Characterization and Applications of Functionalized SBA-15 Mesoporous Silica Synthesized by Economic and Environmentally Friendly Ways

• Main Authors: Shih-Yuan Chen, 陳仕元
• Other Authors: Soofin Cheng
• Format: Others
• Language: en_US
• Published: 2008
• Online Access: http://ndltd.ncl.edu.tw/handle/36136833286861695127

博士 === 國立臺灣大學 === 化學研究所 === 96 === This thesis focused on the preparations and applications of functionalized mesoporous silica materials using block co-polymer P123 as the pore-directing agent with the thought of economy and environmental friendliness. In the first part, mesostructured silica and metal-incorporated SBA-15 materials were prepared without the addition of mineral acids. With the aid of NaCl, ultra-large mesocellular silica foams (MCF) were obtained in the P123-H2O-NaCl system, while ordered mesoporous silica materials with good hydrothermal stability and pore symmetry similar to SBA-15 and MSU-H materials were prepared by adding proper amount of ethanol as the co-solvent. By adding various metal precursors in the P123-H2O-NaCl system, highly ordered Sn-, Ti-, Fe- and Zr-SBA-15 materials with metal loadings up to ~10 mol% were easily obtained. Zr(IV) up to 10 mol% was found to be isomorphously substituted in the silica framework of Zr-SBA-15 materials, whereas extra-framework Fe2O3 clusters were formed in Fe-SBA-15 with Fe loading higher than 5 mol%. Zr-SBA-15 was superior to other metal-incorporated SBA-15 in catalyzing the liquid-phase pinacol-type rearrangement. The catalytic activities of Zr-SBA-15 were better than those of zeolitic materials and metal-incorporated AlPO-5, especially for bulky diol reactants. For Sn and Ti incorporated SBA-15, SnO2, and TiO2 nanocrystallites were formed inside the mesopores of SBA-15 materials when Sn/Si and Ti/Si molar ratios were greater than 3.8 mol%. The SnO2 and TiO2 nanocrystallites were not significantly aggregated and grew into large crystals upon heating (~1000 oC) due to the space confinement of the mesochannels. Concomitantly, the Sn- and Ti-SBA-15 materials were thermally stable up to ~ 1000 oC, superior to that of siliceous SBA-15 material, due to the stabilization of the mesopores by SnO2 and TiO2 nanocrystallites. Moreover, the formation of additionally superficial Ti(IV) with tetrahedral-coordinated environment and the decrease of surface hydroxyl groups were found by calcining the Ti-SBA-15 materials. With calcining at 800 oC, the Ti-SBA-15 materials with Ti/Si ratios of 0.03–0.05, which contained additionally superficial Ti(IV) species, suitable surface hydrophobicity and short mesochannels, could efficient catalyze epoxidation of cyclohexene toward cyclohexene epoxide. In the second part, homogeneously dispersed SBA-15 hexagonal thin platelets with short mesochannels were prepared by adding a proper amount of ZrOCl2 in the conventional SBA-15 synthesis solution. The formation mechanism was comprehensively investigated by in-situ small-angle XRD and freeze-fracture replication TEM techniques. The quick self-assembly of P123 micelles and TEOS induced by Zr(IV) ions nearby the interfaces was proposed to be responsible for the formation of SBA-15 platelets with short mesochannels. Similar route was extended to prepare organic functionalized SBA-15 platelets in one-pot. In addition, the morphology and the length of mesochannels could be fine-tuned from platelet morphology with short mesochannels (150–350 nm) to fiber-like morphology with long mesochannels (> 10 μm) by introducing various amounts of NaCl in the synthesis solution. The organic functionalized SBA-15 platelets with short mesochannels showed higher uptake amounts and faster adsorption rates toward new coccine dye and octadecane than those of SBA-15 fibers with long mesochannels. The functionalized SBA-15 platelets with short mesochannels also gave faster rates in catalyzing liquid phase reactions than those of SBA-15 fibers with long mesochannels, such as propylsulfonic acid functionalized SBA-15 in esterification of carboxylic acids and methanol, and aminopropyl-functionalized SBA-15 in Claisen-Schmidt condensation of benzaldehyde and 2’-hydroxyacetophone to form 2’-hydroxychalcone and flavanone. I believed that the organic-functionalized SBA-15 platelets with short mesochannels facilitate molecular diffusion and are promising in industrial applications.