High-energy-density LiMn0.7Fe0.3PO4 nanorods synthesized by microwave-assisted solvothermal method

Microwave-assisted solvothermal method has been developed for synthesizing LiMn_0.7Fe_0.3PO₄ cathode materials with an olivine structure. The obtained LiMn_0.7Fe_0.3PO₄ nanorods were characterized by X-ray diffraction, scanning and transmission electron microscope, Brunauer-Emmett-Teller surface area measurements, and electrochemical tests. Electrochemical tests clearly indicate that the as-made LiMn_0.7Fe_0.3PO₄ nanorods exhibit two redox activities of Fe³⁺/Fe²⁺ and Mn³⁺/Mn²⁺ couple at galvanostatic charge-discharge process, which is due to the coexistence of Mn²⁺ with Fe²⁺ at 4c sites. The as-synthesized materials have high energy density, excellent rate capability and cycling stability.     

Formation of MSeO4(aq) complexes (M2+ = Mg2+, Co2+, Ni2+, Cu2+, Cd2+) studied as a function of temperature by affinity capillary electrophoresis

Complexation of divalent cations (Mg²⁺, Co²⁺, Ni²⁺, Cu²⁺, Cd²⁺) by selenate ligand was studied by ACE (UV indirect detection) in 0.1 mol/L NaNO₃ ionic strength solutions at various temperatures (15, 25, 35, 45 and 55°C). For each solution, a unique peak was observed as a result of a fast equilibrium between the free ion and the complex (labile systems). The migration time corresponding to this peak changed as a function of the solution composition, namely the free and complexed metal concentrations, according to the complexation reactions. The results confirmed the formation of a unique 1:1 complex for each cation. The thermodynamic parameters were fitted to the experimental data at 0.1 mol/L ionic strength: (25°C) = ?(6.5 ± 0.3), ?(7.5 ± 0.3), ?(7.7 ± 0.3), ?(7.7 ± 0.3), and –(8.1 ± 0.3) kJ/mol and = 2.5 ± 0.2, 4.7 ± 0.4, 4.5 ± 0.6, 8.4 ± 1.1, and 7.2 ± 0.6 kJ/mol for M²⁺ = Mg²⁺, Co²⁺, Ni²⁺, Cu²⁺, and Cd²⁺, respectively. Complexes with alkaline earth and transition metal cations could be distinguished by their relative stabilities. The effect of the ionic medium was treated using the specific ion interaction theory and the thermodynamic parameters at infinite dilution were compared to previously published data on metal–selenate, metal–sulfate, and metal–chromate complexes.     

The binding of Ca2+ and Mg2+ to human serium albumin: A calorimetric study

The binding of calcium and magnesium to human serum albumin has been studied in the pH region 2.5–8.0 by a calorimetric procedure. Both metal ions bind to the carboxylate groups of albumin. 36 and 44 carboxylate groups appear to be involved in the binding of Ca²⁺ and Mg²⁺, respectively. Based on previously reported results that twelve Ca²⁺ ions are the maximum which can bind to albumin, the results given here support previous X-ray crystallographic evidence that three carboxylate groups can be involved in the binding of a Ca²⁺ by a protein. The data also confirm that Ca²⁺ and Mg²⁺ binding is competitive. Binding of the cations to the carboxylate groups appears to involve the breaking of carboxylate-imidazole hydrogen bonds in the protein. Log K, ΔH and ΔS values obtained for the binding of metal ions to albumin in aqueous solution at 25°C are 2.72 ± 0.02, 0.0 ± 0.1 kcal/mole, and 12.4 ± 0.3 cal/mole K for Ca²⁺ and 1.12 ± 0.05, ?0.2 ± 0.1 kcal/mole, and 4.5 ± 0.3 cal/mole K for Mg²⁺, respectively.     

Construction of a Graphene/Au‐Nanoparticles/Cucurbit[7]uril‐Based Sensor for Pb2+ Sensing

The development of highly sensitive and selective methods for the detection of lead ion (Pb²⁺) is of great scientific importance. In this work, we develop a new surface‐enhanced Raman scattering (SERS)‐based sensor for the selective trace measurement of Pb²⁺. The SERS‐based sensor is assembled from gold nanoparticles (AuNPs) and graphene using cucurbit[7]uril (CB[7]) as a precise molecular glue and a local SERS reporter. Upon the addition of Pb²⁺, CB[7] forms stronger complexes with Pb²⁺ and desorbs from AuNPs, resulting in a sensitive “turn‐off” of SERS signals. This SERS‐based assay shows a limit of detection (LOD) of 0.3 nm and a linear detection range from 1 nm to 0.3 μm for Pb²⁺. The feasibility of the assay is further demonstrated by probing Pb²⁺ in real water samples. This SERS‐based analytical method is highly sensitive and selective, and therefore holds promising applications in environmental analysis.     

Mass spectrometric and coincidence studies of double photoionization of small molecules

Current and future coincidence techniques in the study of double and multiple ionization by photon impact are reviewed. New results are presented on the formation of Xe⁺, Xe²⁺ and Xe³⁺ in the region of 4d ^?1 ionization and the triple ionization mechanism is discussed. The thresholds for Xe²⁺ and Xe³⁺ are determined as 33.05±0.3 and 64.1±0.3 eV respectively. Triple ionization of a molecule (OCS) followed by fragmentation into three cations is demonstrated for the first time. The formation and charge separation reactions of several molecular double cations are examined by coincidence techniques: intramolecular isotope effects, rearrangement reactions and slow dissociations are shown to occur in triatomic and other small doubly charged molecular ions.     

The distribution of cerium (III) cations between aqueous and nitrobenzene phases in the presence of dicarbolide anions

Extraction of micro- and macroquantities of Ce³⁺ (C°_Ce = 10^6??10^?1 mole/dm³) with a nitrobenzene solution of dicarbolide (C°_H⁺B^? = 0.04?0.5 mole/dm³) from a nitric acid solution (C°_HNO3 = 0.1?0.3 mole/dm³) was investigated. Coextraction of water and simultaneous extraction of Ce³⁺ and Ba²⁺ ($\text{C}$_Ce⁺ + C_Ba = 0.3 mole/dm³) from 0.3 and 0.5 M HNO₃ was also studied. It was found that the reaction Ce³⁺ + 3H?Ce?³⁺ + 3H (K_Ce/3H) takes place in all cases. The dependence of the apparent exchange extraction constant K_Ce/3H on the initial composition of both phases was determined and the effect of the composition of the aqueous phase on the values of K_Ce/3H and K_Ba/2H was discussed. The stability constant of the CeNO²⁺₃ complex and the hydration number of the Ce³⁺ cation in the organic phase (h³⁺_Ce = 16.2 ± 2) was determined and a linear correlation between individual extraction constants of mono-, bi- and trivalent cations and the hydration numbers in the nitrobenzene phase was found using data from the present paper and values given in literature.     

Complexing Power of Vitamin D3 Toward Various Metals. Potentiometric Studies of Vitamin D3 Complexes with Al3+, Cd2+, Gd3+, and Pb2+ Ions in Water–Ethanol Solution

This study reports the stability constants of complexes with vitamin D₃ and Al³⁺, Cd²⁺, Gd³⁺ and Pb²⁺ ions in a water–ethanol medium (30/70% v/v at 25.0°C). The logarithms of the overall stability constants are: ₁ = 12.4 ± 0.5, 7.6 ± 0.3, 9.33 ± 0.07, and 9.1 ± 0.5, respectively, whereas the logarithms of ₂ are 24.4 ± 0.5 (Al³⁺), 14.3 ± 0.3 (Cd²⁺), and 15.4 ± 0.5 (Pb²⁺). Gd³⁺ forms only the 1:1 complex. These values are compared to those reported previously and correlations are established between the stability constants and physical properties, such as the ionization energy.     

Mesoporous mesocrystal Ce1−xZrxO2 with enhanced catalytic property for CO conversion

Novel mesoporous mesocrystal Ce_1−xZr_xO₂ was synthesized using acetate salt as inorganic species and P123 as surfactant. Transmission electron microscopy reveals that the wall framework consists of a single phase based on the face-centered cubic CeO₂ and the nanocrystals are highly oriented with the crystal axis [001] parallel to the pore channel if the Zr⁴⁺ molar fraction x is 0.3 or less. However, when the Zr⁴⁺ molar fraction is larger than 0.3, a mixture of cubic and tetragonal phases forms and the preferential crystal orientation disappears as revealed by XRD and Raman measurements. The formation mechanism is ascribed to the oriented attachment following the manner of coherent interface. The single phase solid solution at Zr⁴⁺ molar fraction 0.3 demonstrates the best catalytic performance for CO conversion due to the unique mesoporous mesocrystal structure with dominant exposure of highly active {200} planes and an enhanced redox property caused by adequate Zr⁴⁺ incorporation.     

Crystal growth,structural and electrical properties of rubidium and cesium vanadium oxide bronzes

Crystals of the following compounds were grown by cathodic reduction of CsV⁵⁺O or RbV⁵⁺O metls: Cs_0.3V₂O₅ (A), Cs₂V₅O₁₃ (B), CsV₂O₅ (C), Rb_0.4V₂O₅ (D), Rb_0.37V₂O_∼4.8 (E) (a new orthorhombic compound) and Rb_2−xV_3+2xO_8+2x (F). The crystal symmetry and cell parameters of the Rb compounds (which were known for F only) were determined, as well as those of Rb_0.3V₂O₅, which has the structure of A. Magnetic susceptibility and ESR measurements confirm the intermediate valence in E. A, C, and E are semiconductors with activation energies in the range 0.07–0.2 eV. Cs_0.3V₂O₅ (A), in which V⁴⁺ and V⁵⁺ do not occupy distinct crystallographic sites, has the highest electrical conductivity.     

Ferric borate formation in aqueous solution

Potentiometric analyses indicate that previous investigations have overestimated the stability of ferric borate complexes. The FeB(OH) ₄ ²⁺ formation constant result obtained in the present work is_Bβ ₁ ^* = [FeB(OH) ₄ ²⁺ ][H⁺][Fe³⁺]^-1[B(OH)₃]^-1 = (5.4±0.3) x 10^-3 at 25.0°C and 0.7 molal ionic strength. Our result indicates that solution concentrations of FeOH²⁺ and FeB(OH) ₄ ²⁺ are approximately equal in aqueous solution for boric acid concentrations on the order of 0.3 molal. Fe(B(OH)₄) ₂ ⁺ is a minor species in solution compared to FeB(OH)₄ ²⁺ for conditions such that [B(OH)₃][H⁺]^-1≤ 350, and ferric borate complexation is insignificant in solutions such as seawater where [B(OH)₃] ≤ 4× 10^-4 molal.     

Verteilung und Valenz der Kationen in Spinellsystemen mit Eisen und Chrom. III. Gitterkonstanten,Mößbauer-Spektren und Thermokraft der Mischkristalle ZnFeCrO4?Fe2CrO4

Distribution and Valence of the Cations in Spinel Systems with Iron and Chromium. III. Lattice Constants, Mössbauer Spectra, and Seebeck Coefficients of the Solid Solution ZnFeCrO₄? Fe₂CrO₄ For the spinel system Zn_1–x²⁺Fe_x–λ²⁺Fe_λ³⁺(Fe_λ²⁺ · Fe_1?λ³⁺ Cr³⁺)O₄ λ has been determined by lattice constants and ionic distances: λ = 0 in the region 0 ? x ? 0.3; in the region 0.3 < x ? 1 λ increases linearly to 0.44. Mössbauer spectra between x = 0 and x = 0.6 confirm this distribution. All spinels are n-type hopping conductors mainly conducting on the octahedral sites.     

On the hydrolysis of the titanium(IV) ion in chloride media

Determinations of the [Ti(IV)]/[Ti(III) ratio in solutions of titanium(IV) chloride equilibrated with H₂(g), at 25°C in 3 M (Na)Cl ionic medium, have indicated the predominance of the Ti(OH)₂²⁺ species in the concentration ranges 0.5 ? [H⁺] ? 2 M and 1.5 x 10^?3 ? [Ti(IV)] ? 0.05 M. From the equilibrium data the reduction potential has been evaluated Ti(OH)₂²⁺ + 2 H⁺ + e ? Ti³⁺ + 2H₂O, E_oH = (7.7 ± 0.6) x 10^?3 V. The acidification reactions of Ti(OH)₂²⁺ were also studied in 12 M(Li)Cl medium at 25°C by measuring the redox potential of the Ti(IV)/Ti(III) couple as a function of [H⁺]. The potentiometric data in the acidity range 0.3 ? [H⁺] ? 12 M have been explained by assuming Ti⁴⁺ + e ? Ti³⁺, E_o = 0.202 ± 0.002 V Ti⁴⁺ + H₂O ? TiOH³⁺ + H⁺, log K_a1 = 0.3 ± 0.01 Ti⁴⁺ + 2H₂O ? Ti(OH)₂²⁺ + 2H⁺, log K_a1K_a2 = 1.38 ± 0.05.     

Kinetics and mechanism of the reaction of CF3 radicals with NO2

The reaction of CF₃ with NO₂ was studied at 296 ± 2K using two different absolute techniques. Absolute rate constants of (1.6 ± 0.3) × 10⁻¹¹ and (2.1 _−0.3⁺⁰⁷) × 10⁻¹¹ cm³ molecule⁻¹ s⁻¹ were derived by IR fluorescence and UV absorption spectroscopy, respectively. The reaction proceeds via two reaction channels: CF₃ + NO₂ → CF₂O + FNO, (70 ± 12)% and CF₃ + NO₂ → CF₃O + NO, (30 ± 12)%. An upper limit of 11% for formation of other reaction products was determined. The overall rate constant was within the uncertainty independent of total pressure between 0.4 to 760 torr. © 1996 John Wiley & Sons, Inc.     

Dual recognition strategy for ultra-sensitive fluorescent detection of Hg2+ at femto-molar level based on aptamer functionalized sulfur quantum dots

In the present study, a dual recognition strategy for ultrasensitive detection of Hg²⁺ was successfully developed for the first time based on aptamer functionalized sulfur quantum dots (Apt-SQDs). The developed Apt-SQDs not only retained the good fluorescence properties of quantum dots but also overcame the problem of poor selectivity of SQDs for heavy metal ions. This system used the dual recognition strategy, including the combination of S_x^2? and Hg²⁺ and T-Hg²⁺-T structures to excellently identify and capture Hg²⁺, and an ultrahigh sensitivity fluorescent aptasensor was fabricated. The fluorescent aptasensor had a good response to Hg²⁺ at concentrations ranging of 10^?15 to 10^?7 M with an ultralow limit of detection of 0.3 fM, and the response to other metal ions was far less than that to Hg²⁺. It was successfully applied to detect Hg²⁺ in nearby environmental water samples (tap water, lake water and river water) with a good recovery rate. Moreover, portable test papers that would be useful for Hg²⁺ monitoring in environmental water were designed. The dual recognition strategy not only achieves ultrasensitive fluorescent detection of Hg²⁺ but also provides a new insight into the further expansion of the application of SQDs.     

Ceria–Zirconia Nanoparticles as an Enhanced Multi‐Antioxidant for Sepsis Treatment

The two oxidation states of ceria nanoparticles, Ce³⁺ and Ce⁴⁺, play a pivotal role in scavenging reactive oxygen species (ROS). In particular, Ce³⁺ is largely responsible for removing O₂⁻ and ^.OH that are associated with inflammatory response and cell death. The synthesis is reported of 2 nm ceria–zirconia nanoparticles (CZ NPs) that possess a higher Ce³⁺/Ce⁴⁺ ratio and faster conversion from Ce⁴⁺ to Ce³⁺ than those exhibited by ceria nanoparticles. The obtained Ce_0.7Zr_0.3O₂ (7CZ) NPs greatly improve ROS scavenging performance, thus regulating inflammatory cells in a very low dose. Moreover, 7CZ NPs are demonstrated to be effective in reducing mortality and systemic inflammation in two representative sepsis models. These findings suggest that 7CZ NPs have the potential as a therapeutic nanomedicine for treating ROS‐related inflammatory diseases.     

A study of the new perovskite solid solution series SrFexRu1−xO3−y by ruthenium-99 and iron-57 Mössbauer spectroscopy

The magnetic and structural properties of the solid solution SrFe_xRu_1?xO_3?y (0 ? x ? 0.5) have been studied using ⁵⁷Fe and ⁹⁹Ru Mössbauer spectroscopy and other techniques. These phases, which are here reported for the first time, have a distorted perovskite structure. The iron substitutes exclusively as Fe³⁺ and thereby causes oxygen deficiency, but has little effect on the magnetic behaviour of the Ru⁴⁺ until x > 0.2, whereupon the metallic band system begins to revert to a localized electron structure. The properties of a sample with x = 0.3 are complex and intermediate in character. For x > 0.3 the oxygen deficiency is reduced by substantial oxidation to Ru⁵⁺ until at x = 0.5 the system corresponds to Sr₂Fe³⁺Ru⁵⁺O₆.     

Tb3+ PVC-Membrane Electrode Based on 2-{2-(2-Anilinocarbothioyl)hydrazino)-2-oxoacetyl}-N-phenyl-1-hydrazine Carbothioamide

Abstract

The polyvinyl chloride (PVC) membrane containing 2-{2-(2-anilinocarbothioyl)hydrazino)-2-oxoacetyl}-N-phenyl-1-hydrazinecarbothioamide (AHC) as a suitable iophore exhibits a Nernstian response for Tb³⁺ ions over a wide concentration range (1.0 × 10^?6 to 1.0 × 10^?2 M) with a slope of 19.6 ± 0.3 mV per decade and a limit of detection of 6.8 × 10^?7 M in the pH range 3.5–8.5. The proposed sensor revealed very good selectivities (expect for the Pr³⁺ and Ho³⁺ ions) for a wide variety of other metal ions. The practical utility of the electrodes has been demonstrated by its use for the determination of Tb³⁺ in different solutions.     

A study of the reactions of fluorine with hydrogen and methane in the initiation phase using a miniature tubular reactor

A small tubular reactor having an inner diameter of 1–2 mm andused as the source in a molecular beam apparatus is described in detail. This arrangement allows the study of fast reactions with reaction times smaller than 1 msec. The preexplosive reaction phase between F₂ and H₂ and CH₄, respectively, is investigated to find out the initiation reactions. In the F₂/H₂ reaction, initiation is brought about by heterogeneous generation of F atoms or some other surface reaction. Evidence is also obtained for chain branching reactions. In the F₂/CH₄ case the dominant initiation reaction is the homogeneous reaction CH₄ + F₂ → CH₃ + HF + F. The rate constant for the reaction between 300 and 400 K is 10^12.3±0.3 exp[?47 ± 8 kJ/mol/RT] cm³/mol sec. The analysis of the experimental data also yields the rate constant for the propagation reaction CH₃ + F₂ → CH₃ F + F, which is 10^12.3±0.3 exp[?4.6 ±2.1 kJ/mol/RT] cm³/mol sec.     

Comparative study regarding the formation of La1-xSrxCrO3 perovskite using unconventional synthesis methods

The synthesis of strontium-doped lanthanum chromite, La_1−xSr_xCrO₃ (x=0.1 and 0.3), used as an interconnect material for solid oxide fuel cells (SOFC), was investigated using two unconventional synthesis methods: (1) organic precursors’ method based on the thermal conversion of complex combination resulted in the oxidation reaction of 1,2-ethanediol by La³⁺, Sr²⁺ and Cr³⁺ nitrates; (2) combustion synthesis based on the exothermic redox reaction of La³⁺, Sr²⁺ and Cr³⁺ nitrates with urea and glycine as fuels. We also used a mixture of urea and glycine as fuel. The samples were characterized by means of thermal analysis and X-ray diffraction.     

Preconcentration and speciation of inorganic and methyl mercury in waters using polyaniline and gold trap-CVAAS

Applicability of polyaniline (PANI) has been investigated for the preconcentration and speciation of inorganic mercury (Hg²⁺) and methyl mercury (CH₃Hg⁺) in various waters (ground, lake and sea waters). Preliminary experiments (batch) with powdered PANI for the quantitative removal of both Hg²⁺ and CH₃Hg⁺ showed that the retention of Hg²⁺ was almost independent of pH while a pH dependent trend from pH 1 to 12 was seen for CH₃Hg⁺ with maximum retention at pH > 5. Time dependence batch studies showed that a contact time of 10 min was sufficient to reach equilibrium. The K_d values were found to be ∼8 × 10⁴ and ∼7 × 10³ for Hg²⁺ and CH₃Hg⁺, respectively.Subsequently column experiments were carried out with PANI and the separation of the species was carried out by selective and sequential elution with 0.3% HCl for CH₃Hg⁺ and 0.3% HCl-0.02% thiourea for Hg²⁺. This was then followed by further pre-concentration of mercury on a gold trap and its determination by CVAAS. The uptake efficiency studies showed that the PANI column was able to accumulate up to 100 mg Hg²⁺/g and 2.5 mg CH₃Hg⁺/g. This method allows both preconcentration and speciation of mercury with preconcentration factors around 120 and 60 for Hg²⁺ and CH₃Hg⁺, respectively. The interfering effects of various foreign substances on the retention of mercury were investigated.