Effect of excess silicate on the structure formation and textural properties of MTS materials
The synthesis of micellar templated silica (MTS) materials has been conducted with different SiO2/CTAB molar ratios for two different cetyltrimethylammoniumbromide (CTAB) concentrations of 0.02 and 0.07 M to examine the structure formation for cubic (SBA-1) as well as for hexagonal (SBA-3) surfactant arrangement in acidic reaction medium with increasing silicate excess. Reaction products were analyzed with X-ray diffraction, N2 physisorption and TG-MS. It was found that an increase of the silicate concentration leads to the formation of additional silica gel in the resulting MTS material, which causes not only a decrease of specific surface area and pore volume, but also of the mesopore diameter. The latter effect is explained by a proposed embedding theory. Furthermore, with increasing silicate content in the synthesis mixture a phase transformation from hexagonal to cubic pore arrangement was found for the CTAB concentration of 0.07 M and the maximum SiO2/CTAB molar ratio for ordered pore arrangement has been determined.
KeywordsMicellar templated silica (MTS) Silicate excess SBA-1 SBA-3 Pore arrangement Textural properties
Financial support from the Fonds der Chemischen Industrie and the Deutsche Forschungsgemeinschaft (DFG) within the Cluster of Excellence “Engineering of Advanced Materials” is gratefully acknowledged.
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