Synthesis And Characterization Of Hydrothermal Stable Mesoporous Molecular Sieves And Functional Mesoporous Oxides

Mesoporous molecular sieves have attracted considerable attention in the region of chemical engineering, optics, electromagnetics, biomedicine, industrial catalysis, environmental protection, and fabrication of novel nano-object materials due to high surface area, well-defined and adjustable pore diameter of 2-50 nm.It is well known that the hydrothermal method is the most prevailing and effective route for synthesis of mesoporous sieves. Mesoporous molecular sieves synthesized under acid media have many advantages over those prepared in alkaline media such as thicker pore wall, higher hydrothermal stability, using inexpensive template and easy reutilization. However, there are two obvious drawbacks for synthesis of ordered mesoporous molecular sieves with conventional in acid condition. On the one hand, a large amount of liquid was required to synthesize ordered mesostructure. On the other hand, most ordered mesoporous prepared with hydrothermal methods was generally suffered from long crystallization time.With addition small amounts of heteropoly acids or corresponding oxoanions in low concentration liquid acid media, hexagonal ordered mesoporous molecular sieves with highly hydrothermal stability have been rapidly synthesized. Compared with conventional method, the features of our synthesis route are as follows:The reaction products prepared with our synthesis route exhibit highly hydrothermal stability. For instance, the highly hexagonal ordered mesostructure of the molecular sieve was perfectly maintained after treated in 100℃ water over 72 h.The liquid acid utilization has been saliently reduced, and the concentration of HC1 in synthesis media is 3.8 percent less than that of the conventional method.The crystallization time for synthesis of ordered mesoporous molecular was shortened to great extent. To obtain the same physicochemical properties of ordered mesoporous molecular sieve prepared with conventional method, the corresponding crystallization time could be reduced to 6 hours, which is about one-fourth that of conventional synthesis process.In addition, the heteropoly acid can be easily recycled and reused to synthesize SBA-15 via a series of appropriate intermediate disposal process, which indicates that the synthesis route is inexpensive and environmentally benign green method.The reaction products prepared with different P / Mo molar ratio, various PO43", Mo and W oxoanions have been characterized by N2 adsorption-desorption, XRD and TEM. It has been confirmed that the promotable structure for synthesis of ordered mesoporous is MogC^/'octahedra species stabilized by PI23 template other than heteropoly anions.A series of mesoporous molecular sieves with different structure have been synthesized by use of nonionic triblock copolymer PI 23 as template under heteropoly acids media. With addition small amounts of non-fluorids inorganic salts such as NaCl, NaBr and KI, highly hexagonal ordered mesoporous silica moleculare sieves have been rapidly synthesized under pH above 2.0 media. The ordered mesoporous sieve with unusual large pore volume, BJH pore size, and unit cell dimension has been synthesized with addition of NH4HF2 under pH above 4.0 media. The BET surface area, pore volume, BJH pore size and cell of the molecular sieve are 605m2/g, 1.56cm3/g.. 118.3 A and 162.8 A respectively. According to the previous reports, the molecular sieve is the largest hexagonal mesoporous silica structure prepared with a single template up to date. Under pH value above 6.0, MCF-type sieve has been successfully synthesized by use of a single template and addition of KF?2H2O for the first time.UV-Vis and Raman results demonstrate that the hydrophilic moieties of PI23 can interact with HPMo to produce the organic-inorganic hybrid structure REOm[HxMo8O264T"4, which play a key role in synthesis of ordered mesoporous sieves. It has been proved that the protonated degree of [H^MosC^4"]*"4 increases with the pH value decreasing. On the basis of these results, the concept of organic-inorganic hybrid template has been putted forward to synthesize ordered mesoporous silica molecular for the first time. With the aid of heteropoly acids, ordered mesoporous sieves could be synthesized by using nonionic triblock copolymers as a template through the following three routs, if the counterions in the synthesis media are sufficient. When pH value is higher than 2.0, ordered mesoporous sieves have been synthesized by use of (S°Mo")(M+T) synthesis route. At pH value from 1.0 to 2.0, ordered mesoporous sieves have been synthesized with (S°MoT) synthesis route. When pH value is lower than 0.3, ordered mesoporous sieves have been synthesized via (S°Mo")(M+F) synthesis route. To best of our knowledge, it is the first time to report that the ordered mesoporous sieves can be synthesized with nonionic triblockcopolymers such as PI23 as a structure-directing agent via the former two routes.By utilizing mesoporous SBA-15 as a hard "template", two kinds of highly ordered mesoporous aluminosilicates molecular sieves with ultrastable hydrothermal stability have been successfully synthesized via twice recrystallization both in zeolite precursor diluted solution and glycerol media in turn. Herein, ZSM-5 and Beta precursor diluted solution was used to prepare MSAMS-2 and MSAMS-4 respectively. The hexagonal ordered mesoporous structure of MSAMS-2 and MSAMS-4 was maintained perfectly both after steaming at 800 °C for 6 h and treating at 100°C water for 120 h. XRD and N2 adsorption-desorption results demonstrate that the MSAMS-2 can retain it's hexagonal ordered mesostructure after treating in 100°C water over 434 h. According to the previous document reports, MSAMS-2 and MSAMS-4 are the mesoporous molecular sivers with the most hydrothermal-stability up to date. The ultrastable hydrothermal-stability of MSAMS-2 and MSAMS-4 might be ascribed to the synergistic effect of the thicker wall, the high condensation of surface silanol groups, and formation of zeolite five-ring subunits in the mesostructure framework wall and original complementary pores of SBA-15.Ga2O3-Al2O3 prepared with sol-gel method has attracted much attention because the catalysts showed relatively high activity and tolerance toward SO2 for selective catalytic reduction of NOX in presence of oxygen. However, the relatively small surface (BET surface area below 200m2/g) and non-uniform pore size of the Ga2O3-Al2O3 prepared with sol-gel method might limit further improving the activity and tolerance toward SO2 for the reaction. In this paper, Ga2O3 - AI2O3 nanorods with mesoporous structure, high BET surface area (253m2/g) and narrower pore size distribution has been successfully synthesized for the first time by using PI23 as a structure-directing agent. No diffraction peak ascribed to any kinds of Ga2C>3 crystalline form was detected in the XRD patterns of as-syntheiszed and calcined Ga2O3- AI2O3 nanorods because the [(GaTAli.^)OOH] was formed, which originated from interaction between hydrolysis product of gallium nitrate and aluminum tri-isopropoxide with the aid of PI23. After calcined at 600°C, the material was converted into GaA103 or [GaxA\].x)]2Oi (x3 with ID nanostructure reveals more intensive blue emission. In the dissertation, GaaOj rod with regular has been synthesized by using PI23 and CTAB as template, respectively. The diameter of Ga^Cb rod decreases with the template concentration increasing, whereas the Ga^C^ rod would be transformed into cuboid structure if the template concentration in synthesis media is too high. After 900°C calcination, high purity monoclinic /S -Ga2O3 phase (a = 12.22 A, b = 3.04 A, c = 5.81 A, 0 = 103.8°, C2 / m) rod was formed. The PL spectrum of & - Ga2C>3 rod exhibits that the blue emission is very strong, which is comparable with that of (3 - Ga2C>3 nanostructure prepared with other high temperature method.