Characterization of MCM-48 materials

Mesoporous molecular sieves of MCM-48 type were prepared by conventional hydrothermal and novel room temperature syntheses. Scanning electron microscopy (SEM) studies have shown that nonagglomerated uniform spheres of size ca. 0.5 mu m were obtained by the room temperature method. Internal pore structure was studied by X-ray diffraction (XRD), transmission electron microscopy (TEM), and high-resolution nitrogen and argon adsorption. Pore size distributions were calculated from low-temperature nitrogen and argon adsorption isotherms by the nonlocal density functional theory (NLDFT) method. A novel approach to calculating the pore wall thickness of MCM-48 from XRD and gas adsorption isotherms was employed. The approach utilizes intrinsic symmetry of MCM-48 pore structure, cubic Ia3d space group, revealed by XRD and combines the results of the pore size distribution analysis with general geometrical relations between structural parameters of the gyroid minimal surface. The pore wall thickness of MCM-48 calculated from both nitrogen and argon adsorption data was found to be ca. 8-10 Angstrom, in good agreement with the estimates obtained from TEM.