Micellar sensitized catalytic kinetic spectrophotometry for highly accurate and reproducible determination of V（IV） and V（V）

A highly accurate and reproducible micellar sensitized kinetic method was proposed for determination of V（VI）. The method is based on its catalytic effect on the oxidation of Coomassie brilliant blue R 250 （CBB＋） by bromate at pH 2.0. The reaction was monitored spectro- photometrically by measuring absorbance change with a fixed-time method of 5 min at 594 and 552 nm with and without surfactant. The variables influencing the calibra- tion sensitivity were extensively investigated, and the optimal conditions were established. The linear calibration range was 10-1,600 μg.L-1 with a relative SD ranging from 0.35 % to 3.35 % （for five replicate measurements of 75, 500, 1,000, and 1,500 μg.L-1） and a detection limit of 3.8 μg.L-1. The selectivity was also investigated, and greatly enhanced by suitable masking agents. The method was successfully applied to the analysis of V（IV） in pre- sence of excess V（V） up to 25 fold in environmental waters with the recoveries of 100.0 %-102.8 % for V（IV） and 95.7 %-99.7 % for total V. Its accuracy was validated by analysis of certified reference material via the present kinetic method and standard flame atomic absorption spectrometric method after extractive preconcentration with good agreement between certified and found values.     

A novel indicator system for catalytic spectrophotometric determination and speciation of inorganic selenium species (Se(Ⅳ), Se(Ⅵ)) at trace levels in natural lake and river water samples

A novel catalytic kinetic method is proposed for the determination of Se(Ⅳ), Se(Ⅵ), and total inorganic selenium in water based on the catalytic effect of Se(Ⅳ) on the reduction of Celestine blue by sodium sulfide at pH 7.0 phosphate buffer. The fixed-time method was adopted for the determination and speciation of inorganic selenium. Under the optimum conditions, the two calibration graphs are linear with a good correlation coefficient in the range 2-20 and 20-200 μg·L-1 of Se(Ⅳ) for the fixed-time method a...     

Micellar sensitized catalytic kinetic spectrophotometry for highly accurate and reproducible determination of Ⅴ(Ⅳ) and Ⅴ(Ⅴ)

A highly accurate and reproducible micellar sensitized kinetic method was proposed for determination of V(VI). The method is based on its catalytic effect on the oxidation of Coomassie brilliant blue R 250(CBB?) by bromate at pH 2.0. The reaction was monitored spectrophotometrically by measuring absorbance change with a fixed-time method of 5 min at 594 and 552 nm with and without surfactant. The variables influencing the calibration sensitivity were extensively investigated, and the optimal conditions were established. The linear calibration range was 10–1,600 lg L-1with a relative SD ranging from 0.35 % to 3.35 %(for five replicate measurements of75, 500, 1,000, and 1,500 lg L-1) and a detection limit of3.8 lg L-1. The selectivity was also investigated, and greatly enhanced by suitable masking agents. The method was successfully applied to the analysis of V(IV) in presence of excess V(V) up to 25 fold in environmental waters with the recoveries of 100.0 %–102.8 % for V(IV) and95.7 %–99.7 % for total V. Its accuracy was validated by analysis of certified reference material via the present kinetic method and standard flame atomic absorption spectrometric method after extractive preconcentration with good agreement between certified and found values.     

Hydrothermal growth of well-aligned TiO2 nanorod arrays： Dependence of morphology upon hydrothermal reaction conditions

Well-aligned TiO2 nanorod arrays (TNAs) were prepared on pretreated quartz substrates via hydrothermal method.The effect of the different preparation conditions on the growth morphologies of TNAs was systematically investigated by X-ray diffraction (XRD) and field-emission scanning electron microscopy (FE-SEM).The photocatalytic properties were tested by photodegradation of a methyl blue solution.It is demonstrated that the hydrothermal reaction conditions,such as precursor concentration,hydrothermal reaction temperature,and hydrothermal reaction times,can greatly affect the growth of TNAs.Controlling the preparation process,TNAs with 2 μm in length and 140-170 nm in diameter and well-aligned orientation have been successfully prepared.The photocatalytic experiment results indicate that TNAs have much better photocatalytic activity than TiO2 nanoparticles.     

Solid-phase extraction of trace Au（Ⅲ） with SDG and determination by the catalytic spectrophotometric method

The new catalytic kinetic spectrophotometric method for Au(III) determination was developed and validated. It was based on the catalytic effect of gold on the oxidation of sudan red III by ammonium peroxodisulfate ((NH4)2S2O8) with nitrilo triacetic acid as an activator in mi- croemulsion and H2SO4 medium. Under optimum conditions, there was the linearity of the calibration curve in the concentration range from 0 to 20 μg/L Au(III) at 520 nm. The relative standard deviation was 3.0% with a correlation coefficient of 0.9986. The detection limit achieved was 9.75 × 10-5 μg/mL. A new method using a column packed with sulfhydryl dextrose gel (SDG) as a solid-phase extractant has been developed for the preconcentration and separation of Au(III) ions. The method has been applied to the determination of trace gold with satisfactory results.     

Study on SCS-6／Ti-6Al-4V Composite

Fiber reinforced titanium matrix composite is considered as a superior material for advanced lightweight aerospace application. Fiber/matrix interfacial reaction has a significant effect on the mechanical properties of the composites. The SCS-6 SiC fiber reinforced Ti-6Al-4V matrix composite was prepared by foil-fiber-foil (FFF) method at ONERA, France. Stripe samples were cut from the as-consolidated composites and sealed in silicon carbide tube. One group of the samples were annealed for 58h at 550℃, 700℃, 850℃ and 1000℃, the other group were annealed at 1000℃ for 43h, 58h, 80h, 100h, respectively. The interface investigation indicated that the connection between SiC fiber and the matrix is favorite in the composite. And the interface width for as-consolidated composite is only about 0.8μm. The interface width increase with the prolong of annealing time and the increase of annealing temperature. But the increment for the latter is not as high as the former one, which means the annealing time may be the prior factor to influence the interface reaction. The interface width for the composite annealed at 1000℃ for 100h is about 20μm. Interface composition of the composite detected by EDX is as follows: Ti 87.58 wt %, V 4.91 wt %, AI 4.06wt%, Si 3.45 wt %.     

Flow-injection spectrophotometric determination of vanadium with malachite green oxalate by bromate in acidic and micellar medium

A flow injection method is proposed for determining vanadium(V). The method is based on its catalytic effect on the oxidation of malachite green oxalate by bromate. The reaction was monitored spectrophotometrically by measuring malachite green oxalate absorbance at λmax = 625 nm. The reagents and manifold variables, which have influences on the sensitivity, were investigated and the optimum conditions were established. The optimized conditions made it possible to determine vanadium in the ranges of 10-140 ng/mL with a detection limit of 5.2 ng/mL and a sample rate of 20 ± 5 samples/h.     

Non-isothermal kinetics of synthesizing vanadium nitride by one-step method

Vanadium nitride was synthesized by one-step method using V2O5 and carbon black as raw materials in nitrogen atmosphere. The phases of different reaction products prepared in different reaction temperatures were analyzed by X-ray diffraction(XRD), and the dynamic behavior of the process of synthesizing vanadium nitride(VN) by one-step method was studied with non-isothermal thermogravimetry. The mechanism function and kinetic parameters of reaction process were calculated by thermal gravimetric analyses(TGA), and the reaction rate equation was established. The XRD results show that for the samples tested with minimal VN after holding for 4 h at 1273 K, the main phase of products is VN at 1476 K, while some vanadium nitrides transform into vanadium carbides again over 1573 K. It is found that N2 is beneficial to stimulate reduction and proceed carbonization reaction,and the reduction and nitridation reaction can occur simultaneously. The activation energy of preparing VN by one-step method is 104.005 kJ·mol-1, and the frequency factor is 470.52 at 1280–1358 K, and 150.052 kJ·mol-1 and 2.35 9 104 at 1358–1426 K, respectively.     

Highly efficient nanoporous CoBP electrocatalyst for hydrogen evolution reaction

Water splitting is an environment friendly and efficient way to produce hydrogen.Highly efficient and low-cost non-noble metal catalysts play an important role in hydrogen evolution reaction(HER).Dealloying is a simple method to prepare three-dimensional self-supporting nanoporous materials without conductive supports and binders.In this work,we prepared self-supporting nanoporous CoBP electrocatalyst by dealloying method.The influence of the synergistic effect of nonmetallic elements on catalytic activity was investigated.The synergistic electronic effect of Co,B and P atoms on the surface optimizes the H atoms desorption and results in superior HER activity.The bi-continuous structure of nanoporous CoBP provides more active area and favors of electron and electrolyte transfer.The nanoporous CoBP with the B/P atomic ratio of 1/3 exhibits low overpotential of 42 mV at 10 mA·cm~(-2),small Tafel slope of 39.8 mV·dec~(-1) and good long-term stability with no performance decrease for 20 h in alkaline solution.     

Lattice parameters of Ti–4Al–2V alloy with thermal oxidation

In this study, the effect of thermal oxidation on the lattice parameters of Ti–4Al–2V alloy was studied.Samples were oxidized at 450, 600 and 650 °C for 1–7 h in electric furnace under air atmosphere. The lattice parameters were determined using the Cohen method as a function of oxidation time at each temperature. The lattice parameters of as-received alloy are calculated as a = 0.29289 nm and c = 0.46652 nm. The thermal oxidation at 450 °C results in a gradual increase in a-parameter, whereas it goes through a maximum at higher temperatures(600 and 700 °C). The results show that these maximums are reduced to an approximately constant value after a long-time oxidation. The c-parameter generally increases over the whole treatment condition. It is believed that these variations could be due to the dissolution of oxygen atoms in octahedral sites of hcp lattice of titanium.     

Catalytic-kinetic spectrophotometric determination of vanadium (Ⅴ) based on the Celestine blue-bromate-vanadium (Ⅴ)-citric acid reaction

A novel sensitive and relatively selective kinetic method is presented for the determination of V(Ⅴ) based on its catalytic effect on the oxidation reaction of Celestine blue by potassium bromate in the presence of citric acid as an activator.The reaction was monitored spectrophotometrically by measuring the decrease in absorbance of Celestine blue at a maximum absorption wavelength of 540 nm between 0.5 and 9 min (the fixed-time method) in an H3PO4 medium at 45℃.The effect of various parameters such as concentrations of H3PO4,citric acid,potassium bromate and Celestine blue,ionic strength,reaction temperature and time on the rate of V(Ⅴ) catalyzed reaction was studied.The method is free from the most interferences,especially from large amounts of V(Ⅳ).The decrease in absorbance is proportional to the concentration of V(Ⅴ) over the entire concentration range tested (0.025-1.25 μg·mL-1) with a detection limit of 6.80 μg·L-1 (according to statistical 3Sblank/k criterion) and a coefficient of variation (CV) of 1.78％ (for ten replicate measurements at 95％ confidence level).The proposed method suffers from a few interferences such as Cr(Ⅵ) and Hg(Ⅱ) ions.The method was successfully applied to the determination of V(Ⅴ) in river water,lake water,tap water,natural drinking water samples and a certified standard reference material such as SRM-1640 with satisfactory results.The vanadium contents of natural water samples were detected by using both linear calibration curve and standard addition curve methods.The recoveries of spiked vanadium (Ⅴ) into the certified standard water sample were found to be quantitative,and the reproducibility was satisfactory.It was observed that the results of the SRM 1640 were in good agreement with the certified value.     

A novel indicator system for catalytic spectrophotometric determination and speciation of inorganic selenium species （Se（Ⅳ）, Se（Ⅵ）） at trace levels in natural lake and river water samples

A novel catalytic kinetic method is proposed for the determination of Se(IV), Se(VI), and total inorganic selenium in water based on the catalytic effect of Se(IV) on the reduction of Celestine blue by sodium sulfide at pH 7.0 phosphate buffer. The fixed-time method was adopted for the determination and speciation of inorganic selenium. Under the optimum conditions, the two calibration graphs are linear with a good correlation coefficient in the range 2–20 and 20–200 μg·L⁻¹ of Se(IV) for the fixed-time method at 30°C. The experimental and theoretical detection limits of the developed kinetic method were found to be 0.21 and 2.50 μg·L⁻¹ for the fixed-time method (3 min). All of the variables that affect the sensitivity at 645 nm were investigated, and the optimum conditions were established. The interference effect of various cations and anions on the Se(IV) determination was also studied. The selectivity of the selenium determination was greatly improved with the use of the strongly cation exchange resin such as Amberlite IR120 plus as long as chelating agents of thiourea and thiosulphate. The proposed kinetic method was validated statistically and through recovery studies in natural water samples. The relative standard deviations (RSDs) for ten replicate measurements of 2, 10, and 20 μg·L⁻¹ of Se(IV) change between 0.35% and 5.58%, while the RSDs for ten replicate measurements of 3, 6, and 12 μg·L⁻¹ of Se(VI) change between 0.49% and 1.61%. Analyses of a certified standard reference material (NIST SRM 1643e) for selenium using the fixed-time method showed that the proposed kinetic method has good accuracy. The Se(IV), Se(VI), and total inorganic selenium in lake and river water samples have been successfully determined by this method after selective reduction of Se(VI) to Se(IV).     

Spectrophotometric Determination of Trace Amounts of Vanadium(Ⅴ) by Means of Its Catalytic Effect on Oxidation of Azomethine-H by Bromate

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V，Ru共掺杂NiS2 高尔夫微球作为碱性介质析氢反应的高效电催化剂

通过溶剂热法和滴钌法(室温)将钒和钌引入到NiS₂中,并制备了包覆在泡沫镍上的V,Ru共掺杂NiS₂微球(V, Ru)-NiS₂/NF电催化剂。通过硫化过程产生粗糙的高尔夫球状结构暴露出丰富的活性位点,此外,钒和钌的协同作用可以优化NiS₂的电子结构,提供额外的催化活性位点,进一步增强本征催化活性。泡沫镍的加入对催化材料起到支撑作用,避免聚集,同时提高导电性。结果表明,(V, Ru)-NiS₂/NF电催化剂在碱性条件下表现出优异的电催化性能和优异的析氢反应稳定性。在10 mA·cm^-2的电流密度下,(V, Ru)-NiS₂/NF提供了38 mV的过电位,小于商业Pt/C的过电位,并且具有较低的Tafel斜率(80.3 mV·dec^-1)、较高的电化学活性表面(ECSA)和在KOH溶液中24 h出色的稳定性。     

Electrochemical performance of LiFe1−xVxPO4/carbon composites prepared by solid-state reaction

LiFe_1−xV_xPO₄/C cathode materials (x = 0, 0.1, 02, 0.3, 0.4) were synthesized by solid-state reaction using polypropylene as the reducing agent and carbon precursor. XRD results show that Li₉Fe₃P₈O₂₉ and Li₃V₂(PO₄)₃ occur when vanadium was added. TEM images show that most of LiFe_1−xV_xPO₄/C particles take on a spherical or quadrate shape with a size less than 200 nm. Electrochemical tests indicate that LiFe_0.9V_0.1PO₄/C and LiFe_0.8V_0.2PO₄/C have a flat discharge plateau at about 3.45 V versus Li⁺/Li and an initial discharge capacity higher than 150 mAh/g at 0.1 C. LiFe_0.8V_0.2PO₄/C also performed relatively good cycle stability which is attributed to their high electronic conductivity as proved by the electrochemical impedance spectroscopy (EIS). Cyclic voltammogram (CV) curves demonstrate that as increase of content of vanadium, LiFe_1−xV_xPO₄/C presents several couples of redox peaks.     

Structure and magnetic properties of iron-rich Sm-Fe-(V,W)-Ga alloys

The phase composition of the iron-rich Sm-Fe-(V,W)-Ga alloys annealed at 1000 and/or 800°C and the effect of gallium on the magnetic properties of phases found in these alloys are studied. The tungsten and vanadium solubilities in the ternary phase Sm₂{Fe_{1 − y} (V,W) _y }₁₇ (with y ≤ 0.05) was determined. Both elements increase the Curie temperature of this compound but do not change the type of its anisotropy. Gallium was found to be an element stabilizing the Sm₂{Fe_{1 − y} (V,W) _y }₁₇ phase with the Th₂Zn₁₇-type structure; it increases the Curie temperature of the phase and changes the easy axis (EA) direction from the in-plane position to, first, a cone of easy axes and, then, the [0001] direction of the hexagonal lattice. An increase in the gallium content is accompanied by a widening of the homogeneity range of the phase at 1000°C. A phase of composition Sm₃(Fe,W)₂₉ with a monoclinic structure and lattice parameters a = 10.59 ?, b = 8.56 ?, c = 9.66 ?, and β = 97° was detected. Its Curie temperature is T _C = 185°C; the EA is parallel to the ‖[20$ \bar 1 $ \bar 1 ] direction. The gallium solubility in the Sm₃(Fe,W,Ga)₂₉ and Sm(Fe,W,Ga)₁₂ compounds was found to be very low; gallium increases their Curie temperatures.     

Selective Separation and Extraction of Vanadium (V) Over Manganese (II) from Co-Leaching Solution of Roasted Stone Coal and Pyrolusite Using Solvent Extraction

Based on the novel technology for selective separation and extraction of vanadium (V) over manganese (II) from co-leaching solution of roasted stone coal and pyrolusite using solvent extraction, the extraction effect of vanadium (V) and manganese (II) has been studied and many technical conditions have also been optimized. Meanwhile, countercurrent simulation experiments were conducted to verify the results of the experiments. The results indicated that with three countercurrent extraction stages, 99.21% vanadium (V) was extracted using 5% (v/v) N235 and 5% (v/v) secondary octyl alcohol at initial aqueous pH of 3.0 and O/A phase ratio of 1.0. Vanadium (V) could be completely stripped after three-stage countercurrent experiments with 20 wt.% NH₄Cl at O/A phase ratio of 1.0. The process flow sheet for the recovery of vanadium (V), as well as manganese (II), was proposed.     

Cyclic metallurgical process for extracting V and Cr from vanadium slag: Part I. Separation and recovery of V from chromium-containing vanadate solution

The separation and recovery of V from chromium-containing vanadate solution were investigated by a cyclic metallurgical process including selective precipitation of vanadium, vanadium leaching and preparation of vanadium pentoxide. By adding Ca(OH)₂ and ball milling, not only the V in the solution can be selectively precipitated, but also the leaching kinetics of the precipitate is significantly improved. The precipitation efficiency of V is 99.59% by adding Ca(OH)₂ according to Ca/V molar ratio of 1.75:1 into chromium-containing vanadate solution and ball milling for 60 min at room temperature, while the content of Cr in the precipitate is 0.04%. The leaching rate of V reaches 99.35% by adding NaHCO₃ into water according to NaHCO₃/V molar ratio of 2.74:1 to leach V from the precipitate with L/S ratio of 4:1 mL/g and stirring for 60 min at room temperature. The crystals of NH₄VO₃ are obtained by adjusting the leaching solution pH to be 8.0 with CO₂ and then adding NH₄HCO₃ according to NH₄HCO₃/NaVO₃ molar ratio of 1:1 and stirring for 8 h at room temperature. After filtration, the crystallized solution containing ammonia is reused to leach the precipitate of calcium vanadates, and the leaching efficiency of V is >99% after stirring for 1 h at room temperature. Finally, the product of V₂O₅ with purity of 99.6% is obtained by calcining the crystals at 560 °C for 2 h.     

Synthesis and electrochemical performance of La-doped Li3V2-xLax（PO4）3 cathode materials for lithium batteries

La-doped Li3V2-xLax(PO4)3 (x=0.01,0.02,and 0.03) cathode materials for lithium ion batteries were synthesized by the microwave-assisted carbothermal reduction method (MW-CTR).The structures and properties of the prepared samples were investigated by X-ray diffraction (XRD) and electrochemical measurements.The results showed that all the three Li3V2-xLax(PO4)3 samples had the same monoclinic structures and sharper diffraction peaks of the crystal plane compared with those of the undoped Li3V2(PO4)3.The initial charge/discharge specific capacity,coulomb efficiency,and discharge decay rate of all the three Li3V2-xLax(PO4)3 samples were superior to those of the undoped Li3V2(PO4)3 sample,and the Li3V1.98La0.02(PO4)3 sample exhibited the best features among the three La-doped Li3V2-xLax(PO4)3 samples.Electrochemical impedance spectroscopy (EIS) demonstrated that the Li3V1.98La0.02(PO4)3 sample had a lower charge transfer resistance and a higher Li ion diffusion coefficient compared with the undoped Li3V2(PO4)3 sample.     

Thermodynamic and kinetic analysis of CrB2 and VB2 formation in molten Al–Cr–V–B alloy

Transition metal impurities such as chromium (Cr) and vanadium (V) in solution deteriorate electrical conductivity of smelter grade aluminium (Al). These impurities can be removed from solution via boron treatment in which borides form upon their in-situ reaction with boron (B)-bearing substances. However, Cr removal from smelter grade Al solution is not well understood. A disagreement related to chromium boride (CrB₂) formation in molten Al in the presence of other transition metals (V, Ti, Zr, Fe) by adding Al–B master alloy has been reported in literatures. This study presents an effort to understand the mechanism of Cr removal from Al–0.50%Cr–0.50%V (mass fraction) alloy by adding Al–B (AlB₁₂) master alloy at 1023 K in the Al alloy solution. Results indicate that Cr removal from molten Al–0.50%Cr–0.50%V alloy by forming stable borides cannot be achieved at 1023 K; whereas excess of B in the solution preferentially forms aluminium boride (AlB₂) over CrB₂ during boron treatment of molten Al. The underlying kinetics of V removal from molten Al–0.50%Cr–0.50%V alloy revealed that early reaction stage is controlled by [B]/[V] mass transfer through liquid phase and mass transfer coefficient (k_m) was measured to be 9.6×10⁻⁴ m/s. The later reaction stage was controlled by [B]/[V] diffusion through boride (VB₂) ring. This study, therefore, advocates to investigate alternative ways to remove Cr from molten Al.