Chemical Preparation And Properties Of Bismuth Related Nanomateriais

For unique electronic structure of bismuth such as small electron effective-mass, low charge carrier density, and long mean free path, bismuth and its compounds have found great applications in fundamental research and industry. Nanomaterials exhibit many unique properties which are quite different from their bulk materials. Nanosize bimsuth and its compounds which can optimize the physical properties and result into new physical phenomena have attracted more and more attention.In this thesis, we successfully prepared bismuth and bismuth ferrite nanomaterials and investigated the effect of the size and morphologies on their physical properties. The main achievements are as follows:1. A facile thermolysis method was developed to prepare well-defined bismuth nanospheres. The effect of temperature, surfactant and quenching process on the size and morphologies of bismuth nanomaterials were investigated by Scanning Electron Microscopy (SEM) and Transmission Electron Microscopy (TEM). A camel-like shapes located at425nm and575nm in visible range were revealed by UV-NIR spectrophotometer. A new peak located at1940nm in the infrared range was first reported. The diamagnetic magnetization decreases with the decrease of the size of the bismuth nanospheres The result is in accordance with the relationship between the bandgap and diamagnetic magnetization reported in the literature. The optical limiting effect experiment illustrated that it can be used to develop new optical limiting device. The photocatalytic experiment shows that the bismuth nanospheres can be used as a catalyst to degrade the pollutants.2. The highly pure phase nanocrystal BiFeO3was prepared by using the microwave assisted hydrothermal method. The preparation time is much shorter than that of the traditional hydrothermal methods. An interesting phenomenon was observed that BiFeO3with pure phase periodically appeared during the microwave heating process revealed by XRD. The investigation of the magnetic properties of prepared samples also revealed the periodical formation of the pure phase BiFeO3. The magnetization of the three pure phase BiFeO3samples increased as the heating time increased.3. The mirocrystal BiFeO3was also obtained by using a microwave assisted hydrothermal method. An ultrasonic purification method was developed to obtain pure phase BiFeO3from the crude products without using any chemicals and the X-ray diffraction (XRD) testified the effective of this purification method. The morphology of BiFeO3was successfully modulated from microsphere to microcube by using a polyanion poly (methyl vinyl ether-alt-maleic acid)(PMVEMA). With the amount of PMVEMA increasing, the morphology of BiFeO3gradually evolved from microsphere to microcube observed by using SEM. A formation mechanism is suggested to illustrate the morphology evolution of BiFeO3. The magnetic properties of these microcrystals almost unchanged because the crystal size was larger than the superimposing wavelength in the spiral spin arrangement of BiFeO3.4. The introduction of PMVEMA can affect the morphologies of BiFeO3nanocrystal. The XRD results revealed that the introduction of the polyanion PMVEMA did not result into the appearance of impurity phases. BiFeO3nanoplates can be obtained by introduction of a certain amount of PMVEMA and further increasing the amount of PMVEMA resulted into the finer BiFeO3nanocrystals. The magnetic and optical evolution of BiFeO3nanoparticles confirmed that their properties were changed with their size.