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The design and synthesis of functional research of graphene based nanostructures and closed pore silica materials

Author: HuangXiaoDan
Tutor: ZhaoDongYuan; YuChengZhong
School: Fudan University
Course: Inorganic Chemistry
Keywords: Graphene Solvothermal Synthesis Self-assembly Lithium-ion Batteries Closed-pore Silica
CLC: TB383
Type: PhD thesis
Year: 2012
Downloads: 463
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Abstract

Since its discovery in2004, the exponential growth of research has made graphene a hot spot of physics, chemistry, biology and materials science. Endowed by its unique two-dimensional single layer crystal structure, graphene processes many fascinating physical properties and have great application potentials in various fields, such as microelectronics, sensor, optoelectronic devices, energy storage and catalysis. Great efforts have been devoted to the synthesis, investigation and application exploitation of graphene and tremendous achievements have been accomplished. Various graphene-based nanocomposites and nanostructures have been reported and find applications in many areas. The applications of materials largely depend on the structure feature and the properties. In this regard, the developing of convenient and efficient approaches to fabricate well-controlled and functional ized graphene-based nanomaterials, the detailed study of synthesis mechanism and the following application exploitation are the main tasks in the graphene research field in future.Closed-pore silica materials with unique closed porous structures are proved to be promising in microelectronic area as low dielectric constant insulating media. With the development of microelectronic industry, the density and the operating frequency integrated circuit are keeping increasing. Then, the smallest chip device features are required to be downsized to less than10nm. Thus, the packing unit size together with the pore size of closed-pore silicas should be further decreased.In Chapter2, a facile approach for the preparation of SnO2/graphene nanocomposite via solvothermal treatment of SnCl4·5H2O and graphene oxide has been developed. In the nanocomposite, SnO2nanoparticles present a short-rod like morphology, with-40nm in length and-10nm in width. The SnO2nanoparticles are relatively uniform dispersed on the graphene planes, ensuring well contacts between graphene and SnO2. As anode materials for lithium-ion batteries, the SnO2/graphene nanocomposite demonstrated good electricalchemical performance. The hybrid material exhibits a high reversible capacity of838mAh/g in the first cycle and improved cyclic performance (20cycles, the capacity remains at510mAh/g.).In Chapter3, A facile single step solvothermal route has been developed to prepare a composite of Fe3O4nanoparticles and graphene nanosheets. By adjusting the feed ratio, the graphene content in the final products can be successfully controlled. The cycling properties of Fe3O4/graphene nanocomposite as anode materials for lithium-ion batteries have been evaluated by galvanostatic charge-discharge measurements. The effect of graphene additive ratios on electrochemical performance has been investigated. The results show that the nanocomposite with a moderate graphene content of18.5wt%integrates high reversible charge capacity and good cyclic stability, delivering a reversible charge capacity of750.0mAh/g after40cycles and good rate cyclability. And the ratio optimized product also exhibits good rate performance. As the current rate reaches500mA/g, the charge capacity remains stable at about370mAh/g.In Chapter4, nanoporous graphene foams with controlled pore size have been achieved. Our graphene foams process large surface area (851m/g) and the highest total pore volume value (-4.3cm5/g) in all the reported porous graphene materials. More importantly, the pore diameter of the graphene foams can be well controlled from mesopore to marcopore range, by simply employing spherical templates with different sizes. Through the detailed mechanism study, a novel hydrophobic interaction drived assembly mechanism was confirmed. The hydrophobic interaction drives the assembly of graphene oxide and templating spheres into layered nanostructure. After heat treatment, the reduced graphene wrapped tightly on the silica spheres, replicating the spherical morphology. After the removal of silicas, the graphene skeleton hold the porous structure, leading to the final nanoporous graphene foams. With a wet impregnation method, uniform magnetite nanodots (-5nm) were well-separately grafted onto the surface of graphene foam, demonstrating the easy modification of our graphene foams. The application studies demonstrated that NGFs and their derivatives have great application potentials in bioanalysis and lithium-ion batteries.In Chapter5, monodisperse closed-pore silica spheres with small pore diameters have been prepared through a multi-level self-assembly approach. The products show a spherical morphology with uniform size of-120nm in diameter, which are formed by the dense packing of silica coated spherical micelles with-5nm in diameter and-3nm in isolated interior space. It is shown that the use of a cationic surfactant and a synthetic condition that stabilizes the silica coated spherical micelles are responsible for the formation of closed-pore mesostructure

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