Molecular structure of a mineral/water interface: Effects of surface NanoRoughness of α-Al2O3 (0001)

Abstract

Surface disorder on a nanometer scale is shown to have fundamental influence on the molecular structure of α-Al2O 3(0001)/water interfaces which have been studied by sum-frequency vibrational spectroscopy. On rough surfaces, we observe isolated surface hydroxyl groups which do not couple to the network of hydrogen-bonded water molecules of the interface and which we assign to aluminol groups in hydrophobic nanopores of the surface. The pH dependence of O - H stretching vibrations of water molecules at the rough interface . is distinctly different from that of an atomically smooth interface and points to different pK values for deprotonation of surface hydroxyl groups at defect sites and regular terrace sites. © 2008 American Chemical Society.