Characterization of MCM-48 materials

Mesoporous molecular sieves of MCM-48 type were prepared by conventional hy drothermal and novel room temperature syntheses. Scanning electron microsco py (SEM) studies have shown that nonagglomerated uniform spheres of size ca . 0.5 mu m were obtained by the room temperature method. Internal pore stru cture was studied by X-ray diffraction (XRD), transmission electron microsc opy (TEM), and high-resolution nitrogen and argon adsorption. Pore size dis tributions were calculated from low-temperature nitrogen and argon adsorpti on isotherms by the nonlocal density functional theory (NLDFT) method. A no vel approach to calculating the pore wall thickness of MCM-48 from XRD and gas adsorption isotherms was employed. The approach utilizes intrinsic symm etry of MCM-48 pore structure, cubic Ia3d space group, revealed by XRD and combines the results of the pore size distribution analysis with general ge ometrical relations between structural parameters of the gyroid minimal sur face. The pore wall thickness of MCM-48 calculated from both nitrogen and a rgon adsorption data was found to be ca. 8-10 Angstrom, in good agreement w ith the estimates obtained from TEM.