IR Spectroscopy of Surface Water and Hydroxyl Species on Nanocrystalline TiO₂ Films

Abstract

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 δ(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 nm2 over the temperature range 27−150 °C. Two types of coordinated H2O and both terminally bound and 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 (ν(OH) = 3730 cm-1), whereas bridging hydroxyls (ν(OH) = 3670 cm-1) do not appear to be affected by similar H-bonding.