Size-tunable TiO2 nanoparticles in mesoporous silica: Size-dependent performance in selective photo-oxidation

In order to understand the effect of nanoparticle size on photocatalytic activity in gas phase propane oxidation, TiO2 nanoparticles embedded in TUD-1 mesopores were prepared with a high degree of size control in the range 3–8 nm. One sample of TiO2-TUD-1 was prepared with Ti/Si ratio of 2.5, and during the synthesis, it was divided into four parts and hydrothermally treated for different times 8–24 h. The produced samples were characterized by means of XRD, HR-TEM, N2 sorption, and DR-UV-Vis spectroscopy. Characterization data showed that the size of the TiO2 nanocrystals is increasing with the hydrothermal treatment time. The photocatalytic activity of the four investigated samples, with identical TiO2 loading, was performed under the illumination of ultraviolet radiation λ = 335 nm, selectively activating the nanoparticles. Results showed that the initial reaction rate in photocatalytic oxidation of propane was found to be smaller for the TiO2 nanoparticles with an average size of 3.5 nm as compared to the TiO2 nanoparticles with an average size of 7.5 nm. However, the larger total available surface area lead to a higher propane consumption with higher photochemical selectivity toward acetone (desired product), as compared to the 7.5 nm particles