STUDIES OF SURFACE-PROPERTIES OF DISPERSE SILICA AND ALUMINA BY LUMINESCENCE MEASUREMENTS AND NITROGEN ADSORPTION

A new method for the determination of the adsorption energy distributi on of water molecules on disperse silica and alumina surfaces is prese nted. This method takes into account interactions between the surface and hydrated uranyl (UO22+) groups, which are luminescent probes. Chan ges in the spectroscopic characteristics of uranyl ions, measured unde r selective laser excitation, have been used to evaluate the adsorptio n activity of different surface sites. The adsorption energy distribut ions of water molecules, which coordinate the UO22+ ions in the equato rial plane, were evaluated for disperse inorganic oxides on the basis of luminescence measurements and were compared with the energy distrib ution curves calculated from nitrogen adsorption at 77.35 K, which is the standard technique for the characterization of porous materials. I n addition, high-resolution thermogravimetric measurements were perfor med to supplement information about surface properties of the material s studied. The differences in the nature of adsorption interactions fo r nitrogen and water probe molecules are discussed in context of their impact on the shape of the resulting adsorption energy distributions. The low-energy and high-energy parts of these distributions were attr ibuted to the physically and chemically adsorbed water molecules, resp ectively. (C) 1998 Academic Press.