Microwave Synthesis And Characterization Of Bismuth Nanomaterials

With the development of nanotechnology, nanomaterials were widely used in electronics, energy and biology, due to their unique physical and chemical properties. Recently, bismuth nanomaterials have attracted much attention because of their applications in semiconductors, catalysis and biomedicine.Various synthetic methods, such as solvothermal, refluxing, sol-gel and physical methods were used in the synthesis of nanomaterials. Microwave irradiation heating can reduce the reaction time significantly and has the advantage of uniform heating, no heating temperature gradient and no lag effect. Furthermore, microwave irradiation has a short thermal induction period with no convection processes, easy controllability, and low cost. Recently, microwave heating have been widely used in synthetic chemistry and produced great influences. It has also attracted much attention in the synthesis of nanomaterials. In this thesis, studies are focused on the microwave synthesis of bismuth nanomaterials. The advantage, disadvantage and growth mechanism of microwave synthesis bismuth nanomaterials were also discussed and studied for the next application.The main work can be summarized as follows:1. Large-scale highly crystalline Bi2S3nanorods were successfully prepared from bismuth citrate and thiourea by microwave irradiation methods. The influences of reaction time, surfactants, solvents, and precursors on the formation of Bi2S3nanorods were discussed. The microwave irradiation method reduced reaction time by at least80%in the synthesis of Bi2S3nanorods compared with the refluxing method. Cetyltrimethylammonium bromide (CTAB) and β-cyclodextrin (β-CD) were found to be beneficial to the formation of Bi2S3nanorods. N,N-dimethylformamide, ethylene glycol and diethylene glycol were the favorable solvents in the fabrication of these nanorods. It was found that different bismuth and sulfur precursors influenced differently the sizes and morphologies of the Bi2S3nanorods. The proposed growth mechanism of Bi2S3nanorods was also discussed.2. Three-dimensional snowflake-like bismuth sulfide nanostructures were successfully synthesized by simple refluxing at160℃in ethylene glycol, using bismuth citrate and thiourea as reactants. The Bi2S3nanostructure was built up by highly ordered one-dimensional Bi2S3nanorods, which was aligned in an orderly fashion. Ethylene glycol plays a critical role in the creation of bismuth sulfide three-dimensional nanostructures, which serves as an excellent solvent and structure director. Bismuth citrate, a linear polymer, also makes for the formation of the three-dimensional nanostructures.3. Bismuth nanospheres were obtained by microwave heating and solvothermal methods, respectively. Well-separated bismuth nanospheres were successfully synthesized from bismuth citrate and urea in diethylene glycol by a fast and simple microwave irradiation method. In this fabrication, bismuth citrate plays a critical role as a precursor in the formation of bismuth nanospheres. The concentration of urea also has an influence on the size of the bismuth nanospheres. The possible growth mechanism of bismuth nanospheres was discussed on the basis of the investigation of reaction time.In addition, well-separated and uniform bismuth nanospheres (～180nm) were successfully prepared in ethylene glycol using bismuth nitrate as bismuth precursor by a simple hydrothermal treatment. When the poly(N-vinyl-2-pyrrolidone)(PVP)/bismuth-salt molar ratio was increased, different bismuth nanostructures were obtained. PVP plays a critical role as a reducing agent and a surfactant for the formation of bismuth nanomaterials. And bismuth nanoparticles and nanotubes were formed when N,N-dimethylformamide was used as solvent. The possible formation and growth mechanism of bismuth nanotubes were discussed in progress.