The synthesis and characterization of Th-MCM-41 and U-MCM-41 new members of a growing family of hexagonal packed metallo-silicates molecular sieves are described. The synthesis of these materials was achieved by a "liquid crystal templating" mechanism (LCT), with a C16 length chain for the cationic amine surfactant, when the additional metal salt was added to the synthesis mixture, forming large agglomerates imbedded within the silica matrix. For uranium, the synthesis was performed using UO2(NO3)2-6H2O as a precursor whereas for the thorium, the reaction was carried out using Th(NO3)4-5H2O (thorium nitrate pentahydrate) as the metal source. The incorporation of the uranium into the mesoporous material was performed via a complementary basic synthesis, whereas for the latter thorium, an acidic route was utilized. The Th-MCM-41 and U-MCM-41 were characterized by small angle X-ray scattering (SAXS), specific surface areas (Brunauer-Emmett-Teller (BET)), scanning electron microscopy (SEM) equipped with an energy dispersive spectrometer and X-ray photon spectroscopy (XPS). SAXS study revealed the mass fractal scattering characteristics of these materials with fractal dimension in the range of 2.78-2.95 Å. These materials also exhibited a hexagonal array of cylindrical mesopores from 27 to 30 Å in size, surface areas of over 850m2/g, and high thermal and hydrothermal stability. The incorporation of actinide metals into the MCM-41 matrixes was 3.23 (2) at.% of Th and 11.22 at.% for U, respectively. SEM study revealed the particle morphologies with large monolithic aggregates whereas XPS indicates the geometric configuration and coordination of the metal in the silicate. We have found that in U-MCM-41, most of the uranium metal in encounter in an octahedral geometry arrangement whereas in the Th-MCM-41, the corresponding thorium metal is assemble in tetrahedral environment In addition, the catalytic reactivity of these materials was measured for the hydroxylation of phenol and the alkylation of 2,4-di-tert-butylphenol with cinnamyl alcohol.
- Liquid crystal templating
- Mesoporous materials