Photocatalytic Partial Oxidation of Tyrosol: Improving the Selectivity Towards Hydroxytyrosol by Surface Fluorination of
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ORIGINAL PAPER
Photocatalytic Partial Oxidation of Tyrosol: Improving the Selectivity Towards Hydroxytyrosol by Surface Fluorination of TiO2 Hiba Khlifi1 · Filippo Parisi2 · Leila Elsellami1 · Giovanni Camera‑Roda3 · Leonardo Palmisano4 · Riccardo Ceccato5 · Francesco Parrino5
© Springer Science+Business Media, LLC, part of Springer Nature 2020
Abstract The photocatalytic partial oxidation of tyrosol to hydroxytyrosol, the most powerful and expensive natural antioxidant currently known, has been studied in irradiated aqueous suspensions of TiO2 as the photocatalyst. Three TiO2 samples, two commercial (Merck and P25® Evonik) and a home prepared one, have been used bare or surface modified. The influence of surface hydroxylation, surface fluorination, and silver nanoparticles decoration on the selectivity towards hydroxytyrosol has been investigated. The higher the hydroxyl group density, the lower the selectivity. On the other hand, fluorination improved the selectivity towards hydroxytyrosol for all of the samples. In particular, selectivity values up to 10%, i.e. ca. 10 times higher than those obtained with bare sample, were obtained in the presence of fluorinated P25 Evonik TiO2. It is proposed that the higher production of hydroxyl radicals and the lower hydrophilicity of the surface of the fluorinated sample favour hydroxylation of tyrosol and desorption of hydroxytyrosol, respectively, thus hindering the overoxidation of tyrosol. The presence of silver on fluorinated TiO2 was detrimental and it did not significantly improve the selectivity even on bare TiO2. Even if the selectivity hereby reported is relatively low, results show that the surface modification of the photocatalyst and the fluidodynamic optimization of the reacting system could make viable this interesting photocatalytic route of synthesis, which can be used also for the enrichment of some commercial polyphenolic solutions in the very valuable hydroxytyrosol. Keywords Hydroxytyrosol · TiO2 · Selectivity enhancement · TiO2 fluorination
1 Introduction Electronic supplementary material The online version of this article (https://doi.org/10.1007/s11244-020-01287-y) contains supplementary material, which is available to authorized users. * Filippo Parisi [email protected] 1
Laboratoire de Recherche Catalyse et Matériaux Pour l’Environnement et les Procédés URCMEP (UR11ES85), Faculté des Sciences de Gabès/Université de Gabès, Campus Universitaire Cité Erriadh, 6072 Gabès, Tunisia
2
Department of Physics and Chemistry, University of Palermo, Viale delle Scienze Ed. 17, 90128 Palermo, Italy
3
Department of Civil, Chemical, Environmental, and Materials Engineering, University of Bologna, via Terracini 28, 40131 Bologna, Italy
4
Department of Engineering, University of Palermo, Viale delle Scienze, Ed. 17, 90128 Palermo, Italy
5
Department of Industrial Engineering, University of Trento, Via Sommarive 9, 38123 Trento, Italy
Tyrosol (2-(4-hydroxyphenyl) ethanol, Tyr) is the most abundant natural polyphenolic compo
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