The adsorption and photodesorption of oxygen on the TiO2(110) surface

Abstract

We have investigated the adsorption and thermal conversion of molecular oxygen (O2) states on the TiO2(110) surface by making use of the distinct photodesorption behavior of each adsorption state. Oxygen chemisorbs at the oxygen vacancy defect sites on the annealed TiO2(110) surface at 105 K to a saturation coverage of less than 0.12 monolayers (ML), producing mostly the α-O2 species which is observed to undergo slow photodesorption. Upon heating this surface to above 250 K, the α-O2 is converted to the β-O2 state which can photodesorb at a significantly higher rate. The β-O2 species dissociates above 400 K to produce atomic oxygen, eliminating the oxygen anionic vacancies. Both the α- and β-photodesorption processes have a threshold energy at the TiO2 band gap (3.1 eV), indicating a substrate excitation mediated process. The photodesorption time-profile is fitted with an exponential decay function with a cross section of ∼8×10−17 cm2 for the α-O2 and ∼1.5×10−15 cm2 for the β-O2 species at a photon energy of 3.94 eV.

Preparation of a TiO<SUB>2</SUB> Film Coated Si Device for Photo-Decomposition of Water by CVD Method Using Ti(OPr<SUP>i</SUP>)<SUB>4</SUB>

“…Since only the peak for adsorbed carbon, such as CO 2 , was observed, it is considered that the i-PrOH and its derivative organic compounds did not exist in the film. The observed peak values for Ti2p 3/2 electrons is 459.2 eV and in good agreement with the typical binding energy of Ti2p 3/2 electron, 459.2 eV, for the anatase type TiO 2 .…”

“…Titanium dioxide (TiO 2 ) has been expected as a material for the photo-decomposition of water, 1,2) however, the efficiency of the photocatalytic decomposition process of water into oxygen and hydrogen is not sufficiently high since TiO 2 is only active in the ultraviolet region (Eg = 3.2 eV). If there are any chemically stable devices which are useful in the visible region, it is possible to increase the efficiency of the photocatalytic decomposition process of water.…”

“…We have proposed a new design of such devices 3) in which a conventional closed circuit photoelectrochemical cell 1,2,4) employing an anode of the TiO 2 /Si device and a metal (Pt in most cases) cathode is used. The hetero-structure and energyband structure of the TiO 2 /Si device are shown in Figs.…”

Photo‐induced processes in heterogeneous nanosystems. From photoexcitation to interfacial chemical transformations

“…In terms of defect formation, the interaction of O −• 2 anion radicals with photo-holes at the TiO 2 particle surface, which leads to photodesorption of O 2 molecules [9,10] or to dissociation of the O −• 2 anion radical into oxygen atoms, as proposed by Formenti and Teichner [11], can be characterized as recombination decay of photo-induced centers. Clearly, these external and internal cycles compete with each other.…”

“…Note that equation (9) can be cast into the Langmuir-Hinshelwood form when the photon flow ρ is constant. Also note that equation (9) can be used to describe all the experimental dependencies of the reaction rate on light intensity (photon flow).…”