Synthesis And Characterization Of Novel Ordered Mesoporous Materials

Ordered mesoporous materials are of scientific and technological interests because of their tunable pore size, large surface area, regular pore structure, flexible compositions as well as tailored catalytic, conductive and magnetic properties. In order to develop new application of porous materials in sorption, catalyst, nano-reactor and photoelectricity etc., it is important to prepare porous materials with different pore structure, composition adjustable morphologies at micro-, meso-, and macro-scale. To prepare mesoporous materials by employing nonionic block copolymer under acidic condition attracted much attention, because of their excellent properties, such as thick pore wall, tunable morphology and adjustable composition, compared with those which obtained by ionic surfactant under basic conditions. The author of this thesis synthesized some mesoporous materials with different component, construction and morphology, by using nonionic surfactant as structure-directing agent. These investigations may pave the way for the application of mesoporous materials in the fields of catalyst, optics and biomaterial separation. Such materials obtained may have great significance from theoretical and practical aspects. This thesis is arranged as the following:Since the introduction of SBA-15, most synthetic procedures were conducted under hydrothermal conditions. The method is time-consumed, and restricts the potential applications of prepared material synthesized under the acidic circumstance. The author prepared ordered mesoporous silica with large pore size by employing ultrasound irradiation method. Compared with conventional hydrothermal conditions, the method we employed was timesaving and low-temperature. Much highly ordered mesoporous silica could be obtained in very short time. The XRD results and transmission electron microscope (TEM) images showed that the material possessed 2D hexagonal pore structure (P6mm), and well-dispersed rod structure. And the synthetic mechanism was investigated by change of synthetic parameters.Most microporous zeolites are prepared under strong basic condition or neutral condition with present of F ion. But many types of mesoporous materials are synthesized under acidic condition, it is most important that these mesoporous materials have thicker pore wall than those prepared under alkali condition, which contribute to better hydrothermal stability, and introducing the zeolite cell to the pore wall of mesoporous materials may be possible. In recent years, several reports were dedicated to synthesis large pore-sized mesoporous materials with large pore size, by employing zeolite precursor as inorganic source and block copolymer as template under strong acidic condition. Generally, it is believed that the zeolite precursor was a mixture with some fragment of zeolite cell structure, and the mechanism of the zeolite precursor during the preparation of mesoporous materials under acidic condition is not determined. The author of the thesis employed the silica with Double four-ring structure (D4R) as silica source and block copolymer as template to prepared highly-ordered mesoporous silica under acidic condition. 29Si MAS NMR was utilized to observe the transformation of the silicate D4R structure. The results indicated that the structure was decomposed under the acidic condition without the present of copolymer; but it was mostly preserved with the present of copolymer. We proposed that the copolymer played the 2-fold role during the preparation of mesoporous materials. The copolymer were not only the mesostructure-directing agents (template), but also the protector of the D4R structure of silica source by hydrogen-bond. The results were confirmed by other characterizations, such as XRD, TEM, FT-IR and hydrothermal test.Mesoporous silica is chemically inert for the weak acidic properties of silica hydroxy radical. Many methods were employed to introduce metal atom into the pore wall for improvement of the hydrothermal stability and catalytic activity of mesoporous silica. Zirconium oxide is attractive owning to its excellent oxygen conductivity and its acid-base bifunctional catalytic activities. But some disadvantages, such as low surface area, weak acidic property and thermal instability, limited its application. So combine the merit of the zirconium oxide with the advantage of porous materials could create new material with high surface area, and high selectivity in catalytic practice by the effect of the pore size. In recent years, evaporation-induced self assembly (EISA) method were widely employed to synthesize mesoporous materials, because of the low temperature, easily controlled process, the much less limitation of inorganic source, and more importantly, the product was present as thin films. In chapter four, we reported the syntheses of novel Zr-doped mesoporous silica with cubic pore structure, by employing nonionic surfactant P123 as template via EISA procedure. XRD and TEM results confirmed that the product has a diamonded face centered cubic structure with Fd3m symmetry, which was first observed in metal oxide-doped mesoporous silica. Physical preoperties include BET surface area, BJH pore volume and pore size have been determined by N2 adsorption-desorption, and the acidity have been measured by NH3-TPD method. In addition, reaction parameters have been further studied on the synthsis of cubic Zr-doped mesoporous silica.