Spectrophotometric determination of uranium(vi) by the azide reaction

Azide has been investigated as a spectrophotometric reagent for uranium(VI). The system is more sensitive than the thiocyanate reaction. It obeys Beer's law in the range 2–180 p.p.m. of uranium. The colour is sensitive to hydrogen ion concentration ; maximum absorbance and stability are attained at pH 5–5.5. Iron(III) interferes seriously, but can be masked by EDTA. Fe⁺², Cr⁺³, Ni⁺², Th⁺⁴, Cr₂O₇^-2, WO₄^-2, VO₃^- and F^- interfere. The deep yellow colour cannot be extracted with organic solvents. A mono-azido-uranium(Vl) ion is present in dilute solutions; its dissociation constant is 2.3 ±20.27·10^-3.     

Gravimetric determination of tungsten(vi) with n-benzoyl-n-phenylhydroxylamine

Tungsten can be quantitatively precipitated with N-benzoylphenyl-N-hydroxylamine in presence of hydrochloric acid (0.5–1 N). The precipitate can be weighted as WO₂(C₁₃H₁₀O₂N)₂ or WO₃. Molybdenum, vanadium, titanium, and iron can be separated by prior precipitation of these mutais with the above reagent in presence of tartrate ions; tungsten is then determined in tlie filtrate. L'ranium does not interfere, but chromium (VI), fluoride and phosphate do.     

A new reagent for the colorimetric and spectrophotometric determination of phosphorus,arsenic and germanium

A new reagent for the colorimetric and spectrophotometric determination of phosphorus, arsenic and gurmanium is described. It contains Mo(Vl) amd Mo(V) in the ratio of 3 : 2 in an acid medium, 10N with respect to H₂SO₄ and 3N with respect to HCl.The absorption spectra, the influence of temperature, time, quantity of reagent and selectivity of the method have been studied. Beer's law is applicable up to 160 μg for P₂O₅, 220 μg for GeO₂ and 230 μg for arsenic, in 50 ml.     

Gravimetric determination of beryllium with n-benzoylphenylhydroxylamine

N-Benzoylphenylhydroxylamine has been employed in the gravimetric determination of beryllium and in its separation from iron, aluminium and titanium. After suitable adjustment of pH iron, aluminium or titanium is precipitated quantitatively with the reagent; beryllium is subsequently precipitated after raising the pH of the filtrate. The metal may be determined by either igniting the precipitate to beryllium oxide or weighing it as Be(C₁₃H₁₀O₂N)₂.     

5: 6-Benzoquinaldinic acid as an analytical reagent: Determination of thorium and zirconium

Thorium and zirconium are determined in the presence of rare earths, alkaline earths and magnesium, when precipitated from weakly acid solution with 5:6-benzoquinaldinic acid. Thorium is completely precipitated at pH 3.0 as Th(C₁₄H₈O₂N)₄, but though zirconium is precipitated at the lower pH of 1.8, its composition is not stoichiometric and hence is ignited to the oxide before weighing. Co-precipitation of magnesium and alkaline earths is prevented by the addition of ammonium chloride.     

Polarography of Uranium in lactate medium

The polarography of uranium(Vl) in the lactate medium is studied at different pH values. At pH 1 the half-wave potential of the uranium(Vl) wave remains the same as that of the simple ion, but the limiting current increases with increasing concentration of lactate; disproportionation of uranium(V) at the electrode surface is suggested. The rate of disproportionation is calculated. Polarograms observed in the region of pH 5 and 6 are interpreted on the basis of complexation of UO₂²⁺.     

Efficient Recycling of Gold and Copper from Electronic Waste by Selective Precipitation

The recycling of metals from electronic waste (e-waste) using efficient, selective, and sustainable processes is integral to circular economy and net-zero aspirations. Herein, we report a new method for the selective precipitation of metals such as gold and copper that offsets the use of organic solvents that are traditionally employed in solvent extraction processes. We show that gold can be selectively precipitated from a mixture of metals in hydrochloric acid solution using triphenylphosphine oxide (TPPO), as the complex [(TPPO)₄(H₅O₂)][AuCl₄]. By tuning the acid concentration, controlled precipitation of gold, zinc and iron can be achieved. We also show that copper can be selectively precipitated using 2,3-pyrazinedicarboxylic acid (2,3-PDCA), as the complex [Cu(2,3-PDCA-H)₂]_n ⋅ 2n(H₂O). The combination of these two precipitation methods resulted in the recovery of 99.5 % of the Au and 98.5 % of the Cu present in the connector pins of an end-of-life computer processing unit. The selectivity of these precipitation processes, combined with their straightforward operation and the ability to recycle and reuse the precipitants, suggests potential industrial uses in the purification of gold and copper from e-waste.     

Gravimetric determination of beryllium with acetoacetanilide

Summary An organic reagent viz. acetoacetanilide has been found out which precipitates beryllium quantitiatively aboveph 5.5. The complex, Be(C₁₂H₁₀O₂N)₂, containing 2.49% Be can be weighed directly after drying. Beryllium can be precipitated from solutions containing aluminium and iron by masking these foreign elements with EDTA. A method has also been described for the determination of beryllium content in beryl.

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Zusammenfassung Beryllium kann oberhalbph 5,5 mit Acetoacetanilid quantitativ gefällt werden. Der gebildete Komplex, Be(C₁₀H₁₀O₂N)₂, der 2,49% Be enthält, kann gleich nach dem Trocknen gewogen werden. Die Gegenwart von Aluminium und Eisen stört nicht, wenn äDTA als Maskierungsmittel zugegeben wird. Die Bestimmung von Beryllium in Beryll wird ebenfalls beschrieben.

     

新型红色荧光粉Sr3Al2O6的合成和发光性能研究

稀土金属离子激活的多铝酸盐发光材料，在可见光区具有较高的量子效率犤１～４犦，充分显示出这类荧光发光材料，在高效节能、环保、电光源与新一代可见光显示器领域的应用前景犤４～９犦。特别是SrAl２O４∶Eu２＋的持续发光现象的发现犤２，３犦，激起了对以稀土金属离子为激活剂，碱土铝酸盐为基质的长余辉无机发光材料体系的兴趣。研究表明其发光强度和余辉时间是传统硫化物发光材料的十倍以上，利用其长余辉储光－发光特性，有望开发新型发光油漆、涂料、发光陶瓷、发光塑料、薄膜、发光纸、发光纤维犤４犦。早在七十年代，荷兰菲利…     

Visualisation of the local bio-electrocatalytic activity in biofuel cell cathodes by means of redox competition scanning electrochemical microscopy (RC-SECM)

Optimisation of biocatalytic systems for the electroreduction of molecular O₂ in biofuel cell cathodes implies screening of the catalytic activity of enzyme/redoxpolymer assemblies. Os-complex modified electrodeposition polymers are suggested for linking bilirubin oxidase catalysed O₂ reduction via an electron hopping sequence along the redox polymer to the electrode. They can be non-manually precipitated on electrode surfaces by electrochemically induced pH modulation. Cyclic voltammetry provides a good estimation of the electrocatalytic activity of a redox polymer/enzyme modified electrode surface. In addition, scanning electrochemical microscopy operating in redox competition mode (RC-SECM) supplies images of the spatial distribution of the biocatalytic activity.     

Peroxidase catalyzed polymerization of phenol

effect of horseradish peroxidase (HRP) and H₂O₂ concentrations on the removal efficiency of phenol, defined as the percentage of phenol removed from solution as a function of time, has been investigated. When phenol and H₂O₂ react with an approximately one-to-one stoichiometry, the phenol is almost completely precipitated within 10 min. The reaction is inhibited at higher concentrations of H₂O₂. The removal efficiency increases with an increase in the concentration of HRP, but an increase in the time of treatment cannot be used to offset the reduction in removal efficiency at low concentrations of the enzyme, because of inactivation of the enzyme. One molecule of HRP is needed to remove approximately 1100 molecules of phenol when the reaction is conducted at pH 8.0 and at ambient temperature.     

Fabrication and characterization of three-dimensionally ordered macroporous niobium oxide

Three-dimensionally ordered macroporous (3-DOM) niobium oxide was fabricated by aqueous organic gel method through the interstitial spaces between polystyrene spheres assembled on glass substrates. Freshly precipitated hydrous niobium oxide (Nb₂O₅·nH₂O), which was prepared starting from Nb₂O₅, was used in combination with citric acid in an aqueous solution and then was transferred as a niobium source to synthesize 3-DOM Nb₂O₅. The morphologies of porous Nb₂O₅ were characterized by scanning electron microscope (SEM). The thermal decomposition and phase composition of 3-DOM Nb₂O₅ were investigated by Fourier transform infrared spectroscopy (FT-IR), Thermogravimetric–differential thermal analysis (TG–DTA), X-ray diffraction (XRD) and X-ray photoelectron spectroscopy (XPS).     

Eisen(II)-carbonat als Ausgangsmaterial zur Herstellung von röntgenamorphem Eisen(III)-hydroxid sowie von γ-FeOOH und α-FeOOH

X-ray amorphous iron(III) hydroxide is formed on treating FeCO₃ with H₂O₂. However, oxidation of freshly precipitated FeCO₃ by means of air yields — in the absence of foreign cations — γ-FeOOH and α-FeOOH. The latter is obtainable in the pure state provided that FeCO₃ is air-oxidised in alkaline medium (excess of Na₂CO₃).     

Separation of niobium and tantalum with phenylarsonic acid

Phenylarsonic acid permits satisfactory separation of niobium and tantalum and estimation of tantalum from an oxalate solution containing sulphuric acid up to pH 5.8. For complete precipitation of niobium the pH should exceed 4.8. In mixtures, tantalum is precipitated below pH 3.0 and niobium is then precipitated above pH 5.0. When the oxalate concentration is high, recovery of niobium with cupferron is recommended. When the ratio of Nb₂O₅, to Ta₂O₅ exceeds 2:1, reprecipitation of tantalum is necessary. The effect of interfering ions is studied.     

High temperature thermal expansion of BaAl2Si2O8, CaAl2Si2O8, and Ca2Al2SiO7 studied by high-temperature X-ray diffraction (HT-XRD)

Sealing of components for high temperature applications with coefficients of linear thermal expansion (CTE) > 10·10⁻⁶ K⁻¹ can be achieved by glasses from which crystalline phases with high CTE are precipitated. Many sealing glasses also contain further components as e.g. aluminium and hence, not only the desired phase is crystallized, but also additional phases. For this purpose, high temperature XRD was performed in order to determine the CTE of BaAl₂Si₂O₈, CaAl₂Si₂O₈, and Ca₂Al₂SiO₇. In the case of BaAl₂Si₂O₈ and Ca₂AlSi₂O₇ the CTEs were 7.8·10⁻⁶/K and 7.9·10⁻⁶/K, respectively. In the case of CaAl₂Si₂O₈ the CTE is 4.4·10⁻⁶/K. Especially the formation of the latter phase should be avoided for a sealing material of high temperature fuel cells. Sintered specimens of the respective compounds were also characterized by dilatometry.     

A Facile Synthesis of High‐Surface‐Area Sulfur–Carbon Composites for Li/S Batteries

Small‐grained elemental sulfur is precipitated from sodium thiosulfate (Na₂S₂O₃) in a carbon‐containing oxalic acid (HOOC?COOH) solution through a novel spray precipitation method. Surface area analysis, elemental mapping, and transmission electron micrographs revealed that the spray‐precipitated sulfur particles feature 11 times higher surface area compared to conventional precipitated sulfur, with homogeneous distribution in the carbon. Moreover, the scanning electron micrographs show that these high‐surface‐area sulfur particles are firmly adhered to and covered by carbon. This precipitated S–C composite exhibits high discharge capacity with about 75 % capacity retention. The initial discharge capacity was further improved to 1444 mA h g^?1 by inserting a free‐standing single‐walled carbon nanotube layer in between the cathode and the separator. Moreover, with the help of the fixed capacity charging technique, 91.6 % capacity retention was achieved.     

The effects of La2O3 on the early stages of crystallization for MgO-Al2O3-SiO2-TiO2-La2O3 glass-ceramics

The early stages of crystallization for MgO-Al₂O₃-SiO₂-TiO₂-La₂O₃ glasses with different La₂O₃ concentrations were studied by X-ray diffraction (XRD) and transmission electron microscopy (TEM). The glass transition temperature (Tg) of the glass decreases at first and then increases again with increasing La₂O₃ concentration. This indicates that the structure of the glass becomes weaker at first and then stronger again. Lanthanum acts in glasses as network modifier and will usually decrease the network connectivity of the glass structure. Nevertheless, if the La₂O₃ concentration is high enough, the oxygen and other ions start to agglomerate around La, resulting in a more closely packed structure. Heat-treatment of the sample with x = 0.1 at 770–810 °C results in the precipitation of a droplet phase with higher mean atomic weight embedded in a matrix with lower mean atomic weight. The initial crystalline phase magnesium aluminum titanate (MAT) precipitates from the droplet phase. Nevertheless, for the sample with x = 0.4, dendrite-like structure could be observed after heat-treatment of the glass at 810 °C. Furthermore, the crystalline phase first precipitated is the lanthanum containing perrierite, which could be attributed to the rearrangement of the glass structure as an effect of La³⁺ incorporation.     

Interaction of arsenite ions with molybdate in aqueous solution

Interaction of arsenite ions with molybdate ions in aqueous HClO₄ at pH of 3–5 were studied using spectrophotometry. A heteropoly anion (HPA) with the AsMo₄ stoichiometry was revealed. Elemental analysis, X-ray photoelectron spectroscopy, and IR spectroscopy were used to characterize the composition and structure of the cesium salt of As(III)-Mo(VI) HPA precipitated from solution. The comparison of the IR spectra of cesium salts of the synthesized HPA and dimethylarsenite HPA (CH₃)₂AsMo₄O₁₅H^2?, whose structure is known, implies that AsMo₄O ₁₅ ^3? has a similar structure, where the AsO ₂ ^? group is linked by four connected molybdenum octahedra (Mo₄O₁₂)O^2?.     

Zur Konstitution von Alkaliperoxotantalaten(V): Über den Aufbau von K3[Ta(O2)4]

On the Constitution of Peroxotantalates(V) with Alkali Metals: On the Structure of K₃[Ta(O₂)₄] [1] By solving of recently precipitated Ta₂O₅ · aq in a 1.5-molar solution of KOH in 3% H₂O₂ and subsequently cooling at 0°C we obtained colourless single-crystals of K₃[Ta(O₂)₄]. The compound crystallizes tetragonal (spacegroup 142m) with a = 679.5(1) pm, c = 791.2(1) pm, Z = 2 (Guinier-de-Wolff powder data). The determinated crystal structure (four-circle diffractometer, 444 out of 444 I₀(hkl); R = 1.51%, R_w = 1.48%, parameters see text) proves that K₃[Ta(O₂)₄] is isotypic with K₃[Cr(O₂)₄] [2]. The Madelung Part of Lattice Energy, MAPLE, and Effective Coordination Numbers, ECoN, these calculated via Mean Fictive Ionic Radii, as well as charge distribution (CHARDI) are calculated and discussed.     

Studies on lanthanoid sulfites: Part VI. Thermogravimetric study of scandium sulfite pentahydrate

Scandium sulfite was found to crystallize as a pentahydrate both at 25 and 90 °C when precipitated by the action of sulfur dioxide on aqueous suspensions of Sc(OH)₃. Thermogravimetric analysis showed that the anhydrous sulfite is formed by 200 °C but it starts to decompose immediately after its formation. The decomposition leads to an intermediate phase which is stable up to 700 °C in inert (nitrogen) and air atmospheres but decomposes earlier in reductive (hydrogen) environment. The weight remaining, which corresponds to the intermediate level, varies between 58 and 43 %, depending on experimental conditions and thus cannot be assigned to a single compound such as Sc₂O₂SO₄ or Sc₂O₂SO₃. The intermediate phase is amorphous to X-rays but IR spectra indicate the presence of both sulfite and sulfate ions pointing to a mixture. In all atmospheres studied the final decomposition step is the formation of scandium sesquioxide.