Conception de matériaux macroporeux de type opale inverse à des fins photocatalytiques dans le domaine du visible

Abstract

To reduce the pollution due to volatile organic compounds, numerous techniques were developed. One of the most promising is the photocatalysis. However, it presents two major inconveniences in its implementation. The first one concerns the range of activity of the photocatal
yst which is, in the majority of the cases, limited to the energy coming from UV radiation of the sun (5 % of the total energy). The second is the absorption of these photons is relatively weak (20 %).
To solve these problems, the proposed solution was the development of materials capable of absorbing in the visible domain of the light (reduction of the electronic band gap by doping, use of atypical semiconductor) in the form of inverse opal (increase of the time of presence of photons). To do it, three materials were studied: titanium dioxide (doped afterward to reduce the electronic band gap), zinc oxide and vanadate of bismuth (already active in the visible).
The first step of this work concerned the study and the design of the opaline template to understand better the link between beads composing the opaline structure and the defects leads(infers) by these balls in the assembly of the photonic crystal. The highlighting of the intrinsic defects connected to
the assembly of the template allows explaining the majority of the structural defects observed in the inverse opals.
The doping of titania inverse opals aimed at moving the light absorption of materials towards the visible domain of the solar spectrum. The use of cationic doping agent showed a low effectiveness for the improvement of the photocatalytic properties in opposition with the theoretical studies published in the literature. In particular, the doping with vanadium modified profoundly the properties of adsorption of materials, reducing drastically the capacity of the material to photooxidize the tested molecules. The doping in the hafnium, never realized before these researches, allowed to move the range of photocatalytic activity in the field of the visible combine with a reduction of the number of active site within the
material. In parallel, the study of the anionic doping with nitrogen showed a big capacity to increase the photocatalytic activity of materials. This activity is strongly connected to the incorporation way of doping and is thus very dependent on the method of insertion of nitrogen within the crystal. The highlight of these results proves the variation which it is possible to obtain by playing on the incorporation of an ion within the structure. These researches so highlighted the difficulty of prediction of the photocatalytic answers of
materials studied on the mere knowledge of the ions in presence.

Date of Award	5 Feb 2016
Original language	French
Awarding Institution	University of Namur
Supervisor	BAO LIAN SU (Supervisor), Carmela Aprile (President), Benoit Heinrichs (Jury), Alexandru Vlad (Jury), Olivier Deparis (Jury) & Steve Lanners (Jury)