Studies on the equilibrium uptake of some metal ions on a mixed and doped hydrous oxide using radiotracers

A highly sensitive and rapid method has been developed for the extraction-spectrophotometric determination of ultra trace amounts of americium. Americium(III) is selectively extracted from 1–10M HNO₃ medium with a mixture of (0.3M HDEHP+0.1M P₂O₅), both dissolved in xylene, and finally estimated in the organic phase itself absorptiometrically employing Arsenazo-III as the chromogenic reagent. A 60% dioxaneethanol mixture was used for optium colour development. Beer's law is obeyed in the concentration range 0.1–0.7 g Am cm^–3 and as little as 0.11 g Am cm^–3 could be determined with a precision better than ±2%. The molar absorptivity based on Am content is (3.599±0.049)·10⁵ dm³·mol^–1·cm^–1 at 648 nm which is incidentally the highest value reported as yet for its determination. The optimum concentration range, evaluated by Ringbom's method is 0.1–0.6 ppm Am. Common contaminants such as Al³⁺, Co²⁺, Cr³⁺, Fe³⁺, Ni²⁺, Zr⁴⁺, F^–, NO₃ ^–, and SO ₄ ^2- in fairly large quantities and moderate amounts of Pu⁴⁺, Th⁴⁺ and UO ₂ ²⁺ cause no interference in the final assay. Colour development is almost instantaneous and its intensity remains virtually constant for at least 48 hours.     

Structure and oxygen storage capacity of Pr/Nd doped CeO2–ZrO2 mixed oxides

Binary Ce–Zr (CZ), trinary Ce–Zr–Pr (CZP), Ce–Zr–Nd (CZN) mixed oxides were prepared by coprecipitation. The structural and textural properties were characterized by the X-ray diffraction (XRD) analysis, Brunauer–Emmett–Teller (BET) method, Raman and X-ray absorption near-edge spectra (XANES) techniques, while the oxygen storage capacity (OSC) was evaluated under both dynamic and static conditions at 500 °C. The doping of Pr or Nd cations causes the lattice deformation of the tetragonal Zr-rich mixed oxides to form a pseudocubic structure and prevents the phase demixing after calcination in flowing steam/air at 1050 °C for 5 h. After the hydrothermal ageing treatment, the doped samples show higher BET surface areas and better oxygen mobility. Pr exists mainly in the form of trivalent cations in the aged CZP and functions primarily as the doping element with large ionic radius instead of redox couple Pr³⁺/Pr⁴⁺, which may introduce more Ce³⁺ species and hereby more lattice defects. Among the aged samples, CZP shows the best oxygen storage capacity and the fastest oxygen release rate.     

NiO and ZrO2-based catalysts in the reaction of complete methane oxidation

The reaction of complete methane oxidation over deposited catalysts (NiO/ZrO₂ and NiO/YSZ) and binary oxides NiO_ZrO₂ produced by co-precipitation, by the sol gel method, and using a bio-template (NiO content in the samples, 10.1 mol %) is investigated. It is shown that binary oxides cause methane oxidation at lower temperatures than their deposited analogue: the temperature of methane half-transformation is 470, 500, and 520°C for binary oxides, while T ₅₀ = 570°C for NiO/ZrO₂. Major factors affecting the activity of binary oxides in the methane oxidation reaction are determined: the dispersion of the active phase (NiO) and the availability of the second component with high mobility of the lattice oxygen.     

Spectroscopic properties of Pr3+ ions in a PbWO4 single crystal

Site-selective fluorescence laser spectroscopy of Pr (3+) ions in lead tungstate single crystal were investigated at temperatures from 10 to 300 K. The site-selective emission spectra and fluorescence decays from the (3)P J ( J = 0, 1, 2) and (1)D 2 states were analyzed. The (3)P J ( J = 0, 1, 2) level shows its predominantly radioactive character with the typical greenish-blue luminescence ascribed to (3)P J transition. The emission from the (1)D 2 level is only observed when this level is directly excited. The decay kinetic of the (1)D 2 level was measured under site-selective excitation and discussed in terms of cross-relaxation. The up-conversion emission from levels (3)P 1 and (3)P 0 following excitation of the (1)D 2 state was observed in the PbWO 4 crystal between 10 and 300 K. The main up-conversion mechanism, together with the understanding the quenching of the (1)D 2 fluorescence in this Pr (3+) heavily doped PbWO 4 were discussed. The presence of the complex structures of the emission spectra and different decay profiles indicate that several processes contribute to the quenching of the (1)D 2 fluorescence of Pr (3+) ions. It was found that the up-conversion fluorescence intensity had a quadratic dependence on the laser input power. The temporal behavior of the up converted emission indicates that an energy-transfer up-conversion is the dominant process.     

Ab initio analysis of some fluoride and oxide structures doped with Pr and Yb

Doping effects are analyzed by means of the ab initio perturbed ion (aiPI) method via substitution of the fluorides and oxides of zirconium, hafnium, and thorium. Lattice relaxation is simulated through the calculation of vibrational breathing modes and substitutional effects on the compound are thereby analyzed. In addition, the band gaps (in the pure species) and impurity levels (where substitutional ions Pr⁺⁴ and Yb⁺³ are considered in the doped species) of the fluorides are estimated via the transition energy calculated at the aiPI‐optimized geometry of the pure and doped crystal clusters by means of the configuration interaction with single excitations (CIS) method that accounts for electronic correlation. © 2003 Wiley Periodicals, Inc. Int J Quantum Chem, 2004     

Studies on the equilibrium uptake of some anions on a mixed and doped hydrous oxide

A mixed hydrous Fe(III)?Zr(IV) exhibits enhanced adsorption of anions in comparison to its constituent oxides. The uptake has been observed at pH 2.0, as a function of initial salt concentration and the product shows specific affinity for Cl^?, SO ₄ ^2? and PO ₄ ^3? ions. Doping the mixed oxide with Sn(II) improves its sorption capability for halide ions, while no significant enhancement is observed in the case of polyvalent anions.     

Structural phase stability and magnetism in Co2FeO4 spinel oxide

We report a correlation between structural phase stability and magnetic properties of Co₂FeO₄ spinel oxide. We employed mechanical alloying and subsequent annealing to obtain the desired samples. The particle size of the samples changes from 25 nm to 45 nm. The structural phase separation of samples, except sample annealed at 900 °C, into Co-rich and Fe-rich spinel phase has been examined from XRD spectrum, SEM picture, along with EDX spectrum, and magnetic measurements. The present study indicated the ferrimagnetic character of Co₂FeO₄, irrespective of structural phase stability. The observation of mixed ferrimagnetic phases, associated with two Curie temperatures at T_C1 and T_C2 (>T_C1), respectively, provides the additional support of the splitting of single cubic spinel phase in Co₂FeO₄ spinel oxide.     

Electrical properties and stoichiometry in La2NiO4

The electrical properties of La₂NiO₄ have been studied with respect to the stoichiometry of the material. The conductivity of reduced compositions has been measured between 20 and 1000 K and compared to that of the air-prepared ones. Nonstoichiometry is present in both cases and produces disorder leading to Anderson localization and to the definition of a mobility edge in the σ_x²−y² itinerant band. Air-prepared compounds contain in addition a large number of Ni³⁺ states which may overlap the itinerant σ_x²−y² band. For reduced materials containing small amounts of Ni³⁺, the electrical properties can be described below 200 K by a hopping conductivity at the Fermi level within a sharply peaked density of states. The results are well described within the frame of the Mott theory of variable range hopping. Above 200 K highly reduced materials exhibit direct excitation of holes from Ni³⁺ states to the mobility edge in the itinerant band. Under conditions appropriate to air-prepared materials, the Fermi level is shifted toward the itinerant band and a major contribution to the conductivity arises from hopping at the Fermi level. At high temperature a progressive excitation of carriers from the localized states is anticipated with an eventual exhaustion region. This last assumption is corroborated with a shift of the conductivity maximum to higher temperature for increasingly reduced materials.     

Transmission line model of mixed ionic and electronic conductor: the case of hydrous ruthenium oxide

Composite membranes made of RuO₂·xH₂O dispersed in an insulating polymer matrix were prepared and used as separators in a conductivity cell filled with H₂SO₄ electrolyte solution. The volume fraction of RuO₂·xH₂O was varied between 7 and 18 % and x between 0 and 2.4. The total capacitance of the composite membranes was determined either from galvanostatic charging using a four-electrode configuration or potential cycling using a three-electrode configuration. In the first case, protons are the only charge carriers at the boundaries of the composite membranes. In the four-electrode configuration, a transmission line that accounts for the pseudocapacitive nature of RuO₂·xH₂O was used to describe successfully the voltage–time profiles of composite membranes with active material contents above 10?V _f%. The total capacitance determined with both setups increases for 0?≤?x?≤?0.6, and the values are identical in this interval of x. However, the trends diverge afterwards, and the capacitance values measured in the four-electrode configuration are higher by a factor of 2 for x?=?2.4. Unlike in the three-electrode configuration, charge storage in the four-electrode configuration is not limited to the sites accessible to both electrons and protons.     

Structural and Magnetic Properties of Pr2BaCuO5 Oxide

The Pr₂BaCuO₅ oxide has been prepared by using a precursor method. X‐ray and neutron diffraction data reveal that this mixed oxide crystallizes with the so‐called Nd₂BaPtO₅‐type structure, showing tetragonal symmetry and space group P4/mbm. Magnetic susceptibility, magnetization and specific heat measurements reveal that Pr₂BaCuO₅ oxide behaves as antiferromagnet, where the Pr³⁺ and Cu²⁺ sublattices become simultaneously ordered at 15 K. Preliminary neutron diffraction studies confirm this proposed antiferromagnetic ordering and it can be described by the wave vector k = [0,0,0].     

Phase transition in a [Ag2HgI4:0.2AgI] mixed composite system doped with KI

A novel mixed composite system, [Ag₂HgI₄:0.2AgI]: _x KI, (x = 0.2, 0.4, 0.6 mol %), was prepared and [Ag₂HgI₄:0.2AgI] composite system was used as the host. Electrical conductivity was measured to study the transition behavior at frequencies of 100, 120 Hz, 1, and 10 kHz in the temperature range of 90–170°C. Conductivity increased sharply during the α-β phase transition. Upon increasing the dopant-to-host ratio, the conductivity of the superionic system exhibited Arrhenius (thermally activated)-type behavior. X-ray powder diffraction, DTA, DTG and TGA were performed to confirm the doping effect and transition in the host. The phase transition temperature decreased with an increase in the dopant concentration. Activation energies in eV for pre- and post-transition phase behavior are also reported.     

Effect of gamma-irradiation on surface and catalytic properties of Co3O4 doped with NiO

NiO-doped Co₃O₄ samples precalcined at 500 °C were subjected to various doses of -rays within the range 0.2-1.6 MGy. The particle size and BET-surface areas of different samples were determined using XRD and nitrogen adsorption at -196 °C. The catalytic reactions studied were conversion of ethanol and isopropanol at 250-400 °C using a micropulse technique and H₂O₂ decomposition in aqueous solution at 30-50 °C. The results revealed that the -irradiation brought a significant decrease in the particle size of Co₃O₄ phase with subsequent increase in the S_BET surface areas. The treatment brought also a progressive decrease in the total conversion of both alcohol (dehydration and dehydrogenation) falling to a minimum value (about 20% of its initial activity) at a dose of 0.8 MGy. The catalysts retain their initial activity upon exposure to a dose of 1.6 MGy. On the other hand, the catalytic activity in H₂O₂ decomposition of the investigated system decreased progressively by increasing the dose of -rays and the catalysts lost more than 90% of their initial activity upon exposure to a dose of 1.6 MGy.     

系列Ti4L6-笼基配合物的合成与结构研究

金属有机笼（Metal-Organic Cages,MOCs）作为一种新型的分子容器,因其具有特殊的空腔结构及其在分子识别/分离、药物传输和催化等方面具有诱人的应用前景而受到学者广泛地关注.但是,在过去几十年里,化学家们主要致力于构筑各种具有特定功能的MOCs,而进一步将MOCs组装成先进的超分子材料,在这方面研究较少.在前期工作中,本课题组构筑了一例可溶于水、超稳定且具有配位组装功能的钛-有机四面体笼（Ti₄L₆,L=帕莫酸）,并利用Ti₄L₆笼作为原料,通过两步反应实现了与不同金属离子的配位组装.在本项工作中,在不同溶剂热的条件下,利用Ti₄L₆笼分别与Mn²⁺、Nd³⁺、Ba²⁺和Ca²⁺离子反应,得到了系列Ti₄L₆-笼基配合物,分别为：（Me₂NH₂）₉（Me₄N）[Mn₃（Ti₄L₆）₂-（H₂O）₉（DMF）₆]·Guests（PTC-241,DMF=N,N-二甲基甲酰胺）;（Me₂NH₂）₅[Nd（Ti₄L₆）（H₂O）₂（DMF）₅]·Guests（PTC-242）;（Me₂NH₂）₂[Ba₄（Ti₄L₆）（OH）₂（H₂O）₈（TEA）₅]·Guests（PTC-243,TEA=三乙醇胺）;（Me₂NH₂）₂[Ca₃（Ti₄L₆）（H₂O）₈（DEA）₂]·Guests（PTC-244,DEA=二乙醇胺）;（Me₂NH₂）₂[Ca₃（Ti₄L₆）（H₂O）₁₅]·Guests（PTC-245）,并采用X射线单晶衍射、红外（IR）光谱分析、热分析仪（TGA）和X射线粉末衍射（PXRD）等方法对这些化合物进行了结构表征.X射线单晶衍射结果表明,PTC-241是由ΔΔΔΔ-[Ti₄L₆]和ΔΔΔΔ-[Ti₄L₆]-Mn₃笼通过弱作用力（氢键和π-π堆积）交错堆积形成的超分子手性化合物;PTC-242是由Ti₄L₆-Nd笼通过氢键作用堆积形成的超分子化合物;PTC-243是一条直线形的Ti₄L₆-Ba₄链;而PTC-244和PTC-245则是两个具有峰窝状结构的二维Ti₄L₆-Ca₃层.另外,我们还研究了PTC-244和PTC-245的荧光性质.     

Novel fast lithium-ion conductor LiTa2PO8 enhances the performance of poly(ethylene oxide)-based polymer electrolytes in all-solid-state lithium metal batteries

At present, replacing the liquid electrolyte in a lithium metal battery with a solid electrolyte is considered to be one of the most powerful strategies to avoid potential safety hazards. Composite solid electrolytes (CPEs) have excellent ionic conductivity and flexibility owing to the combination of functional inorganic materials and polymer solid electrolytes (SPEs). Nevertheless, the ionic conductivity of CPEs is still lower than those of commercial liquid electrolytes, so the development of high-performance CPEs has important practical significance. Herein, a novel fast lithium-ion conductor material LiTa₂PO₈ was first filled into poly(ethylene oxide) (PEO)-based SPE, and the optimal ionic conductivity was achieved by filling different concentrations (the ionic conductivity is 4.61 × 10^?4 S/cm with a filling content of 15 wt% at 60 °C). The enhancement in ionic conductivity is due to the improvement of PEO chain movement and the promotion of LiTFSI dissociation by LiTa₂PO₈. In addition, LiTa₂PO₈ also takes the key in enhancing the mechanical strength and thermal stability of CPEs. The assembled LiFePO₄ solid-state lithium metal battery displays better rate performance (the specific capacities are as high as 157.3, 152, 142.6, 105 and 53.1 mAh/g under 0.1, 0.2, 0.5, 1 and 2 C at 60 °C, respectively) and higher cycle performance (the capacity retention rate is 86.5% after 200 cycles at 0.5 C and 60 °C). This research demonstrates the feasibility of LiTa₂PO₈ as a filler to improve the performance of CPEs, which may provide a fresh platform for developing more advanced solid-state electrolytes.     

Behavior of (La,Sr)CoO3- and La2NiO4-based ceramic anodes in alkaline media: compositional and microstructural factors

The behavior of dense ceramic anodes made of perovskite-type (x = 0.30–0.70; y = 0–0.05; z = 0–0.20) and K₂NiF₄-type (Me = Co, Cu; x = 0–0.20) indicates significant influence of metal hydroxide formation at the electrode surface on the oxygen evolution reaction (OER) kinetics in alkaline solutions. The overpotential of cobaltite electrodes was found to decrease with time, while cyclic voltammetry shows the appearance of redox peaks characteristic of Co(OH)₂/CoOOH. This is accompanied with increasing effective capacitance estimated from the impedance spectroscopy data, because of roughening of the ceramic surface. The steady-state polarization curves of in the OER range, including the Tafel slope, are very similar to those of model Co(OH)₂–La(OH)₃ composite films where the introduction of lanthanum hydroxide leads to decreasing electrochemical activity. La₂NiO₄-based anodes exhibit a low electrochemical performance and poor stability. The effects of oxygen nonstoichiometry of the perovskite-related phases are rather negligible at high overpotentials but become significant when the polarization decreases, a result of increasing role of oxygen intercalation processes. The maximum electrocatalytic activity to OER was observed for A-site-deficient , where the lanthanum content is relatively low and the Co⁴⁺ concentration determined by thermogravimetric analysis is highest compared to other cobaltites. Applying microporous layers made of template-synthesized nanocrystalline leads to an improved anode performance, although the effects of microstructure and thickness are modest, suggesting a narrow electrochemical reaction zone. Further enhancement of the OER kinetics can be achieved by electrodeposition of cobalt hydroxide- and nickel hydroxide-based films. Dedicated to Professor Dr. Yakov I. Tur’yan on the occasion of his 85th birthday.     

Ammoxidation of propylene over SnO2?Sb2O4 mixed oxide catalysts doped with Ga, In or Tl

In studying the catalytic activities of SnO₂–Sb₂O₄ (SnSb=11) mixed oxides doped with Ga, In or Tl in the ammoxidation of propylene, a selectivity improvement was observed when the dopants Ga₂O₃ and Tl₂O₃ were used in low concentrations. At higher concentrations and for In₂O₃ the characteristics of the dopant prevail, disclosing that the admixed oxides are not evenly distributed in the bulk, but that the doping is rather confined to the surface layers of the catalyst.

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, Ga, In Tl 673 . , Ga₂O₃ Tl₂O₃ (0,5–2 . %). In₂O₃ . , , .

     

Structural,optical, electrical,and photocatalytic properties of manganese doped zinc oxide nanocrystals

Manganese-doped and undoped ZnO nanocrystals were synthesized via wet-chemical methods. The structure, physico-chemical, electrical and optical properties of the as-prepared products were characterized by using the X-ray diffraction (XRD), UV-vis diffuse reflectance spectroscopy (DRS), photoluminescence spectroscopy (PLS) and electrochemical impedance spectroscopy (EIS) techniques. The photocatalytic activity of Mn-doped ZnO nanocrystal (mixed phases) has been examined under the visible-irradiation by using photocatalytic oxidation of rhodamine B (RhB) dye as a model reaction, and compared with that of known system such as pure ZnO nanocrystal (single-phase). The results showed that Mn doped ZnO nanocrystals bleaches RhB much faster than undoped ZnO upon its exposure to the visible light. The enhancement of the photocatalytic activity was discussed as an effect due to the Mn doping in the Mn-doped ZnO semiconductors, which shifts the optical absorption edge to the visible region and alters the electron-hole pair separation conditions. These factors are responsible for the higher photocatalytic performance of Mn/ZnO composites.