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Indexed by:期刊论文

Date of Publication:2003-12-01

Journal:JOURNAL OF CHEMICAL TECHNOLOGY AND BIOTECHNOLOGY

Included Journals:SCIE

Volume:78

Issue:12

Page Number:1246-1251

ISSN No.:0268-2575

Key Words:photocatalytic selective oxidation; cyclohexane; titanium dioxide; oxide semi-conductors; nanosize particles

Abstract:The structure, physical characteristics and photocatalytic selective oxidation properties of nanometer-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 less than or equal to973 K, that the rutile structure begins to emerge at annealing temperatures greater than or equal to973 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(l) at g = 1.926 and a weak broad Bulk-Ti3+ signal (11) 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. (C) 2003 Society of Chemical Industry.