Syntheses And Properties Of Tungstate/Molybdate Micro-nano Materials

In recent years, the world-wide environmental problems have become more and more serious. The large quantity of industrial waste water containing heavy metal ions and organic pollutants discharged into river without any treatment, and as a consequence bring great hazards not only to the ecological environment but also to human health. Therefore, scientists in certain field are devoted to how to remove these contaminants effectively. Due to the unique and excellent properties of nanomaterials in water treatment process, rapid adsorption or degradation of contaminants could be achieved. In this paper, a series of tungstate and molybdate micro/nano materials with fine morphologies were successfully synthesized via simple liquid methods. The impacts of the relevant experimental conditions on the morphology of the sample were studied, and the possible formation mechanism was also proposed based on the experimental observation. Finally, the effect of such materials employed as absorbents in water treatment was investigated carefully. The main contents and innovations are as follows:1. Erythrocyte-like calcium molybdate (CaMoO4) hierarchical structures were successfully synthesized by a modified slow-release coprecipitation strategy. The structure of the as-prepared products was characterized by X-ray diffraction, Fourier transform infrared and Raman spectroscopy. The morphology was observed with scanning electron microscopy. The results displays that it is conducive to the formation of uniform erythrocyte-like CaMoO4, while peach-like CaMoO4 with a broad size distribution form in a way of direct binding; Due to the the inhibition of Mo7O246- hydrolysis in cidic conditions, erythrocyte-like CaMoO4 still the main morphology, and it is similar to the mode of direct bind between Ca2+ and MoO42- in alkaline conditions. Moreover, the photoluminescence spectrum of the erythrocyte-like CaMoO4 reveals a strong and broad emission peak at 536 nm. The erythrocyte-like CaMoO4 exhibits high removal rate and good stability for the Methylene Blue (MB), suggesting its potential application in water treatment.2.3D flower-like ZnWO4 was successfully synthesized by a anionic surfactant sodium dodecyl sulfate(SDS)-Urea assisting hydrothermal method. The structure of the as-prepared products were characterized by X-ray diffraction (XRD) and the morphological studies were detected with scanning electron microscopy. It has been found that the morphology of ZnWO4 was transformed from OD, 1D to 3D flower-like structure due to the synergistic effect of SDS-Urea. Served as an adsorbent, the as-prepared 3D flower-like ZnWO4 exhibits more excellent adsorption performance for Cu2+ than that of commercial activated carbon and its adsorption capacity reaches up to 293.1 mg·g-1, which might be ascribed its large BET specific surface areas, abundant pore structures and negative charge. The adsorption dynamics between the flower-like ZnWO4 and Cu2+ indicates that kinetics model is fit to the pseudo second-order equotion and the adsorption isotherm is fit to Freundlich model.3. Mesoporous NiWO4 nanospheres with chestnut-like shapes were synthesized by hydrothermal method without any additives at a relatively low temperature. The structure was characterized by X-ray diffraction (XRD), Fourier transform infrared spectroscopy (FT-IR) and the morphology was detected with scanning electron microscopy (SEM). The possible formation mechanism was discussed on the basis of the morphologies of NiWO4 at different intervals of reaction time. In addition, it has been found that the morphology of NiWO4 is dependent upon the reaction temperature to some extent, and the formation mechanism is based on typical Ostwald ripening process. Owing to its unique mesoporous structure and large specific surface area, the NiWO4 nanospheres exhibit a superior removal rate for cationic dyes compared with activated carbon. Importantly, mesoporous chestnut-like NiW04 nanospheres could preserve high adsorption activity even after being recycled three times, suggesting it is an promising adsorbent in water treatment. The adsorption dynamics between the mesoporous NiWO4 and MB indicates that the kinetics model is fit to pseudo second-order equotion and the sorption isotherm is fit to Freundlich model.