| Summary: | 碩士 === 國立中央大學 === 化學研究所 === 93 === The silica-surfactant mesostructures have been formed by tetraethyl orthosilicate and hexadecyltriethylammonium bromide under strongly acidic conditions. First, the synthesis conditions have been optimized in order to obtain the well-ordered cubic (Pm3n) mesostructure via sucrose-assisted synthesis. The stability of the materials toward washing with water was improved by increasing the synthesis time from 4 to 48 hr.
Secondly, tetra-n-alkyl orthosilicates with different chain lengths have been also used as the silicate sources. We found that the ability for the preservation of the cubic (Pm3n) mesophase at high temperatures depends on the type of silicate sources, following the order TBOS < TPOS < TEOS < TMOS. The use of TMOS, rather than TEOS, as a silicate source not only prevents the phase transformation in the conventional synthesis of SBA-1 at temperatures above 313 K, but also allows the rapid formation of the cubic mesostructure within one hour at 323 K.
Finally, the addition of alcohols offers an effective synthetic approach for controlling the phase behavior of cubic SBA-1 (Pm3n mesophase) over a broad temperature range. The cubic Pm3n mesophase can be stabilized at high synthesis temperatures, simply by adding short-chain alcohols such as methanol and ethanol, or polyols (glycerol and D-sorbitol) as cosolvents during the synthesis. The addition of medium-chain alcohols like 1-butanol, on the other hand, results in the formation of a hexagonal mesophase rather than a cubic mesophase.
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