Synthesis of Ultra-Fine Columbite Powder MgNb2O6 by the Polymerized Complex Method

Pure MgNb₂O₆ powders with high specific surface area and high crystallinity have been successfully synthesized by the Polymerized Complex (PC) Method. A solution of water, citric acid, ethylene glycol and niobium and magnesium ions, was polymerized at 130°C by the water elimination and was calcined at 400°C for 2 h. The precursor formed was calcined at temperatures from 700°C to 1000°C in air to obtain the columbite phase. Thermal analysis, Raman spectroscopy, x-ray diffraction, adsorption/desorption hysteresis and scanning electron microscopy were used to investigate the polymer decomposition and the columbite phase evolution. No evidence for phase separation of crystalline MgCO₃ and Nb₂O₅ in Raman spectra and x-ray diffraction pattern as distinct intermediates were found, and the MgNb₂O₆ probably is formed through a single-step decomposition of oxycarbonate intermediate, as other double oxide synthesized by the PC Method, as indicated by the thermal decomposition of the precursor.     

Preparation and Characterization of Compositions Based on PbO-MgO-Nb2O5 Using the Sol-Gel Method

Lead Magnesium Niobate, Pb(Mg_1/3Nb_2/3)O₃ (PMN), is an important relaxor ferroelectric material. A significant problem exists, however, in the preparation of this material: it is very difficult to prepare pure phase, without the presence of a pyrochlore impurity phase which degrades the dielectric properties. Depending on the processing conditions, the amount of pyrochlore phase varies.Considering the ternary diagram PbO-MgO-Nb₂O₅, different compositions have been prepared by a simple sol-gel method at room temperature using Pb(CH₃COO)₂, Mg(CH₃COO)₂, Nb(OC₂H₅)₅ as precursors. After the heat treatment, the samples obtained were analyzed by XRD and EPMA with the purpose of studying the compositions formed.From the analysis of these results, it seems to be that the appearance of pyrochlore can be related to the reactivity of the MgO and/or the presence of other phases of the binary system PbO-Nb₂O₅. An excess of Pb and Mg is necessary for compositions to be formed near the PMN. The control of the amount of these two elements is very important because an excess of MgO would lead to rich compositions in Mg as a secondary phase.     

Synthesis and characterization of Al-and Y-Al-citrates as potential precursors for YAlO3

Al-and Y-Al-citric complexes have been synthesized in ethylene glycol medium at conditions close to the ones used in polymerized complex method and their composition and spectral characteristics have been studied. Proofs have been found for the formation in the bimetallic system of a mixed-metal Al-Y-complex. Doubly ionized and esterified ligands take place in the Al-complex. All of the ligands forming Y-Al-complex are mono-or doubly esterified. Deprotonation of the alcoholic group takes place in the formation of the mixed-metal complex. Both complexes contain adduct-bonded ethylene glycol. Heating of the bimetallic complex or of the polyester resin formed leads to not phase-homogeneous YAlO₃-along with cubic YAlO₃, its orthorhombic modification as well as Y₄Al _l2O₉ are found by X-ray diffractometry.     

Synthesis of CdS and ZnS nanowires using single-source molecular precursors

Single-source molecular precursors were used to synthesize II-VI compound semiconductor nanowires for the first time. Cadmium sulfide and zinc sulfide nanowires were prepared using cadmium diethyldithiocarbamate, Cd(S2CNEt2)2, and zinc diethyldithiocarbamate, Zn(S2CNEt2)2, respectively, as precursors in a gold nanocluster-catalyzed vapor-liquid-solid growth process. High-resolution transmission electron microscopy studies show that the CdS and ZnS nanowires are single-crystal wurtzite structures with stoichiometric compositions. In addition, photoluminescence measurements demonstrate that these nanowires exhibit high-quality optical properties. The applicability of our approach to the synthesis of other compound and alloy semiconductors nanowires as well as nanowire heterostructures of these materials is discussed.     

Volatile magnesium octahydrotriborate complexes as potential CVD precursors to MgB2. Synthesis and characterization of Mg(B3H8)2 and its etherates

The solid-state reaction of MgBr2 and NaB3H8 at 20 degrees C, followed by sublimation at 80 degrees C and 0.05 Torr, affords Mg(B3H8)2 as a white solid. Similar reactions with MgBr2(Et2O) and MgBr2(Me2O)1.5 afford the crystalline ether adducts Mg(B3H8)2(Et2O)2 and Mg(B3H8)2(Me2O)2, respectively. In contrast, reactions of MgBr2 with NaB3H8, the presence of excess solvent result in the formation of nonvolatile, probably ionic, magnesium compounds of the type [MgLx][B3H8]2. The adducts Mg(B3H8)2(Et2O)2 and Mg(B3H8)2(Me2O)2 are the first crystallographically characterized magnesium complexes of the B3H8- ligand; in both structures, the magnesium center adopts a distorted cis-octahedral geometry with two bidentate B3H8 groups and two Et2O ligands. Owing to their volatility, Mg(B3H8)2(Et2O)2 and Mg(B3H8)2(Me2O)2 are potential precursors for the deposition of MgB2 thin films, although preliminary efforts to employ them as chemical vapor deposition sources produce boron-rich MgBx films instead, with x approximately 7. Finally, the synthesis and structure of Cp2Mg(thf) are described: this mono-thf adduct of Cp2Mg bears two eta5-Cp groups, unlike other Lewis base adducts of Cp2Mg, which contain one eta5-Cp group and one eta1- or eta2-Cp group.     

Synthesis of polymeric organic semiconductors using semifluorinated polymer precursors

The transesterification of 1,1,1,3,3,3-hexafluoroisopropyl acrylate (HFIPA) homopolymers and block copolymers with methyl acrylate (MA) or n-butyl acrylate (n-BuA) were investigated for the efficient synthesis of p-type and n-type organic semiconductor acrylates. HFIPA, MA, and n-BuA are readily prepared in a one-pot synthesis by Cu(0) reversible deactivation radical polymerization in high yield with low dispersity to give poly(HFIPA)₁₀₀, PMA₁₀₀-b-poly(HFIPA)_x, and PnBuA₁₀₀-b-poly(HFIPA)_x (x = 100, 50,25). The transesterification of poly(HFIPA)₁₀₀ was also studied using ¹⁹F NMR spectroscopy. Based on this method, a series of eight homopolymers and three copolymers based on semiconductor motifs commonly found in organic light-emitting diodes, organic thin-film transistors, and organic photovoltaics were synthesized with narrow dispersity and conversions up to 99%. These experiments demonstrate that poly(HFIPA) can provide a useful building block in the synthesis of organic electronic materials, providing a simpler route to complex materials which may be challenging to access directly via controlled radical polymerization. © 2018 Wiley Periodicals, Inc. J. Polym. Sci., Part A: Polym. Chem. 2018 , 56, 2183–2191     

Structure and dehydration of layered perovskite niobate with bilayer hydrates prepared by exfoliation/self-assembly process

The crystals of an H-form niobate of HCa₂Nb₃O₁₀·xH₂O (x=0.5) being tetragonal symmetry (space group P4/mbm) with unit cell parameters a=5.4521(6) and c=14.414(2) Å were exfoliated into nanosheets with the triple-layered perovskite structure. The colloid suspension of the nanosheets was put into dialysis membrane tubing and allowed self-assembly in a dilute KCl solution. By this method, a novel layered K-form niobate KCa₂Nb₃O₁₀·xH₂O (x=1.3, typically) with bilayer hydrates in the interlayer was produced. The Rieveld refinement and transmission electron microscope (TEM)/selected-area electron diffraction (SAED) observation indicated that the orientations of the a-/b-axis of each nanosheet as well as the c-axis are uniform, and the self-assembled compound had the same symmetry, tetragonal (P4/mbm) with a=5.453(2) and c=16.876(5) Å, as the H-form precursor; the exfoliation/self-assembly process does not markedly affect the two-dimensional lattice of the layer. The large basal spacing resulted from the interlayer K⁺ ions solvated by two layers of water molecules. The interlayer bilayers-water was gradually changed to monolayer when the temperatures higher than 100 °C, and all the water molecules lost when over 600 °C. Accompanying the dehydration, the crystal structure transformed from tetragonal to orthorhombic symmetry. Water molecules may take an important role for the layer layered compound to adjust the unit cell to tetragonal symmetry.     

聚乙二醇辅助合成氧化镁及其处理含铅溶液的性能

以聚乙二醇（PEG-10000）辅助,在室温（25℃）-F由MgCl2-6H2O与Na2CO3通过层一层自组装制备出具有六棱柱状形貌的MgO,并以其对含铅溶液的吸附为探针反应,研究其对重金属离子的吸附性能．研究结果表明,所制备氧化镁的前驱体为MgCO3·3H2O;经600℃焙烧得到的六棱柱状MgO比表面积大于55m^2／g,具有良好的吸附性能;对含铅溶液的吸附过程符合Langmuir等温吸附,饱和吸附量达到390mg／g．     

Determination of lead in aluminum and magnesium antacids using electrothermal atomic absorption spectrometry

This paper proposes a method for the determination of lead in aluminum and magnesium antacids employing electrothermal atomic absorption spectrometry (ET AAS). The pyrolysis and atomization temperatures established during the optimization step were 700 and 2200 °C, respectively, using phosphate as the chemical modifier. Under these conditions, a characteristic mass of 25 pg, and limits of detection and quantification of 0.40 and 1.35 μg L⁻¹, respectively were obtained. Some experiments demonstrated that the calibration can be performed employing the external calibration technique using aqueous standards. The precision expressed as relative standard deviation (RSD %) was 4.03% for an antacid sample with lead concentrations of 284.5 μg L⁻¹. The proposed method was applied for the determination of lead in five antacid samples acquired in Salvador City, Brazil. The lead content was varied from 87 to 943 μg g⁻¹. The samples were also analyzed after complete dissolution by inductively coupled plasma mass spectrometry (ICP-MS). No statistical difference was observed between the results obtained by both of the procedures performed.     

X-ray photoelectron spectroscopy study of neodymium niobate and tantalate precursors and thin films

Neodymium niobate NdNbO₄ (NNO) and tantalate NdTaO₄ (NTO) thin films (~100 nm) were prepared by sol-gel/spin-coating process on Al₂O₃ substrate with LaNbO₄/PbZrO₃ interlayer and annealing at 1000°C. Surface chemistry was investigated by X-ray photoelectron spectroscopy (XPS). The core-level XPS studies of sol-gel NNO and NTO were performed for the first time. The binding energy differences Δ(O―Nb) and Δ(O―Ta) were used to characterize average energies of Nb―O bonding in NNO (322.9 eV) and Ta―O bonding in NTO (504.2 eV). The XPS demonstrated single valence state of Nd (Nd³⁺) in precursors. Nd concentration (at. %) decreases from 22% in precursors to 7% in films considering the substrate contains C, Al, Si, Pb, and Zr elements (37%) at Nb or Ta (5%) and O (51%). The X-ray diffraction analyses verified formation of the monoclinic (M-NdNbO₄ or M′-NdTaO₄), orthorhombic (O-NdNbO₄) and tetragonal (T-NdTaO₄) phases in precursors and films. Single valence state of Nd³⁺ was confirmed in these films designed for the application in environmental electrolytic thin film devices.     

活性镁及活性氢化镁的合成

研究了在真空下90-150℃间使蒽镁分解生成高活性镁. 再常压加氢, 制得氢化镁的方法. 这一过程中, 镁的活化可循环使用蒽, 基本上不消耗任何试剂, 在分解前用过渡金属化合物掺杂到蒽镁中去可改善活化镁的氢化行为. 当蒽镁中掺杂5%的Cp2TiCl2时, 吸氢温度可降至90℃.     

Synthesis and structural studies of lanthanide substituted bismuth-titanium pyrochlores

The identity of the pyrochlore phase seen during the synthesis of ferroelectric Bi_4−xLn_xTi₃O₁₂ Aurivillius oxides is shown to be Bi_2/3Ln_4/3Ti₂O₇. This pyrochlore is only stable for Ln³⁺=Sm³⁺ or smaller. For larger lanthanides the layered Aurivillius oxide is favoured. The presence of six-fold disorder, associated with the Bi 6s² lone pair electrons, is believed to stabilise the unexpected stoichiometry of this oxide. Precise structures, obtained by Rietveld refinement from synchrotron X-ray diffraction data, of three examples Ln³⁺=Eu, Ho and Yb are presented.     

Synthesis of Polysantol and related sandalwood-type odorants using magnesium α-bromoketone enolates

The syntheses of the commercial sandalwood-type odorant Polysantol^® and several structurally related compounds are described. The methodology followed is based on a selective and efficient magnesium-mediated aldol reaction of the starting material, α-campholenic aldehyde and different α-bromoketones. Dehydration of the resulting secondary alcohol and reduction of the carbonyl group allowed the completion of the syntheses of the target molecules in 30-56% overall yields.     

Physicochemical and photocatalytic properties of the ZnO particles synthesized by two different methods using three different precursors

ZnO particles with different morphological forms and various scale sizes were successfully synthesized as photocatalysts using two different methods (sol–gel and precipitation) and three precursors (zinc acetate dihydrate, zinc nitrate hexahydrate, and zinc sulfate heptahydrate). These materials were calcined at 500 °C for 3 h and characterized by various physicochemical techniques such as X-ray diffraction, Fourier transform infrared, transmission electron microscopy, S_BET, and UV–vis diffuse reflectance. The results showed that the crystalline structure, size, and morphology of the ZnO particles are strongly influenced by the preparation method and by the nature of the precursor used as reactant. The photocatalytic efficiency of the synthesized photocatalysts was evaluated by the photodegradation of methyl orange in aqueous solution under UV-A light. The results showed that the ZnO nanoparticles prepared the by sol–gel method from zinc acetate are more efficient than those prepared by the precipitation method.     

Processing and characterization of Pb(Mg,Nb)O3-PbTiO3 thin films from metal alkoxide-derived gels

The sol-gel processing is one of promising methods to fabricate well-derived integrated thin films at relatively low temperature. Ferroelectric niobates films do afford the possibilities for adding the values by the hybridization with semiconductor and/or electro-optic systems. The molecular level designing of the precursor solution was stressed as well as the control of key processing factors. The advantages of this sol-gel have been extended to prepare the ferroelectric Pb(Mg, Nb)O₃-PbTiO₃ solid solution films integrated on Si wafers. The crystallization of the films with desired crystal structure could be promoted by the controlled partial hydrolysis of designed alkoxide solution in the intermediate state and the pre-heated treatment of alkoxide-derived films in flow of water vapor and oxygen gas mixture.     

Synthesis and characterization of processable polyborate precursors

Polyborates have been formed by disproportionation and polycondensation of trimethoxyboroxine and also of trimethoxyboroxine and boric acid. The crtiical role of stoichiometry in the formation of polyborates without requiring incorporation of a metal counter ion is revealed. The emphasis is on integration of this chemistry with fabrication processes. Incorporation of an appropriate linear organic polymer is shown to yield the required rheological and thermal characteristics in this regard. These polyborates are inferred to be suitable as precursors for boron nitride in geometrical forms that can be processed as supported structures. However, they are also determined to be unsuitable as precursors for boron nitride fibers, oriented or isotropic, primarily due to their low glass transition temperature.     

Synthesis,characterization and biological screening studies of mixed ligand complexes using flavonoids as precursors

Flavonoids are a group of plant phenolics that provide various health benefits through cell signalling pathways and antioxidant effects. In the present study, a new series of mixed ligand complexes of Co(II), Ni(II), Cu(II) and Zn(II) were synthesized by incorporating curcumin and quercetin flavonoid precursors. The structural features of the synthesized complexes were explored using elemental analysis, thermogravimetric analysis, UV–visible, infrared, NMR, mass and electron paramagnetic resonance spectral analyses and conductivity measurements. These data support an octahedral geometry of the synthesized complexes. In silico biological activity score for the ligand was predicted using PASS online software. ADMET properties were studied using VLS3D online software. Anti‐inflammatory and antioxidant activities were experimentally validated which prove that theoretical predictions are in agreement with the experimental results. Interestingly the synthesized complexes interact with calf thymus DNA through groove binding mode. Moreover, they have good potential to cleave pUC19 DNA. Minimum inhibitory concentration values of the synthesized complexes reveal that they have better antimicrobial efficacy than the ligands.     

Synthesis of jasminaldehyde using magnesium organo silicate as a solid base catalyst

Synthetic talc (magnesium organo silicates; MOS) was synthesized by sol–gel method under non-hydrothermal conditions and modified by introducing amine/diamine functionalities in the interlayer space. The applicability of amine/diamine functionalized MOS was studied as catalysts for the synthesis of jasminaldehyde or -pentylcinnamaldehyde by condensation of 1-heptanal with benzaldehyde. The effect of amine/diamine functionality, amount of catalyst, benzaldehyde to 1-heptanal molar ratio and temperature on the selectivity of jasminaldehyde was studied in detail. The highest conversion of 1-heptanal (99%) with 82% selectivity of jasminaldehyde was achieved using MOS3 as a catalyst. The rate constant for condensation of 1-heptanal with benzaldehyde was calculated under optimized reaction conditions. This is the first report on application of MOS as a solid base catalyst for the condensation of 1-heptanal with benzaldehyde.