Study On The Controllable Design,Synthesis And Photocatalytic Performance Of Functional Materials Based On Tungstate

Tungstate has become one of the most active research fields of functional materials because of its outstanding performance in clean energy production,electrocatalysis,photocatalysis and electronic storage.As catalytic reactions mostly occur on the surface of semiconductor materials,catalytic materials with specific morphology,composition and structure can be synthesized purposedly through the precise regulation of various parameters in the reaction process,so as to significantly improve their performance.However,the growth mechanism involved in the controllable design of tungstate nanomaterials and the relationship between structure and performance are still uncertain,which requires further research and exploration.Taking tungstate as the main research object,this project adopts the synthesis method of hydrothermal self-assembly,takes the function of photocatalysis as the guidance,designs,tailores and modifies the material and its composition,and finally realizes the directional synthesis and assembly of the specificproperties and structural materials.The main content of this thesis are as follows:1.This chapter content reported the dodecahedron Co₄W₆O₂₁（OH）₂·4H₂O compound,which was prepared by a simple hydrothermal synthesis method,achieving the controllable amplification synthesis of the compounds by adjusting hydrothermal process temperature,time,and the regulation of additives.And its structure was analyzed,indicating that the compound presented silverton-type structure.In addition,the photocatalytic properties of the compound were also explored.The UV-vis absorption spectrum showed that the absorption band edge was 562 nm and it displays good stability in the photocatalytic degradation of rhodamine solution.2.This chapter content reported the nano-heterojunction of Co₄W₆O₂₁（OH）₂·4H₂O/Ag₂O microsphere,which was prepared by hydrothermal process.The photocatalytic degradation performance of rhodanmin B dye solution was studied,the uv-vis results showed that the photoabsorbance intensity activity of the heterojunction was significantly higher than that of pure Co₄W₆O₂₁（OH）₂·4H₂O/Ag₂O nanoparticles,which is due to the small band gap and large absorption coefficient of Ag₂O.Under visible light irradiation,a small amount of metallic silver will be formed on the surface of Ag₂O nanoparticles.The metallic silver nanoparticles are used as electron absorbents to clear the valence electrons of Ag₂O nanoparticles,enhancing the photocatalytic activity of Co₄W₆O₂₁（OH）₂·4H₂O/Ag₂O heterojunction.3.This chapter content reported the in situ hydrothermal self-assembly method to prepare iron doped Co₄W₆O₂₁（OH）₂·4H₂O nano materials,investigating the influence of iron doping of different concentrations on the structure and performance of Co₄W₆O₂₁（OH）₂·4H₂O by the theory and experiment.Since the ion radii and electron orbitals of iron and cobalt are similar,we speculate that iron will occupy part of cobalt in the hexahedral position.The formation energy of iron in octahedral position with different concentrations was calculated by DFT,and the formation energy is most stable when the ratio of iron to cobalt is equal.UV-vis analysis results show that the iron atomsare partly replaced by cobalt atoms to form Fex Co4-x WOH,which plays an indispensable role in promoting the light absorption,and good photocatalytic activity.Thanks to the unique spherical structure and Fenton catalysts,they not only can react with iron material to generate hydroxyl free radicals,but also quickly capture light electronic to improve the separation in the presence of H₂O₂ photoinduced carriers.4.This chapter content repoted the nano heterojunction of FeCo WOH/TiO₂microspheres was synthesized by secondary hydrothermal method.The uniform TiO₂nanowires were prepared by commercial P25 TiO₂ in hydrothermal reaction,and with TiO₂ nanowires as a seed,3D FeCo WOH/TiO₂ heterojunction catalyst were constructed via the second hydrothermal reaction.Then we emphaticallydiscussthe interaction between FeCo WOH and TiO₂,using Zeta potential to analyze the amount of charge on their respective surfaces,which indicated that the heterostructure was obtained by the electrostatic self-assembly of FeCo WOH and TiO₂ nanowires.XPS results showed that the chemical environment of the two elements did not change during the process of the combination.BET results indicated that the specific surface area of FeCo WOH/TiO₂increased compared with FeCo WOH in the process of secondary hydrothermal reaction with TiO₂ nanowires as the seed,and the catalytic performance also improved to some extent.Because the charge transfer between the nano-TiO₂ photocatalyst and FeCo WOH was not limited by the interfacial heterogeneous structure.5.This chapter content reported the octahedron CuWO₄ micro-nano structure,which was fabricated via a simple self-assembly,solvothermal method,obtaining the various morphology（nanoparticles,closed umbrella structure,octahedral and etching eight surface shape）,and comparing the photocatalytic performance for CuWO₄nanoparticles and the octahedron.UV-vis results show that the light absorption intensity of octahedron CuWO₄ was stronger than that of CuWO₄ nanoparticles,and compared with CuWO₄ nanoparticles,octahedron CuWO₄ showed higher degradation capacity.This result indicates that CuWO₄ microstructures with more regular octahedral（111）faces can provide more effective photocatalytic activity sites.According the research of the formation process of the octahedral CuWO₄,we discover that octahedron CuWO₄ was formed by the self-assembled of nanoparticles.In the reaction process,fewer and smaller particles was observed and then disappear,this is because the larger grain growth at the expense of the smaller particles,which is a typical Ostwald ripening process.Through the investigation of additives and metal cation precursor,the results show that the presence of ethylene glycol（EG）and Cl-plays a very important role in the formation of the unique form of CuWO₄.