Swollen and highly ordered MCM-41 type materials with varied pores sizes, but with similar wall thicknesses, have been directly synthesized in the absence of auxilliary organics by controlling the preparation conditions. The most important parameter in the synthesis in order to control the pore opening is the cetyltrimethylammonium (CTMA+) concentration in the synthesis gel. Our results suggest that the mechanism of swelling is related with the replacement of some CTMA+ species by others cations in the interface formed between the liquid crystal and the silica surfaces. This approach could open new insights into the mechanism of formation of MCM-41 type materials as well as having in addition an important impact on the preparation of large mesoporous materials.
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