Abstract :
[en] In this work, a TiO2 aqueous sol-gel process was developed to produce, at large scale, photocatalysts with hydrophilic property and high activity, both under visible and UV/visible light, for water and air remediation.
The first step was to develop an easy aqueous sol-gel synthesis of pure TiO2 at laboratory scale. The synthesis protocol was simplified to reduce the synthesis time, the temperature and the number of steps as washing step. The physico-chemical and photocatalytic properties of the obtained materials have been characterized to assess the production of hydrophilic coatings on stainless steel and the formation of efficient photocatalysts for the degradation of three pollutants (methylene blue, p-nitrophenol or acetaldehyde) under different shapes (film or powder) and in different phases (liquid or gaseous). Then this synthesis has been up-scaled to a volume of 5 L and deposited with a pilot line on stainless steel. The produced coating was characterized and compared to the laboratory material to show the successful operation of up-scaling.
In second part, the aqueous synthesis was adapted to produce TiO2 catalysts doped with Fe3+, Ag+, Cu2+, Zn2+, Cr3+, Al3+, Mn2+, and Co2+ ions and Pt metallic nanoparticles in order to improve their activity. Some dopants showed an increased photoactivity and some mechanisms were proposed to explain these modifications of activity with doping. Furthermore, cost comparison at laboratory scale showed that Zn2+ doping may be considered for industrial applications. Using this method, a large scale Zn-doped TiO2 photocatalyst was synthesized with properties homologous to the lab-scale product.
The third step was to study the redispersion property of the nanocrystalline TiO2 colloids. Indeed, the powders obtained by air drying of these colloids can be redispersed in water to produce colloids which are compared to the initial one. Five cycles of drying-redispersion were achieved on selected colloids. A mechanism was proposed to explain this interesting property, acid present in the synthesis seems to be the main factor. This would be very useful for an industrial application of this synthesis allowing to reduce the volume and weight for transportation and storage.
In the last part of this work, the aqueous TiO2 photocatalyst was modified to extend his activity towards visible light. In this aim, silylated porphyrin and nitrogen-based reagents were used. The silylated porphyrin was synthesized in laboratory and co-hydrolysed with a titanium precursor in aqueous medium to produce hybrid TiO2 photocatalyst. Results showed that the porphyrin fragments are held to the resulting matrix through strong Si-O-Ti covalent bonds limiting leaching of the former and an increased photoactivity under visible was obtained. Concerning nitrogen doping, three N-precursors were used: urea, ethylenediamine and triethylamine. Results showed the incorporation of nitrogen in TiO2 materials allowing absorption in visible region and improvement in visible activity on the remediation of polluted water with p-nitrophenol. The best doping, regarding cost, activity and ease of synthesis, was successfully up-scaled to volume of 5 L and compared to commercial Degussa P25 material.
