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

Abstract

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 (ν = −34 cm−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 (≡Si–O−) surface. This inference is corroborated by DRUV–VIS results. Calcination in air/N2 at 823K resulted in the formation of well-dispersed -U3O8/-U3O7 moieties, accompanied by a marginal decrease in the concentration of UO2 2+ 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.