Preparation of hexagonal cerium oxide nanoflakes by a surfactant-free route and its optical property
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Hexagonal cerium oxide nanoflakes have been synthesized by using a surfactant-free route. Transmission electcron microscopy (TEM), x-ray diffraction (XRD), infrared spectroscopy (FTIR), thermogravimetric and differential thermal analysis (TG-DTA), Brunauer–Emmett–Teller adsorption isotherm (BET), photoluminescence (PL), and ultraviolet–visible (UV–VIS) were used to characterize the sample. The mean size of the nanoflakes is about 30 nm and the specific surface is about 70.08 m2·g−1 when annealed at 400 °C. The acidity and superfluous NH4NO3 play a key role on the formation of nanoflakes in which there exists Ce (IV) and very little Ce (III). The nanoflakes exhibit a wide PL emission peak among 350–400 nm, strong absorption ranged from 200–450 nm, and strong reflection in the visible region. As the sizes of as-prepared samples decrease, a clear blue shift in the absorbing edge is observed. The linear relationship between ⌬Eg and D is shown in a log–log plot. The as-prepared cerium oxide nanoflakes can be widely used as UV absorbent and polishing materials.
I. INTRODUCTION
Cerium oxide is a technologically important material because of its wide applications in catalysts, ultraviolet (UV) absorption,1 polishing materials,2,3 etc. These applications are mainly related to its storage and transport behaviors of oxygen.4 The cerium oxides that have nanosize and good dispersancy are used as a promotor in three-way catalysts for the elimination of toxic autoexhaust gases,5–9 oxygen sensors,10 fuel cells,11,12 etc. In recent years, people have been attracted to the research of cerium oxide nanoparticles. Bo Tang et al.13 synthesized cerium oxide single-crystalline nanowires using H2O2 as an oxidizer and template agent by a surfactant-free route. Chengchun Tang et al.14 synthesized cerium hydroxide nanotubes by hydrothermal treatment of CeCl3 in NaOH solution at temperatures ranging from 100 to 150 °C. Raffaella Lo Nigro et al.15 prepared nanostructured oriented cerium oxide films grown on random metallic substrates. All the samples mentioned above have outstanding properties, such as the Raman-allowed modes shifting and broadening, lattice expansion, transition from boundary diffusion to lattice diffusion, blue shift in UV absorption spectra, etc. The preparation of cerium oxide materials such as nanoparticles, nanowires, nanotubes, and films has been
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Address all correspondence to this author. e-mail: [email protected] DOI: 10.1557/JMR.2007.0408 3006
J. Mater. Res., Vol. 22, No. 11, Nov 2007
described, but there has been little review of sheet nanostructured cerium oxide materials. In this study, we prepared hexagonal cerium oxide nanoflakes using a direct precipitation method in a water solution. Results from transmission electcron microscopy (TEM), x-ray diffraction (XRD), infrared spectroscopy (FTIR), thermogravimetric and differential thermal analysis (TG-DTA), Brunauer–Emmett–Teller adsorption isotherm (BET), photoluminescence (PL), and ultraviolet–visible (UV– VIS) analysis showed that the hexagonal cerium oxi
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