Synthesis of pure and iron-containing mesoporous silica. Effect of washing and removal of template on the porous structure.

摘要

Synthesis of pure and iron-containing mesoporous silica are carried out in the presence ofcetyltrimethylammonium from mixtures containing different salts and hydrochloric acid.Ferric salts decrease the pH of the synthesis system, unless this effect is buffered by thecomplexation with fluoride ions. Introduction of iron in the final product increases with thepH of the synthesis system, being favoured in the nearly neutral fluoride systems. Samplesobtained from neutral batches show thick pore walls, relatively low pore volume and specificsurface areas but their properties are not affected by washing. Washing procedures andthermal activation are responsible for severe modifications of pore structure of samplesynthesized at acidic pH. Low silica condensation at acidic pH and room temperature isresponsible for thin unstable silica walls. When surfactant molecules are extracted by washingor calcination, the porosity shrinks and disordered microporous solids are formed fromordered mesophases with 40 ? micelles.