Adsorption Energy Evaluation from Luminescence Spectra of Uranyl Ions (UO22+) Adsorbed on Disperse Silica Surfaces

✍ Scribed by Yu.D. Glinka; M. Jaroniec; V.M. Rozenbaum

• Publisher: Elsevier Science
• Year: 1997
• Tongue: English
• Weight: 281 KB
• Volume: 194
• Category: Article
• ISSN: 0021-9797
• DOI: 10.1006/jcis.1997.5149

✦ Synopsis

of the corresponding interaction potentials (see (4) and ref-Luminescent measurements are utilized to evaluate the adsorperences therein), and also the effects of the shape and depth tion energy for hydrated uranyl groups on the disperse silica surof the adsorption potential on the dynamics of intramolecular face. The position of the UO 2/ 2 0-0 electronic transition and the vibrations with regard to the intermolecular and lateral interfrequencies of intramolecular vibrations appearing in luminesactions (5, 6). In most cases the vibrational dynamics can cence spectra were used in that evaluation. The method is based be studied by using of simple adsorbates, such as H 2 , N 2 , on the dependence of the adsorption bond force constants corre-O 2 , CO, and CO 2 , on the surface of crystals. Typical effects sponding to each type of surface sites on the respective perturbain such investigations are displacement and shape changes tion energy of uranyl ions. To calculate the corresponding force of spectral lines through energy transfer and polarizing acconstants of adsorption bonds, a vibrational problem is solved.

The molecular adsorbate on the silica surface is modeled by means tion of the surface (7, 8), vibrational Stark effect (9, 10), of hypothetical diatomic and triatomic molecules with C ϱ£ and C 2£ and Davydov splitting of vibrational states (11,12). Due to symmetry, in which the UO 2/ 2 ion is predominantly fixed on the simplicity of these adsorbates, the correct theoretical descripsilica surface through one and two water molecules, respectively. tion of vibrational dynamics can be achieved. The situation The perturbations of stretching and deformational vibrations of changes essentially in the case of large polyatomic molecules hypothetical molecules by the presence of the substrate are considand molecular associates. A general solution of the direct ered. It has been shown that due to a large value of uranium mass vibrational problem becomes very difficult because there is the proposed models can be used for the analysis of vibrational a large number of degrees of freedom. However, the solution spectra of hydrated uranyl groups adsorbed on the silica surface.

of such a vibrational problem is very important for the mod-A comparison of experimental data with theoretical calculations ern theory of solids as well as for adaptation of model represhows one to suggest that hydrated uranyl groups are attached to sentations to real conditions, at which filling of the insulathe surface by means of two water molecules. The adsorption energy for hydrated uranyl groups physically and chemically ad-tors' surface occurs. This can be achieved by using various sorbed on the silica surface were evaluated.