The Study Of Synthesis And Sun Light Photocatalytic Activities Of Bismuth Tungstate（Bi₂WO₆） Microcrystalline

With the development and progress of modern science and technology,people found that semiconductor materials have many special physicochemicalproperties and show many practical applications which prompt the researchers tostudy, gradually moving towards the more deeper areas. The combination ofsemiconductor materials and photocatalytic technology make the problems of thepollution of the environment and generating new energy solved. Bi₂WO₆，a newtype of light catalyst, is a kind of high efficiency, non-toxic, price cheapmaterials, applying broadly in the dielectric, sterilization, photocatalysis etc.Owing to the microscopic morphology of the inorganic materials has importantinfluence on its performance quality and its effective use in industry and life, sothrough exploring the controllable factors of the preparation progress can preparethe specific morphology, size, surface structure of powder materials and get tothe purpose of improving visible light catalytic performance of the material. AndBi₂WO₆is a narrow band gap materials with various morphology, therefore,controlling the growth conditions of Bi₂WO₆, can prepare the differentmorphology and structure of the Bi₂WO₆nano materials; can effectively improvethe physical and chemical properties, and improve its sun light catalyticperformance, and develop new applications.The microcrystalline of Bi₂WO₆was synthesized with Bi（NO_3）3·5H₂O andNa₂WO₄·2H₂O as raw materials by a hydrothermal process in this paper. Theeffect of different hydrothermal temperature, hydrothermal time, precursorsolution pH value, nW/Bi, precursor solution concentration on the structurecomposition, microstructure, surface and catalytic properties under natural sunlight of the Bi₂WO₆product was mainly investigated, and the optimum processconditions for Bi₂WO₆microcrystalline was summed up; The formation and growth mechanism of Bi₂WO₆under different process factors was furtherexplored; Finally the influence of other factors on the Bi₂WO₆microcrystallineunder the different template agent and template agent environment wasinvestigated. The different morphology of Bi₂WO₆under what conditions can beprepared and the effect of specific morphology of Bi₂WO₆microcrystalline onthe photocatalytic performance were mainly investigated.The microcrystalline of Bi₂WO₆was synthesized with Bi（NO_3）3·5H₂O andNa₂WO₄·2H₂O as raw materials by a simple hydrothermal process. Whentemperature at110℃-200℃, time in1.5h²4h, pure phase products can beprepared; With the increase of temperature and time, The strength andcrystallinity of the diffraction peak of the product increased, and had anisotropicgrowth along the （131） plane; The product synthesized is convoluted assemblyby lots of two-dimensional nanoplates and form the stable round cake structurewith the size of the prepared product gradually becoming bigger, round cakegradually thickening, becoming dense,which has a certain role in promoting lightcatalytic performance; Photocatalysis test results show that: Photocatalyticactivity of Bi₂WO₆microcrystalline for decomposition of Rhodamine B undernatural sunlight irradiation at160℃,12h was best.Under the hydrothermal conditions of160℃,12h, through the adjustmentof the precursor solution pH value, the sample can be successful synthesizedwith round pancake, cross sheet etc different morphology and good catalyticperformance. The pH value of solution has a great influence on the size andmorphology of the product. When the amount of OH-increasing, the structure ofthe product tend to loose structure due to OH-playing the role of tractioninhibitors. The photocatalysis test of the sample under the natural sun light showthat the samples have higher catalytic efficiency for decomposition ofRhodamine B in a relatively short period of time （150min）, and the productprepared at pH=5has the best light catalytic performance, which the degradationrate reaches as high as above85%in150min.Under the hydrothermal conditions of160℃,12h, pH=1.2, by keeping theconcentration constant of Bi3+, the different product can be prepared throughadjusting n（W）/n（Bi） mole ratio by changing the amount of Na₂WO₄·2H₂O in thesolution. The different n（W）/n（Bi） had an effect on the synthesis of Bi₂WO₆ microcrystalline in the hydrothermal process; When the n（W）/n（Bi） was in therange of0.5:1.0–2:2, the microcrystalline of Bi₂WO₆with an orthorhombicstructure could be obtained. The Bi₂WO₆microcrystalline possessed a superiorcrystallinity at the n（W）/n（Bi） of1:2. The morphology of Bi₂WO₆transformedfrom card-like sphere structure to densely sphere structure with the in-crease ofW/Bi mole ratio. The Bi₂WO₆microcrystalline exhibited an intensive absorptionfor ultraviolet, and its band gap decreased with the increase of W/Bi mole ratio.The calculated value of the band gap of the Bi₂WO₆microcrystalline prepared atthe n（W）/n（Bi） of1.5:2.0was2.58eV. The last sun light photocatalysis test showthat loose ball-flower hole structure has the superior light catalytic performance,there has a certain relationship with the sample hole structure and impurities.The effect of methenamine （methenamine）, polyethylene glycol （PEG）4000（PEG-4000）, polyvinylpyrrolidone （PVP）, and L-tryptophan four different kindsof surfactants on the crystallite structure composition, morphology and catalyticperformance of the Bi₂WO₆was studied, the results show that joining in differenttemplate agents can generate different morphologies. When add in PVP, themorphology was more uniform;When add in L-tryptophan, the product wasbar-like shape which has not appeared yet in the research report, and the bar-likemorphology whether is benefit to the light catalytic performance of the productremains to be further research. Changing the pH value of the precursor solutioncan control the morphology and properties of the product under joiningmethenamine and PEG-4000conditions. The results showed that the pure phaseBi₂WO₆microcrystalline can be prepared in the acidic and neutral conditions; thecubic system of Bi3.84W0.16O6.24mixed phase will appear in the alkalineconditions; the morphology of the products is neat, uniform under joiningmethenamine, especially the product is the size of about1μm and uniform flatshape round cakes at pH=7. The last light catalytic performance also showedjoining methenamine was better than the PEG-4000, and the product has thehighest photocatalytic efficiency at pH=7. In order to studying the templateagents reaction first with which ion, the influence of the different joining way ofdifferent template agents on the product was studied. The results show that whentemplate agent joining to WO₄^2-solution, the morphology and performance ofthe product was better than the first joining to Bi3+solution. And when the methenamine first joining to WO₄^2-solution, the morphology and light catalyticperformance of product is the best.