Study On The Synthesis And Modification Of Hollow Mesoporous Silica

Hollow mesoporous silica possesses the characters of mesoporous materials, such as high specific surface area, large pore size and pore volume, uniform pore size distribution and favorable stablity, and the hollow structure, which can accelerate the diffusion and adsorption of molecule, endow it with the ability of containing guest molecule. Thus, hollow mesoporous silica is an ideal supporter of catalyst, which caused the great interest of researchers.Through the soft-template method, this research using dodecylamine (DDA) and polyvinylpyrrolidone (PVP) as the combined template, and tetraethoxysilane (TEOS) as silica source, successfully synthesize the hollow mesoporous silica (HMS) with worm-like pore in the ethanol-aqueous system, whose surface area is up to 928 m2g-1, and the pore size is 3 nm. With characterization of small angle X-ray diffraction (XRD), Scanning electron microscope (SEM), Transmission electron microscope (TEM), and N2 adsorption-desorption method (BET), studying the effect of template and influence of synthesized condition on the surface morphology and pore properties, furthermore, the mechanism was illustrated logically. The results indicated that, temperature has significant effect on the Hydrogen bond in the self-assembly process, and the high temperature resulted in collapse of mesoporous structure, enlargement of pore size and the decrease of specific surface area; whereas, the different ethanol-aqueous ratio would lead to the change of interfacial tension, which influenced the particle size of HMS materials.Based on the synthesis of HMS, adding tetrabutyl titanate (TBOT) as titania source, finally the hollow mesoporous composite SiO2-TiO2 (HMTS) was synthesized. The result showed that, HMTS materials possessed not only mesoporous structure of SiO2 but also anatase TiO2, and that they are connected by the Si-O-Ti bond. However, the self-assembly process between precursor and template was influenced by the the excessively fast hydrolysis rate of titania source, leading to the decrease of specific surface area. In the photocatalytic experiment of methylene blue (MB), the samples withTBOT additive amount of 1.0 g (TS10) showed the better adsorption ability and photocatalytic activity, whereas along with the increase of TBOT additive amount, the pore size of HMTS materials decreased, and the photocatalytic activity declined obviously.Besides, taking HMS as supporter, H2PtCl6·6H2O as platinum source, Pt was loaded on the surface of HMS materials by the impregnation method and the Pt/HMS catalyst was successfully obtained. Moreover, the Pt particles possess face-centred cubic structure, the crystallinity and crystallite size promoted along with the increase of Pt loading amount; Whereas, the specific surface area, pore size and pore volume of Pt/HMS materials had a decline with the increasing Pt loading amount. In the experiment of benzene methanol oxidation, the Pt particles with particle sizes of 2-8 nm showed better catalytic activity, whereas when the Pt particle increase, there appear particles aggregation and pore blocking on the surface of HMS supporter, which result in the decline of conversion and selectivity.