Investigation On The Preparation And Structure-activity Relationship Of The Modified Ceria Semiconductor Nanomaterials

Ceria（CeO₂）nanomaterials have the properties of high oxygen buffering capacity,large dielectric constant,high thermal stability,high chemical stability,adjustable band gap,fast ion transfer rate,being safe and non-toxic,low cost,and simple preparation,which have received extensive attention and application in the field of semiconductor,energic catalysis,environmental catalysis,biocatalysis,etc.The physicochemical properties of CeO₂ nanomaterials depend on the shape,size,composition,and surface state,and thus performances of CeO₂ closely related to structure,namely the strong structure-activity relationship.Elucidating this structure-activity relationship could provide theoretical basis and experimental guidance for the controlled design and synthesis of CeO₂-based nanomaterials with specific structures to achieve better application performance.In this dissertation,modified CeO₂ nanomaterials were prepared by using solvothermal method,impregnation method,and calcination method,structure-activity relationship of which was also investigated.The main research contents and conclusions are summarized as follows.1.Oxygen-vacancy-content regulation and oxidase-like activity of CeO₂ nanomaterialsCeO₂ nanomaterials modified with polyvinylpyrrolidone（PVP）were prepared using solvothermal method（PVP/CeO₂）.It was found that the surface oxygen-vacancy content of flower-like PVP/CeO₂ nanomaterials is linearly improved with increasing reaction duration.The oxidase-like activity of PVP/CeO₂ nanoflowers was studied by exploiting 3,3’,5,5’-tetramethylbenzidine as the substrate.It was found that the oxidase-like activity of PVP/CeO₂ can be improved by high oxygen-vacancy content.Calculation results show that surface PVP molecules can synergize with oxygen vacancies and thus enhances the adsorption of reactant molecules on the surface of nanoenzymes.As a result,PVP/CeO₂ nanoflowers have higher oxidase-like performances than other CeO₂-based nanomaterials.2.Thermal stability of flower-like PVP/CeO₂ nanostructureIn O₂,PVP molecules on the surface of PVP/CeO₂ flower-like nanostructure decomposed with the increase of heating temperature and the nanoparticles in the flower-like nanostructure were agglomerated.At temperatures above 700 ^oC,nanoparticles with strain at the corners would undergo a structural decomposition.In a vacuum environment,PVP molecules of PVP/CeO₂ nanoflowers would be carbonized and fluorite phase CeO₂ would be reduced into hexagonal phase Ce₂O₃ with increasing the heating temperature.When the temperature is above 500 ^oC,Ce₂O₃ nanoparticles sublimated from the edge to the center.Theoretical calculation results show that PVP/CeO₂nanoflowers are more prone to structural decomposition in the oxidizing environment at high temperatures,while the material transformation and sublimation in the reducing environment are thermodynamic spontaneous behaviors.3.Surface-state regulation and structure-activity relationship of Mn-doped CeO₂ nanorodsCeO₂ nanorods with adjustable surface state were prepared by combining hydrothermal method,impregnation method and calcination method.High-valence Mn element can enhance the surface redox property of CeO₂ nanomaterials and improve the stability of bulk Ce⁴⁺cations.Using the elimination of soot nanoparticles as the application model,the performance of Mn-doped CeO₂nanorods is closely related to the state of Mn cations.It was found that Mn-doped CeO₂ nanorods have the best performance of eliminating soot nanoparticles,when the surface Mn²⁺/Mn³⁺/Mn⁴⁺percentages are approximately equal.Theoretical calculation results demonstrate that the approximately equal Mn²⁺/Mn³⁺/Mn⁴⁺ratios can promote the interaction between CeO₂ and carbon nanoparticles,and improve the ability of CeO₂ to adsorb and activate O₂ molecules.4.Co₃O₄/CeO₂ nanostructure and its structure-activity relationshipCo₃O₄/CeO₂ nanostructures containing Co₃O₄-CeO₂ heterogeneous interfaces were prepared by using solvothermal method and calcination,the structure-activity relationship of which was investigated by using the eliminating carbon nanoparticles as application model.It was found that Co₃O₄-CeO₂ heterogeneous interfaces can significantly decrease the elimination temperature of carbon nanoparticles,while the relative content of heterogeneous interfaces has little effect on this elimination temperature.When the relative content of heterogeneous interface is low,Co₃O₄/CeO₂nanostructures have a large specific surface area,the number of active sites is 2.55 times that of pure CeO₂ nanosheets,and its ability to activate O₂ molecules is strongly improved,which can significantly reduce the elimination temperature of carbon nanoparticles.When the relative content of heterogeneous interface is increased,the specific surface area and number of active sites of Co₃O_4/CeO₂ nanostructures are reduced,but their ability to activate NO molecules is dramatically enhanced,resulting in high intrinsic activity and low elimination temperature of carbon nanoparticles.