Synthesis and acid functionalization of cerium oxide nanoparticles

Colloidal cerium oxide has been obtained by controlled oxidation of soluble Ce(III) salts in hydrothermal conditions. The homogeneous nucleation of CeO₂ through thermolysis of this oxidizing solution allows the formation of well dispersed colloidal particles. Under optimal conditions, well crystallized particles with an average size of 8 nm are obtained. The surface is terminated by acetate groups which can be substituted by grafting phosphonic acids or phosphoric acids. Particularly, the grafting of 2-carboxyethylphosphonic acid or phosphonoacetic acid increases the acidic character of the surface as observed by impedance spectroscopy.     

Synthesis and catalytic properties of microemulsion-derived cerium oxide nanoparticles

The synthesis of cerium dioxide nanoparticles using an inverse microemulsion technique and precipitation method was investigated. Cerium hydroxide nanoparticles were synthesized by adding diluted ammonia to n-heptane–surfactant–cerium nitrate system. The micelle and particle size in the range of 5–12 nm were controlled by varying the molar water to surfactant ratio and analyzed by dynamic light scattering (DLS), small angle X-ray scattering (SAXS) and high-resolution transmission electron microscopy (HRTEM). Cerium hydroxide nanoparticles were isolated and subsequently treated at 100–600 °C to obtain nanoscale ceria. Crystallite sizes of cerium dioxide in the range of 6–16 nm were estimated by Scherrer analysis by X-ray diffraction (XRD) and HRTEM. The catalytic activity of particles annealed at 400 and 600 °C in soot combustion reactions was characterized by temperature-programmed oxidation (TPO) indicating a size-dependant activity. Crystallite sizes and catalytic stability of elevated ceria systems were tested in second combustion cycles.     

Fabrication of cerium oxide nanoparticles: characterization and optical properties

Ceria (CeO(2)) is a technologically important rare earth material because of its unique properties and various engineering and biological applications. A facile and rapid method has been developed to prepare ceria nanoparticles using microwave with the average size 7 nm in the presence of a set of ionic liquids based on the bis (trifluoromethylsulfonyl) imide anion and different cations of 1-alkyl-3-methyl-imidazolium. The structural features and optical properties of the nanoparticles were determined in depth with X-ray powder diffraction, transmission electron microscope, N(2) adsorption-desorption technique, dynamic light scattering (DLS) analysis, FTIR spectroscopy, Raman spectroscopy, UV-vis absorption spectroscopy, and Diffuse reflectance spectroscopy. The energy band gap measurements of nanoparticles of ceria have been carried out by UV-visible absorption spectroscopy and diffuse reflectance spectroscopy. The surface charge properties of colloidal ceria dispersions in ethylene glycol have been also studied. To the best of our knowledge, this is the first report on using this type of ionic liquids in ceria nanoparticle synthesis.     

Micellization behavior of anionic gemini surfactants-templated manufacture of cerium oxide nanoparticles

A series of anionic gemini surfactants (GS) were synthesized from the reactant of N, N-dimethylaminoethanol (DMEA) with dicarboxylic acid diester (DADE), after the DADE was synthesized from pyromellitic dianhydride (PMDA) and fatty alcohol. Through rational design, benzene ring was introduced into the molecular structure to work as spacer group; carboxylic acid ammonium salt with hydroxyl as functional hydrophilic head group, and double-alkyl chain performed as hydrophobic tail chains. Then, surface active properties and micellization behavior were investigated respectively. It is found that these novel molecular structure dramatically improved the surface active properties, including critical micelle concentration (CMC: 10^?3?mol/L), surface tension (γ_min: 26.5?mN/m), conductivity and absorption at interface. Moreover, GS were able to form intermolecular hydrogen bonds, which, together with rigid spacer group, greatly affected the micellization behavior in bulk solution. More importantly, the self-assembly of aggregation with different morphologies can be controlled via adjustment to solution concentration or tail chain length. Finally, GS were applied as soft templates for the shape controllable synthesis of cerium oxide (CeO₂) nanoparticles, and CeO₂ nanoparticles in diverse shapes were eventually obtained and verified, such as dorayaki shape (double-pancake shape), rod-cluster shape, lamellar shape, butterfly shape and dendrite shape.     

稀土二氧化铈在生物领域的最新研究进展

氧化铈纳米粒子因其优异的催化活性而一直以来备受关注.它的催化性质来源于表面铈离子可以快速地进行Ce4+和Ce3+转变,能够根据环境很容易地接受或失去电子.长久以来,其应用均集中在工业催化方面.然而近年来,它被发现具有多种生物酶,如超氧化物歧化酶、过氧化氢酶、磷酸酶、过氧化物酶和氧化酶等的模拟活性,以及具有羟基自由基及氮氧化物自由基清除的能力.这些多重酶活性使其在生物方面有着众多极具前景的潜在应用价值.目前,在生物领域其已被开发用于生物检测、疾病诊断及治疗、药物载体及生物支架等方面.本文主要介绍其多种生物酶活性、活性原理,及在生物领域中的最新研究进展.     

Density functional studies on hydrogen-bonded complexes

Results of density functional calculations will be reported on a variety of hydrogen-bonded complexes, ranging from weak to strong hydrogen bonds. The charged bimolecular NH₃? NH complex and the dimers of water and methanol were investigated using a local approximation of the exchange-correlation potential and two different nonlocal potentials with gradient corrections. In the case of the water dimers, the dependence of the results on the extension of the atomic basis set has also been investigated. The equilibrium structures of all complexes have been determined. Dipole moments, hydrogen-bond lengths, and hydrogen-bonding energies, calculated with corrections for the basis-set superposition error using the counterpoise method, have been found to agree well with the corresponding experimental results. © 1994 John Wiley & Sons, Inc.     

Density functional studies of single molecule magnets

A method for the calculation of the second-order anisotropy parameters of single molecular magnets from the single particle orbitals is reviewed. We combine this method with density functional calculations to predict the magnetic anisotropy parameters of several single molecule magnets: Mn₁₂-acetate, Mn₁₀, Co₄, Fe₄, Cr₁ and V₁₅. Comparison with available experimental data shows that it is possible to predict these values quite accurately from density functional wavefunctions.     

Density functional theory model study of size and structure effects on water dissociation by platinum nanoparticles

Size and structure effects on the homolytic water dissociation reaction mediated by Pt nanoparticles have been investigated through density functional theory calculations carried out on a series of cubooctahedral Pt(n) nanoparticles of increasing sizes (n = 13, 19, 38, 55, 79, and 140). Water adsorption energy is not significantly influenced by the nanoparticle size. However, activation energy barrier strongly depends on the particle size. In general, the activation energy barrier increases with nanoparticles size, varying from 0.30 eV for Pt(19) to 0.70 eV for Pt(140). For the largest particle the calculated barrier is very close to that predicted for water dissociation on Pt(111) (0.78 eV) even though the reaction mediated by the Pt nanoparticles involves adsorption sites not present on the extended surface.     

Density functional model studies of uranyl adsorption on (001) surfaces of kaolinite

The adsorption of uranyl on two types of neutral (001) surfaces of kaolinite, tetrahedral Si(t) and octahedral Al(o), was studied by means of density functional periodic slab model calculations. Various types of model surface complexes, adsorbed at different sites, were optimized and adsorption energies were estimated. As expected, the Si(t) surface was found to be less reactive than the Al(o) surface. At the neutral Al(o) surface, only adsorption at protonated sites is calculated to be exothermic for inner- as well as outer-sphere adsorption complexes, with monodentate coordination being preferred. Adsorption energies as well as structural features of the adsorption complexes are mainly determined by the number of deprotonated surface hydroxyl groups involved. Outer-sphere complexes on both surfaces exhibit a shorter U-O bond to the aqua ligand of uranyl that is in direct contact with the surface than to the other aqua ligands. This splitting of the shell of equatorial U-O bonds is at variance with common expectations for outer-sphere surface complexes of uranyl.     

Density functional theory study of small vanadium oxide clusters

Density functional theory is employed to study structure and stability of small neutral vanadium oxide clusters in the gas phase. BPW91/LANL2DZ level of theory is used to obtain structures of VOy (y=1-5), V2Oy (y=2-7), V3Oy (y=4-9), and V4Oy (y=7-12) clusters. Enthalpies of growth and fragmentation reactions of the lowest energy isomers of vanadium oxide molecules are also obtained to study the stability of neutral vanadium oxide species under oxygen saturated gas-phase conditions. Our results suggest that cyclic and cage-like structures are preferred for the lowest energy isomers of neutral vanadium oxide clusters, and oxygen-oxygen bonds are present for oxygen-rich clusters. Clusters with an odd number of vanadium atoms tend to have low spin ground states, while clusters with even number of vanadium atoms have a variety of spin multiplicities for their ground electronic state. VO2, V2O5, V3O7, and V4O10 are predicted to be the most stable neutral clusters under the oxygen saturated conditions. These results are in agreement with and complement previous gas-phase experimental studies of neutral vanadium oxide clusters.     

二氧化铈纳米微粒过氧化物酶活性及其在葡萄糖检测中的应用

合成了一种稳定和水溶性的聚丙烯酸修饰CeO2 NPs,利用动态光散射(DLS)、傅里叶变换红外光谱(FT-IR)和X射线光电子能谱(XPS)进行表征.结果表明,CeO2 NPs能够催化H2O2氧化3,3′,5,5′-四甲基联苯胺(TMB)发生显色反应,表现出过氧化物模拟酶催化活性.利用Raman和顺磁共振(EPR)光谱技术研究了其催化机理.基于CeO2 NPs催化TMB变色反应对H2O2浓度的依赖性和葡萄糖氧化酶能够催化溶解氧氧化葡萄糖产生H2O2的原理,构建了一种简单、灵敏、选择性高的测定血清中葡萄糖的检测方法.在优化条件下,测定葡萄糖的线性范围为0.5~10 mmol/L,检出限(3σ)为0.1 mmol/L.对1.0 mmol/L葡萄糖进行11次平行测定,其相对标准偏差为2.4%.该方法已成功用于血清样品中葡萄糖的测定.     

Density functional studies on chromium catalyzed ethylene trimerization

Mechanism of ethylene trimerization using chromium catalyst is investigated using density functional methods. Recent experimental results indicate Cr-based homogeneous catalysts to follow metallacycle pathway in ethylene tri-, teta- and oligomerization reactions. Given the importance of chlorinated Cr-based active catalysts in these reactions, we have used “bare” minimal ligands like Cl^? and considered catalytic cycles with neutral or cationic intermediates starting with [Cr(II)Cl₂(ethylene)₂] and [Cr(II)Cl(ethylene)₂]⁺, respectively. We have compared both ‘Cossee’ and the ‘metallacycle’ mechanisms on these model systems utilizing density functional computations at B3LYP/LANL2DZ(d,p) level. The metallacycle mechanism with cationic Cr(II)–Cr(IV) intermediates is found to be the most favored path, with oxidative coupling of two coordinated ethylene to form the chromacyclopentane being the rate determining step (RDS). We also found that with neutral intermediates the Cossee pathway rather than the metallacycle mechanism is followed. Thus in spite of the simplicity of using just Cl^? as ligand in the model catalytic intermediates, our computational results match remarkably well with many recent and important experimental findings.     

Density functional theory studies on copper phenanthroline complexes

Density functional theory calculations have been employed to investigate the role of structural properties of copper phenanthroline complexes for DNA-cleavage activity. Structural changes imposed on the coordination geometries of Cu(phen)(2)(+,2+) (phen = 1,10-phenanthroline) linked by a serinol bridge (abbreviated as Clip) were studied, as well as their energetic profiles. Our calculations show that structures of these copper complexes (in this work named as clipped complexes) strongly depend on the position of the link, rather than on the copper oxidation state. Ionization energies slightly differ among the three selected complexes, while inner-sphere reorganization energies more markedly depend on the serinol link. However, the relative rates of the redox reaction of Cu(phen)(2), Cu(2-Clip-phen), and Cu(3-Clip-phen) were found not to correlate with their relative DNA-cleavage activity experimentally observed. Thus, the serinol link mainly affects the structural properties of copper phenanthroline complexes rather than their electronic properties. Docking simulations of clipped and nonclipped Cu(I) phenanthroline complexes on a DNA 16mer, d[CGCTCAACTGTGATAC](2), were finally performed to assess how different structural properties could affect the formation of DNA adducts. This analysis revealed that the most stable adducts of Cu(phen)(2+) and Cu(3-Clip-phen)(+) with DNA bind in the minor groove, whereas Cu(2-Clip-phen)(+) binds preferentially into the major groove.     

Density functional studies on the Pauson--Khand reaction.

The Pauson--Khand reaction represents a one-step Co(2)(CO)(8)-catalyzed synthesis of cyclopentenone through [2 + 2 + 1] assembly of one molecule each of alkene, alkyne, and carbon monoxide. Density functional studies (B3LYP/631LAN) on the reaction pathway of the Pauson--Khand (PK) reaction reported here for the first time provides valuable information on the structures and energetics of various intermediates and transition states. The PK reaction consists of olefin insertion, CO insertion, and reductive elimination steps. The olefin insertion step was found to be an irreversible step that determines the stereo- and regiochemistry of the overall reaction. The following steps are low activation energy processes and reversible. The bond-forming events occur only on one of the two metal atoms, while the second metal atom not only acts as an anchor that fixes the metal cluster to the organic substrate but also exerts electronic influences on the reaction at the first atom.     

Precipitation-redispersion of cerium oxide nanoparticles with poly(acrylic acid): toward stable dispersions

We exploit a precipitation-redispersion mechanism for complexation of short chain polyelectrolytes with cerium oxide nanoparticles to extend their stability ranges. As synthesized, cerium oxide sols at pH 1.4 consist of monodisperse cationic nanocrystalline particles having a hydrodynamic diameter of 10 nm and a molecular weight of 400 000 g mol(-1). We show that short chain uncharged poly(acrylic acid) at low pH when added to a cerium oxide sols leads to macroscopic precipitation. As the pH is increased, the solution spontaneously redisperses into a clear solution of single particles with an anionic poly(acrylic acid) corona. The structure and dynamics of cerium oxide nanosols and their hybrid polymer-inorganic complexes in solution are investigated by static and dynamic light scattering, X-ray scattering, and chemical analysis. Quantitative analysis of the redispersed sol gives rise to an estimate of 40-50 polymer chains per particle for stable suspension. This amount represents 20% of the mass of the polymer-nanoparticle complexes. This complexation adds utility to the otherwise unstable cerium oxide dispersions by extending the range of stability of the sols in terms of pH, ionic strength, and concentration.     

Density functional studies of cation–water complexes

By using density functional ab initio techniques the equilibrium structure, binding energy, and electronic distribution were determined for [X(H₂O)_n]^+k. Specifically, when X = H, Li, and Na, k=+1 and when k=+2, X = Be and Mg. In all cases the number of water molecules varies from one through four. A correlation between the distribution of the positive charge and the binding energy of the complex was encountered. A connection between simple arguments used to describe solvation in the bulk and the results obtained here for clusters was established. © 2000 John Wiley & Sons, Inc. J Comput Chem 21: 63–68, 2000     

Simple one-step preparation of cerium trifluoride nanoparticles

Cerium trifluoride have great potential in material applications for luminescent materials, composite materials or ionic conductors especially in the form of nanoparticles and nanoobjects. In this work, nanoparticles of CeF₃ were prepared by simple one pot reaction of ionic liquid 1-butyl-3-methylimidazolium hexafluorophosphate (bmimPF₆) with CeO₂ and by reaction of CeO₂ with KPF₆ in ionic liquid 1-butyl-3-methylimidazolium chloride (bmimCl). Prepared nanoparticles were analyzed by XRD and SEM analysis. Average diameter of prepared nanoparticles resulting from Sherrer formula is 12 nm. Nanoparticles did not form ordered agglomerates and could be used in the form of separate nanoparticles which are desired in some applications.     

Structural studies of cerium tantalates

Structural data obtained from neutron diffraction studies of some cerium tantalate phases are presented, including the first report of the high temperature structure of a CeTaO₄ phase, Ce_0.85TaO_3.84 deduced from in situ data recorded at 900°C in vacuum. It was found that this material transformed from the low temperature LaTaO₄ type phase to the orthorhombic A2₁am structure reported here, with a unit cell of a=5.64062(2) Å, b=14.81609(6) Å and c=3.93482(1) Å. This data agrees well with the previously proposed structural transformations.