Abstract
Carbohydrates share 75 % of the total plant biomass resources. After chemical modifications, a variety of higher added value molecules can be obtained with potential ability to replace some chemicals issued from petrochemicals. Nevertheless, the conventional glycochemistry does not comply completely with the green chemistry principles. With the aim of producing biosourced molecules, the development of greener procedures is needed. One possible approach investigated in my Ph-D thesis is to integrate photo-activated catalyst to prompt selective transformation of carbohydrates. More specifically, my Ph-D work aims at focusing on the photocatalytic mechanisms involved in the selective photo-oxidation of free glucose under standard white light illumination (Air Mass 1,5G) using Au/CeO2 as a photocatalyst. A better understanding of the involved mechanisms is an essential unit block to deepen the fundamental knowledge in this rising field while developing new pathways allowing selectively to convert other hydroxyl functions of the sugar. The Au/CeO2 photocatalyst synthesized by photo-reduction of Au3+ species in solution exhibits the best photocatalytic properties with respect to glucose oxidation. One important highlight of my work is the evidence of a kinetic competition upon glucose photo-oxidation between surface-driven catalysis and photocatalysis activity when associated to Au/CeO2 photocatalyst. The different experimental results suggest that the size of gold nanoclusters is the one important parameter governing this competition and that the ratio between the two competitive reactions is a function of time driven by size evolution of the gold nanoclusters upon photo-oxidation. Regarding the photocatalytic reaction, our results support that selective glucose photo-oxidation stems from CeO2 bandgap excitation rather than plasmonic resonance of the gold nanoclusters. Electron spin resonance spectroscopy highlights the existence of radical species formed in solution under illumination, which are part involved in the glucose photo-oxidation reaction. Other gold-supported photocatalysts as Au/g-C3N4, Au/TiO2, Au/BiOCl, Au/Fe3O4 or Au/Fe3O4/CeO2, were prepared to explore the possibility to modify the reaction selectivity by controlling the oxidation strength of the valence band of the supporting material. The preliminary results, still in progress, constitute a first attempt to modify the selectivity of the photo-oxidation reaction