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

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.