IR spectroscopy of surface water and hydroxyl species on nanocrystalline TiO2 films

The speciation of water and hydroxyl groups bound to the surface of a nanocrystalline titania film has been investigated by in-situ infrared spectroscopy as a function of temperature. Calibration of the absorbance of the delta (H2O) mode at 1625 cm(-1) by thermogravimetry has enabled an estimation of the concentration of surface H2O present during thermal dehydration of the films, which varied from 5 to 0.65 molecules per nm(2) over the temperature range 27-150 degreesC. Two types of coordinated H2O and both terminally bound and nm bridging hydroxyls have been identified by the temperature-dependent behavior of their corresponding O-H stretching modes. Hydrogen bonding was observed between coordinated H2O and terminally bound hydroxyls (v(OH) = 3730 cm(-1)), whereas bridging hydroxyls (v(OH) = 3670 cm(-)1) do not appear to be affected by similar H-bonding.