Electron traps and their effect on the surface chemistry of TiO2(110) (original) (raw)
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The Journal of Physical Chemistry C, 2009
The reactions of molecular oxygen with bridging hydroxyl groups (OH b 's) formed by H 2 O dissociation on bridging oxygen vacancies (V O 's) of TiO 2 (110) are studied at low and high OH b coverages as a function of the O 2 exposure, using scanning tunneling microscopy, temperature programmed desorption, and electron stimulated desorption techniques. In agreement with prior studies, oxygen adatoms (O a ), hydroperoxyls (HO 2 ), and terminal hydroxyls (OH t ) are observed as intermediates of the reactions with O 2 ultimately leading to H 2 O as a product. Here, we show that water plays an important role in the room-temperature reactions of O 2 with both partially and fully hydroxylated TiO 2 (110). On partially hydroxylated surfaces, water is found to be involved in the reaction cycle that leads to the consumption of O a and V O sites thus resulting in a practically O a -and V O -free surface. In these reactions, water is observed to participate in multiple wayssas a reactant, product, and catalyst. On fully hydroxylated TiO 2 (110), water is found to mediate the diffusion of surface species such as OH b that would otherwise be stationary and thus brings reactants together, catalyzing the reactions with O 2 . As a result, the O a , HO 2 , and OH t intermediates are not observed in STM, while OH b species are available on the surface.
Bridging Hydroxyls on Anatase TiO2(101) by Water Dissociation in Oxygen Vacancies
The journal of physical chemistry. B, 2017
Titanium dioxide is a promising candidate for photocatalytic H2 fuel production, and understanding water splitting on TiO2 surfaces is vital toward explaining and improving the generation of H2. In this work, we electron irradiate anatase TiO2(101) at room temperature to create metastable surface oxygen vacancies in order to investigate their ability to dissociate H2O. Our scanning tunneling microscopy investigations suggest that the surface oxygen vacancies can dissociate H2O by forming bridging OH species. This claim is supported by theoretical calculations from the literature and our previously published spectroscopic measurements.
Israel Journal of Chemistry, 2005
We review the adsorption and desorption of molecular oxygen on a reduced TiO 2 (110) surface. This system is known to play a fundamental role in heterogeneous photocatalysis. Periodic calculations are performed with the objective of characterizing the variety of stable species of O 2 that are known to exist on the TiO 2 surface. The implications of our results for recent experiments are discussed. We also consider a direct optical excitation mechanism for the ultraviolet (UV) light-desorption process and model the most stable O 2 /TiO 2-x system as a cluster. High-level ab initio calculations of the excited states and interaction matrix elements are performed using different orbitals, separately optimized for the target states. The nonadiabatic and dipole-moment couplings are calculated directly from the correlated wave functions by a special transformation to bi-orthonormal (dual) orbital sets to preserve their structure. The method used for the electronic structure calculations is described in detail. Finally, the effect of the electronic coupling in the UVphotodesorption dynamics is analyzed in detail.
Oxidation and Photo-Oxidation of Water on TiO 2 Surface
The Journal of Physical Chemistry C, 2008
The oxidation and photo-oxidation of water on the rutile TiO 2 (110) surface is investigated using density functional theory (DFT) calculations. We investigate the relative stability of different surface terminations of TiO 2 interacting with H 2 O and analyze the overpotential needed for the electrolysis and photoelectrolysis of water. We found that the most difficult step in the splitting of water process is the reaction of a H 2 O molecule with a vacancy in the surface to form an adsorbed hydroxyl group (OH*). Comparison to experiment shows that the computed overpotential for O 2 evolution (0.78 V) is available under the experimental conditions required for both oxygen and hydrogen evolution.
Electron Transfer-Induced Dynamics of Oxygen Molecules on the TiO2(110) Surface
Science, 2004
Diffusion of oxygen molecules on transition metal oxide surfaces plays a vital role for the understanding of catalysis and photocatalysis on these materials. By means of time-resolved scanning tunneling microscopy, we provide evidence for a charge transfer-induced diffusion mechanism for O 2 molecules adsorbed on a rutile TiO 2 (110) surface. The O 2 hopping rate depended on the number of surface donors (oxygen vacancies), which determines the density of conduction band electrons. These results may have implications for the understanding of oxidation processes on metal oxides in general.
Modelling and Simulation in Materials Science and Engineering, 2008
The atomic geometry of a TiO 2 (1 1 0) surface upon creation of an oxygen defect site and formation of a hydroxyl group was investigated using 3 × 1, 2 × 2 supercells by spin polarized density functional theory calculations. It was found that both the removal of a bridging O atom and the formation of an OH group lead to distortion in the atomic positions of the neighboring atoms depending on the choice of the unit cell used in the calculations. The scanning tunneling microscopy (STM) simulations performed using the 2 × 2 unit cell suggest that both an oxygen vacancy and a hydroxyl group should be observed experimentally as a bright protrusion but of different shapes. The O vacancy exhibits a spherical shape whereas the OH group was elongated perpendicular to the [0 0 1] direction. In contrast, in the 3 × 1 supercell, the OH group appears as a bright spot while the oxygen defect looks darker. These findings clearly suggest that a proper geometry is necessary to reproduce experimental STM images of an oxygen vacancy and a hydroxyl group on a TiO 2 (1 1 0) surface.
Water Photo-Oxidation over TiO2—History and Reaction Mechanism
Catalysts
Photocatalytic water oxidation over titanium dioxide (TiO2) was overviewed by surveying briefly the history of water photo-oxidation, followed by profiling the research for the molecular mechanism of oxygen evolution reaction (OER) at the TiO2 surface. As the experimental approach to investigate the reaction mechanism, ESR, NMR, and STM were described as well as FTIR spectroscopy. Detection of reactive oxygen species, which are the intermediate species in the OER, was also involved in discussing the mechanism. As the theoretical approach to the reaction mechanism, some research with density functional theory (DFT) for anatase (101) surface was illustrated. Since the OER activity of rutile TiO2 is higher than that of anatase, and the rutile (011) surface has been assigned to the oxidation facet, we performed a DFT calculation for a (011) surface model molecule. The results were successfully discussed with the reported mechanism. The first oxidation step occurs at the bridging OH site...