| Under the sunlight irradiation, semiconductor photocatalytic materials have the abilities to split water, photodegrade organic pollution, photo-reduce carbon dioxide and so on. They are considered to have great potentials in solving the problem of energy shortage and environmental pollution. However, TiO2as a representative of traditional photocatalyst can only excited by ultraviolet light because of its wide band gap. Only4%of the solar energy can be utilized. The problem limited the practical application of the photocatalyst. Thus, it is expected to explore advanced photocatalyst which have high photocatalytic activities under visible light irradiation. As an n-type semiconductor, hematite (a-Fe2O3) is the most stable phase among iron oxides and has been regarded to be a promising photocatalytic material owing to its high absorbance of visible light, low processing cost, high resistance to corrosion and nontoxicity. The photocatalytic activity of hematite is strongly dependent on its structure and morphology. Therefore, preparing hematite with varied morphologies becomes very significant.In this paper, we synthesized hematite with varied morphologies by hydrothermal/solvothermal method. The as-prepared samples were characterized by X-ray diffraction, Scanning Electron Microscope and UV/Vis spectroscopy. Based on the experimental analysis, we proposed the growth mechanisms of the samples. The photocatalytic properties were evaluated by measuring the decomposition of rhodamine B (RhB). Specific contents of this paper are listed as follows:In Chapter one, we briefly introduced the research background and the overview of related works. Firstly we introduced the essential knowledge of nano material. Secondly the mechanism and application of semiconductor photocatalysis were introduced, and the development of visible light excited photocatalyst was summarized. Thirdly, we emphasized preparation method of hematite and the latest progress of hematite in the area of photocatalysis. Finally the significance of topic selection and the main research contents were put forward. In Chapter two, we studied the preparation, characterization and photocatalytic property of hematite porous spheres. FeCl3as iron source was dissolved in ethylene glycol monomethyl ether and then urea as precipitator was added. After the solvothermal reaction, amorphous precipitates, which might be attributed to metal alkoxides and showed spherical morphology, were obtained. The hematite porous spheres could be obtained since the amorphous precipitates were treated by high temperature. Urea played a key role in the formation of the amorphous precipitates because ammonia which was formed by the decomposition of urea under high temperature could provide alkaline reaction environment. The minute quantity of water in the reaction system was bad for formation of spherical morphology. Part of Fe3+ions did not react to form precipitates due to the complexing of ethylene glycol monomethyl ether. A plausible growth process which mainly contains two stages was proposed based on the experimental results. Firstly the amorphous sphere was formed by the agglomeration of nanoparticles. Secondly the crystallization of the amorphous sphere and remove of its organic component under high temperature treatment leaded to the formation of porous structure. The hematite porous spheres have strong visible light response and exhibit high efficiency on the decolorization of RhB aqueous solution in the presence of H2O2under visible light irradiation.In Chapter three, we studied the preparation, characterization and photocatalytic property of hematite hollow polyhedrons. We developed a facile one-pot template-free hydrothermal method to prepare α-Fe2O3hollow polyhedrons. Ferric chloride hexahydrate as iron source was dissolved in water and then C4MimBF4(1-Butyl-3-methylimidazolium tetrafluoroborate) was added. Based on our experimental analysis, we found C4MimBF4played an important role on the formation of the hollow polyhedron structure with uniform size. In detail, BF4-is the key for the formation of the hollow polyhedron structure because of its coordination with Fe3+, while C4Mim-contributes to improve the uniformity of the samples. A single hollow polyhedron with smooth surfaces has18facets (twelve (101) and six (111) planes) and it has a single-crystalline thin shell. The growth process was proposed based on the experimental results, which mainly contains three stages including the formation of FeOOH, FeOOH dehydrated to form α-Fe2O3and surface recrystallization, and core dissolved. The growth mechanism is similar to the previously reported reversed crystal growth. The as-obtained α-Fe2O3hollow polyhedrons have strong visible light response and exhibit high efficiency on the decolorization of RhB aqueous solution in the presence of H2O2. The high photocatalytic activity is attributed to the unique hollow structures.In Chapter four, there were three contents. Firstly hematite with different morphologies was prepared by hydrothermal method. Secondly we prepared Fe2O3, Zn-doped Fe2O3films and tested their photocurrent. Thirdly Fe2O3/TiO2composite was prepared and Fe2O3polyhedron and Fe2O3near-sphere were chosen to load TiO2, and then experimental results were discussed.In Chapter five, a concise summery of the contents was given and the experimental problems were analyzed. Besides, suggestions and prospects were proposed for further study. |
