Synthesis and characterization of CeO 2 nanoparticles by low temperature hydrothemal and solvent thermal process
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Synthesis and characterization of CeO2 nanoparticles by low temperature hydrothemal and solvent thermal process Eric Y.H. Teo 1, Ming Lin 2, Ziyuan Fu 1, 2, Seng.C. Ng 1, 2, Siliang Song 1, 2, Jun C. Tan 1, 2 1
School of Engineering, Republic Polytechnic, Singapore. Materials Science & Characterization Lab, Institute of Materials Research and Engineering, Singapore. 2
ABSTRACT Ceria has been aggressively explored for applications as a fuel cell electrolyte or in catalytic converter due to its high oxygen ion conductivity, or as a UV absorption material. It is proven that the properties and applications of ceria nanoparticles are related to their morphologies and sizes. This ability to control the shape and morphology of CeO2 nanoparticles allows the corresponding tuning of their chemical and physical properties. Most of the applications require the use of non-agglomerated nanoparticles, as aggregated nano-particles lead to inhomogeneous mixing, poor sinterability and compromised properties. However, nanocrystals with a primary particle size < 5 nm have a strong tendency to agglomerate. In this work, nano-crystalline particles of CeO2 have been synthesized by a low temperature hydrothermal and solvent thermal synthesis process. Using the precursors of Ce(NO3)3.6H2O:NaOH in different mixing ratio, using polyvinylpyrrolidone (PVP) as the surfactant, the CeO2 particles were synthesized via 24 h hydrothermal and solvent thermal process treatment at reaction temperature of 100 °C and 180 °C using Teflon-lined hydrothermal autoclave. We have optimized the conditions for the two synthesized methods, hydrothermal and solvent thermal, to yield highly crystallized particle with controllable shape, sizes and morphology. X-ray diffraction (XRD) and high-resolution transmission electron microscope (HR-TEM) analysis were used to characterize the crystalline and morphology of the synthesized CeO2 nanoparticles. The optimal reaction condition to prepare the CeO2 of the desired octahedron shaped fluorite structure was established. Based on the results, the hydrothermal synthesis method yields nanocrystalline CeO2 sizes of ~6 nm, while the solvent synthesis method yields nanocrystalline CeO2 sizes of 2-3 nm at the optimal conditions. The hydrothermal synthesis method produced better particles in terms of crystallinity and morphology under HR-TEM. Temperature also plays a part in crystallinity and sizes of the CeO2 nanoparticles. The crystallinity and size of the CeO2 nanoparticles increases when using higher treatment temperature for both hydrothermal and solvent thermal methods. The growth mechanism of the shape and morphology of the CeO2 will also be discussed.
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INTRODUCTION Rare earth materials such as Ceria, one of many nanostructured functional materials, have been widely studied due to their attractive properties for a wide range of applications such as catalysis [1,2], fuel cells [3,4] , gas sensors [5,6], and optics [7,8]. In recent years, much progress have been made in the synthesis of Ceria nanostructures with varyin
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