Spectral Features of Photostimulated Oxygen Isotope Exchange and NO Adsorption on “Self-Sensitized” TiO_2–x/TiO₂ in UV–Vis Region

Abstract

We have investigated the photoactivated O 2 adsorption/desorption, the isotope equilibration (POIEq), and the isotope exchange (POIEx) in the O 2 −(TiO 2−x /TiO 2 ) (Degussa P-25) system, as well as the adsorption and POIEx in the NO−(TiO 2−x /TiO 2 ) systems. The photoactivation spectra of the hole centers O s − generation, of POIEq, and of the NO photoadsorption were measured in the 300−500 nm range using a continuously adjustable wavelength light source. The spectral characteristics of the NO photoadsorption are close to those of POIEq Both electron-donor and hole centers are manifested in these processes. For O 2 photodesorption, CO oxidation, POIEx, and POIEq the hole centers O s − are responsible. In the case of O 2 and NO photoadsorption both types of centers are active. The maxima of POIEq and of NO photoadsorption are placed near 420 nm beyond the edge of the TiO 2 bandgap absorption. It was found that not only does the N 18 O−Ti 16 O 2 exchange occurs under the illumination but also it can be activated by a preliminary sample illumination in vacuum as it was observed for POIEq. The photoactivation spectrum does not coincide with the absorption spectra of the F-type centers (F + and F-centers, i.e., oxygen anion vacancies filled with one or two e − , respectively) and of Ti 3+ . The formation of the 2D structures, "core−shell" TiO 2−x /TiO 2 , on the parts of the surface region and the decreasing of bandgap on these parts are supposed based on the kinetic data (the "fast" excitations in the bulk under UV irradiation and the "slow" excitations on the surface under the visible irradiation) and on the spectral data (maximum action is near 420 nm for both electronic and hole centers).

Laser-flash-photolysis-spectroscopy: a nondestructive method?

“…The photooxidation of lattice bound oxygen via photogenerated holes resulting in the release of molecular oxygen has been proposed as a mechanism for O 2 formation by Salvador 56 and for the gas phase photocatalytic oxidation of organic compounds by Pichat 57,58 and Lisachenko. 59 The idea behind the mechanism of photoelectronic processes including the excitation energy transfer to the surface-atom bond resulting in the formation of an oxygen vacancy is also supported by other experimental techniques such as ion and electron bombardment, where the kinetic energy of the accelerated ions is transferred to the TiO 2 lattice. 60,61 Actually, Fukushima et al 62 observed the anatase to rutile transition during the TiO 2 lm formation by means of ion bombardment.…”

Exciton Channel of Photoactivation for Redox Reactions on the Surface of 2D ZnO Nanostructures

“…The kinetic equations for the calculation of R x , R q , and R PA from the kinetics of the partial pressures O 2 32 , O 2 34 , and O 2 36 are similar to those published in ref . Compared to ref , the present kinetics is complicated on account of the photoadsorption (formulas are provided in the Supporting Information).…”

“…The kinetic equations for the calculation of R x , R q , and R PA from the kinetics of the partial pressures O 2 32 , O 2 34 , and O 2 36 are similar to those published in ref . Compared to ref , the present kinetics is complicated on account of the photoadsorption (formulas are provided in the Supporting Information). R q is proportional to O 2 pressure, and the pressure changes slightly due to PA. To eliminate this dependency, we plot K q ≡ R q / N , where N is the number of O 2 molecules in the gas phase in a reactor chamber.…”

“…The POIE being chosen as a test reaction has been successfully used earlier − to study the mechanism of photoactivation of heterogeneous reactions.…”

“…The ZnO sample had a natural isotopic composition. The details of the experimental setup and of the results processing are given in ref .…”