Synthesis of hexagonal mesoporous silica in acidic medium - (II) Effect of synthetic temperature and time, and a comparison with the synthesis in basic medium

Hexagonal mesoporous silica were synthesized in acid medium by using cetyltrimethylammonium bromide (C(16)TMABr) as template and tetramethyl orthosilicate (TEOS) as silica source. The effect of synthetic temperature and time were investigated. The results were further compared with the synthesis in base medium. It is shown that the mechanism for acid synthesis of hexagonal mesoporous silica is different from that for base synthesis since different interaction occurs between inorganic species and surfactants in these two routes. For the acid synthesis, the formation of hexagonal structure depends on the existence of stable surfactant micelle other than the condensation of silica species, thus, the factors favorable to the condensation, such as high temperature and long reaction time, are not able to improve the quality of the samples. High temperature is even an adverse condition. Therefore, the acid synthesis should be performed at room temperature.