Mixed Dissociative and Molecular Water Adsorption on Anatase TiO₂(101)

Abstract

The adsorption properties of water on the stoichiometric (101) surface of anatase TiO2 in the temperature range 160–400 K has been studied by synchrotron radiation core level photoelectron spectroscopy. O 1s spectra give clear evidence for the formation of a first layer of water that comprises both H2O and OH. The composition is 0.77 ± 0.05 ML H2O and 0.47 ± 0.05 ML OH. Decreasing the coverage by heating leads to a decreased H2O/OH ratio. The results are very similar to those recently reported for water on rutile TiO2(110) and show that the previously proposed model of molecular adsorption only on anatase TiO2(101) must be revised.

Specific Facets-Dominated Anatase TiO2: Fluorine-Mediated Synthesis and Photoactivity

“…[87]. Chemically dissociated water molecules were shown to be energetically favored on {001} facets, whereas water molecules are expected to physically adsorb on {101} surfaces [13,18,88], though partial dissociation within the first layer of water on anatase surface was recently observed by Walle et al by surface-sensitive photoelectron spectroscopy [89]. Anyway, by considering that dissociated water may facilitate the transfer of photogenerated carriers and the formation of reactive radicals, {001} facets are expected to be much more effective for photo-redox reactions than {101} facets.…”

Structure of a Water Monolayer on the AnataseTiO2(101)Surface

“…The interpretation of STM images for higher * feliciano.giustino@materials.ox.ac.uk coverages proved more challenging due to the appearance of an unexpected 2×2 superstructure. Then, in contrast with the prevailing view of molecular adsorption of water on anatase, the authors of a recent high-resolution XPS study [21] reported the presence of OH groups at the surface, and challenged the accepted model of the interface. From an analysis of the XPS spectral intensities the authors of Ref.…”

“…From an analysis of the XPS spectral intensities the authors of Ref. [21] proposed that, at monolayer coverage, 23±5% of the water molecules dissociate into a hydroxyl and a proton.…”

“…[21] using first-principles calculations. Our approach consists of calculating the O-1s core-level spectra of interface models where water is adsorbed either molecularly or dissociatively, and comparing our ab initio spectra to the experimental data of Ref.…”

“…Our approach consists of calculating the O-1s core-level spectra of interface models where water is adsorbed either molecularly or dissociatively, and comparing our ab initio spectra to the experimental data of Ref. [21]. The present analysis is motivated by the very high accuracy (<0.2 eV) that can now be achieved in DFT calculations of core-electron binding energies, as demonstrated by recent work [22][23][24].…”