Amphiphilic Molecules Directed Low Temperature And Liquid Synthesis Of Low Dimension Semiconductor Nanomaterials And Their Properties

The fabrication of nanoparticles is one of the important sections of nanoscience and nanotechnology, and also the base to investigate the distinctive properties and applications of nanostructures. Among all the synthesis methods to nanoparticles, liquid methods, especially the method using water as solvent, have attracted intensive interest because of their low cost and environmental benign characteristic. In this thesis, based on the colloid and interface science, a series of low dimensional semiconductor namomaterials and their self-assembly nanostructures have been synthesized by taking advantage of the morphology modulating effect of amphiphilic molecules. The modulating mechanism of the amphiphilic molecules has been discussed. The optical properties and the photocatalysis performance of the as-obtained products have also been investigated.By making use of the property that micelle can be form by amphiphilic molecules, carbon disulfide (CS₂) as sulfur source, at lower temperature (40 or 50 oC), ZnS hollow nanospheres and nanotubes were synthesized by the assistance of different amphiphilic molecules PVP and SDBS, respectively. The as-prepared ZnS hollow nanospheres had good photocatalytic activity.By the microemulsion-mediated solvothermal method assisted by amphiphilic molecules CTAB, high-aspect-ratio ZnS nanowires were fabaricated. Moreover, ZnS nanorods and bamboo-leaf-like ZnS nanostructures were also obtained by modulating the reaction parameters. Especially, hollow bamboo-leaf-like ZnS nanostructures formed by radiating those bamboo leaves with electron beam during the TEM investigation.As a kind of polydentate ligand, ethylenediamine (en) can interact with the metal ions on the surface of nanocrystals, which make it like a kind of amphiphilic molecule. By introducing a certain amount of ethylenediamine into aqueous solution and adopting hydrothermal treatment, clewlike ZnS self-assembly nanostructure composed of ZnS nanowires were synthesized. Also, this method can produce not only pure ZnS nanostructures but also many kinds of ion doped ZnS nanostructures because of the strong anchor ability of ethylenediamine. And the morphology of the clewlike selfassembly nanostructure was maintained very well by the doped products. By the doping of Eu3+ ions, the photoluminescence emission intensity was much enlarged. For the large specific surface area, the as-obtained products possessed better photocatalysis property and some of them were visible-light responsive. Moreover, this kind of self-assembly nanostructure could be separated from the photocatlysis system easily by simple settlement.By taking advantage of the selective adsorption of amphiphilic molecule CTAB on different crystal faces and with water as reaction medium, PbS nanorods, nanobelts, nanovelvet-flowers, dendritic nanostructures and faceted and cubic Ag2S nanocrystals were fabricated.A novel water/glycerol/polyvinylpyrrolidone (PVP) ternary system was developed to realize the successful growth of PbS nanocubes with a narrow size distribution and sharp facets and edges using a one-step synthesis at room temperature for the first time. The synthesis was very fast, high yield, environment-friendly, and low cost. The product possessed uniform dimensionality, high crystallinity and better dispersibility. After dispersing the nanocubes in water or ethanol, the as-formed colloidal suspensions can maintain excellent stability for more than two year under ambient conditions. Uniform silica layers were successfully coated onto the nanocubes via a modified St?ber method to enhance their performance for promising applications. Moreover, by soaking the as-prepared PbS/SiO₂ core–shell nanocubes in hydrochloric acid aqueous solution, well-resolved cubic SiO₂ nanoboxes were obtained.By making use of the strong tendency toward 1D growth of crystal with lamellar intrinsic crystal structure and modulating the reaction conditions properly, with water as the reaction medium, Bi₂S₃ nanorods bundles as well as three-dimensional flower-like nanostructures were synthesized at room temperature, andα-Ni(OH)₂ nanobelts, nanowires, short nanowires, andβ-Ni(OH)₂ nanoplates were successfully prepared in high yields and purities by a convenient hydrothermal method under mild conditions from very simple systems composed only of NaOH, NiSO₄, and water. Furthermore, porous NiO nanobelts, nanowires, and nanoplates could also be obtained by annealing the as-prepared Ni(OH)₂ products.Under the assistance of amphiphilic molecule PVP, flower-like ZnO nanostructures self-assembled by nanorods were fabricated by hydrothermal route. The tip of the nanorods was cuspidal or flat depending on the amount of PVP as used. Pb, Cu, Co doped ZnO flower-like nanostructures self-assembled by nanorods were also prepared by this method. And all the dopants had influence on the morphology and the self-assembly style of the products in various degrees, in which the existence of Co ions resulted in the decreasing of the nanorods number in the self-assembly nanostructures, and three, four or six arms of ZnO nanostructures formed when the Co concentration was higher.Based on the research in this thesis, several conclusions are drawn in the following:(1) It is no doubt that amphiphilic molecules play important roles in the morphology control during the synthesis of nanomaterials, which is usually realized by the formation of micelles or selective absorption on different crystal faces. Moreover, the adsorption of amphiphilic molecules is helpful to prevent the aggregation of the nanoparticals. But the effect of amphiphilic molecules dose not take place independently, the other parameters of the synthesis system can not be neglected. (2) When the crystals have strong tendency toward 1D growth, the morphology control effect of amphiphilic molecules is not obvious. The reason for that is crystals with strong tendency toward 1D growth usually possess lamellar intrinsic crystal structure, the amphiphilic molecules tend to insert into the interbedded space but adsorb on the surface of the crystals, as a result, the morphology control effect of amphiphilic molecules was weakened. Moreover, when ligands with strong coordination ability exist in the synthesis system, such as ethylenediamine, they interact with the metal ions on the surface of nanocrystals, which make it like a kind of amphiphilic molecule, so the addition of a small amount of amphiphilic molecules can not make obvious morphology control effect.(3) By controlling suitable conditions and designing proper synthesis systems, it is possible to realize the fabrication of nanomaterials with various morphologies in aqueous medium, which lays better foundation for industry batch production.