Phase equilibria and crystal chemistry of the R-Cu-Ti-O systems (R=lanthanides and Y)

As part of the study of interaction of the Ba₂RCu₃O_6+z (R=lanthanides and Y) superconductor with SrTiO₃ buffer, phase equilibria of the subsystem, R₂O₃-TiO₂-CuO (R=Nd, Y, and Yb), have been investigated in air at 960 °C. While the phase relationships of the two phase diagrams with smaller R (Y and Yb) are similar, substantial differences were found in the Nd₂O₃-TiO₂-CuO system, partly due to different phase formation in the binary R₂O₃-TiO₂ and R₂O₃-CuO systems. R₂CuTiO₆ and R₂Cu₉Ti₁₂O₃₆ were the only ternary phases established in all the three diagrams. R₂Cu₉Ti₁₂O₃₆ belongs to the perovskite-related [AC₃](B₄)O₁₂ family which is cubic Im3. Depending on the size of R³⁺, R₂CuTiO₆ crystallizes in two crystal systems: Pnma (R=La-Gd), and P6₃cm (R=Dy-Lu). The structure and crystal chemistry of the Pnma series of R₂CuTiO₆ (R=La, Nd, Sm, Eu, and Gd) are discussed in detail in this paper. Patterns for selected members of R₂CuTiO₆ have also been prepared and submitted for inclusion in the Powder Diffraction File (PDF).     

Cationic hexamethylbenzene-diene cobalt complexes

Cationic complexes [(diene)Co(??-C₆Me₆)]⁺ (diene is buta-1,3-diene (2a), 5-isopropyl-2-methylcyclohexa-1,3-diene (2b), cycloocta-1,3-diene (2c), and cyclohexa-1,5-diene (2d)) were synthesized by the reaction of [Co(??-C₆Me₆)₂]⁺ (1) with dienes in a CH₂Cl₂-Me₂CO mixture. In the absence of dienes, cation 1 undergoes hydrogenation to form [(1,2,3,4,5,6-HMCD-1,3)-Co(??-C₆Me₆)]⁺ (HMCD is hexamethylcyclohexadiene, 2e). Structures [2c?Ce]PF₆ were determined by X-ray diffraction analysis. According to the DFT calculations, the Co-C₆H₆ bond in the complexes with conjugated dienes is stronger than that in the complexes with nonconjugated dienes.     

Physical and chemical properties of PAN-derived electrospun activated carbon nanofibers and their potential for use as an adsorbent for toxic industrial chemicals

A recently developed carbon material, electrospun Activated Carbon nanoFiber (ACnF), exhibits strong potential for use as an adsorbent for toxic industrial chemicals (TICs). As-prepared ACnF contains as much as 9.6?wt% nitrogen, creating a basic surface that enhances acid-gas adsorption. ACnF shows 4–20 times greater HCN adsorption capacities and 2–5 times greater SO₂ adsorption capacities in dry nitrogen, compared to commercially available activated carbon fiber cloth (ACFC) and Calgon BPL? granular activated carbon, which are considered here as reference adsorbents. ACnF has 50?% of the micropore volume (0.30?cm³/g) of these reference adsorbents, which limits its adsorption capacity at high concentrations for volatile organic compounds (>500?ppm_v). However, at low concentrations (<500?ppm_v), ACnF has a similar capacity to ACFC and about three times the VOC adsorption capacity of Calgon BPL?. ACnF’s small fiber diameters (0.2–1.5?μm) allow for higher mass transfer coefficients, resulting in adsorption kinetics nearly twice as fast as ACFC and eight times as fast as Calgon BPL?. ACnF drawbacks include hydrophilicity and reduced structural strength. The rapid adsorption kinetics and high capacity for acidic TICs warrant further investigation of ACnF as an adsorbent in respiratory protection and indoor air quality applications.     

Synthesis and structural characterization of heterometallic thorium aluminum polynuclear molecular clusters

Aluminum can undergo hydrolysis in aqueous solutions leading to the formation of soluble molecular clusters, including polynuclear species that range from 1 to 2 nm in diameter. While the behavior of aluminum has been extensively investigated, much less is known about the hydrolysis of more complex mixed-metal systems. This study focuses on the structural characteristics of heterometallic thorium-aluminum molecular species that may have important implications for the speciation of tetravalent actinides in radioactive waste streams and environmental systems. Two mixed metal (Th(4+)/Al(3+)) polynuclear species have been synthesized under ambient conditions and structurally characterized by single-crystal X-ray diffraction. [Th(2)Al(6)(OH)(14)(H(2)O)(12)(hedta)(2)](NO(3))(6)(H(2)O)(12) (ThAl1) crystallizes in space group P2(1)/c with unit cell parameters of a = 11.198(1) ?, b = 14.210(2) ?, c = 23.115(3) ?, and β = 96.375° and [Th(2)Al(8)(OH)(12)(H(2)O)(10)(hdpta)(4)](H(2)O)(21) (ThAl2) was modeled in P1? with a = 13.136(4) ?, b = 14.481(4) ?, c = 15.819(4) ?, α = 78.480(9)°, β = 65.666(8)°, γ = 78.272(8)°. Infrared spectra were collected on both compounds, confirming complexation of the ligand to the metal center, and thermogravimetric analysis indicated that the thermal degradation of these compounds resulted in the formation of an amorphous product at high temperatures. These mixed metal species have topological relationships to previously characterized aluminum-based polynuclear species and may provide insights into the adsorption of tetravalent actinides on colloidal or mineral surfaces.     

Method of composition heterogeneity reduction in copolymer of butadiene with isoprene in ionic coordination polymerization with supported titanium catalysts

Compositional heterogeneity of copolymers of butadiene with isoprene in copolymerization with supported titanium catalyst was investigated. The causes of compositional heterogeneity were found based on solution of an inverse problem of formation of the molecular weight distribution. It was shown that the pre-hydrodynamic effects in a turbulent reactor at the stage of the reaction mixture formation allowed the synthesis of more uniform composition of the copolymer.     

High performance liquid chromatography method for determination of methyl-5-benzoyl-2-benzimidazole carbamate (mebendazole) and its main degradation product in pharmaceutical dosage forms

Methyl-5-benzoyl-2-benzimidazole carbamate (mebendazole) is a drug used as an anthelmintic. A high performance liquid chromatography method has been developed in this study to determine mebendazole and its degradation product in the pharmaceutical dosage forms (tablets and suspension). The expected major degradation product of mebendazole in the dosage forms has been prepared, and identified as 2-amino-5-benzoylbenzimidazole. The proposed HPLC assay was found to be selective, accurate (% recoveries were in the range of 99.9-100.9) for both, mebendazole and the degradation product, repeatable and reproducible (replicate measurements for short and long term measurements showed % RSD of 相似文献   

Micellar effects on the electrochemistry of dopamine and its selective detection in the presence of ascorbic acid

The electrochemistry of dopamine (3-hydroxytyramine) was studied by cyclic voltammetry at a glassy carbon electrode in the presence of cetyltrimethylammonium bromide (CTAB) and sodium dodecyl sulfate (SDS) micelles at different pH. The anodic peak potential (E(pa)) and peak current (I(pa)) were found to be remarkably dependent on the charge and the concentration of the surfactant. The E(pa) and I(pa) change abruptly around the critical micellar concentration (CMC) of the surfactants and reach a plateau above the CMC. The E(pa) at the plateau shifts to more positive values in the cationic CTAB micellar solution, e.g. from 180 mV vs SCE in aqueous solution at pH 6.8 to 410 mV in CTAB micelle, whilst it shifts to less positive values in the anionic SDS micellar solution, e.g. 150 mV at pH 6.8. Therefore, the overlapped anodic peaks of dopamine and ascorbic acid in the mixture of the two compounds in aqueous solutions can be separated in CTAB micelles since the micelle shifts the E(pa) of ascorbic acid to less positive values. The two peaks are separated by ca. 400 mV at pH 6.8 in CTAB micelle, hence dopamine can be determined in the presence of 100 times excess of ascorbic acid. In SDS micelle and in the presence of ascorbic acid, the I(pa) of dopamine is greatly enhanced due to the catalytic oxidation of the latter that enables quantitative determination of both compounds.     

Determination of manganese in grain by potential titration with catalytic end-point indication

A method of catalytic potential titration for the determination of trace manganese by using crystal violet ion selective electrode is reported in this paper. It is based on the catalytic effect of manganese (II) on the oxidation of crystal violet by potassium periodate in the presence of nitrilotriacetic acid (NTA). The experiments indicated that this technique showed high sensitivity and high accuracy. The results of determination of trace manganese in grain could be compared with the results obtained by means of atomic absorption spectrometry.     

Determination of calcium, magnesium and strontium in soils by flow injection flame atomic absorption spectrometry

Several procedures for the determination of Ca, Mg and Sr in soils have been compared on the basis of the accuracy of analysis of two NIST reference materials (Montana Soils SRM 2710 and SRM 2711). Samples were dissolved in a mixture of hydrofluoric and nitric acids in sealed vessels in a microwave oven and in teflon beakers on a hot plate. The digests obtained from both dissolution methods were evaporated to dryness in an attempt to remove silicon. Boric acid was added to prevent the precipitation of the lanthanum releasing agent (as lanthanum fluoride) and potassium was added as an ionization buffer. Determinations were made by flame atomic absorption spectrometry with both the nitrous oxide-acetylene flame and the air-acetylene flame, with calibration either by standard additions or against external standards matrix matched with respect to nitric acid, boric acid, lanthanum and potassium. The silicon remaining in the solution was also determined by external calibration. A single-line flow injection manifold was used to overcome any problems due to the presence of high dissolved solids. A volume of 300 mul was injected into a water carrier stream flowing at 8 ml min(-1). To determine Ca in the air-acetylene flame, it was necessary to remove silicon. Magnesium was determined in either flame without complete removal of the silicon, however, for the determination of Sr, it was necessary to remove the silicon and use the nitrous oxide-acetylene flame. The indicative value for Sr in SRM 2710 was too low: the value determined was 360+/-30 mug g(-1).     

Pushing the detectability of voltammetry: how low can we go?

The coupling of adsorptive accumulation with catalytic reactions results in remarkably low (sub-picomolar) detection limits. This review assesses various strategies for attaining such dual-amplification effects, that lead to the most sensitive voltammetric technique, adsorptive-catalytic stripping voltammetry (AdCtSV).