Shape-controlled Synthesis Of Nano-sized Oxides By Wet-chemical Route

Most of the developed synthetic methods to nano-materials are complicated in process, expensive in cost, this work of the thesis has explored a series of new wet chemical methods, which present low requirements in equipment and strong adaptability, to synthesize some typical semiconductor nanocrystals with controllable sizes and morphologies under relatively mild and simple conditions. Relatived mechanisms were discussed. The main points can be summarized as follows:(1) The precursors, zinc carbonate (Zn₅(CO₃)₂(OH)₆), were synthesized in hydrothermal conditions with zinc acetate (Zn(CH₃COO)₂) as zinc source, urea (CO(NH₂)₂) as alkaline source, and nonionic polyurethane (PU) as template.Zinc oxide (ZnO) powders were obtained when the synthesized precursors were calcined under 400℃for 2h. The influence of the reaction temperature,the reaction time and surface active agent on the morphology and structure of the product was researched. And the optimum conditions that synthesize the zinc oxide crystal of morphology controlled with a high degree of crystallinity will be found. The morphology and structure of ZnO powders were investigated by X-ray diffraction (XRD), scanning electron microscope (SEM) and differential scanning calorimetry(DSC), and initially raised the formation mechanism of the flower-shaped nano-zinc hydroxide and zinc oxide.(2) Indium hydroxide (In(OH)₃) crystals were synthesized at different temperature by a simple sodium dodecyl sulfate (SDS)-aid by hydrothermal method, and the optimum reaction temperature of preferential growth along[1 0 0]direction of In(OH)₃ was predicted by X-ray diffraction (XRD) analysis. Indium oxide (In₂O₃) powders were obtained when the synthesized precursors were calcined. According to the optimum reaction temperature, In(OH)₃ intersecting-rods and urchin-like microspheres were successfully synthesized at 122.5℃without SDS and at 105.0℃with 2.56g of SDS, respectively. And In₂O₃ obtained after calcination can inherit the morphology of the precursor.(3) Lanthanum hydroxide(La(OH)₃), were synthesized by a simple low-temperature precipitation method with lanthanum nitrate as raw materials and ammonia as precipitating agent. Lanthanum oxide (La₂O₃) powders were obtained when the synthesized precursors were calcined under 750℃for 2h. The phase structures and morphologies of nanorods were characterized by X-ray diffraction (XRD), Thermal analysis(TG-DSC), scanning electron microscopy (SEM) and Transmission electron microscopy(TEM). The growth mechanism of lanthanum hydroxide nanorods and the effects of temperature on their morphology were investigated. The result showed the growth of the six-phase lanthanum hydroxide was along the crystal direction, and the aspect ratio of lanthanum hydroxide nanorods increases with the increment of temperature. And the product La₂O₃ obtained can inherit the morphology of the precursor.(4) Gallium oxide hydroxide (GaOOH) crystals were synthesized by a simple hydrothermal method at 90-200℃for 18 h. The phase structures and morphologies of products were characterized by X-ray powder diffraction (XRD), field emission scanning electron microscopy (FESEM) and high-resolution transmission electron microscope (HRTEM). And the growth mechanism of the precursor GaOOH was been discussed,as well as the impact of temperature on the morphology. The precursor exhibit intersecting morphology and regular diamond-like cross section with a diagonal length ratio of 2:1. The formation of diamond-like cross section is due to homogeneous growth of lattice planes, namely {1 1 0}, along [ 410],[ 4 10],[ 4 10] and [ 410] directions of orthorhombic GaOOH. Moreover, the formation of the trunk was due to the growth along [0 0 1] direction. And Ga₂O₃ obtained by calcining precursor can inherit better the morphology of that. The morphology of Ga₂O₃ obtained by calcining precursor can inherit better that of the precursors.