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Synthesis and characterization of bismuth based nano materials

Author: ShiLin
Tutor: ZhaoDongYuan
School: Fudan University
Course: Physical and chemical
Keywords: methods soft template hard template semiconductors nano-materials nanocrystals nanoparticles
CLC: TB383
Type: Master's thesis
Year: 2011
Downloads: 78
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Abstract

Bismuth-related inorganic materials, such as Bi2S3、Bi2O3、BiFeO3 and so on, have attracted much attention owing to their significant applications in superconductors, catalysis, thermo electronics, solar cell, et al. Nano-materials are recognized to be of prime importance for both fundamental research and technical application, due to their specific properties which is different from the bulk materials. In recent years, varied bismuth-related inorganic nano-materials with different morphologies have been synthesized. However, they have not well-defined morphologies, are low-quality and possess large sizes. This thesis bases on systhesis of bismuth-related inorganic nano-materials with small sizes.In chapter 2, reaction between bismuth oleate complex and thioacetamide, used as the bismuth precursor and the sulfur precursor respectively in the presence of oleic acid, leads to monodisperse, single-crystal Bi2S3 nanoparticles of～3 nm. The obtained Bi2S3 nanocrystals possess high surface area of up to 305 m2 g-1. The initial Bi/S molar ratio of the precursors plays an important role in tailoring the morphology of Bi2S3 nanoparticles. The typical Bi2S3 nanodots can be synthesized under a wide temperature or concentration with the initial Bi/S molar ratio fixed at 1/2. Some nanoparticles and nano fibers are formed when the initial Bi/S molar ratio increases to 2/3. While when the initial Bi/S molar ratio is 1/4, the typical Bi2S3 nanodots aggregated severely. Formation of the Bi2S3 nanostructures is studied by a series of TEM characterization. The whole process can be divided into tow stage. At the initial stage, the nucleation is burst and finished in a short time. The growth is also fast. At the latter stage, the growth is very slow and almost stops, so this stage can extend to a very long time. Increasing reaction temperature will lead to some nanorods, resulting from a faster growth rate.In chapter 3, using the glacial acetic acid as the solvent and associate coordination agent, Bi(NO3)3·5H2O、Fe(NO3)·9H2O in the acetyl acetone solution were introduced into the channels of the SBA-15 which was as the hard template via the wet-impregnation method. After annealing, a highly dispersed BiFeO3 nanoparticles/SAB-15 composite was obtained. The BiFeO3 phase could not be achieved if ethanol was used as the solvent instead of glacial acetic acid. The thermal-treatment temperature was also invested. It was found that the size of the BiFeO3 nanoparticles increased as the annealing temperature increased. The BiFeO3 phase could be maintained even after acclaiming at 900℃for 2 h. In chapter 4, using the Bi(NO3)3·5H2O as the bismuth source, NaOOCCH3 as the base, nearly monodisperse Bi2O3 nanodots were synthesized by hydrolysis in a polyol medium. The capping agent OA and amount of NaOOCCH3 were investigated. It was found that the OA could confine the size of the nanocrystals. Smaller nanoparticles formed as more NaOOCCH3 was introduced. When 0.41 g of NaOOCCH3 was used, well-define nanobelts were formed which were composed by ultrafineα-Bi2O3 nanoparticles. When the reaction temperature increased to 200℃, Bi2O3 nanoparticles were reduced by OA to large Bi nanoparticles.

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