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Three - dimensional structural analysis of complex porous material preparation and electron tomography

Author: Yuan
Tutor: ZhaoDongYuan；YuChengZhong
School: Fudan University
Course: Inorganic Chemistry
Keywords: Porous materials Electron tomography Perfluorooctanoic acid Helical mesoporous materials Self-assembly
CLC: TB383.4
Type: PhD thesis
Year: 2010
Downloads: 405
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Abstract

With the rapid development of modern science and technology, materials down to the nanometer scale. Nano-porous material because of its having a large specific surface area, high porosity, low density, high permeability, can be assembled, the high adsorption properties, and many other properties, which are widely used for biological sensors, drug delivery, gas separation, energy storage and the field of fuel cell technology, nano-catalysis and photonics scientists caused widespread concern. Porous materials as a new type of nano-materials, while other nanomaterials manufacturing plant, to become the focus of academic research. In-depth understanding of the mechanism of the formation, structure and nature of the relationship, as well as \The structural analysis is an important link in the process of the design synthesis - structural characterization - the nature of the application, and the bridge is essential Contact synthesis of functional materials with practical application. Of this thesis, the synthesis of complex porous material with electron tomography (ET) technical analytic structure the main line, novel pore structure, such as the accumulation of complex concentric circles mesoscopic structure, multi-level spiral structure, hard ball ordered mesoporous materials and sequence macroporous foam packing structure, conduct a comprehensive analysis and three-dimensional reconstruction, which in-depth probing and digging hidden within the structure of the information, to better explore and reveal the formation mechanism of the material as well as the structure and morphology of the transition mechanism to achieve material design preparation, laid the foundation for the understanding of the structure and function of the material, as well as further functional studies. Chapter ionic surfactant as a structure directing agent, perfluorooctanoic acid additives mixed the total template prepared series of concentric circles, a multi-level spiral mesoporous materials with multiple symmetry and complex structure. Due to the limitations of two-dimensional TEM sample thickness, for a long time, how to determine the concentric mesoscopic structures has been an open question. Tight spiral or concentric circles arranged in a two-dimensional hexagonal structure contains symmetry elements of traditional crystal symmetry and more complex, and the nuances of the two structures in order to identify the following scale of a few nanometers. Therefore, in the first section, we take advantage of the ET technology in three orthogonal directions ultrathin sections Figure (-0.26 nm), due to the slice completely eliminate the thickness of the impact, a true reflection of the structural information present in the material within the therefore, tight spiral and concentric structures can distinguish small differences in the level of a few nanometers, to determine the ultimate success of the complex concentric mesoscopic structures. For spiral mesoporous materials, the chirality and pitch of the helix spiral structure are two important parameters, how to accurately and efficiently obtain these two parameters is one of the concerns of the researchers. For a complex multi-stage helical structure, i.e. on the basis of the pore spiral on the external morphology of the two spiral material, the determination of the structural parameters is very difficult, the study of the internal bore there are few reported. In the second quarter, we take advantage of the ET ultrathin sections directly observed trend of the internal pore confirmed within spiral hand, and came to the conclusion in the direction of multi-level spiral structure in the inner and outer spiral. In addition, we also obtained by calculating the helical fingerprint of the location and distribution in a multi-stage helical structure exists. This is the first time using the ET method to parse both the traditional crystal structures have unusual geometry complex mesoscopic structures reported in to provide a new method for the parsing of complex structures. Chapter III, the use of ionic surface active agent and perfluorooctanoate molecular additives, adjusting the proportion in mass of the two to obtain a range of silica material having a different helical parameter structure consists simple straight bars helix to complex multi-stage helical The structural changes of the screw type or concentric type. In the previous chapter the basis of structural analysis, through theoretical calculation reveals a multi-stage helical Cause and mutual transformation of the inner and outer spiral relationship. Quantitative calculation shows that the generation of the outer spiral can ease the inner spiral, but also to maintain a two-dimensional hexagonal symmetry, is a more stable equilibrium. Topology principle, we propose to spiral from the straight rod bent rod structure transition mechanism (helix-coil transition), the multi-level spiral is the intermediate product of this process of transformation. Due to the limitations of the structural parameters of the outer spiral, by the changes in the helix of the inner spiral outwardly is limited, exceeding the limit will produce structural mutation, i.e. a screw-type or concentric type structure. The final structure of the material is surface area decreased to maintain this balance between the two products, and a two-dimensional hexagonal symmetry. The work provides a new way for a synthesis and characterization of novel spiral mesoporous materials, more systematic and in-depth to explore the mechanism of growth and structural transformation. Currently, various spiral silica mesoporous materials have been widely synthesized, but rarely has a helical structure of ordered mesoporous silicone (PMOs) have been reported, silicone material has easier functionalized skeleton hydrophobicity adjustable nature, and thus has the potential broader application than pure inorganic silicon, is expected to play a greater role in chiral catalysis and chiral separation. Chapter IV, in the understanding of the conversion mechanism between the spiral mesoscopic structure, we ethyl bridged organic-inorganic hybrid silicon source to replace inorganic silicon source, by a similar method, successfully controlled synthesis having a spiral silicone material and concentric pore structure. Importantly, through modulation of perfluorooctanoic acid in an amount, the first observation the straight pore Ordering from hexagonal structure transition process to the spiral channels and then to concentric channels, the structure of the material in this PMO conversion never before been reported. Our study helps to understand the behavior of macromolecules collaborative assembly of the hybrid materials as well as the conversion of their morphology and structure, design and control synthesis the novel pore configuration PMO materials have important significance. Perfluorooctanoic acid self-assembly behavior of ionic surfactants in alkaline systems, we studied perfluorooctanoic acid and non-ionic block copolymer in acidic system interaction (Chapter V). By regulating the the perfluorooctanoic acid / block copolymer ratio, observed with rod-like morphology of highly ordered two-dimensional hexagonal mesoscopic structures to with the structural transformation of the edges and corners of the multilamellar vesicles. Important is this transition from a two-dimensional hexagonal rod head start, our findings suggest that multilamellar vesicles is gradually transformed from the hexagonal structure, rather than by organic - inorganic precursor solution cooperative self-assembly The direct formation of structural transformation mechanism provides a key clue. We proposed the perfluorooctanoic acid molecule is to adjust the hydrophobicity of the surfactant to interact with the block copolymer of EO portion, resulting in the increase of the structure factor, causing changes in the structure. This work reveals the mechanism of action between the perfluorinated carboxylic acid molecules and block copolymers, certain guiding significance for the synthesis of novel porous materials. Chapter ET technology system to study the packing structure of the macroporous ordered silica foam (MOSFs), the success of the three-dimensional structure of the single-layer, double-layer, multi-layer MOSFs information. In simple terms, this inorganic - organic composite vesicles first large area gathered together and experience a fusion between process and eventually form a three-dimensional super-structure with the polycondensation of silica species and dehydration. Macroscopic scale, the soap bubble accumulation is generally considered to be taken to the surface area of ??the principle of minimum, we found that the principle also applies to the accumulation mode of layered the MOSF nano materials. Our contribution to the accumulation principle of macro soap bubble to expand to nanometer organic - inorganic composite vesicle assembly up, this novel macroporous having a wide range of applications for the design of synthetic or foam material has an important significance. Chapter VII, with a variety of advanced characterization methods, such as synchrotron radiation small-angle scattering, electron crystallography, ET technology, successfully resolve the surface of mesoporous silica materials piled orderly distribution with double sets of holes hard ball and the internal structure. High resolution synchrotron radiation to confirm the overall structure to Fm3m (cubic close-packed) with P63/mmc (hexagonal close-packed) were mixed symmetry, but the intensity ratio of the main peak with the traditional Fm3m symmetry materials are significantly different, reflecting the material within huge difference in structure; obtained three-dimensional electronic potential energy diagram confirmed the presence of tetrahedral and octahedral its precise location, and confirm that the main peak intensity ratio; ET enables us to directly observe the precise the measured accumulation ball and the accumulation of voids size. The XRD simulation to explore the main index diffraction intensity changes caused by the accumulation of the existence of voids, further confirmed the mechanism of accumulation of hard ball. In addition, we also studied the mechanism of the formation of the close-packed hexagonal plate morphology and its cubic and hexagonal mixed hard ball accumulation. The work on the one hand a reasonable explanation of the double sets of hole distribution phenomenon accurately confirm the presence and size of the hole accumulation gap proved hard ball accumulation mechanism, on the other hand, shows the characteristics of a variety of advanced characterization methods, through a joint application, learn from each other, in order to better resolve the complex structure of the material, which has a universal significance of the later novel material synthesis and characterization of complex materials.

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