Ce(C_8H_8)_2和Ce(C_8H_8)_2~-的化学键性质

结合改进的重叠模型Xa-SW法和Ziegler过渡态法,通过将中心原子与配体的作用选成离子聚集、中心原子只有s和p轨道参与成键、中心原子只有d轨道参与成键、中心原子只有f轨道参与成键、中心原子的s、p、d和f轨道同时参与成键5种类型,从能量角度分析了Ce(C_8H_8)_2和Ce(C_8H_8)~-_2的化学键性质。     

Integrated scheme for micro-determination of iron oxidation states in silicates and refractory minerals

A mirco-analytical scheme incorporating four methods is described for the determination of iron(II) and iron(III) in both hydrofluoric acid-soluble and refractory minerals. The acid-soluble minerals are analyzed for FeO by direct constant-current potentiometric titration with potassium dichromate, and a separate solution is titrated similarly after Zn/Hg reduction to give total iron. The micro-determination of FeO in chromite and other refractory minerals involves dissolution in a cerium(IV)/phosphoric acid mixture and constant-current potentiometric and indirect titration of excess of cerium(IV) (phosphatocerate) with iron(II). Lithium tetraborate micro-fusion is required for measurement of total iron by atomic absorption spectrometry or spectrophotmetry. The average relative standard deviation ranged between 0.73 and 1.08%.     

Oxygen exchange properties in the new pyrochlore solid solution Ce2Sn2O7-Ce2Sn2O8

The phase-pure cerium stannate pyrochlore (Ce₂Sn₂O₇) has been prepared for the first time. The structure and oxidation states of both cations were carefully reviewed, and the compound was unambiguously replaced within the rare-earth stannate series. As a consequence of the low stability of trivalent cerium in oxide phases, one oxygen per formula unit could be intercalated by calcination under O₂ at 400 °C, leading to the new Ce₂Sn₂O₈ pyrochlore. This latter phase is subject to oxygen under-stoichiometry from 400 to 700 °C. However, oxygen deintercalation seems to be in competition with cerium oxide segregation at high temperature, leading to the formation of cerium deficient pyrochlore phases.     

Gibbs energies of formation of hydroxides of lanthanides and yttrium

The pH values of the formation of hydrates in solutions of yttrium(III), cerium(III), samarium(III), europium(III), erbium(III), and ytterbium(III) were determined by conductometric titration. The solubility products and Gibbs energies of formation for hydroxides for the elements listed were calculated. The average Gibbs energy of dissolution for lanthanide hydroxides was found to be approximately 149.83 ± 0.90 kJ/mol. The Gibbs energies of formation for hydroxides of the remaining lanthanides were assessed on this basis.     

Determination of oxygen to uranium ratio in irradiated uranium dioxide by controlled potential coulometry

This work reports the determination of oxygen to uranium (O/U) ratio in irradiated UO_2+x fuel pellet of burnup of ca. 34 GWd/t by controlled potential coulometry. The method is based on the dissolution of the nuclear fuel in strong phosphoric acid (SPA) at 180–190 °C under an inert atmosphere. After dissolution, 8% sulphuric acid is added in order to obtain a 20% SPA in 8% sulphuric acid. A controlled potential coulometric determination of uranium(VI) is carried out at ?0.60V vs. ferri-ferrocyanide. The uranium(IV) contained in an aliquot of the fuel solution is oxidised to uranium(VI) with cerium(IV) sulphate, and the total uranium content is then determined by coulometry. Optimum experimental conditions have been established using simulated irradiated fuel solution containing various fission products which include cerium, tellurium, palladium, ruthenium, molybdenum and zirconium. Interference of the fission products and the possible removal of their interferences by preelectrolysis at +0.5 V vs. saturated calomel electrode (SCE) have been investigated. The accuracy of the coulometric method is confimed by polarographic measurement using several unirradiated UO_2+x fuel of known stoichiometry.     

不同形态铈改性的TiO2纳米管阵列的制备及其可见光光电响应性质

采用电化学阴极还原和阳极氧化法,制备了还原态铈和氧化态铈改性的TiO2纳米管阵列,通过扫描电子显微镜(SEM)和X射线衍射(XRD)表征样品形貌和晶相,得出还原态铈以单质铈纳米纤维形式存在于TiO2纳米管内及表面,单质铈改性的TiO2纳米管经阳极氧化后,以CeO2和单质Ce形式共存.测定样品的光电流响应并计算样品的能带宽度.结果表明:单质铈改性的TiO2纳米管阵列在可见光区光电流响应较TiO2纳米管增强,单质铈添加存在最佳值,在10 mmol·L-1溶液中制备的单质铈改性的TiO2纳米管阵列光电流响应最强,能带宽度E9减少到2.88 eV,并且随着单质铈含量的增加,载流子浓度增大,且平带电位向负向移动.单质铈改性的样品经阳极氧化后,样品在紫外光区和可见光区光电流响应都增强,但其在可见光区的响应强度要小于单质铈改性的TiO2纳米管在可见光区的响应强度.     

Determination of radiocerium in fission products by extraction chromatography using di-(2-ethylhexyl)phosphoric acid

An extraction chromatographic method is described for the determination of cerium in a fission product mixture. Cerium(IV) is separated on a column of siliconized kieselguhr saturated with di-(2-ethylhexyl)phosphoric acid (HDEHPA). After washing the column with a mixture of sodium bromate and nitric acid, cerium is eluted by a mixture of 5M HNO₃ and 0.1M ascorbic acid. The optimum conditions for the quantitative sorption and elution of cerium were found, and the reproducibility of the yield was verified. The influence of other fission and corrosion products (Mg, Fe, Al, U) on the sorption and elution of cerium was studied. The method has been successfully applied for the determination of cerium in artificial and natural mixtures of fission products.     

Ce3+ adsorption on hydrated MnO2

The adsorption of Ce³⁺ on hydrated manganese dioxide (HMD) was studied as a function of concentration, temperature and pH of the cerium solution labelled with¹⁴¹Ce. The steady state values of cerium adsorption at various concentrations fit well with the classical Freundlich isotherm. The effect of temperature on equilibrium adsorption values was utilized to determine the change in the standard enthalpy ΔH ^o of the cerium uptake process and its value (ΔH ^o=10.57) indicates that the uptake process proceeds via ion exchange.¹⁴¹Ce desorption studies, from HMD in water, HCl and unlabelled CeCl₃ solution, confirmed the ion exchange nature of the cerium uptake process as well as its reversibility.     

In situ electro-oxidation and liquid-liquid extraction of cerium(IV) from nitric acid medium using tributyl phosphate and 2-ethylhexyl hydrogen 2-ethylhexyl phosphonate

The process of in situ electro-oxidation of Ce(III) to Ce(IV) followed by its extraction into the organic phase has been investigated for its applicability in the separation of Ce from nitrate medium. Solvent extraction of cerium from nitric acid after its electro-oxidation to fourth valency state was carried out using tributyl phosphate (TBP) and 2-ethylhexyl hydrogen 2-ethylhexyl phosphonate (KSM-17, equivalent to PC-88A). The efficiency of the extractants at different aqueous phase nitric acid concentrations and different electrode potentials were determined. Various reducing agents such as hydroxylamine hydrochloride, sodium nitrite, ferrous sulphate as well as complexing agents like EDTA, oxalic acid etc, were studied as strippants for the back extraction of cerium from the loaded organic phase. The method developed for the extraction of cerium was further extended to the partitioning of cerium from Ce-Am mixture obtained during the KSM-17 based extraction chromatographic elemental fractionation of PUREX High Activity Waste (HAW) solutions. Recovery of Ce obtained in the extraction experiments by batch as well as by continuous flow organic phase was >95% with good radiochemical purity.     

Formation and oxidation state of CeO(2-x) nanotubes

Well-crystalline CeO(2-x) nanotubes are synthesized via a mild hydrothermal reaction route using cerium nitrate and ammonium hydroxide as reactants. The CeO(2-x) nanotubes have the same structure as the bulk CeO2 but larger lattice parameter. The measurement of the ratio of M5/M4 edge shows the valence reduction of cerium ions for the CeO(2-x) nanotubes.     

电化学阻抗谱法研究铈改性TiO2纳米管阵列光电极裂解水产氢动力学

通过阳极氧化法在纯钛板上制备TiO2纳米管阵列电极.在光电化学电解池阳极中加入供电子物质乙二醇,显著减小了TiO2纳米管的电荷传递阻抗,促进了光电催化裂解水产氢反应.采用阴极电沉积和阳极氧化法制备了单质铈和氧化铈共同改性的TiO2纳米管阵列半导体光阳极,其平带电位向电负方向移动.采用电化学阻抗谱法(EIS)对改性后TiO2纳米管阵列在光电催化裂解水产氢中的电子传输性能以及界面性质进行了表征,确定了各阻抗弧对应的电极过程.采用合理的等效电路模型计算了电极的电子传输动力学参数.结果表明,经铈改性后的TiO2纳米管阵列膜电阻明显减小,有利于氢气的产生.探讨了单质铈与氧化铈促进TiO2纳米管阵列电荷传输的作用机理.     

SEMICONDUCTOR MATERIALS Ce-SnO2/Sb2O5 AND Pd-SnO2/Sb2O5 FOR CREATING SENSITIVE ELEMENTS OF SENSORS FOR HYDROGEN

Theoretical and Experimental Chemistry - Materials based on tin dioxide doped with antimony with additions of cerium and palladium are synthesized in order to create highly sensitive and...     

新试剂10－（2－羧基苯偶氮）－9－菲酚的合成及与铈显色反应的研究

本文研究新试剂１０－（２－羧基苯偶氮）－９－菲酚（简称ＣＡＰ）的合成，测定试剂的离解常数。研究了试剂ＣＡＰ与铈（Ⅳ）的显色反应。在表面活性剂ＯＰ存在下，光度法测定球墨铸铁中铈的含量，结果较满意。     

Rapid column extraction method for actinides in soil

Summary The determination of actinides in environmental soil and sediment samples is very important for environmental monitoring as well as for emergency preparedness. A new, rapid actinide separation method has been developed and implemented that provides total dissolution of large soil samples, high chemical recoveries and effective removal of matrix interferences. This method uses stacked TEVA Resin^ò, TRU Resin^ò and DGA-Resin^ò cartridges from Eichrom Technologies (Darien, IL, USA) that allows the rapid separation of plutonium, neptunium, uranium, americium, and curium using a single multi-stage column combined with alpha-spectrometry. The method combines a rapid fusion step for total dissolution to dissolve refractory analytes and matrix removal using cerium fluoride precipitation to remove the difficult soil matrix. By using vacuum box cartridge technology with rapid flow rates, sample preparation time is minimized.     

Enhanced photocatalytic activity of cobalt-doped CeO2 nanorods

In this paper, CeO₂ and cobalt-doped CeO₂ nanorods synthesized by surfactant free co-precipitation method. The microstructures of the synthesized products were characterized by XRD, FESEM and TEM. The structural properties of the grown nanorods have been investigated using electron diffraction and X-ray diffraction. High resolution transmission electron microscopy studies show the polycrystalline nature of the Co-doped cerium oxide nanorods with a length of about 300?nm and a diameter of about 10?nm were produced. The X-ray Photoelectron spectrum confirms the presence of cobalt in cerium oxide nanorods. From BET, the specific surface area of the CeO₂ (Co-doped) nanostructures (131 m²?g^??) is found to be significantly higher than that of pure CeO₂ (52 m²?g^??). The Co-doped cerium nanorods exhibit an excellent photocatalytic performance in rapidly degrading azodyes acid orange 7 (AO7) in aqueous solution under UV illumination.     

A facile enantioselective synthesis of 2-(2-aminoethyl)allylsilanes, new synthons for piperidine synthesis

The synthesis of chiral (2-substituted-2-aminoethyl)allylsilanes by cerium mediated trimethylsilylmethylmagnesium chloride addition to the ester group of non racemic chiral β-aminoesters is described.     

Synthesis and characterization of single-crystal Ce(OH)CO3 and CeO2 triangular microplates

Single-crystal cerium hydroxide carbonate (Ce(OH)CO3) triangular microplates with the hexagonal phase have been successfully synthesized by a hydrothermal method at 150 degrees C using cerium nitrate (Ce(NO3)3.6H2O) as the cerium source, aqueous carbamide as both an alkaline and carbon source, and cetyltrimethylammonium bromide (CTAB) as a surfactant. Single-crystal ceria (CeO2) triangular microplates have been fabricated by a thermal decomposition-oxidation process at 650 degrees C for 7 h using single-crystal Ce(OH)CO3 microplates as the precursor. The shape of the Ce(OH)CO3 microplate was sustained after thermal decomposition-oxidation to CeO2. The products were characterized by X-ray powder diffraction (XRD), transmission electron microscopy (TEM), field-emission scanning electron microscopy (FE-SEM), differential scanning calorimetric analysis (DSC), and thermogravimetric analysis (TG).     

Growth behaviour of cerium-based conversion coating on Zn-5%Al alloy

Cerium-based conversion coatings were deposited on a Zn-5%Al alloy by immersing the alloy in cerium nitrate aqueous solutions with various immersion times. The growth behaviour of the cerium-based conversion coating on the Zn-5%Al alloy was investigated by the electrochemical impedance spectroscopy (EIS), SEM, energy dispersive spectroscopy (EDS), and XPS techniques. The results reveal that the coating mainly consists of ZnO, Zn(OH)₂, Ce(OH)₄, Ce(OH)₃, CeO₂, and Ce₂O₃. The growth of the cerium-based conversion coating is accompanied by metal dissolution. The dissolution mainly occurs on the η-Zn surface of the phase boundary and continues to extend to the Zn-rich phase as the coating grows. EIS results show that with increasing immersion time, the corrosion resistance of the Ce conversion coating gradually increases in the early growth stage and then decreases when the cracks appear.     

2-Nitrodiphenylamine as a versatile high-potential reversible oxidation-reduction indicator

The use of 2-nitrodiphenylamine as a reversible indicator has been investigated in the titration of iron(II) with cerium(IV) sulphate, potassium dichromate and sodium vanadate in sulphuric acid media. Accurate results can be obtained with cerium(IV) sulphate in 0.5–5.0 M acid, with potassium dichromate in 5.0–7.0 M acid, and with sodium vanadate in 5.0–7.5 M acid. With cerium(IV) sulphate the titrations are preferably conducted in 2.0 M sulphuric acid or in a 1.0 M. sulphuric acid-1.0 M pechloric acid medium. Tungstic acid, acetic acid, arsenic(III) and manganese(II) do not interfere. In titrations of iron(II) with dichromate and vanadate, the colour changes at the end-point are much more vivid with 2-nitrodiphenylamine than with ferroin.     

CeO2/TiO2光催化剂的制备及其可见光脱氮性能

采用溶胶-凝胶和浸渍掺杂两步法合成了CeO₂/TiO₂光催化剂,并对催化剂的理化结构进行表征分析;以吡啶-正辛烷体系为模拟油品氮源,研究了该催化剂在可见光作用下的光催化脱氮行为,并探究了光催化脱氮的最佳反应条件。 结果表明,掺杂的铈主要以CeO₂的形式存在,且增强了催化剂在可见光区的吸收;在可见光辐照150 min的条件下,铈的掺杂量质量分数为8%,所制备的CeO₂/TiO₂催化剂投入量为1.0 g/L时,模拟油品中吡啶的脱氮率高达76.45%。