Tudy On Synthesis And Properties Of Tungstate Nanomaterials

In this thesis, Preparation, catalytic and adsorption properties of tungstate nanomaterials were investigated. ZnWO4nanoparticles were synthesized by solvothermal method successfully. It was used for formation of5-phenyl-lH-tetrazoles. Compared to other different morphology ZnWO4nanoparticles showed high catalytic activity. The possible catalytic mechanism of this reaction has been proposed. The photocatalytic degradation process about Methylene blue of three different morphologies samples were also explored. ZnWO4—CdS composite photocatalysts were successfully synthesized by a facile hydrothermal process. It was utilized as a photocatalysis for the degradation of Methylene blue and the mechanism has been investigated. Cotton-like NiWO4mesoporous materials were synthesized by hydrothermal method. The decolorization of Methylene blue under different conditions were studied and its thermodynamics, kinetics process were also investigated.The details are summarized as follows:1. Preparation and catalytic properties of ZnW04nanoparticlesZnW04nanoparticles have been synthesized by a facile solvothermal method. The products were characterized by X-ray diffraction (XRD), transmission electron microscopy (TEM), N2adsorption/desorption (BET), UV-vis absorption spectroscopy in detail. On the one hand, ZnWO4nanoparticles were utilized as the catalyst for the formation of5-phenyl-lH-tetrazoles from [3+2] cyclo-addition reaction. The results show that the yield reaches81%when0.2mmol catalyst was used at110℃for10h. At the same time, amorphous and nanorods ZnWO4were synthesized by direct precipitation method and hydrothermal method, respectively. They were also used for catalytic this reaction. However, the yield only reaches43%and65%for amorphous and nanorods. Clearly, ZnW04nanoparticles displays superior catalytic performance. This high activity might be attributed to the larger surface area and more active sites that originates from the small size and good dispersibility of ZnWO4nanoparticles. This catalytic reaction mechanism were further researched. By pyridine adsorption, the surface acidity of catalyst ZnW04was measured using infrared spectroscopy. Studies have shown that the surface acidity of the three different morphology of sample are exist. Nanoparticles ZnWO4has a significantly stronger surface acidity than the two. On this basis, ZnWO4-WO3and ZnWO4-ZnO were prepared under the same experimental conditions in order to research activity substance during this catalytic reaction. W atoms and Zn atoms of ZnWO4nanoparticles are effectively promote the catalytic activity, In addition, the surface acidity of the catalyst is also an important factor that affect the catalytic activity. On the other hand, ZnW04nanoparticles were used in photocatalytic degradation MB, high photocatalytic activity of ZnWO4nanoparticles was appeared. The degradation rate reached94.6%after60min under UV light. However, the degradation rate only reaches81.9%and84.4%for amorphous and nanorods after120min irradiation under UV light. It might be attributed to the large specific surface area and good crystallinity. Good crystallinity is conducive to promote the separation of photo-generated electrons and holes. Accordingly, amorphous ZnWO4has a lower photocatalytic acivity. In addition, ZnW04nanoparticles has a approximately four times surface area than amorphous and nanorods, the larger surface area, the more activity sites lead to the high catalytic activity.2. Study on visible light photocatalytic ZnWO4-CdS synthesis and its photocatalytic propertiesZnWO4—CdS composite photocatalysts with different CdS dose were successfully synthesized by hydrothermal process. The products were characterized via powder X-ray diffraction(XRD), transmission electron microscopy(TEM), and UV-Vis absorption spectrum. ZnWO4—CdS composite were used as photocatalysts for degradation Methylene blue in visible light. The results show that, ZnWO4-CdS composites have better photocatalytic activities compared to single ZnWO4nanorods. We also investigated in detail about the factors affecting the photocatalytic properities, such as the CdS doped amount, pH, and the type of dyes. The photocatalysts display the best activity on degradating Methylene blue solution when CdS doping concentration was0.3in alkaline solution. In the catalytic process, the active substance:generated electrons and holes, hydroxyl radical (·OH) are participated commonly. Furthermore, the photocatalytic mechanism of ZnWO4—CdS composites were simply discussed. Activity of the photocatalyst does not significantly decrease after three cycles.3. Preparation and efficient adsorption properties of NiWO4Cotton-like NiWO4mesoporous materials were synthesized by hydrothermal method when NiSO4and Na2WO4as raw materials. The products were characterized via powder X-ray diffraction (XRD), scanning electron microscopy (SEM). The adsorption of Methylene blue on NiWO4nanomaterials were discussed in detail. Some factors affecting the adsorption properities were investigated, such as pH, adsorption temperature and the concentration of dyes. The results show that, the high decolorization rate was appeared in room temperature, it is decline when raising or lowering the temperature. A better adsorption was appeared in neutral conditions. NiW04has a good adsorption with cationic dyes especially Methylene blue. The thermodynamic and kinetic processes of NiWO4adsorption were further studied. The date show that, the processes of Methylene blue decolorization on NiWO4can be in line with Langmuir equation and second-order rate equation.