Synthsis, Assembly, And Properties Of Inorganic Micro (Nano) Crystals

In this thesis, novel synthetic methodologies have been developed to prepare inorganic micro (nano) crystals with specific shapes, for that morphology controlled synthesis and the large-scale self-assembly of the nanoscale building blocks into complex structures have been the focus of significant interests in materials chemistry and device fabrications. Morphology controllable synthesis and assembly of several inorganic micro (nano) crystals have been carried out, and their morphology and shape dependent properties have been investigated. The main points are summarized as follows:1. A simple route has been explored to synthesize sulfides micro (nano) structures through directly hydrothermal decomposition of the as-formed diethyldithiocarbamate precursor in its mother solution. A series of microstructures have been obtained, including ZnS hollow spheres, Bi2S3 microstructures, and PbS polyhedra.A facile one-pot synthesis of ZnS hollow spheres has been carried out, for the first time, via a chemical transformation induced inside-out Ostwald ripening process from a single source precursor. The as-obtained ZnS hollow spheres have sizes in the range of 220-350 nm, and the size and shell thickness can be controlled by adjusting the reaction temperature and reaction time, respectively. Photoluminescence spectra show a dominant emission peak at 470 nm accompanied by several weaker peaks. UV-vis measurement reveals that the obtained ZnS hollow spheres exhibit "hollow effect". The formation process of ZnS hollow spheres has been discussed.For the first time, Bi2S3 nanostructures from paper folding flower-like structures to nanobelts/multibranches were obtained through similar procedure. The synthesized Bi2S3 flower-like structures are constructed with folding of self-assembled nanosheets. HRTEM investigation shows that an individual nanobranch is composed of multiple nanosheets with single crystalline nature. Cyclic voltammograms of the Bi2S3 nanostructures are measured to investigate their electrochemical hydrogen storage behaviors. It was found the capacity of electrochemical hydrogen storage is susceptible to the morphology and structure of Bi2S3 nanostructures, and Bi2S3 roses have superior capacity than that of Bi2S3 nanobelts. The morphology evolution from flower-like nanosheets to multibranched nanobelts has been investigated. It may be determined by both the instinct crystal structures of Bi2S3 and the folding-splitting crystal growth mechanism.When extent this procedure to the synthesis of PbS, cubes and truncated octahedra have been obtained selectively. The influence of experimental parameters on the shapes of the PbS micro-crystals have been investigated and it was found that the concentration of PVP and the precursor and the reaction time are key factors for shape controlled synthesis of PbS microcrystals. PbS cubes and truncated octahedral can be selectively obtained by using different amount of PVP. The growth mechanism and the shape evolution progress have been discussed briefly.2. Monodisperse a-Fe2O3 microspheres and hollow spheres of different shapes have been selectively synthesized through the hydrothermal process. The a-Fe2O3 microspheres exhibit egg-like, cube-like, peach-like and white-gourd-like shapes, as well as hollow structures, all of them have good dispersibility, uniform size, and well-defined shapes. Monodisperse Fe3O4 microspheres have also been prepared. The relationship between the magnetic properties and the shapes and structures of theα-Fe2O3 microspheres has been studied. Ferromagnetic investigation shows that the coercivity and the magnetization saturation values of Fe2O3 samples are closely related to their shapes and structures. Egg-like a-Fe2O3 microspheres exhibit high coercivity of 3800 Oe, while cube-like hollow structures show extremely high coercivity of 7800 Oe at room temperature. When CTAB is used as structure directing reagent, a-Fe2O3 rhombohedrons are the main products. The rhombohedron nanocrystals show coercivity of 920 Oe, remanent magnetization of 0.17 emu/g, and saturation magnetization of 0.44 emu/g exhibiting different magnetic properties from a-Fe2O3 microspheres. A hydroxide precursor of Fe8O8(OH)8Cl1.35 have been captured in all the shape evolution process of a-Fe2O3. And the decomposition and assembly of the precursor nanorods toα-Fe2O3 microspheres as well as the Ostwald ripening process are responsible for the shape evolution of Fe2O3 samples.3. Simple solution methods have been explored to synthesize Ag loaded oxides semiconductor hierarchical structures with high photocatalytic activities. Radical-shaped ZnO microprisms were synthesized via a facile low temperature solution route, then, metal silver was facilely deposited on the surface of ZnO to form Ag/ZnO microstructures. The results showed that the deposition of metal Ag nanospecies were achieved successfully by simply aging the solution at 75℃, and the radical-shaped microstructures of ZnO were well maintained. The Ag/ZnO microstructures exhibit much lower PL emission intensity than that of radical-shaped ZnO microprisms, while much higher photocatalytic activity than that of the pure ZnO. Ag-TiO2 composite hollow structures have been obtained via a one-pot surfactant-assisted hydrothermal method. TEM measurement reveals that the sample is composed of hollow spheres and their tube-like aggregates. The surfactant cetyltrimethylammonium bromide plays a key role in the construction of the Ag-TiO2 hollow structures, which involves templating the CTAB micelles. These microstructures are characterized to ascertain their antibacterial activity which was investigated using the disk agar diffusion method, showing potential antibacterial activity against Echerichia Coli bacterium of clinical interest.4. Prussian blue nanocubes and nanoellipsoids have been synthesized selectively with variation of reaction temperature via a hydrothermal process. Both the nanocubes and nanoellipsoids have a narrow size distribution and a good dispersibility. UV-vis spectra showed that the excitonic peaks of the nanocubes and nanoellipsoids are 683 nm and 674 nm, respectively. Cyclic voltammograms of PB nanocubes and nanoellipsoids modified carbon paste electrodes showed two pairs of redox peaks and a dramatic catalysis for the reduction of H2O2. The possible formation mechanism of different shaped Prussian blue nanoparticles has been discussed and their shape related properties are briefly explored.