Controlled Synthesis, Characterization And Performce Of Ceria Or Yttria Micro/Nanostructures

The fabrication of rare earth nano/micro-materials has been intensively studied in recent years, owing to their novel optical, acoustic, electric, magnetic, thermal and catalytic properties and promising application in many fields. Rare earth oxide is an important kind of rare earth materials and has been extensively investigated and used. Among them, CeO2 is a cheap and widely used light rare earth oxide. CeO2 and its composites have been widely applied in the fields of high technology, such as ceramics, three-way catalyst, oxygen sensors, UV absorbent, glass-polishing material and electrolytes and electrodes in solid oxide fuel cells (SOFCs).Y2O3 has been used in solar cell, superconductor, oxygen sensors, fluorescence powder, advanced ceramics, and so forth. In this thesis, CeO2 and Y2O3 were selected and several novel micro/nano-structures and morphologies of them have been prepared via various preparation methods by selectively controlling the synthesis conditions. The mechanisms of the synthesis is proposed and summarized. The properties of the products have been investigated and their applications have been explored, which may provide synthetic approaches and theoretical foundation for the synthesis of other rare earth micro/-nanomaterials.The main contents and results of this dissertation are summarized as follows:1.Synthesis and characterization of CeO2 micro-/nanostructures.1.1 Synthesis and characterization of nanosized CeO2 by low-temperature hydrothermal method.CeO2 nanoparticles with controllable sizes have been successfully synthesized via a facile one-step low temperature hydrothermal synthesis route.It is found that the particle size of ceria increases with the increase of reaction temperature, which indicates that particle size of CeO2 can be readily controlled by varying the reaction temperature.1.2 Synthesis and characterization of CeO2 microdisks.Self-assembled hierarchical Ce(SO4)2 microdisks were firstly synthesized via a solvolthermal method without employing template or surfactant. After calcining the Ce(SO4)2 microdisks at 1100℃for 4 h, ceria microdisks were obtained. The ceria microdisks are with an average diameter and thickness of about 9.1μm and 320 nm, respectively. UV-vis result revealed that the as-prepared ceria microdisks show strong absorption in the ultraviolet band. La2O3 and Sm2O3 microdisks were also prepared using the same procedure.2.Synthesis and characterization of ceria composites via low-temperature molten salt method.CeO2-ZrO2 nanosized solid solution had been synthesized via molten salt method at as low temperature as 200℃for the first time. Ce2TiO5 was also prepared and its photodegradation of methyl orange have been investigated. Results show that the as-prepared Ce2TiO5 has photodegradation ability of methyl orange.3.The synthesis and the formation mechanism of Y2O3.3.1 Synthesis and characterization of yttrium oxide hollow microrectangles/microsquares.Self-assembled yttrium sulfate hydrate and yttrium oxide hollow microrectangles/microsquares were successfully synthesized for the first time by a facile solvothermal method in the absence of surfactants or templates. Interestingly, the morphology of Y2O3 can be easily changed by varying concentrations of reactants. Photoluminescence properties of the as-prepared Y2O3 also were simply studied.3.2 Mixed-solvothermal synthesis and characterization of triprism-like Y2O3.Microprisms with equilateral triangle cross section were firstly synthesized via a mixed-solvolthermal method using triethylenetetramine as the precipitator. It is found that the composition of solvent, reaction time and kinds organic alkalis have great effects on the morphology of the final products.