In situ ATR/FTIR study of mesoporous silicate syntheses

Real time, in situ ATR/FTIR monitoring of M41S-type mesoporous silicate syntheses were performed which enabled the observation of simultaneous changes in both the organic and inorganic phases of the reaction mixtures. The spectra are dominated by incompletely polymerized, surfactant/silicate composites which form in the solution and/or gel phases, and coexist with the precipitated solid product. The majority of the observed spectral changes take place during the initial heat up stage of the syntheses. The hydrocarbon tail section of the surfactant exhibits increasing packing disorder as the temperature rises. Increased headgroup ordering is observed during the M41S formation which can be attributed to silicate anionic exchange with hydroxide ions, and the expulsion of water of hydration from the headgroup region as condensation of the encapsulating inorganic sheath proceeds. Using a gel composition which generates the D4R cubic octomer, Si8O208- species, the strong surfactant ordering ability of this polyanion is seen in the early stages of the synthesis. The rapid decomposition of this silicate species is accompanied by a sudden increase in the packing disorder of the hydrophobic region of the micelle. These results illustrate the great utility of in situ ATR/FTIR in probing the synergies of this dual phase system.