Encapsulation, characterization and catalytic properties of uranyl ions in mesoporous molecular sieves

Occlusion of uranyl ions (UO22+) in the pore channels of mesoporous MCM-41 and MCM-48 molecular sieves was accomplished using direct template ion-exchange method, and the samples were characterized by X-ray diffraction (XRD), Fourier transform infrared spectroscopy (FT-IR), diffuse reflectance ultraviolet-visible spectroscopy (DRUV-VIS), and fluorescence spectroscopy. A shift in U=O stretching IR band (Deltanu = -34cm(-1)), and the appearance of broad and diffused bands in the fluorescence spectra (480-620 nm) of the UO22+-exchanged samples indicate a definite electronic interaction of UO22+ species with the silicate (equivalent toSi-O-) surface. This inference is corroborated by DRUV-VIS results. Calcination in air/N-2 at 823 K resulted in the formation of well-dispersed alpha-U3O8/alpha-U3O7 moieties, accompanied by a marginal decrease in the concentration of UO22+ groups. The binding of UO22+ species to mesoporous materials framework remained intact even after calcination. The molecular sieves loaded with uranium oxide species showed appreciable activity, both for the oxidation of CO and for adsorption/decomposition of CH3OH. (C) 2002 Elsevier Science B.V. All rights reserved