Molecular Structure of a Mineral/Water Interface: Effects of Surface NanoRoughness of α-Al2O3 (0001)

High Resolution Image Download MS PowerPoint Slide Surface disorder on a nanometer scale is shown to have fundamental influence on the molecular structure of α-Al 2 O 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 p K values for deprotonation of surface hydroxyl groups at defect sites and regular terrace sites.