The Controlled Synthesis And Formation Mechanism Of Low-Dimensional Carbon Materials And Nanorod Structured Magnesium Borate

The aim of this dissertation was to explore the controlled synthesis processes of low-dimensional carbon materials and nanorods structured magnesium borate. The as-prepared nanomaterials were characterized in detail and their formation mechanism was also briefly discussed. The main contents are summarized as follows:1. Onion-like fullerenes (OLFs) were prepared by chemical vapor deposition at 700℃with zeolite NaY as support. Based on the shape-selective behavior of Y-type zeolite and the high resolution transmission electron microscopic observation of OLFs microstructure, the formation of OLFs was suggested in accordance with the vapor-solid formation pattern, by which graphitization occurred in successive stages from the core to surface.2. Iron or iron carbide-encapsulating OLFs were formed from the different carbon species. Their morphology and structure were characterized and confirmed by analyzing XRD patterns, SEM and HRTEM images. The resulting carbon morphology showed much dependence on carrier gases. When proper hydrogen flow was used as carrier gas, iron-including OLFs were the end products; on the contrary, when hydrogen flow was absent, nanotubes were formed. The measurement of complex permittivity and permeability show that iron-encapsulating OLFs have higher dielectric and magnetic loss than graphite.3. The development of OLFs applications has been influenced due to the strong hydrophobicity of OLFs. In order to overcome this limitation, the as-prepared OLFs were purified through reflux in nitric acid, and were further chemically modified on surface through reflux with potassium in toluene. The results show that the compound of OLFs(OH)_n was formed by analyzing FT-IR spectra of the samples before and after modification.4. A simple controllable method was introduced to solve catalyst preparation problems, by which well-aligned carbon nanotubes (CNTs) were synthesized from ferrocene-ethanol solution using an inductively coupled plasma technique. The experimental results prove that this process can not only take advantage of the characteristics of plasma, thus greatly facilitating the formation of well-aligned CNTs, but also simplify the preparation procedures of metal catalysts. The experimental results indicate that the optimal conditions for well-aligned CNTs are: 1% (wt) ferrocene solution concentration, 250 W feeding power, 80 Pa reaction pressure. The field emission characteristics of the well-aligned CNTs films were measured in a vacuum chamber, revealing their potential application for cold cathode in the next generation of high performation electronic devices.5. The two strategies of top-down and bottom-up preparation of twodimensional carbon material, graphene, were investigated. The results indicatethat the size of graphene films was influenced by hydrogen concentration ininductively coupled plasma. Multilayer graphene films were obtained bybottom-up method, which was less than 10 run in thickness. On the other hand,multilayer graphene films were prepared through graphite-wearing process inethanol solutioin. Their layer numbers were mainly distributed in the range of10-15. The experimental results also show that water was not suitable asmedium for preparing graphene films, because its higher polarity than ethanolwas unfavorable for the formation of flat graphene films.6. Single-crystalline magnesium borate nanorods were fabricated by a solvothermal method under supercritical conditions. This reaction condition enabled the formation of one dimensional nanostructure magnesium borate without the involvement of surfactants. The detailed microstructures of as-synthesized products were characterized by X-ray diffraction, scanning electron microscopy, transmission electron microscopy and X-ray photoelectron spectroscopy. It was found that the morphology and phase of the products were strongly dependent on the reaction conditions, such as the ratio of Mg/B, temperature, reaction time, and solvent media. The formation process of Mg₂B₂O₅ nanorods was illustrated based on scanning electron microscopic observations of the different reaction stages. This technique may also have great potentials in realizing other nanostructured materials.