Ordered mesoporous solids, synthesi condensation

By contrast, the mechanisms of the synthesis of ordered mesoporous solids are very dilferent from those of silicate and phosphate frameworks. For control over the synthesis of mesoporous solids, the key is to understand the interactions of micellar surfactants with condensable inorganic framework-building units. Synthetic routes are also being developed to prepare mesoporous silicates made up of nanoparticles of zeolites, with the aim of combining advantages of microporous and mesoporous solids. 

Synthesis of pure and iron-containing mesoporous silicas are carried out from CTMA mixtures containing different salts and hydrochloric acid. Ferric salts decrease the pH of the synthesis batch, except when complexed by fluoride ions. Samples obtained from neutral batches in the presence of fluoride are stable when washed and calcined. For syntheses at acidic pH and low temperature, a low degree of silica condensation is responsible for thin unstable silica walls. When surfactant molecules are extracted by washing or calcination, the porosity shrinks and disordered microporous solids are formed from ordered mesophases with 40 A micelles. 

The synthesis of these ordered materials involves a structuring agent, which is a surfactant (cationic, anionic, or nonionic). The surfactant molecules form aggregates whose interactions with the silicate precursors direct the condensation toward an ordered solid containing the surfectant Removal of the surfactant by extraction or calcination leads to the mesoporous material. The surfectant plays the role of the template in the construction of the porous structure of the solid. 

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