porous anatase TiO2 for environmental applications: Synthesis process and transport characteristics study
We have measured Raman scattering spectra of pure and iron-doped Ce1-xFex2+(3+)O2-y (x = 0, 0.06, and 0.12) nanocrystals. According to the x-ray diffraction study, Fe doping produces contraction of the CeO2 unit cell, leading to the Raman mode hardening. Contrary to expectation, the F-2g Raman mode exhibits softening and broadening by changing the valence state of Fe dopant, as a consequence of the electron-molecular vibration coupling. This finding supports the assumption that additional charge in highly oxygen-deficient pure and Fe-doped CeO2-y samples are not only localized at Ce3+ ions but also delocalized onto Ce(Fe)-O(V-O)-Ce(Fe) orbitals. Delocalization of electrons from Ce3+ ions causes insulator-to-metal transition in highly oxygen-deficient nanoceria. The far-infrared reflectivity spectrum of nanoceria shows metalliclike reflectivity, which in the low-frequency region is well fitted with the Hagen-Rubens approximation for metals. Photoluminescence measurements revealed the existence of a defect-related band in the energy gap of CeO2-y. The electron-molecular vibration (phonon) coupling constants lambda and density of electron states at the Fermi level per spin and molecule N(0) were determined within the framework of Allen's theory. The proposal of an energy band structure of nanoceria is also presented. [hide]
Principal Investigators
Igor Stankovic (CoPI)
Scientific Computing Laboratory Belgrade, Serbia ►
Zorana Dohcevic-Mitrovic (CoPI)
Center for Solid State Physics & New Materials Belgrade, Serbia ►
Martin Kroger (PI)
Polymer Physics, ETH Zurich, Switzerland ►
Investigators
Zoran V. Popovic
Center for Solid State Physics & New Materials Belgrade, Serbia ►
Alexsandar Golubovic
Center for Solid State Physics & New Materials Belgrade, Serbia ►
Maja Scepanovic
Center for Solid State Physics & New Materials Belgrade, Serbia ►
Mirjana Grujic-Brojcin
Center for Solid State Physics & New Materials Belgrade, Serbia ►
Alexsandar Belic
Scientific Computing Laboratory Belgrade, Serbia ►
Slobodan Vrhovac
Scientific Computing Laboratory Belgrade, Serbia ►
Involved Students
Sonja Askrabic
Center for Solid State Physics & New Materials Belgrade, Serbia ►
Milan Zezelj
Scientific Computing Laboratory Belgrade, Serbia ►
Dusan Vudragovic
Scientific Computing Laboratory Belgrade, Serbia ►
Jelena Smiljanic
Scientific Computing Laboratory Belgrade, Serbia ►
Jaksa Vucicevic
Scientific Computing Laboratory Belgrade, Serbia ►
Milos Radonjic
Scientific Computing Laboratory Belgrade, Serbia ►
Marko Mladenovic
Scientific Computing Laboratory Belgrade, Serbia ►
Titanium dioxide (TiO2) is an important photo catalyst due to its strong oxidizing power, non-toxicity and long-term photo stability. The interest in nano-crystalline anatase TiO2 has been driven by its potential for a variety of technological applications including photo catalysis, electrochemical solar cells, optoelectronic devices, chemical sensors, and dielectric material of thin-film capacitors. Together with cerium dioxide (CeO2), porous TiO2 is seen as a material for the production of molecular hydrogen from water using sun energy in a photo catalytic reaction process. In addition, nanocrystalline anatase TiO2 is a weak magnetic semiconductor with proven room temperature ferromagnetism. This opens the possibility for the use of TiO2 in second-generation spintronic devices. Its ferromagnetic properties can be enhanced with the addition of transition metals such as iron, cobalt, or vanadium. Approximately 4 million tons of TiO2 are consumed annually worldwide. the principle use today being that of a bright white pigment.The enumerated properties of TiO2: catalytic, porous structure, and ferromagnetism, can be fully utilized only if they are combined: (i) Applications such as pollution monitoring or leak localization in chemical plants require high sensitivity and selectivity. By discriminating between different patterns of diffusion it is possible to enable this class of sensors to recognize different molecules (ii) The distribution of TiO2 pore diameters determines the collision frequency of molecules with the pore walls and thus also the frequency of catalytic reactions. Porous media can be specifically designed and engineered so as to balance between rates of reactant inflow, chemical reaction, and outflow. (iii) In photo-hydrolysis, hydrogen is produced from solar energy. In order to achieve this ambitious goal, it is necessary not only to understand the surface interaction between TiO2 and the molecules of water, hydrogen and oxygen, but also the transport of water into the nanopores as well as the transport of oxygen and hydrogen out of them. (iv) Finally, an external magnetic field could be applied as additional parameter during the technological process in which porous TiO2 media is synthesized. If brought to application, porous structures with anisotropic geometries could be created, i.e., elongated pores in magnetic field direction. In Gräel dye solar cells, such pore geometries would lead to shorter electron diffusion paths towards the metal electrode and improve the efficiency of the whole system.
The main objectives of this project are: (1) synthesis of porous TiO2 nanocrystals through the utilization of a novel and cost effective sol-gel method and the full characterization of the obtained structural and optical properties and (2) creation of multi-scale models and simulations specifically designed for the development of environmental TiO2 based technology.
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Selected conferences (co-)organized by project members
IWNET 2009
08 Sep - 10 Sep 2009, Eternal Spring City of Cuernavaca, Mexico ►29 March 2024 mk