Soutenance publique de thèse de doctorat en Sciences - Thomas Lourdu MADANU

Investigating slow photon effect in inverse opal photonic structures for photocatalytic applications

Jury

• Prof. Alexandru VLAD (institut de la matière condensée et des nanosciences, UCLouvain)

• Prof. Olivier DEPARIS (département de physique, UNamur)

• Prof. Catherine MICHAUX (département de chimie, UNamur)

• Prof. Bao-Lian SU (département de chimie, UNamur)

• Prof. Benoit CHAMPAGNE (département de chimie, UNamur)

• Prof. Alain KRIEF (département de chimie, UNamur)

• Prof. Yu LI (Wuhan University of Technology)

Résumé

Photocatalytic hydrogen generation from water is one of the most sustainable and eco-friendly energy conversion processes since it utilizes naturally available resources like sunlight and water, to produce a zero-emission fuel. Significant efforts have been made to actualize this process, but the minimum solar-to-hydrogen conversion efficiency required to implement it at the industrial scale has not been achieved. Reasons for this include insufficient solar light absorption, inefficient exploitation of absorbed light to generate charge carriers, sluggish charge transfer kinetics, and ineffective charge utilization to drive surface redox reactions. The primary challenge in this process is light absorption. Strategies employed so far to improve solar light absorption have focused mainly on the choice and modification of materials. However, the strategy of modifying the propagation of light to enhance light harvesting is underexplored. Photonic structures, thanks to their periodic structures with alternating refractive indices, possess unique ability to modify the propagation of light, particularly the ability to reduce the group velocity of light at specific frequencies and localize it within the structure. These ‘slow photons’ can be used to enhance light harvesting and photocatalytic activity, especially when their frequencies are tuned to the electronic absorption of the photocatalyst.
 
In this thesis, we investigate the utilization of slow light in inverse opal TiO2-based photonic structures to enhance light harvesting in photocatalytic dye degradation and then in hydrogen generation from water, our ultimate objective. Firstly, we synthesized high-quality inverse opal TiO2 photonic structures and embedded them with visible light responsive BiVO4 nanoparticles. The frequencies of slow photons generated in the TiO2 photonic structure were tuned through lattice parameter and incidence angle variations to the electronic absorption of BiVO4, to obtain up to a seven-fold increase in photocatalytic dye degradation compared to the non-structured compact films. Secondly, since slow photons are limited to narrow spectral regions, we generated slow photons at multiple spectral regions by synthesizing bilayer inverse opal structures with different periodicities in each layer, to achieve a two-fold increase in photoactivity compared to the monolayer structures. Finally, we employed slow photon-assistance in photocatalytic H2 generation over inverse opal TiO2 sensitized with CdS, Au, and Pt nanoparticles, to achieve an 8-fold increase in H2 evolution, under optimal tuning conditions, compared to that over pristine inverse opal TiO2.
 

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