Due to their large field of industrial applications ranging from catalysis to electronic, transition metal oxides are of great interest. However the major drawback of the available oxides is their low specific surface area (for example 25 m²/g for TiO2), which limits their use. The preparation of ordered mesoporous materials with a high specific area is thus an interesting way to take benefit of the intrinsic properties of transition metal oxides. Combining our experience in the field of surfactant based systems and in the preparation of silica mesoporous materials, we have developed a simple and effective route for synthesizing ordered mesoporous titania with a high surface area in short synthetic period. We propose in the framework of a PhD to design catalyst having an activity under visible light and to extend the methodology to other oxides.
Description
The PhD student will have to design catalyst having an activity under visible light. Indeed, anatase TiO2 can only absorb around 3% of the solar light which contains a small amount of ultraviolet photons. One way to expand the spectral domain toward visible consists in the coupling of titania with another semiconductor. Here, we will dope the mesoporous TiO2 with zinc by using the « milling » method. To form nanoparticlules in the mesoporous framework, the zinc precursor will be introduced in the hybrid mesophase. The surfactant removal will be performed either, by flash calcination, or by the classical calcination in a muffle furnace. The aim is to doped the mesoporous titania with a high loading of zinc. Results will be compared with the ones from the classical doping methods, which have already be employed at SRSMC. We will also investigate the synthesis of bimodal (meso/macroporous) titania. This bimodality should favor the transport guest species to framework binding sites. The synthesis procedure of the bimodal mesoporous TiO2 will be developed by the candidate. All the synthesized materials will be characterized by SAXS, nitrogen adsorption-desorption analysis, TEM, EDX, ATG, Raman, XPS…. Their photocatalytic under both ultraviolet and visible light will be tested and compared with the ones of the benchmarked oxides. The mechanism of TiO2 synthesis will also be adapted to the preparation of other oxides such as ZrO2 and MgO or mixed oxides. These oxides play a key role in catalysis. For example zirconium oxide is used as catalyst or catalyst support for various reactions. These compounds are already available but they have a low specific surface area. To increase the specific surface area of these oxides a promising way deals with the use of the method developed for the synthesis of mesoporous TiO2 by substituting the titanium precursor by the required alkoxides. Il has been reported that Zr-MCM-41 catalyzes the oxidation of cyclohexane by H2O2. This reaction will be used to evaluate the catalytic efficiency of the mesoporous zirconium oxides. This reaction is of particular important since cyclohexanone is involved in many industrial processes such as the production of nylon.
30/04/2014
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