X-ray photoelectron (XPS) experiments at normal and grazing emission are performed, demonstrating the labile nature of the anatase TiO 2 (101) surface after argon cluster ion sputtering and the propensity of oxygen vacancies to migrate subsurface at room temperature. Near-ambient XPS (NAP-XPS) shows that molecular water adsorbs on the anatase TiO 2 (101) surface at pressures of 0.6 mbar and above, at room temperature, in a mixed molecular and dissociated state. Water adsorbs in a similar fashion on both sputtered and stoichiometric surfaces and reaches a saturation point between 0.6 and 1.8 mbar at room temperature. This means there is little difference in reactivity with regards to water adsorption on both sputtered and stoichiometric surfaces, giving credence to the theory that anatase has superior photocatalytic activity over rutile due to the tendency of oxygen vacancies to lie subsurface, therefore being able to contribute to photocatalysis without being quenched by adsorbates.

A combination of synchrotron radiation photoelectron spectroscopy and near-edge X-ray absorption fine structure (NEXAFS) spectroscopy has been used to study the adsorption of phenylphosphonic acid (PPA) on anatase TiO 2 (101) single crystal at coverages of 0.15 monolayer (ML) and 0.85 ML. The photoelectron spectroscopy data suggest that at 0.15 ML coverage PPA adsorbs in a bidentate geometry following deprotonation of both phosphonate hydroxyl groups, leaving the PO group unbound. At 0.85 ML there is a shift to a mixed bidentate/ monodentate binding mode. The carbon K-edge NEXAFS spectra were recorded at two azimuths. Our calculations show that for PPA on anatase TiO 2 (101) the phenyl ring is oriented 65 ± 4°away from the surface plane with an azimuthal twist of 57 ± 11°away from the [101] azimuth.

The adsorption of p-aminobenzoic acid (pABA) on the anatase TiO2(101) surface has been investigated using synchrotron radiation photoelectron spectroscopy, near edge X-ray absorption fine structure (NEXAFS) spectroscopy, and density functional theory (DFT). Photoelectron spectroscopy indicates that the molecule is adsorbed in a bidentate mode through the carboxyl group following deprotonation. NEXAFS spectroscopy and DFT calculations of the adsorption structures indicate the ordering of a monolayer of the amino acid on the surface with the plane of the ring in an almost upright orientation. The adsorption of pABA on nanoparticulate TiO2 leads to a red shift of the optical absorption relative to bare TiO2 nanoparticles. DFT and valence band photoelectron spectroscopy suggest that the shift is attributed to the presence of the highest occupied molecular orbitals in the TiO2 band gap region and the presence of new molecularly derived states near the foot of the TiO2 conduction band.

The interaction of the ionic liquid [C4C1Im][BF4] with anatase TiO2, a model photoanode material, has been studied using a combination of synchrotron radiation photoelectron spectroscopy and near‐edge X‐ray absorption fine structure spectroscopy. The system is of interest as a model for fundamental electrolyte–electrode and dye‐sensitized solar cells. The initial interaction involves degradation of the [BF4]− anion, resulting in incorporation of F into O vacancies in the anatase surface. At low coverages, [C4C1Im][BF4] is found to order at the anatase(101) surface via electrostatic attraction, with the imidazolium ring oriented 32±4° from the anatase TiO2 surface. As the coverage of ionic liquid increases, the influence of the oxide surface on the topmost layers is reduced and the ordering is lost.