| One of inexpensive functional rare earth oxides, ceria (CeO2) nanomaterials has attracted much attention for promising applications in catalysts, fuel cells, gas sensors, oxygen pump, mechanical polishing, ultraviolet blocks, and luminescent materials due to its oxygen storage capacity via facile Ce4+/Ce3+redox cycles, high mechanical strength, and optical property. Recent reports showed that the performance of nanomaterials strongly depends on the size, structure, morphology, crystal face exposed, and defect, among which morphology is a critical factor in determining the performance of CeO2nanomaterials. Hence, controlling the nanocrystal growth process and preparing CeO2nanostructure with different morphology and superior performance have become an advanced research project in rare earth based oxides areas.The shape-controllable CeO2nanomaterials were successfully synthesized by novel hydrothermal (solvothermal) synthesis process. The crystal phases, surface chemical component, and morphology of products were characterized by X-ray diffraction, X-ray photoelectron spectroscopy, scanning electron microscope, and transmission electron microscope. The effect of morphology and chemical component on optical properties of CeO2was investigated in detail through UV-vis spectrophotometer and fluorescence spectrometer. The main contents of research are as follows:1. CeO2nanopolyhedra and square-like nanoparticles were selectively synthesized by a novel hydrothermal synthesis process with the aid of different surfactants. CeO2nanopolyhedra were prepared using polyvinyl pyrrolidone as surfactant, while square-like CeO2nanoparticles were prepared using ethylenediamine as surfactant. The possible morphology-selective synthetic mechanism was proposed. X-ray photoelectron spectroscopy measurement revealed that the main valence of cerium irons in the nanopolyhedra was tetravalent, and the subordinate was trivalent which might result in formation of oxygen vacancies.2. CeO2nanorods of15-20nm in diameter and100-200nm in length were successfully synthesized by a novel chloride-assisted hydrothermal synthesis process using CeCl3·7H2O as cerium source. Under similar hydrothermal conditions, use of Ce(NO3)3·6H2O instead of CeCl3·7H2O as cerium source results in the growth of CeO2nanoparticles rather than nanorods. The absorption edge of CeO2nanorods showed an obvious blue-shift compared with nanopariticles. Photoluminescence spectra of CeO2nanorods exhibited a stronger light emission than the nanoparticals. The synthetic mechanism of CeO2nanorods has been proposed and can be mainly attributed to the coordination interaction between ethylenediamine and chlorine ions.3. CeO2nanoparticles were successfully synthesized by a novel hydrothermal synthesis process usingN2H4·H2O as mineralizer. The dosages of N2H4·H2O influence crystallite size and lattice parameter of nanoparticles. The reason for variation of the particle size with the dosages of N2H4·H2O was discussed in detail. The variation for lattice parameter was attributed to both lattice relaxation and valence effect of Ce ions. In addition, the dosages of N2H4·H2O influence band gap energy and photoluminescence intensity. The band gap energy increased from3.12to3.19eV with the increase of N2H4·H2O from2to6mL. The photoluminescence intensity increased with the increase of N2H4·H2O from2mL up to6mL and then decreases. Photoluminescence response of these nanoparticles was dependent on both absorbance and degree of oxygen vacancies in the products.4. Shape-controllable CeO2nanostructures with different components were successfully synthesized by a novel solvothermal synthesis using mixed solvents with different volume rations of ethanol to water. CeO2nanostructures was gradually converted from nanocolumns to nanoparticles (～5nm) with increasing of volume ratios of ethanol to water. Compared with column-like CeO2nanostructure, there are more oxygen defects and Ce3+ions in nanoparticles. The Ce3+ions can be distributed either in region of sesquioxide Ce2O3or around oxygen-vacancy in CeO2, among which the Ce2O3was amorphous. |
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