Selective photocatalytic syntheses of valuable carbonyl molecules in environmentally friendly conditions using hydrothermally prepared Nanorod/Nanotube-Like TiO2

• Efficient Nanorod/nanotube-like TiO 2 was obtained by hydrothermal (HT) process. • 130 °C in HT is insufficient to transform crystalline TiO 2 into its precursor, unlike HPRT. • New information was obtained by XPS, PL and DRS depending on TiO 2 crystallinity. • The HT samples showed much higher photocatalytic activity and selectivity. • The photocatalytic and photolytic reaction pathways were different. Nanorod/nanotube-like TiO 2 photocatalysts were prepared hydrothermally at 130, 155, or 180 °C starting from commercial anatase (Merck) or home-made rutile TiO 2 samples, which were then calcined at different temperatures. After the hydrothermal process, the anatase or rutile TiO 2 samples mainly rearranged into a mixture of low crystallinity anatase solid with a high specific surface area (up to 336 m 2 /g). The samples were characterized by XRD, SEM, BET, XPS, DRS, FT-IR, TGA, PL, and (photo)current analyses. New relationships between the TiO 2 crystallinity and the XPS, PL and DRS analysis results were obtained. TiO 2 catalysts were used for the partial oxidation of 3-methylpyridine, 3-pyridinemethanol and 4-methoxybenzyl alcohol to the corresponding carbonyl molecules and showed much better results than the commercial anatase one, used for comparison. The calcination temperature influenced the product conversion rate and the product selectivity, the latter being obviously mainly dependent on the type of substrate. In fact, those calcined at 300 °C after hydrothermal treatment showed the best results in terms of both photoactivity and selectivity towards the oxidation products of 3-methylpyridine and 3-pyridinemethanol, while those calcined at 500 °C proved to be more efficient for the oxidation of 4-methoxybenzyl alcohol. The presence of scavengers during photocatalytic reactions was also used to indicate which radical species and/or directly photoproduced electrons and holes influenced the reaction rate and selectivity towards the oxidation product.