Mesoporous Molecular Sieves MCM-41 with a Hollow Tubular Morphology

The synthesis of the MCM-41 materials with novel hollow tubular morphology in high alkaline condition was studied in detail. The tubular structure can be obtained in a narrow range of water/C₁₆TMAB molar ratio, in which lamellar membranes consisting of the hexagonal arrangement of rod micelles exist. Tubular structures result from a membrane-to-tubules transformation. Adding a proper amount of salts into the synthesis gel of higher water/C₁₆TMAB molar ratio can help forming tubular structure. Temperature of the reaction system has to be controlled near 30°C in order to obtain the tubular MCM-41. Incorporation of aluminum into the framework affects the morphology and crystallinity of resultant MCM-41 products. But the stirring rate does not have an appreciable effect on the formation of tubular morphology. The sample synthesized with the C₁₆TMACl-silicate system with a suitable water content leads to about 70% in tubular morphology, and the hexagonal structure of MCM-41 channels was formed from a lamellar intermediate. Surfactants with shorter carbon chain length (n < 16) would inhibit the formation of tubular morphology. The product of the C₁₂TMAB-silicate system was in particulate form and that of C₁₄TMAB-silicate in broken tubular morphology.