Synthesis Of Mesocrystal Ceria-based Solid Solution Materials And Their Catalytic Performance

Cerium oxide nanostructurs is one of the most important rare-earth oxide materials,due to their unique crystal structure, optical properties, high thermal stability, electricalconductivity and diffusivity, and the ability to store and release oxygen, which have foundbe widely used in everywhere. The physicl and chemical properties of cerium oxide arestrongly dependent on their microstructures, including size, morphology, andsurface-to-volume etc. As a result, the control of pore structure and micromorphology ofnanosized CeO2and their application research are urgently needed solving. In thisdissertation, we report the synthesis and characterization of mesostructured andmorphology controlled ceria based nanomaterials and ceria-based solid solution, as well astheir catalytic properties in CO oxidtion and degradation of methylene blue.The results showed that the cubic-like mesocrystal CeO2could be obtained byhydrothermal reaction, when C5H9NO4:Ce(NO3)36H2O was5:1(the molar ratio), reactiontemperature was200℃, reaction time was10hours, calcination temperature was300℃and calcination time was3hours. The UV–visible adsorption spectrum exhibited thered-shift phenomenon compared with commercial CeO2particles. The reason might be theexistence of the twin boundaries in this unique structure. A possible formation mechanismof cubic-like mesocrystal CeO2is concluded on account of the nanocrystals aggregationalong with the epitaxial orientation following the manner of coherent interface.Mesoporous mesocrystal Ce1-xLaxO2composite materials were fabricated viaevaporation-induced self-assembly (EISA) according to the different proportion of ceriumlanthanum, during which the triblock copolymers P123was used as a surfactant to modifythe properties of the target materials. When the La3+molar fraction was0.2, its SAEDimages were neither typical polycrystalline diffraction pattern nor single crystal latticestructure，the SAED images were made up of elongated lattice. It shows that Ce0.8La0.2O2issolid solution of mesocrystal structure. The Ce0.8La0.2O2composite material displays thebest catalytic performance for CO conversion due to the unique mesoporous mesocrystalstructure and can decolorize concentration of400mL40mg/L of methylene blue solutionup to100%in30min.Mesoporous mesocrystal Ce1-xSmxO2composite materials were fabricated viaevaporation-induced self-assembly (EISA) according to the different proportion of cerium samarium, during which the triblock copolymers P123was used as a surfactant to modifythe properties of the target materials. Doping of Sm2O3could influence the structure ofsolid solution if the Sm3+molar fraction was0.2or less, TEM demonstrated that the wallframework consists of a single phase based on the face-centered cubic CeO2and itsorientation is not affected. However, when the Sm3+molar fraction was0.3, a mixture offace-centered cubic and body-centered cubic phases formed and the preferential crystalorientation disappeared. When x was0.3，The Ce0.7Sm0.3O2composite material displaysthe best catalytic performance for CO conversion due to the unique mesoporousmesocrystal structure and can decolorize concentration of400mL40mg/L of methyleneblue solution up to100%in35min.