Structure and microstructure of nanoscale mesoporous silica spheres

The addition of alcohol to the synthesis of a mesoporous silica material will induce a transition from hexagonal (MCM-41) to cubic (MCM-48) to a lamellar phase and finally to silica spherical particles (SSP), as the alcohol adopts the role of cosurfactant. This will evolve to a cosolvent function as the alcohol concentration is further increased. X-ray diffraction suggests that a phase regression phenomenon occurs, in contradiction with the g-value. Transmission electron microscopy reveals the structure and the microstructure of the mesoporous silica spherical particles. It is shown that the SSP consists of a core of a truncated octahedron with the MCM-48 cubic structure and radial cylindrical pores grown on the surface of the truncated octahedron. This structure model and a possible formation mechanism are discussed. (C) 2004 Elsevier SAS. All rights reserved.