Synthesis And Catalytic Performance Of TiO₂,Bi₂WO₆ Based Three-dimensional Spherical Structure Assembled By Nanosheets

One of the great challenges in the twenty-first century is unquestionably shortage of energy and the environmental crisis.How to utilize and transfer solar energy,wind energy,green chemical energy and other new and renewable energy has become the main way to solve these problems.The catalyst system need higher demand whether in photocatalytic degradation or direct alcohol fuel cells.Nano materials with three-dimensional layered structure?including porosity and morphology?of photocatalysts can not only enhance light harvesting and improve molecular diffusion/transport kinetics,but also increase the surface area and the amount of active sites,which accelerate the surface reaction kinetics.In addition,three-dimensional layered structure including channels and pores benefits to accelerate the transformation of charge carriers within the electricatalytic system and increasing the diffusion rate of electrolyte,on the other hand benifits to the unhindered flow of reactants and products,which effectively improve the catalytic performance of system in electrocatalytic applications.Nano materials with three-dimensional layered structure have wide applications in the field of photo-electro catalysis owing to its unique morphology.Titanium dioxide?TiO₂?has good chemical stability and good photocatalytic activity.However,there are some critical issues which restrict its photocatalytic applications for example narrow range of photo-response and the fast recombination rate of photoinduced electro-hole pairs.Moreover,Titanium dioxide?TiO₂?has long-term stability in acidic and alkaline solutions and superior poison?CO?tolerance,which is widely used in electrocatalytic application.However,it still has some issues such as large intrinsic resistance.TiO2 nanomaterials with two phase coexistence can form heterostructure to accelerate the separation of electron-hole pairs,on the other hand can improve electron transfer rate.Therefore,in the thesis we mainly focus on the photo and electric performance of heterostructures based on TiO₂?Anatase-B?with the three dimensional layered structure.However,TiO₂ nanomaterials only response to UV light,Bi₂WO₆ nanomaterials are widely used in photocatalytic application due to its excellent photocatalytic properties in visible light.Therefore,we also focus on the photo and electric performance of heterostructures based on Bi₂WO₆ with the three dimensional layered structure.There are main parts:1)The photocatalyst design and properties based on TiO₂ microspheres assembled by nanosheets.TiO₂?Anatase-B?microspheres assembled by nanosheets and different mass ratio of Ag₂O/TiO₂?Anatase-B?double heterostructures were prepared by solvothermal method.The photocatalytic performance of TiO₂?Anatase-B?microspheres,Ag₂O/TiO₂?Anatase-B?double heterostructures and P25 were evaluated by the photocatalytic decolorization of MO under visible irradiation.The Energy bands and charge carriers transition of Ag₂O/TiO₂?Anatase-B?were investigated.The photo electro-hole pairs were excited on Ag₂O and TiO₂?B?under visible light.Anatase TiO₂dominate the photoelectrons transfer from Ag₂O to Anatase.Then due to the TiO₂?B?existence,the photoelectrons can be transfered from Anatase to Ti O₂?B?,which effectively accelerate the electronic transmission rate and promote the separation of photoinduced electrons and holes.2)The electrocatalyst design and properties based on TiO₂ microspheres assembled by nanosheets.TiO₂?Anatase-B?and TiO₂?Anatase?microspheres assembled by nanosheets are prepared by one-step solvothermal process.Pt/TiO₂?Anatase-B?and Pt/TiO₂?Anatase?catalysts synthesized by the chemical precipitation method are applied to alcohol electrooxidation.Pt/TiO₂?Anatase-B?catalyst exhibits superior electrocatalytic activity and stability compared with that of Pt/TiO₂?Anatase?and Pt/C catalysts for methanol and ethanol in acidic and alkaline media,which is attributed to the large specific surface area,the porous channels to provide more active site to contact electrolytes,accelerate liquid fuel to diffuse into catalyst,the gaseous product to escape and the electron-transfer between liquid and the surface of the electrode.In addition,the mixed anatase-TiO2?B?phase can further enhance the electronic conductivity due to a possible built-in charge transfer driving force for the electrons to pass through the interfaces of anatase and TiO2?B?more easily,which can avoid the in-situ second reaction and intermediates adsorbed on the surface of electrode.3)The photocatalyst design and properties based on Bi₂WO₆ microspheres assembled by nanosheets.Bi₂WO₆ microspheres assembled by nanosheets and nanosheets were synthesized by hydrothermal reaction.The diameter of Bi₂WO₆ microspheres are3³.5?m with the optimum conditions.Ag₂O/Bi₂WO₆ heterostructures with different mass ratio were synthesized by the chemical precipitation method and the size of Ag₂O nanoparticles were 5¹5 nm.The photocatalytic performance of pure Bi₂WO₆ samples and Ag₂O/Bi₂WO₆ heterostructures were evaluated by the photocatalytic decolorization of RhB solution under simulated solar irradiation.The Ag₂O/Bi₂WO₆ heterostructures exhibited an obviously enhanced photocatalytic activity than Bi₂WO₆ samples.And photocatalytic activity of the Ag₂O/Bi₂WO₆ microspheres is higher than that of the Ag₂O/Bi₂WO₆ nanosheets.The Ag₂O/Bi₂WO₆ heterostructure can improve the separation rate of photoinduced electro-hole pairs.Bi₂WO₆ microspheres assembled by nanosheets have large specific surface area and more channels,which are beneficial to load Ag₂O nanoparticles,provide more active site to adsorp organic dye,improve the light capture rate and more transfer and diffusion paths of small molecules.4)The electrocatalyst design and properties based on Bi₂WO₆ microspheres assembled by nanosheets.Pt nanoparticles with a diameter of 0³ nm are uniformly coated on the surface of the Bi₂WO₆ microspheres assembled by nanosheets through chemical precipitation method.Pt/Bi₂WO₆ catalyst was used for the electrooxidation.Comparing with Pt/C catalyst,Pt/Bi2WO6 catalyst exhibit an increased catalytic activity toward alcohol electro-oxidation in alkaline media.Bi₂WO₆ microspheres assembled by nanosheets have large specific surface area,which is beneficial to load Pt nanoparticles and more active site to contact electrolyte.Moreover,channel structure can accelerate liquid fuel to diffuse into catalyst,the gaseous product to escape and the electron-transfer between liquid and the surface of the electrode.