Studies on Mesoporous Self-Organizing Aluminosilica

A detailed study on the preparation of highly ordered MCM-41 molecular sieves based on our new ̈delayed neutralization̈ process is presented. The rate of acidification does not have an apparent effect on the XRD patterns of MCM-41 but affects the morphology. The synthesized products give a thicker constant wall thickness (about 1.70 nm) of mesopore and a sharp pore size distribution. However, the structural order depends on the carbon chain length, the amount of alcohols as cosurfactants, and the synthetic temperature. A tubular morphology of the MCM-41 material, with hollow tubules 0.3 to 3 μm in diameter, can be obtained by careful control of the surfactant-water content and the rate of condensation of silica under high-alkalinity conditions. In tubules-within-a-tubule, the wall of the tubule consists of coaxial cylindrical pores of nanometers characteristic of MCM-41. The hierarchical order structure takes place through a "liquid crystal phase transformation" mechanism in which an anisotropic membrane-to-tubule phase change is involved.