1H, 29Si and 1H, 23Na heteronuclear shift correlation in octosilicate via cross-polarisation.

Solid-state magic-angle spinning was used to study octosilicate, a layered sodium polysilicate hydrate. Conventional one-dimensional NMR spectra detect two distinct proton and silicon sites and a single sodium species. Heteronuclear shift correlation experiments have shown that only one type of proton is involved in efficient cross-polarisation to all the silicon and sodium sites. Such selectivity could be caused by a favourable position for, and suitable rigidity of, this strongly hydrogen-bonded proton. The latter requirement can be used to propose a simple model of the interlayer space in octosilicate.

Nanoscale imaging of molecular adsorption.

In situ atomic force microscope observations were made of the adsorption of anions (1- or 2-) of the organic diacid 5-benzoyl-4-hydroxy-2-methoxybenzenesulfonic acid from aqueous solution onto the (0001) surface of hydrotalcite (HT), a layered clay. This adsorption process is believed to mimic the ion-exchange reactions that occur within the layers of HT and other layered clays. Atomic force microscope images of the (0001) surfaces of HT, acquired in aqueous solutions, reveal an ordered structure with respect to magnesium and aluminum atoms. In the presence of the anions, atomic force microscopy indicates pH-dependent adsorption onto the formally cationic HT surface. The anion coverage is governed by electroneutrality and steric interactions between the bulky anions within the adsorbed layer, whereas the orientation of the anions with respect to the HT surface is dictated by coulombic interactions and hydrogen bonding between the anion's sulfonate moiety and clay hydroxyl triads. These observations reveal that the reversible adsorption of molecular species can be examined directly by in situ atomic force microscopy, providing details of surface stoichiometry and adlayer symmetry on the local, molecular level.