Study On Synthesis, Structure And Functionization Of Ordered Mesoporous Materials

In recent years, periodic mesoporous materials with uniform pore diameters and high specific surface area have been widely used as catalysts, catalyst supports, chemical sensors, electrical and optical devices, and shape/size selective adsorbents for environmentally hazardous chemicals. Although the synthesis and application of ordered microporous solids (such as zeolites) have been well established, numerous attempts to obtain geometrically regular mesoporous materials were unsuccessful until in the early 1990s. Ordered mesoporous silica MCM-41, as a developing material with periodic inorganic and surfactant-based structure, has been the research hotspot both at home and abroad since 1992. Chemical modification was applied to various fields as a functionized method. More and more researchers have devoted to functionizing MCM-41 with organic or inorganic species and improving the properties of the mesoporous silica molecular sieves. This dissertation introduces the mesoporous silica sieves MCM-41 with regular structure and excellent chemical and thermal stability. The characteristics of the mesostructure and the optical properties of the synthesized materials were investigated by means of XRD, IR, TEM, The N₂ adsorption-desorption, photoluminescence spectra, et al. Meanwhile, the application of mesoporous materials in separation is attempted. This dissertation mainly consists of the following several aspects.1. The mesoporous silica MCM-14 was prepared through the hydrothermal treatment in acid media. The as-synthesized samples show the uniform pore size of 2.1 nm and long-distance ordered arrangement of hexagonal structure, which is typically ordered mesoporous structure. The pore size could be adjusted through second hydrothermal treatment with the addition of 1,3,5-trimethyl-benzene (TMB) as organic assistant expander.2. Manganese oxide nanoclusters were loaded into the ordered mesoporous MCM-41 by using impregnation technique. Analysis results show that the nanoclusters of manganese oxide could be successfully confined and distributed into the pores of MCM-41. Because of the existence of manganese oxide nanoclusters, the periodic integrity of pore channels is reduced. Besides, Mn loading MCM-41 materials with different pore size show that the red-shift of absorption edges can be seen in the absorption spectra and the intensity of photoluminescence at 350 nm was reinforced with the increasing loading amount of manganese oxide nanoclusters in the pores.3. Europium oxide nanoclusters were synthesized in ordered mesoporous MCM-41by using the same method as mentioned above. Analyses results of Eu loading MCM-41 materials with different pore size show that the intensity of photoluminescence at about 613 nm is increased and PL band is widened (361 nm excitation), but the photoluminescence intensity is still very weak.4. With the pretreatment of silylation modification, it is more convenient for Eu(DMB)3phen to be loaded into the MCM-41 pore channels. However, loading the Eu chelate into the ordered mesoporous structure reduces the long-distance ordered arrangement. However, it is discovered that the purification of fluorescence is increased and the PL intensity is strengthened than the materials with the embedding of Eu2O3 above. The PL intensity of Eu(DMB)3phen-MCM-41 materials are increased gradually with increasing Eu addition. But the PL intensity tends to be stable when niEu/msi is over 1.5. The porous support materials were prepared with the mesoporous silicon oxide. SEM analysis and porosity test show that the porous support materials have a large number of narrow pores with the size below 1 um. The pores with open ends take up 62.5% of the total pore number. The mesoporous composite membrane was prepared on the support porous silica materials using mesoporous molecular sieves as the membrane material adopting sol-gel painting-covering technique. SEM analysis shows that mesoporous molecular sieves cover on the support materials in lamellar structure and the prepared mesoporous separation membrane keeps the pore structure and the pore-size distribution of MCM-41. The attempt to the air separation by the composite membrane discovers that the molecular sieves membrane has good separation performance for O2/N2 and the separation coefficient a O2/N2 can reach 0.73. Considering the separation mechanism, it is proposed to be the interaction of Knudsen diffusion and pressure diffusion.