States of H2O adsorbed on oxides: An investigation by near and mid infrared spectroscopy

The states of water adsorbed on fumed SiO2, Al2O3 and TiO2, from high to low hydration conditions, have been investigated by infrared spectroscopy in the mid-IR (where νasym, νsym and δH2OδH2O modes absorb), and near-IR (in particular the δ + νasym zone) regions. The most specific information provided by spectral features in the mid-IR (MIR) were those related to the lowest hydration condition attained by outgassing at room temperature. Conversely, the δ + νasym pattern appeared a useful source of insights on the states of water adsorbed even at the highest level of surface hydration obtained by exposing the materials to water vapour pressure at room temperature. Peculiar H-bonding environments for H2O molecules within and at the surface of adsorbed multilayers have been proposed.