Directional Synthesis Of Mesoporous Materials And Their Catalytic Applications

Because of their high specific surface area, large pore volume, ordered pore array, adjustable and narrowly pore size distribution, mesoporous materials have been paid much attentions in the fields of both the material and catalysis science for the past decade. Significantly large progresses were already attained on the studies of mesoporous materials, with numerous papers being published in various kinds of journals all over the world. A few aspects of this kind of materials, such as, the directionally controlled synthesis of mesoporous silica, the synthesis of non-silica mesoporous materials and the functionalization of mesoporous materials, however, are still waiting for further exploration. These topics constitute, in fact, the difficulties and focuses currently in the filed of mesoporous materials and are what the present dissertation was concerned about. Besides, some catalytic applications of the non-silica mesoporous materials synthesized in this dissertation were also addressed.The first part of the dissertation, i.e., the chapter 2, dealt mainly with the directionally controlled synthesis of mesoporous silica.Temperature is one of the most important influencing factors for the synthesis of mesoporous materials. MSU-type mesoporous materials are usually synthesized at a temperature ranging of above the ice point of water and below the cloud point of surfactant. No report on the synthesis of MSU at a temperature below the ice point of water could be found in literatures, and it was even believed that a MSU mesostructure could not be generated when the temperature was higher than the cloud point of the surfactant. In this dissertation, it was found, however, that the applicable range of temperature for the synthesis of MSU could be extended largely to that from far below the ice point of water (-25 oC) to much higher than the cloud point (140 oC). The textural properties of the MSU synthesized had been regulated by changing the synthesizing temperature. The MSU synthesized at a temperature higher than the cloud point of surfactant was identified to possess a multimodal mesoporous structure. A possible mechanism had been proposed for the above variation of mesoporous structure with the temperature.The effect of addition of small molecular additive, cyclohexane, to the batch for the synthesis of MSU was, for the first time, investigated systematically. The addition of cyclohexane had been proved to be cable of another approach, besides changing the synthesizing temperature, to regulate the textural properties of MSU. It was observed that, with the increase of the amount of cyclohexane, the MSU synthesized suffered from a transformation from a wormlike mesostructure to a lamellar one, while its morphology changed from solid balls to hollow vesicles, being an indicative of a transformation of MSU-1 to MSU-V. For the temperature higher than the cloud point of surfactant, the MSU synthesized in the presence of cyclohexane displayed a monomodal mesoporous structure, being in contrast to a multimodal one synthesized in the absence of cyclohexane.The control of the textural properties of MCM-41 had been achieved by changing the synthesizing temperature. It was found that MCM-41 could be synthesized at a temperature as low as -10 oC. The textural properties of MCM-41 changed continuously with temperature, and the crystal size of the MCM-41 synthesized at a low temperature had a much smaller particle size and smooth surface than at a high temperature. To interpret the change of the textural properties with temperature, a possible mechanism had been proposed.The second part of this dissertation, involving chapters 3~7, were concerned about the synthesis of non-silica mesoporous materials and their and catalytic applications and the.In chapter 3, mesoporous Ti-Co oxides were synthesized via the sol-gel route, being a supramolecular assembly of the surfactant AEO9. The mesoporous Ti-Co oxides synthesized were identified to possess a high specific surface area, narrowly distributed pore size and a pore wall consisting of the Co-incorporated anatase crystals. The mesoporous Ti-Co oxides had been employed, for the first time, as the catalysts for the oxidation of cyclohexane and a considerable high performance were achieved. An as high as 8.0 % conversion of cyclohexane at a 93.7 % selectivity to KA oil (cyclohexanol and cyclohexanone) had been obtained under the optimal conditions.In chapter 4, mesoporous Ti-Co oxides were synthesized via a replication route, using MSU as the hard template. The mesoporous Ti-Co oxides synthesized were identified to possess a similar mesostructure with the hard template. The pore wall of the mesostructure comprised of the Co-incorporated anatase crystals. When employed as the photocatalysts for the degradation of dye, the mesoporous Ti-Co oxides presented a much higher activity than the pure TiO2, under whether UV or sunlight irradiation.In chapter 5, mesoporous Ti-Ag oxides were synthesized via a supramolecular assembly of polyglycerol, using TBOT and AgNO3 as inorganic sources and glycerol and triethanolamine as organic sources. The template polyglycerol was in situ generated, being catalyzed by the triethanolamine. Because of the coordination with Ag+ ion, the alkalinity of triethanolamine was reduced, and thus, the degrees of the polymerization and crosslinking of polyglycerol could be regulated by changing the molar ratio of Ag/Ti. Through this way, a series of mesoporous Ti-Ag oxides with various Ag/Ti molar ratios had been synthesized. The characterizations to the mesoporous Ti-Ag oxides mesoporous showed that these materials possessed a considerably high BET specific surface area and porosity, with their pore walls consisting of Ag-containing anatase crystals. It was found that, at a lower Ag/Ti molar ratio, the Ag+ ions were incorporated into the framework of the anatase, while at a higher Ag/Ti molar ratio, a part of the Ag+ ions segregate as Ag clusters from the framework of anatase, covering partially the surfaces of the anatase crystals. The mesoporous Ti-Ag oxides synthesized had been employed as the photocatalysts in the antibacterial experiments, using several typical bacteria. It was shown that these mesoporous materials possessed a broad-spectrum antibacterial performance, with a high efficiency and low MIC, which is benefited from the mesostructures and the concerted photocatalysis between the anatase crystals and Ag clusters.In chapter 6, numerous mesoporous Ti-M oxides were synthesized using the method developed in chapter 5. All the Ti-M oxides were identified to posses a mesostructure, with a high BET specific surface area, uniform mesopores and narrow pore size distribution. It suggests that the novel method developed in chapter 5 is of appreciable universality. The catalytic performances of the mesoporous Ti-O-M oxides synthesized had been evaluated by a few reactions, such as, the photocatalytic oxidation of cyclohexane, the dehydration of lactic acid to acrylic acid and the oxidative dehydrogenation of lactic acid to pyruvic acid. For the photocatalytic oxidation of cyclohexane, an as high as 2.8 % conversion of cyclohexane, being ten times of the best result ever reported in literatures. For the dehydration of lactic acid to acrylic acid and the oxidative dehydrogenation of lactic acid to pyruvic acid, much higher performances were obtained over the mesoporous Ti-M oxide catalysts than over the supported M/Ti oxide catalysts. It was also found that the mesoporous Ti-M oxide catalysts displayed a considerable stability during the above reaction, with almost no leaching of the active metal component M, due to the incorporation of the component M into the framework of the anatase crystals.The third part of the dissertation, i.e., the chapter 8, dealt mainly with the functionalization of mesoporous materials. Two kinds of magnetic core-shell mesostructured materials, namely MTS and MMSU, were prepared respectively by covering the nano-sized magnetic cores, cobalt ferrite, with a sol containing the TS-1 precursors or a sol conventionally used for the synthesis of MSU. The materials prepared were characterized by means of XRD, DRS UV-Vis, SEM, N2-physorption and magnetism determination. It was shown that the MMSU had a morphology of micro-ball with an average diameter of ca. 400 nm and the shell of the micro-ball consisted of the nano-sized MSU particles. The MTS had a morphology of elliptic micro-ball with an average of ca. 200-300 nm, and the shell of the elliptic micro-ball consisted of the nano-sized TS-1 crystals. Both the MMSU and MTS were determined to possess a high BET specific surface area, large pore volume and obvious magnetism. The MTS was also employed as the catalyst for the oxidation of phenol to dihydroxybenzene, and a slightly higher activity was observed over the MTS than over the conventional TS-1. After the reaction, the MTS could be readily recovered by a magnet.