Morphology, structural properties and reducibility of size-selected CeO 2− x nanoparticle films (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).
Ag Nanoparticles on Reducible CeO 2 (111) Thin Films: Effect of Thickness and Stoichiometry of Ceria
The Journal of Physical Chemistry C, 2015
The growth and structures of Ag nanoparticles on CeO 2−x (111) thin films with different thicknesses, morphologies, and reduction degrees have been systematically studied by scanning tunneling microscopy (STM), X-ray photoelectron spectroscopy (XPS), and low energy electron diffraction (LEED). The CeO 2−x (111) thin films were epitaxially grown on Cu(111). With increasing the ceria thin film thickness, the size of the terraces decreases along with the increase of the number of open monolayers and defects. In most cases, Ag exhibits three-dimensional (3D) growth with constant particle densities on the CeO 2−x (111) surfaces at 300 K. Ag mainly populates the sites at the ceria−ceria step edges instead of ceria terraces, independent of the thicknesses but influenced by the reduction degree of the ceria films. On the fully oxidized ceria films, the particle density is directly proportional to the number of step edges of ceria, which is related to its thickness on Cu(111). On the slightly reduced ceria films which were prepared by annealing the fully oxidized ceria films in ultrahigh vacuum, single surface oxygen vacancies and their linear agglomerates are observed, but they do not anchor Ag particles during Ag deposition. While on the strongly reduced ceria films produced by decreasing the oxygen pressure during ceria film growth, large defect sites related to surface and subsurface oxygen vacancies are found; they can anchor the Ag nanoparticles, leading to the random distribution of Ag nanoparticles on ceria terraces upon deposition. Upon heating, the Ag nanoparticles undergo serious sintering before desorption at 800 K on the fully oxidized CeO 2 films. While on the reduced ceria films, the sintering and desorption processes are slowed down at the same annealing temperatures as those on CeO 2 . This result suggests that the defects on reduced ceria surfaces can enhance the thermal stability of Ag nanoparticles during annealing.
Applied Physics Letters, 2010
This study reveals that the Ce 4+ to Ce 3+ ratio in CeO 2 nanoparticles ͑Ͻ20 nm͒ increases with increasing temperature under a hydrogen atmosphere. Such anomalous behavior is due to the physical effect of nanoparticle sizes on increasing the oxidation state of Ce ions in CeO 2 , which is stronger than the chemical effect of hydrogen reduction. This discovery offers an effective way to independently control the specific surface area and Ce 3+ concentration of CeO 2 nanoparticles.
2015
Cerium oxide (CeO2) or ceria has been shown to be an interesting support material for noble metals in catalysts designed for emission control, mainly due to its oxygen storage capacity. Ceria nanoparticles were prepared by precipitation method. The precursor materials used in this research were cerium nitrate hexahydrate (as a basic material), potassium carbonate and potassium hydroxide (as precipitants). The morphological properties were characterized by high resolution transmission electron microscopy (HRTEM), scanning electron microscopy (SEM) and X-ray diffraction (XRD), Fourier transform infrared spectroscopy (FTIR) and UV-Vis spectrophotometer. XRD results showed face centered cubic CeO2 nanoparticles for annealed nanoparticles at 1000°C. SEM measurement showed that by increasing the calcinations temperature from 200 to 600°C, the crystallite size decreased from 90 to 28 nm. The SEM results showed that the size of the CeO2 nanoparticles decreased with increasing temperature. T...
Catalysts, 2019
Ceria-based oxides have been widely explored recently in the direct decomposition of N2O (deN2O) due to their unique redox/surface properties and lower cost as compared to noble metal-based catalysts. Cobalt oxide dispersed on ceria is among the most active mixed oxides with its efficiency strongly affected by counterpart features, such as particle size and morphology. In this work, the morphological effect of ceria nanostructures (nanorods (ΝR), nanocubes (NC), nanopolyhedra (NP)) on the solid-state properties and the deN2O performance of the Co3O4/CeO2 binary system is investigated. Several characterization methods involving N2 adsorption at −196 °C, X-ray diffraction (XRD), temperature programmed reduction (TPR), X-ray photoelectron spectroscopy (XPS) and transmission electron microscopy (ΤΕΜ) were carried out to disclose structure–property relationships. The results revealed the importance of support morphology on the physicochemical properties and the N2O conversion performance...
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.
Synthesis, structural and magnetic properties of CeO2 nanoparticles
Micro & Nano Letters, 2010
With a view to investigate the influence of nanometric size on the structural, surface, and magnetic properties of nanocrystalline Ti 0.95 Co 0.05 O 2-diluted magnetic semiconductors, prepared by a novel simple controllable peroxide-assisted reflux chemical route followed by annealing at different temperatures, a systematic investigation has been undertaken. Structural characterizations such as X-ray diffraction followed by Rietveld refinement, electron diffraction pattern, Fourier transform infrared, Raman scattering, and X-ray photoelectron spectroscopy (XPS) measurements have shown anatase phase formation in nanocrystalline Ti 0.95 Co 0.05 O 2 without any additional impurity phases. The modified reflux chemical route was effective in obtaining pure phase Ti 0.95 Co 0.05 O 2 nanoparticles. Surface morphological investigations by using transmission electron microscopy and atomic force microscopy measurements showed the predominant effect of random distribution of nanoparticles on the aggregation behavior and local microstructural changes. The deconvoluted XPS core level Co 2p spectral study manifested the oxidation state of Co as +2 and is found to be stable with varying particle size and annealing temperature. The ferromagnetic behavior was investigated by vibrating sample magnetometer, magnetic force microscopy, and electron spin resonance measurements. These magnetization studies showed all the samples are ferromagnetic at room temperature without
Materials Chemistry and Physics, 2017
CeO 2 nanoparticles have been prepared by gel combustion method. The as-prepared nanoparticles were calcined at 500, 550 and 600 C. The crystallite size of the nanoparticles has been determined using X-ray diffraction. Catalytic activity has been studied by measuring the Tafel slope in oxygen reduction reaction in cyclic voltammetery. The nanoparticles samples showed higher catalytic activity than bulk ceria sample. Surprisingly, smaller size nanoparticles with large surface area showed less catalytic activity than larger size nanoparticles. Positron annihilation, X-ray photo electron spectroscopy and photoluminescence studies indicated the presence of oxygen vacancies as well as larger surface defects. It has been found that surface defect concentration increased with the increase in calcination temperature and the catalytic activity of the nanoparticles is directly correlated to the surface defect concentrations.