Synthesis of mesoporous materials by supramolecular templating approach and its application

Abstract

The pore size of mesoporous silica has been controlled by mixed surfactant systems of cationic CTAB and nonionic $C_{16}EO_{10}$, which have the same length of hydrophobic chain. The pore size can be increased maintaining the characteristics of an ordered array of pores by CTAB with small ratios of $C_{16}EO_{10}$ and moderate amount of acid, since the EO chains of $C_{16}EO_{10}$ can be embedded into silica matrix to create micropores. At high ratios of $C_{16}EO_{10}$, a different structure based on $C_{16}EO_{10}$ templates exhibiting high d spacing was observed by X-ray diffraction pattern and the large pore could be attributed to the dense layer of EO chain in addition to the hydrophobic core. At high concentrations of HCl in reactant gel mixtures, separated mesophases were observed, mainly attributed to the preferential strong hydrogen bonding between $C_{16}EO_{10}$ and hydrolyzed product of TEOS compared with the charge coupling interaction between CTAB and silicate species. Mesoporous silica with 2D-hexagonal mesophase via $(S^+I^-)$ and $(S^+X^-I^+)$ synthetic routes was successfully synthesized within ca. 2hrs of reaction time under microwave-hydrothermal conditions at 373K. The cubic mesophase, MCM-48, was also synthesized successfully by using microwave method within ca. 2hrs at 373K without the addition of ethanol, but prolonged microwave radiation had a negative effect on the structural ordering, resulting in disordered network structure consisting of short wormlike channels. Several nonionic surfactants such as $C_{16}EO_{10}$, $C_{18}EO_{10}$ and $C_{18}H_{35}EO_20}$ were used as structure-directing agents via $(S0H^+)(X^-I^+)$ synthetic route under microwave radiation. Therefore, the ordered mesophases were synthesized successfully within very short crystallization time compared with the conventional hydrothermal heating. In addition to the uniform and fast dielectric heating of water, the microwave activates water molecules resulting in th...