Hydrothermal Synthesis, Characterization And Performance Research Of Several Functional Nanomaterials

Nanostructured materials have aroused a worldwide interest because of their unique properties and their potential applications in many fields. Many studies found that the structure, dimension, shape and size of nanomaterials play an important role in theirproperties. Therefore, how to effectively control these factors has been frontier fields and hot research topics in materials science, condensed physics and materials chemistry. Recently, hydrothermal method has become one of the most popular methods for preparing nanomaterials due to its unique characteristics such as simple, high effective, controllable and so on. The morphologies and properties of nanomaterial can be adjusted only by the solution process. In this thesis, novel hydrothermal methods were carried out to prepare function nanomaterials with different compositions, morphology and microstructures in the presence of small organic molecules or macromolecules acting as the morphology-controlling agent. The preparation parameters were fully optimized, the properties and the growth mechanisms were also investigated and proposed. The control of size and shape of nanomaterials during the synthesis process has been successfully realized, and some novel synthetic routes to functional nanomaterials have been established. The main contents of this work are summarized as follows.(1) A simple hydrothermal method has been developed for the one-step synthesis of copper sulfur-core/carbon-sheath nanocables and spheres in solution. The obtained nanostructures were characterized by various measurements. HRTEM and selected-area electron diffraction (SAED) confirm that the core of the resulted cable is a single crystal with a hexagonal phase corresponding to the covellite CuS. These copper sulfur@carbon nanocables formed through the hydrothermal reduction /carbonization in the presence ofβ-cyclodextrin (β-CD) acted as both the structure directing agent and the C-source of sheath. The influence of the reaction time, reaction temperature, different sulfur source and different solution system on the final products was investigated in detail. The possible formation mechanism for copper sulfur-core/carbon-sheath cables was also proposed. Moreover, by using hot hydrochloric acid to dissolve the CuS cores and further thermal treatment at high temperature under vacuum, Graphitic structure carbon nanotubes and hollow nanospheres can be obtained.(2) Complex Sb₂S₃ and Sb₂Se₃ nanostructures with a sheaf-like hierarchical morphology were prepared on a large scale by a simple hydrothermal method in the presence of poly(vinyl pyrrolidone) (PVP). X-ray diffraction (XRD), scanning electron microscopy (SEM), transmission electron microscopy (TEM), high-resolution transmission electron microscopy (HRTEM), and UV-Vis-NIR spectroscopy were used to characterize the products. The results indicate that three-dimensional (3D) Sb₂S₃ and Sb₂Se₃ complex nanostructures were constructed by the fractal splitting growth. The time-dependent shape-evolution process suggests that initial stages of the growth comprise nanorod seeds. These PVP-stabilized nanorods develop in subsequent growth stages to a dumbbell structure and complete their development as a closed sphere with an equatorial notch. It has been demonstrated that PVP plays a key role in the formation of such hierarchical nanostructures. Our work may shed some light on the design of other well-defined complex nanostructures, and the as-grown architectures may have potential applications.(3) Lead hydrogen phosphate (LHP) nanowires have been synthesized on a large scale via a facile and mild hydrothermal process using Pb-phytic acid complex as the single precursor. The optical and ferroelectric properties of LHP nanowires were well studied, the room-temperature photoluminescence (PL) spectrum of the as-prepared nanowires indicated that under the excitation wavelength of 375 nm, the sample shows a strong emission peak at 460 nm. The typical P-E hysteresis loops of LHP nanowires show that the remnant polarization (PR) is equal to its maximum polarization (PS), and with voltage increasing, the polarization gradually decreases and eventually becomes zero, which is different from other ferroelectric materials. It is proposed that the hydrogen bond in the LHP crystal structure may be responsible for this difference. The as-prepared LHP nanowires can be used for investigating hydrogen-bonding effects in ferroelectrics.(4) Monoclinic PbCrO4 nanorods, nanowires and amorphous PbCr4O13 nanotubes have been successfully prepared via a simple hydrothermal treatment in the presence of L- lysine. The morphology and crystal structure of the products can be adjusted only by changing the reaction temperatures. The lead chromate/lead sulfide composites can be further synthesized by using the amorphous nanotubes as the template. The morphology, structure and properties of the as-synthesized products were characterized by XRD, SEM, TEM, HRTEM, SAED and UV-Vis. It is fount that the UV absorption edge of the obtained PbS nanocomposites is blue-shift as compared to that of bulk materials owing to the quantum effect of nanomaterials. As an important semiconductor material, lead sulfide nanocrystals could be used to prepare PbS/polymer nanocomposites with unique optics properties.In conclusion, several nanostructured materials with novel morphology and interesting properties have been successfully synthesized by simple hydrothermal routes in the presence of small organic molecules or macromolecules working as the morphology controlling agent. The morphologies and properties of nanomaterials can be easily adjusted only by our solution processes. Recently, polymer/inorganic nanoparticles composites have attracted much research interest because of their unique properties. Thanks to that a great deal of nanomaterials can be produced on a large scale by using our synthesis methods, so this research work can shed great light on the preparation of polymer/inorganic nanoparticle composites in the future.