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Organic - organic co- assembly of mesoporous materials : synthesis , mechanism and nature

Author: GuDong
Tutor: ZhaoDongYuan
School: Fudan University
Course: Inorganic Chemistry
Keywords: Mesoporous materials Synthesis Carbon Vesicle Single crystal Organic - organic co - assembly
CLC: TB383.4
Type: PhD thesis
Year: 2011
Downloads: 671
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Abstract

Ordered mesoporous carbon materials with large specific surface area and pore volume, high mechanical stability and surface chemical inertness, good electrical conductivity characteristics, and therefore has a broad application prospects in the field of adsorption, separation, catalysis and electrochemistry. Although activated carbon as represented by the traditional porous carbon material has been widely used, but the pore size distribution is not homogeneous enough, and more for the smaller size of the micropores, is not conducive to the transfer of macromolecules in the inner bore, which limits its large molecular adsorption, lithium-ion batteries and other high-tech applications in the field of. Emerging field of organic - organic co-assembly synthesis of mesoporous materials synthesis of mesoporous polymer and carbon materials are developed in recent years. However, due to the poor as the skeleton of the organic polymer material thermal and mechanical stability of the skeleton polymer materials more demanding, thus far, organic - organic co-assembly synthesis of ordered mesoporous carbon material few reports, and its development is relatively slow. Recently, our group and several other international research group reported a new synthetic route Ordered Mesoporous Carbon, has aroused great concern. However, the structure and morphology of the mesoporous carbon material compared to conventional mesoporous materials is not rich enough, the mechanism is still not clear enough, but the study in the material is still very limited. Therefore, in-depth study on organic - organic co-assembly of mesoporous carbon can not only enrich refer the structure and morphology of the mesoporous carbon material, but also on the practical application of great significance. In this thesis revolves around the use of organic - Organic Synthesis of mesoporous carbon materials were assembled. Primarily from materials synthesis, mechanism and nature to enrich the types of materials, in-depth understanding of the Synthesis mechanism to improve the nature of the material. Second, water emulsion was synthesized by a multi-layer vesicle-like structure of mesoporous carbon material. Selection of low molecular weight soluble resol phenolic resin as a carbon precursor, TEOS as the silicon source, a triblock copolymer F127 as a template. Control silica and phenolic resin sol - gel process in aqueous solution successfully synthesized a class of onion-like mesoporous carbon / silica composite multilayer vesicles material. The size of the product in the range of 100-250 nm, the number of layers in the layer 3-9. By lye or HF etching away the silicon oxide component in the composite material can be obtained pure carbon material. Can also be removed by calcination under an atmosphere of air or microwave digestion method of the organic component in the system, to obtain a pure silicon oxide multilayer vesicles. Compare three different high-resolution transmission electron micrograph of the material found there are many carbon atoms connected in between the layers of the vesicles. The third chapter of the thesis, we study in detail the state of the assembly system of ternary eutectic silicon species and phenolic resin composite skeleton, and dismantling the wall component synthesis of mesoporous silica with a large tunnel hole material. First, the synthesis of ternary eutectic assembly with a two-dimensional hexagonal structure of the block copolymer - phenolic resin - silicon oxide ternary complex material, and further use of the microwave digestion method to remove organic components, the original block copolymer the space occupied by the formation of mesoporous main bore wall in the location occupied by the phenolic resin be disassembled to form a large tunnel hole. Nitrogen adsorption results show that the average pore size of the material to achieve 22.9nm, far greater than the lattice parameters of the material 14.2nm, implies that the material has a pore tunneling, combined with high-resolution transmission electron microscopy results suggest that materials tunnel hole size not less than 9.0nm. The fourth chapter of the thesis, we use an aqueous solution of organic - organic co-assembly method synthesized FDU-16 mesoporous carbon material has a rhombic dodecahedron morphology. By controlling the synthesis conditions and the use of ultra-thin slices, high resolution scanning electron microscopy, scanning transmission electron microscopy, and frozen scanning electron microscope techniques conducted a detailed study of the structure and growth process of the material, that the resulting mesoporous carbon material having a single crystal \High resolution scanning electron microscopy and synchronous scanning transmission electron microscope (STEM) of the sample observation showed FDU-16 carbon single crystal thin slices along the [111] and [100] directions, respectively bore Ordering pattern having a body-centered cubic structure consistent Ordering structure of [111] and [100] crystal plane, and the orderly arrangement of the pores throughout the particles, which explains the mesoporous particles having a pore structure of the \Based on the experimental observations, we propose a laminated layer growth mechanism to understand the growth process of the mesoporous carbon the single crystal FDU-16's. Fifth chapter, we use the method of heat treatment and transition metal catalyzed synthesis of the with glassy carbon skeleton ordered mesoporous carbon material, such material used in lithium-ion battery cathode materials exhibit to 470mAh / g reversible capacity. Compared with the amorphous carbon, graphite material having a better electrical conductivity, and therefore expect the mesoporous carbon material having a graphite wall with a view to having a better electrochemical properties. The glassy carbon is graphite is a low-crystalline state, which itself is composed by a sp2 hybridized carbon atom and having a lamellar structure of the graphite, in the two-dimensional scale, but in the third dimension is almost amorphous. The mesoporous graphite material wall having a product obtained by the conventional nano-casting method because of its graphite sheet layers and channels in the vertical direction, did not show a prominent electrochemical characteristics. Organic - organic co-assembly method for the synthesis of mesoporous carbon has a positive phase of mesoscopic structure, skeleton continuity in reversed-phase material, so if its walls made of crystal skeleton is conducive to growth layer graphite sheet along the channel direction, thus greatly improving its conductivity. This part of the work around the crystallization of the FDU-15 mesoporous wall carbon skeleton conduct research to find the best technical solution, by the relatively high temperature heat treatment method and transition metal catalysis. FDU-15 material is heat-treated materials to 2200 ° C to crystallization, but the specific surface area decreased. The use of transition metal catalysis, crystallization temperature dropped to 10 ° C, to maintain the orderly structure under the premise of a glassy carbon skeleton FDU-15 material. The Electrochemical Studies have shown that the mesoporous glassy carbon has a reversible capacity of 470mAh / g, much higher than the theoretical capacity of 372 mAh / g of graphite materials, and has potential applications in the field of lithium-ion batteries. The sixth chapter, a summary of the full text.

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