6533b7d2fe1ef96bd125f2bb

RESEARCH PRODUCT

Micro/nanostructured thin films : synthesis by ALD of composites associating TiO2 inverse opals and gold nanoparticles for photocatalysis applications

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The aim of this work was to improve the photocatalytic properties of titanium dioxide (TiO2) thin films, a semiconductor that is widely used for photocatalysis applications, particularly for the treatment of polluted water. For this purpose, two complementary approaches were studied: increasing the surface area available for photocalatytic reactions and coupling between TiO2 and gold nanoparticles.. For the first approach, TiO2 thin films with different morphological structures were fabricated by Atomic Layer Deposition: dense and porous flat films, and inverse opals films.In order to evaluate photocatalytic activity of the different films, the degradation of methylene blue in aqueous solution was studied under UV irradiation of the photocatalysts. The maximum of degradation was reached using inverse opals films. Porous flat films led to a faster degradation than dense flat films. These results showed that the larger the surface of the photocatalyst is, the higher the photocatalytic activity is obtained. In the case of the plane films, two kinetic regimes were observed. This was explained by a hindrance of the active sites by the reaction products which limits le reaction rate after a few hours of degradation. In the case of inverse opal films, only one kinetic regime was observed. The surface area available for the reactions is sufficiently large that the congestion of the active sites does not play a major role in the overall kinetics of the reaction.For the second approach, we sought to improve the photocatalytic activity with the synthesis of composite films coupling TiO2 with gold nanoparticles. A protocol allowing the deposition of gold nanoparticles between two TiO2 deposition steps using the ALD device has been developed. Flat and dense composite films, as well as inverse opals films were synthesized. The study of the degradation of methylene blue using these films as photocatalysts under UV exposure showed a 50% higher reaction rate for TiO2/Au inverse opal films compared to pure TiO2 inverse opals. Under UV exposure, the transfer of electrons promoted at the conduction band of TiO2 towards the gold nanoparticles limits the recombination of charges in TiO2 which is detrimental to the photocatalytic process. Photocatalytic tests under visible irradiation have shown a much faster degradation kinetics thanks to the mechanisms involving the plasmon resonance of gold nanoparticles.In conclusion, the results of this thesis validate the approach of improving the photocatalytic properties of TiO2 films by incorporating gold nanoparticles in inverse opal TiO2 films.