Three-Dimensional Cubic Mesoporous Structures of SBA-12 and Related Materials by Electron Crystallography

The chemical potential difference between homopolymer fractions in block copolymers can be readily used to selectively design, and cooperatively assemble, inorganic species into highly ordered three-dimensional (3d) periodic composite arrays of separated mesoscale regions. The actual details and symmetry of these regions and their long-range order can only be determined by 3d imaging and analysis with high-resolution electron microscopy (HREM). Of particular interest is the differentiation between configurations with very similar organization energies, such as the cubic and hexagonal (SBA-2) closed-packed structures. Mesoporous silica SBA-12 and functionalized SBA-12 (SH−SBA-12) have been synthesized from the 3-mercaptopropyl group by using nonionic surfactant C18H37(CH2CH2O)10 (C18EO10, Brij 76) under acidic hydrothermal condition. Relatively large single-phase domains were obtained in SH−SBA-12. The 3d structural solution of SH−SBA-12 was obtained by Fourier analyses of HREM images. The structure is composed of spherical cavities, which are arranged in a cubic close-packed structure, in which each cavity is connected to the twelve nearest-neighbor cavities through openings parallel to the 〈110〉 directions. HREM images of SBA-12 taken over large sample regions show that SBA-12 is a mixture of mostly the cubic close-packed phase, which consist of beautifully crystalline narrow bands with the same 3d structure in twin relation to each other and a relatively small amount of the 3d hexagonal close packed phase.