| Developing the functional composite materials with complementary integration of structures and functions is an important direction in the field of materials physics and chemistry at present. As an important functional material, layered double hydroxides (LDHs) have been widely applied in pollution control, chemical separations, optoelectronic materials, biomaterials and catalytic materials due to the special two-dimensional (2D) layer structures, tunable micro/nanostructures and chemical compositions, and universal biocompatibility. At present, it is exigent to design LDHs based composites from micro to macroscale and study the corresponding properties and functions, due to the designing, assembly and integration of multifunction devices based on 2D nano sheets, especially the development of functional graphene composites. However, it is still a challenging and intriguing mission to control the physical and chemical properties of LDHs based composites via controlling the micro structures and optimizing the chemical compositions of materials at micro-nano scales.The controlled fabrication of hierarchically structured materials is a hotspot of interest of the materials scientists in the relevant field due to the potential applications in optics, adsorption, catalysis and separation. Hierarchically structured materials with dual or multiple morphologies are attracting significant attention owing to its synergism and coupling effect on micro-nano scales. The unique morphology and structure may lead to the enhanced optical, electronic, catalytic properties and sensing properties. Hierarchically structured LDHs based composites that are comprised of nanoscaled 2D building blocks and sub-microscaled overall morphology can prevent LDHs nanoplatelets from aggregating in liquid phase and allow separation and recycling of composites from solution and enhance the mechanical properties.The coupling effects from structures and functions of materials generate structural and function integration, implying that the properties of composites can be tuned by controlling the microstructures and optimizing the chemical compositions. The object of the dissertation is set to partly solve the limitations in the present layered materials research area, for which we have synthesized several kinds of novel LDHs based composites by combining the biological template method and in situ growth technique. Effects of preparation technology, micro structure, chemical composition and coupling effects on LDHs based composite properties were systematically investigated. The relationships among composition microstructure-preparation technology-properties of composites were investigated. The main research work and contents are listed as follows:1. The controlled synthesis of hierarchically structured LDHs films by in situ growth on surface Al substrates was performed in this work, and the application of the resulting LDH films in infrared emissivity control was demonstrated. A series of LDH films with gradient in morphologies were obtained by tuning the hydrothermal times and temperatures. The role of the microstructure of LDHs films for the control of infrared emissivity is investigated. The infrared emissivity value of the films increased gradually with the increasing of hydrothermal times, indicating that the infrared emissivity of LDH films can be controlled by controlling infrared reflection and infrared absorption. Because of the controlled morphological and tunable structure of LDH sheets, the as-fabricated LDH films possess morphology-dependent infrared emissivity properties, which have promising application in low infrared emissivity materials and thermal control materials. It is confidently anticipated that the research can provide new approaches for fabricating LDHs based composites. Meanwhile, the prepared LDHs films can be extended to fabricate other LDHs based materials for application in the field of absorbing materials.2. The hierarchically structured ZnO and Al2O3 were fabricated by modified biotemplate method employing metal cations of Zn-Al LDHs as metallic precursors. In order to obtain the hierarchically structured ZnO fibers, the surfaces of cotton fibers were first coated with a layer of ZnO seed. Then, the multi-scale architectures are designed by in situ growth of ZnO nanorod on the the surfaces of cotton fibers in the Zn(NO3)2/hexamethylenetetramine hydrothermal system. The microscaled Al2O3 fibers are fabricated via a simple biotemplate method employing cotton fibers as bio-templates. The hierarchical architectures are designed by in situ growth of AlOOH nanocrystal on surface of Al2O3 microtube walls in a closed hydrothermal system, followed by heat treatment. This approach provides a facile and simple way to fabricate the hierarchically structured metal oxides fibers for use in fields such as adsorbents, catalysis, porous ceramics, and optoelectronic devices.3. The hierarchically porous LDHs/ZnO composites were prepared by a biotemplated synthesis method employing metal cations of Zn-Al LDHs as metallic precursors. This synthesis technique involves the growth of LDHs nanosheet on surface AlOOH/cotton, and also involves sacrificing the biotemplate to make the synthesized products have hierarchical structures. This route enables the fabrication of hierarchical structure composites, and avoids environmental pollution. Due to the special surface structural of LDHs/ZnO composites and electrostatic interaction between the positively charged layer and the organic functional groups of bovine serum albumin (BSA), the prepared hierarchically structured LDHs/ZnO composites are practically usable for BSA separation.4. The multi-component ZnO/LDHs/Al2O3 composites were fabricated using metal cations of Zn-Al LDHs as metallic precursors. In order to optimize the chemical compositions of ZnO/LDHs/Al2O3 composites, the multi-component LDHs based composites can be observed by controlling the hydrolysis of the zinc salts and crystal growth of LDHs in the Zn(NO3)2/hexamethylenetetramine hydrothermal system. In order to optimize the microstructures of LDHs based composites, the hierarchically structured LDHS/Al2O3 composites can be observed by controlling the crystal growth kinetics and thermodynamics in the Mg(NO3)2/urea hydrothermal system. The prepared composites have high surface area and large pore volume. As compared to the calcined LDHs/ZnO composites, the BET specific surface area of optimized composites was increased from 42.32 m2/g to 292.51 m2/g, and the corresponding BSA adsorption capacity was also enhanced.5. The BSA/ZnO and BSA/LDHs hybrids were fabricated using metal cations of Zn-Al LDHs as metallic precursors. In assembly process, zinc ions were first adsorbed onto the surface of the BSA via electrostatic interactions, and the adsorbed metal ions become nucleation sites for the growth of ZnO by the hydrolysis of the zinc ions, forming the BSA/ZnO nanoparticles. Interaction between these nanoparticles then leads to the formation of self-organized flowerlike architectures that have nanoscale features and that are comprised of individual flower petals. The interconnected petals further form 3D flower-like BSA/ZnO hybrids by driving force of crystal growth. The unique morphology and nanoscale structure may lead to the enhanced optical, electronic, biocatalytic properties and biosensing properties. Utilizing the electrostatic interactions between BSA and Al3+, the hybrid sol was prepared by the assembly of Al3+ and BSA. Then, the BSA/LDHs hybrids were prepared by an in situ growth method, which involves direct growth of LDHs platelets on the surfaces of the hybrid sol. The developed preparation routes of protein-inorganic hybrid can be extended for the preparation of other hierarchical LDH based materials for separation, catalysis, adsorption, sensor, and optical applications.In summary, the aim of this thesis is to develop the multi-level, multi-dimensional LDHs based composites with integrated properties by introduction of biological structures or incorporation of biological components. These systemic theoretical studies reveal the intrinsic relationship between the LDHs nanoplatelets and biological structures as well as the in situ growth mechanism of LDHs. This would pave a new way to design and assembly other 2D materials for applications in research and industrial fields. We believe that the valuable investigations offer a theoretical gist for controlling the microstructures and morphology of hierarchically structured materials, and made a big progress in the design and preparation of functional composite materials for corresponding application. |
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