| To synthesize highly hydrothermally stable mesoporous materials, the mixture of fluorocarbon and hydrocarbon surfactants was used to obtain the highly stable multilayered silicate vesicles. We found that the fluorocarbon surfactant could not only improve the hydrothermal stability of mesoporous structure under high temperature, but also act as a vesicle-template to sustain the vesicle-like structure during high temperature hydrothermal treatment (100-160℃). But further increase the hydrothermal temperature could generate mesoporous structure with radial channels. Following these results and conclusions, we found that adding fluoride ion in the synthesis system could get radially oriented pore channels as well. There is no doubt that the existence of TPA+ in solution could improve hydrothermal stability and acidity of aluminosilicate material. Use NaOH as alkali instead of TPA+ and lower reaction temperature could form hollow hexagonal polyhedral without any template.In the first chapter, we briefly introduced the mechanism of synthesizing mesoporous materials and the factors that influence the pore structure and particle morphology. Three kinds of structures (vesicle-like, radially arranged pore structure and hollow structure) were introduced in detail. The methods to improve the hydrothermal stability of mesoporous materials were described. The detailed information about aluminium in aluminosilicate structure was also showed in this chapter.In the second chapter, nano-sized multilayered silica vesicles have been synthesized through a dual-template way by using CTAB (cetyltrimethylammonium bromide) and FC-4 (C3F7O(CFCF3CF2O)2CFCF3CONH(CH2)3-N+(C2H5)2CH3I-) as the co-templates and tetraethyl orthosilicate (TEOS) as the siliceous precursor. According to TEM, XRD and N2 sorption analysis, with the increasing of FC4/CTAB, the formation of multilayered silica vesicles passed through the route of the normal mesoporous silica spheres (MCM-41) to irregular hexagonal structures with cavities inside MCM-41 spheres and finally to the small sized multilayered siliceous vesicles. The possible mechanism of the two kinds of micelles cooperation was discussed. Furthermore, the vesicular structure was also obtained after hydrothermal treatment at 150℃, which maintained high surface area even after boiling in water for 48 h. The third chapter, the multilayered aluminosilicate material and mesoporous spheres with wormhole-like or radial oriented pore structure have been synthesized by directly aging the original reactants gel at high temperature. Scanning electron microscopy (SEM) and transmission electron microscopy (TEM) confirmed that all the particles were mesoporous spheres and no bulk zeolite particles exist.In forth chapter, the hydrothermally highly stable mesoporous aluminosilicate spheres with radial channels were synthesized in the CTAB-NaF-TPAOH system through a one-step procedure at high hydrothermal temperature. The characterization by transmission electron microscopy (TEM), X-ray diffraction (XRD), nitrogen adsorption/desorption analysis,27Al MAS solid state NMR spctroscopy, pyridine adsorption FT-IR combined with the typical hydrothermal treatments showed that this kind of materials exhibited large surface area, specific pore arrangement, strong acidity and high hydrothermal stability. Due to the accessible radial pore arrangement and high acidity, the catalytic activity for Friedel-Crafts alkylation of toluene with benzyl alcohol was excellent with 100% conversion of benzyl alcohol.With the hypothesis that the zoning Al in amorphous aluminosilicate particles could also happen when synthesis in dilute solution, relatively proper silicon to aluminum molar ratio and synthesis conditions. The last chapter is about synthesizing hollow hexagonal particle with harsh conditions, such as hydrothermal treatment, high pH value, and assistant of fluoride ions were used to dissolve silicate from Si-rich area. It is not only a one-pot synthesis but also does not need any template to support the hollow structure during the condensation of silicate structure. Originating from CTAB templated hexagonal mesoporous particles, mesoporous hollow hexagonal particles with different shell thickness were synthesized and the possible mechanism was proposed. |
