| Recently we have realized that the rapid development of various industrial departments indeed results in much serious contamination problems. The living surroundings are now becoming much weaker since it is high time to take measures to reduce environment contaminations. In recent years, with the emergence of more advanced scientific technologies, some researchers have found that it has good effect on the dispose of many organic pollutants to utilize photo catalysis techniques. What’s more, the categories of photo catalysts from the original titanium dioxide composites series are becoming more plentiful of many new kinds materials. Among these, some metal tungstate salts materials have attracted amount affections.Fundamental on this background, we focused on some study about the cobalt tungstate materials, involved in the synthesis ways, characterization and control of crystalline structure and morphology, basic optical properties, potential application and probable chemical reaction process respectively.The crystalline structure of transition metal(II) tungstate would be superior to generate either tetrahedron scheelite system or the monoclinic wolframite system with the variation of cation ion radius. While the Co WO4 micro material usually appeared to be the latter one and belonged to the P2/c space group.From the aspect of synthesis ways, in comparison with benefits and shortcomings of many preparation methods, the microwave hydrothermal method was used to prepare cobalt tungstate materials. Additionally, we have also researched the influences of technical conditions on the crystalline phase and microstructure of final products.XRD results showed that microwave hydrothermal route was a valid way of composing Co WO4 micro powder particles. The characteristic diffraction peaks of samples were coincident with the JCPDS No.72-0479 and the calculated crystal constant was a=4.9478 nm,b=5.6827 nm,c=4.6694 nm,α=β=γ=90°,which belonged to the monoclinic system. SEM results showed that the microstructure tended to be in short rod shape and the agglomeration phenomenon existed in some extent. The results of process route study indicated that the variation of p H value of precursor had great impact on the crystalline structure of final products. When the p H value was no more than 2, the final product in WO2.77 structure would be precipitated. When the p H values lay at 3-5.5, the cobalt tungstate would be crystallized in the Co4W6O21(OH)2?4H2O structure accord with the JCPDS No.47-0142 of crystal constant a=1.2858 nm, belonging to the cubic system. When the p H values lay at 6-8, the reaction product tended to generate Co WO4 crystalline phase. And when the p H value was no less than 9, the Co O or Co(OH)2 structure would be precipitated finally. Additionally, the hydrothermal reaction temperature and time would have effect on the microstructure of products. The crystallization process of product would not be sufficient and the micro appearance would be random since the low temperature and short time. It would promote the growth of final product crystallines to prolong the reaction time and rise the reaction temperature. In comprehensive consideration of parameter range and economic cost, the optimal preparation process of Co WO4 nano materials was assured to react under T=170°C for t=80min at p H=8.From the view of fundamental optical properties, the experiment of ultraviolet-absorption spectrum(UV-vis) and photoluminescence(PL) on cobalt tungstate in different structures was conducted and analyzed. The results showed that in Co WO4 crystalline structure there existed two absorption peaks which lay at ultraviolet area of 225-275 nm and visible area of 550-600 nm. While these two peaks were at about 250 nm in ultraviolet area and 550 nm in visible area of Co4W6O21(OH)2?4H2O structure. Moreover, the relative intensity of the peak in ultraviolet area of two different structures was greater than the latter one. Meanwhile, by Lambert-Beer’s Law, and Kubelka-Munk formula, the band gap widths of these two structures were supposed to be 3.41 e V and 3.18-3.81 e V.From the application area aspect, the photo catalysis behavior of these two kinds of structures and the dielectric ceramics of Co WO4 powders were researched. On study of photo catalysis, the Rhodamine.B(Rh.B), methyl orange(MO) and methylene blue(MB) dyes were on behalf of typical organic pollutant molecule. The catalysts solutions of different concentrations were prepared and the decline in concentrations was recorded under the situation of darkness and Xe-lamp light to check the photo catalysis ability of two substances. The results showed that in case of Xe-lamp radiation situation, the Co WO4 micro powders appeared good catalytic capability on the MB molecule and much weaker in catalysis of MO, while scarcely in the Rh.B solutions. However, the Co4W6O21(OH)2?4H2O micro crystallines seemed to have hardly effect in catalyzing MO dye while to be strong in catalysis of Rh.B and MB molecules. Moreover, the Co4W6O21(OH)2?4H2O micro crystallines prepared at different p H values could be distinguished in the catalytic level and tendencies. Besides, on the study of Co WO4 ceramics, the samples should be prepared at first. The Co WO4 micro powders should be thermally processed on condition of 750 to 900°C, then sintered at 1000°C and 1200°C to form the ceramics. The ceramics would be pressed to thin section to test its qualification factor(Qf) and relative dielectric constant(εr). The results showed that the Qf and εr equaled 22133 GHz and 13.272 at 1000°C while they reduced to 21935 GHz and 12.975 at 1200°C.From the respective of reaction process, the probable formation process of products was discussed in combination of tungsten-oxygen octahedron structure and condensation property of tungstate composites. The change in p H values of precursors was supposed to cause the different coordinate configuration and space orientation of tungsten and cobalt elements. While under the influence of temperature and pressure, the raw agents would be dehydrated and precipitated, finally to form the different products at different conditions.According to our study, abundant preparation experiment about micro cobalt tungstate was conducted and the structure and morphology was characterized. Besides, combined with previous research experience, the application potential of cobalt tungstate composites was explored. The results of our work will significantly help to deepen the comprehension of cobalt tungstate materials. |
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