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| Photocatalytic oxidation Research/Technology Areas: Photocatalytic selective epoxidation of styrene by molecular oxygen over highly dispersed titanium dioxide species on silica Photocatalytic oxidation (PCO) currently receives enormous attention because of its potential application in environmental treatment and fine chemical synthesis. For photocatalytic selective oxidation, styrene epoxidation is of industrial importance and TS-1 has been used to catalyze this reaction with H sub 2 O sub 2 as oxidant. In terms of oxidant, dioxygen (O sub 2) is clearly the most desirable due to its ready availability and high reduction potential. Current research looks at photocatalytic selective epoxidation of styrene over highly dispersed TiO sub 2 nanoparticles in SiO sub 2 matrix with molecular oxygen under mild conditions. The structure, physical characteristics and photocatalytic selective oxidation properties of nanometre-size TiO2 particles produced by a sol–gel method were studied by X-ray diffraction (XRD), diffuse reflectance spectroscopy (DRS), X-ray photoelectron spectroscopy (XPS), electron paramagnetic resonance (EPR) and photocatalytic selective oxidation measurements. Analysis of the XRD results shows that sol–gel-produced TiO2 nanoparticles have the anatase structure at annealing temperatures 973 K, that the rutile structure begins to emerge at annealing temperatures 973 K and the particles have the pure rutile structure at 1023 K. DRS indicates that the obtained TiO2 nanoparticles exhibit a blue shift with decreasing crystallite size. Analysis of the XPS results shows that the TiO2 nanoparticles have a lot of oxygen vacancies. The EPR spectrum of TiO2 at 77 K is composed of a strong isotropic EPR Surface-Ti3+ signal(I) at g = 1.926 and a weak broad Bulk-Ti3+ signal (II) at g = 1.987. Quantitative EPR indicates that both signals show a size and temperature dependence. Photocatalytic oxidation of cyclohexane into cyclohexanol with high selectivity and activity has been obtained by activation of molecular oxygen over sol–gel-produced TiO2 nanoparticles under mild conditions in dry solvent, which reveals that the quantum size effect and surface state effect of nanoparticles are key points for governing the selective photocatalytic reaction. The photocatalytic oxidation mechanism under dry solvent is different from that in aqueous solutions. |
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