Computer-Aided Design of Nanoceria Structures as Enzyme Mimetic Agents: The Role of Bodily Electrolytes on Maximizing Their Activity (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).
O vacancies on steps on the CeO2(111) surface
Physical Chemistry Chemical Physics, 2014
Cerium dioxide is a compound important for heterogeneous catalysis, energy technologies, biomedical applications, etc. One of its most remarkable properties is low O vacancy (O vac ) formation energy E f . Nanostructuring of ceria was shown to decrease E f and to make the oxide material more active in oxidative reactions. Here we investigate computationally formation of O vac on CeO 2 (111) surfaces nanostructured by steps with experimentally observed structures. To facilitate the search for O vac + 2Ce 3+
A dipole polarizable potential for reduced and doped CeO2 obtained from first principles
Journal of Physics: …, 2011
In this paper we present the parameterization of a new interionic potential for stoichiometric, reduced and doped CeO 2 . We use a dipole polarizable potential (DIPPIM: the dipole polarizable ion model) and optimize its parameters by fitting them to a series of density functional theory calculations. The resulting potential was tested by calculating a series of fundamental properties for CeO 2 and by comparing them against experimental values. The values for all the calculated properties (thermal and chemical expansion coefficients, lattice parameters, oxygen migration energies, local crystalline structure and elastic constants) are within 10-15% of the experimental ones, an accuracy comparable to that of ab initio calculations. This result suggests the use of this new potential for reliably predicting atomic scale properties of CeO 2 in problems where ab initio calculations are not feasible due to their size limitations.
A Study of Lattice Expansion in CeO 2 Nanoparticles by Transmission Electron Microscopy
Nanoceria was produced by an aqueous precipitation technique in the presence of an organic stabilizer. The stable suspensions were diafiltered to remove reaction byproducts. Particles were characterized by transmission electron microscopy with images used to size the particles, and selected-area electron diffraction was used to determine the lattice structure and the lattice constant. For all particles studied, the electron diffraction data were consistent with that of CeO 2 and not Ce 2 O 3 , as predicted by some researchers for very small particles sizes. At particle diameters of ∼1 nm, the lattice expansion approached 7%. In agreement with earlier researchers, we interpret this effect as due to the formation of substantial amounts of Ce 3+ with corresponding oxygen vacancies, but within the fluorite lattice structure of CeO 2. Even at a particle size of 1 nm, there was a measurable oxygen storage capacity, consistent with a still-reducible CeO 2 structure, rather than the fully oxidized Ce 2 O 3 .
O-vacancy and surface on CeO2: A first-principles study
Journal of Physics and Chemistry of Solids, 2010
Atomic and electronic structures of CeO 2 (1 1 1), (1 1 0) and (1 0 0) surfaces are investigated using the first-principles density functional theory taking into account the on-site Coulomb interaction. Both the stoichiometric and O-deficient surfaces are examined in order to clarify the overall features. The CeO 2 (1 1 1) is found to be the most stable surface, followed by the and surfaces, consistent with experimental observations. Three surfaces exhibit different features of relaxation. Large relaxations are found at the (1 1 0) and (1 0 0) surfaces, while very small changes are observed at the (1 1 1) surface. It is found that the O-vacancy occurs more readily at the (1 1 0) surface as compared with the (1 1 1) surface. Furthermore, the formation energies of the O-vacancy in the surfaces are lower than that in the bulk. The energetically favorable O-vacancy locates in the second O-atomic layer for the (1 1 1) while at the surface layer for the . The excess electrons left with the removal of the O atom are distributed in the first two layers with certain (a considerable) fraction filling the Ce-4f states.
Toward the Innovative Synthesis of Columnar CeO 2 Nanostructures
Langmuir, 2006
We report on the preparation of supported columnar CeO 2 nanostructures by a simple catalyst-free chemical vapor deposition process at temperatures as low as 623 K. A suitable choice of experimental parameters enables us to control the structural and morphological features of the resulting ceria nanosystems.
Physical chemistry chemical physics : PCCP, 2014
The chemical activity of oxygen vacancies on well-defined, single-crystal CeO2(111)-surfaces is investigated using CO as a probe molecule. Since no previous measurements are available, the assignment of the CO ν1 stretch frequency as determined by IR-spectroscopy for the stoichiometric and defective surfaces are aided by ab initio electronic structure calculations using density functional theory (DFT).
Investigation of Electronic Structure of Ceo2: First Principles Calculations
international journal of chemical sciences, 2016
In this paper, we present the first ever theoretical Compton profiles and electron momentum densities along with energy bands and density of states of rare earth oxide CeO2. We have employed the linear combination of atomic orbitals method to compute these electronic properties. For this, we have applied local density approximation, generalized gradient approximation and recently developed second order generalized gradient approximation within the frame work of density functional theory. The energy band gap of CeO2 is found to be in good agreement with the available data. Theoretical anisotropies in Compton profiles along [100], [110] and [111] directions are explained in terms of energy bands.