A Study of Lattice Expansion in CeO 2 Nanoparticles by Transmission Electron Microscopy (original) (raw)
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Journal of Nanoparticle Research, 2013
A correlation between the particle size and the lattice parameter has been established in cerium oxide nanoparticles. The variation in the lattice parameter is attributed to the lattice strain induced by the introduction of Ce 3? due to the formation of oxygen vacancies. Lattice strain was observed to decrease with an increase in the particle size. The Ce 4? to Ce 3? ratio in CeO 2 nanoparticles increases with increasing the calcination temperature in air atmosphere. Such anomalous behavior is due to the physical effect of nanoparticle sizes on increasing the oxidation state of Ce ions in CeO 2. Keywords Cerium oxide Á XPS Á XRD Ceria (CeO 2) is an inorganic compound broadly used in sensors, electrochromic, and anticorrosive coatings, and also in diverse catalysts and in the capacity of an abrasive material. Upon transition into a nanocrystalline state, ceria significantly changes its physicochemical properties, at that, the character of these changes is unusual enough (Ivanov et al. 2009). One of the major intrinsic properties of nanocrystalline ceria is a clearly marked dependence of a unit cell parameter on particle size. It is generally accepted that such an effect originates from partial reduction of Ce 4? into Ce 3? and corresponding formation of oxygen vacancies in ceria crystal lattice (Tsunekawa et al. 1999; Wu et al. 2004). Strongly pronounced non-stoichiometry gives rise to one of the most intriguing properties of ceria, namely its biological activity. It has been shown that CeO 2-x powders and sols (aqueous and nonaqueous) are effective scavengers of free radicals and other reactive oxygen species (ROS) and possess autoregenerative properties (Chen et al. 2006). Such a combination of properties as well as nontoxic nature and excellent biocompatibility makes nanocrystalline ceria a unique material that can protect cells from oxidative stress. In particular, CeO 2-x particles can increase cell longevity and survival potential of various micro-and macroorganisms (Ivanov et al. 2008; Colon et al. 2009). It was also shown that CeO 2-x is promising in view of treatment of various human diseases including cancer (Chen et al. 2006; Colon et al. 2009). In view of the fact that nanoceria biological activity is size-dependent (Chen et al. 2006), extensive study of physical and chemical properties of CeO 2-x is required paying special attention to its oxygen non-stoichiometry. Several reports were made dealing with dependence of oxygen non-stoichiometry and unit cell parameter on the particle size in CeO 2-x (Tsunekawa et al. 1999; Wu et al. 2004; Hailstone et al. 2009).
Morphology, structural properties and reducibility of size-selected CeO 2− x nanoparticle films
Beilstein Journal of Nanotechnology, 2015
Non-stoichiometric ceria nanoparticles (NPs) were obtained by a gas aggregation source with a magnetron and were mass-selected with a quadrupole mass filter. By varying magnetron power, Ar gas flow, and the length of the aggregation tube, NPs with an average diameter of 6, 9, and 14 nm were synthesized and deposited onto a substrate, thus obtaining NP films. The morphology of the films was studied with scanning electron microscopy, while high resolution transmission electron microscopy was used to gain a deeper insight into the atomic structure of individual NPs. By using X-ray photoelectron spectroscopy we analyzed the degree of reduction of the NPs of different diameters, before and after thermal treatments in vacuum (reduction cycle) and in O2 atmosphere (oxidation cycle) at different temperatures. From this analysis we inferred that the size is an important parameter only at intermediate temperatures. As a comparison, we evaluated the reducibility of an ultra-thin ceria film wit...
Synthesis of CeO2 nano-aggregates of complex morphology
Ceramics International, 2013
Cerium oxide with spheric, flowerlike and needle-like shapes has been synthesized by a simple microwave assisted method using diethylene glycole in mild conditions. The effect of reaction temperature on the crystal structure and morphology were thoroughly discussed. The structural evolutions and morphological characteristics of the nanostructures were investigated using X-ray diffractometery, scanning and transmission electron microscopy, Fourier transform infrared spectroscopy, TGA/DSC and BET analysis. By changing experimental conditions pure CeO 2 fluoritic phase or cerium formate with complex morphology were formed. High porosity CeO 2 nanostructures, retaining the end-reaction morphology, were readily obtained by calcination of cerium precursor. This simple and economic soft chemical method leads to nanostructured-micrometric aggregates of cerium oxide with high specific surface area suitable for catalytic applications.
Synthesis of nanocrystalline CeO2 particles by different emulsion methods
Materials Characterization
Cerium oxide nanoparticles were synthesized using three different methods of emulsion: (1) reversed micelle (RM); (2) emulsion liquid membrane (ELM); and (3) colloidal emulsion aphrons (CEAs). Ammonium cerium nitrate and polyoxyethylene-4-lauryl ether (PE4LE) were used as cerium and surfactant sources in this study. The powder was calcined at 500 °C to obtain CeO2. The effect of the preparation procedure on the particle size, surface area, and the morphology of the prepared powders were investigated. The obtained powders are highly crystalline, and nearly spherical in shape. The average particle size and the specific surface area of the powders from the three methods were in the range of 4–10 nm and 5.32–145.73 m2/g, respectively. The CeO2 powders synthesized by the CEAs are the smallest average particle size, and the highest surface area. Finally, the CeO2 prepared by the CEAs using different cerium sources and surfactant types were studied. It was found that the surface tensions o...
Synthesis and characterization of CeO2 nanoparticles by hydrothermal method
Elsevier
Crystalline structure, phase and surface morphology of ceria nanostructure was discussed in detail in the recent work. Our latest work is persistent on ceria nanostructure by conventional and plant extract – mediated synthesis starting from cerium nitrate as precursors for putrefaction of pollutant in the industrial wastewater. The crystalline structure, surface morphology, phases, functional groups and size were examined by assorted characterization techniques like powder X-ray diffraction pattern (XRD), Fourier transform infrared spectroscopy (FTIR) and Scanning electron microscopy (SEM). Therefore, the pure phases of ceria nanostructure were investigated by XRD analysis. The surface morphology, shape and unique size of synthesised ceria established through electron microscopy were reported in detail.
Materials Today: Proceedings, 2017
Cerium oxalate decahydrate was subjected to a thermal decomposition to obtain nanocrystalline ceria. It was shown that conditions during dehydration strongly influence morphology of the final product. If one performs dehydration of the precursor under a vacuum or in air, CeO 2 can be obtained in pseudomorph, i.e. the precursor's crystal shape is retained. An increase of water vapor pressure leads to the formation of different intermediates and fragmentation of the precursor's crystals. Investigation by various physical methods (TEM, XRD, and BET) provided the information that the final product consisted of CeO 2 particles 5-6 nm in size.
CeO2/CeF3 composite nanoparticles: Fabrication by fluorination of CeO2 with tetrafluoromethane gas
Materials Chemistry and Physics, 2018
The interaction of CeO 2 nanoparticles with CF 4 gas at high temperature results in the formation of CeF 3 crystalline phase on the surface of nanoparticles. The lattice parameters of CeF 3 phase in CeO 2 /CeF 3 composite nanoparticles correspond to CeF 3 bulk. In the process of formation of CeF 3 crystalline phase, the Ce 3+ ions can occupy the various positions in crystal lattice: normal sites and perturbed sites arising due to location of O 2− ions near to Ce 3+ ions. The energy transfer between Ce 3+ ions occupying normal and perturbed sites in CeF 3 phase has been observed.
In-situ fabrication of Ce-rich CeO2 nanocatalyst for efficient CO oxidation
Journal of Alloys and Compounds, 2019
Ceria is widely utilized in the field of CO catalysis due to its outstanding oxygen storage/release capacity (OSC/ORC). In this study, Ce precursor is successfully injected into the plasma electrolytic oxidation (PEO) film in silicate electrolyte through the addition of EDTA-2Na during PEO process. The atomic percentage (at. %) of Ce in PEO film can reach up to 14.80, which is the highest among all the related works. Annealing treatment in air ambient leads to the crystallization and oxidation reaction of Ce species, which mainly exist in the PEO film in amorphous phase and Ce 4.667 (SiO 4) 3 O. During the annealing process, CeO 2 nanocrystals (~100 nm) are
Catalysis Surveys from Asia, 2005
The influence of SiO 2 , TiO 2 , and ZrO 2 on the structural and redox properties of CeO 2 were systematically investigated by various techniques namely, X-ray diffraction (XRD), Raman spectroscopy (RS), UV-Vis diffuse reflectance spectroscopy (DRS), X-ray photoelectron spectroscopy (XPS), high-resolution transmission electron microscopy (HREM), BET surface area, and thermogravimetry methods. The effect of supporting oxides on the crystal modification of ceria was also mainly focused. The investigated oxides were obtained by soft chemical routes with ultrahigh dilute solutions and were subjected to thermal treatments from 773 to 1073 K. The XRD results suggest that the CeO 2 -SiO 2 sample primarily consists of nanocrystalline CeO 2 on the amorphous SiO 2 surface. Both crystalline CeO 2 and TiO 2 -anatase phases were noted in the case of CeO 2 -TiO 2 sample. Formation of cubic Ce 0.75 Zr 0.25 O 2 and Ce 0.6 Zr 0.4 O 2 (at 1073 K) were observed in the case of CeO 2 -ZrO 2 sample. The cell 'a' parameter estimations revealed an expansion of the ceria lattice in the case of CeO 2 -TiO 2 , while a contraction is noted in the case of CeO 2 -ZrO 2 . The DRS studies suggest that the supporting oxides significantly influence the band gap energy of CeO 2 . Raman measurements disclose the presence of oxygen vacancies, lattice defects, and displacement of oxide ions from their normal lattice positions in the case of CeO 2 -TiO 2 and CeO 2 -ZrO 2 samples. The XPS studies revealed the presence of silica, titania, and zirconia in their highest oxidation states, Si(IV), Ti(IV), and Zr(IV) at the surface of the materials. Cerium is present in both Ce 4+ and Ce 3+ oxidation states. The HREM results reveal well-dispersed CeO 2 nanocrystals over the amorphous SiO 2 matrix in the case of CeO 2 -SiO 2 , isolated CeO 2 and TiO 2 (A) nanocrystals and some overlapping regions in the case of CeO 2 -TiO 2 , and nanosized CeO 2 and Ce-Zr oxides in the case of CeO 2 -ZrO 2 sample. The exact structural features of these crystals as determined by digital diffraction analysis of HREM experimental images reveal that the CeO 2 is mainly in cubic fluorite geometry. The oxygen storage capacity (OSC) as determined by thermogravimetry reveals that the OSC of mixed oxides is more than that of pure CeO 2 and the CeO 2 -ZrO 2 exhibits highest OSC.