DEUTERIUM NMR INVESTIGATION OF BENZENE ADSORBED ON BOEHMITE GLASSES

The structure of boehmite glasses adsorbed with deuterated benzene was studied by deuterium nuclear magnetic resonance. Macroscopic, monodomain boehmite glasses with long-range structural order were prepared by two distinct routes: air-drying and freeze-drying sol-gels of aluminum alkoxide to yield glassy plates and plugs, respectively. The deuterium NMR spectra of adsorbed benzene (approximately 10% C6D6 by weight) is indicative of high adsorbate mobility in the glasses; the spectra show quadrupolar splittings which reflect the nature of the long-range structural order and morphology in the glasses. The angular dependence of the quadrupolar splitting for the air-dried boehmite plate indicates a uniplanar arrangement of the ultrafine boehmite primary particles. The spectra also exhibit substantial anisotropic magnetic susceptibility influences. Quadrupolar splittings in the freeze-dried plug are consistent with a uniaxial arrangement of the ultrafine boehmite particles. Spectra having the plug symmetry axis at 90-degrees to the spectrometer field showed an unusual 2-D powder pattern which, when simulated, gives information about the dynamics of the adsorbed benzene; i.e., the rate of surface translational diffusion of the adsorbate influences the appearance of the NMR spectrum.