Preparation and characterization of niobates. Part VI: Synthesis, XRD, SEM and piezoelectric studies of potassium and barium-doped lead strontium niobates

Lead niobates belong to orthorhombic symmetry and acquire tetragonal symmetry at 570°C. Some lead-based ceramic compounds have been synthesized and their structural and ferroelectric properties studied. Strontium, barium and potassium were used to reduce the transition temperature and to control the grain growth, thereby electrical properties. The transition temperature was found to decrease from 465°C to 282°C with dopants. The transition temperature was drastically reduced with the addition of barium. This can be attributed to the suitability of doping ion in determining the transition temperature and other piezoelectric constants. Powder X-ray diffraction studies were carried out and orthorhombic symmetry was confirmed. The lattice constants were calculated through diffraction patterns. The average grain size was measured from the scanning electron microscopy (SEM) pictures taken on fractured surfaces of the samples.     

Removal of Copper and Lead from Aqueous Solution by Adsorption onto Cross-Linked Chitosan/Montmorillonite Nanocomposites in the Presence of Hydroxyl–Aluminum Oligomeric Cations: Equilibrium,Kinetic, and Thermodynamic Studies

Adsorption removal of Cu (II) and Pb (II) on cross-linked chitosan/Al₁₃-pillared montmorillonite (CCPM) was examined in solutions. The chitosan dosage was drastically reduced in the new nanocomposite, which is made from the treated clay (Al₁₃-pillared montmorillonite). Several important parameters that influenced the adsorption of Cu (II) and Pb (II) ions, such as cross-linked chitosan-to-clay ratio, pH, temperature, initial concentration, dosage, and contact time effect, were systematically investigated. Result showed that in the nanocomposite with cross-linked chitosan-to-clay ratio of 0.45:1, the maximum removal efficiencies of Cu (II) [pH 6.5, dosage 10 g/L, initial Cu (II) concentration 100 mg/L, contact time 2 h, 298 K] and Pb (II) [pH 6.0, dosage 5 g/L, initial Pb (II) concentration 100 mg/L, contact time 2 h, 298 K] were 96.0% and 99.5%, respectively. Kinetic and isotherm studies have indicated that the adsorption process of Cu (II) or Pb (II) nanocomposites was better fitted by the pseudo-second-order equation and the Freundlich equation, with chemical adsorptions as the rate-limiting step. The metal–ion affinity to the functional groups of CCPM followed the order Pb (II) > Cu (II). The thermodynamic parameters ΔH and ΔS values showed that the sorption process of Cu (II) or Pb (II) was spontaneous (ΔG < 0), was endothermic (ΔH < 0), and had decreased entropy (ΔS < 0). HNO₃ (0.1 M) could be a good desorbent in the recovery of metal ions after adsorption and regeneration of the adsorbent.     

柱撑粘土的制备与表征

作者以辽宁某地的钙基膨润土为原料，首先对其钠化改型得到适合制备柱撑粘土的基质，然后较系统地考察了制备聚合羟基Al离子的工艺条件，并运用X射线衍射分析（XRD），比表面积测定煅烧试验等手段一撑粘土进行了表征。结果表明：在温度80－90℃，老化温度与时间分别为室温和96h的条件下制备聚合羟基Al离子将其嵌入蒙脱石层间，可得到层间距d(001)值与比表面积分别为1.9194nm和147.2m^2/g的本撑粘土，300℃煅烧后其层间距稳定在1.8394nm，具有较好的热稳定性。     

新型MFSK最佳相干解调器

本文推广了作者在1999年提出的方法和结论[1],讨论了在信号各频率振幅受到的衰减不一致并存在有色加性高斯噪声(IGDF-ACGN)信道条件下,M进制FSK(MFSK)信号的最佳相干解调问题。导出了最佳解调器的结构,说明了该解调器中有关参数的估计方法,以及实现时遇到的矢量、矩阵运算的有关快速算法。从理论和计算机模拟实验两方面说明了所导得的最佳解调器,不仅在IGDF-ACGN信道条件下是最佳的,而且在加性高斯白噪声(AWGN)信道条件下也是最佳的。文中给出了误码率的计算机模拟曲线。     

Intensities of IR stretching bands as a criterion of the strength of Lewis acid sites in ZSM-5 zeolites with bivalent cations

The DFT calculations were applied to investigate the impact of the nature of bivalent cations M (M = Mg²⁺, Ca²⁺, Sr²⁺, Zn²⁺, Mn²⁺, Co²⁺, Ni²⁺) in cation-exchanged ZSM-5 zeolites on the Lewis acid site (LAS) strength. Intensities and shifts of IR stretching bands of adsorbed methane were calculated. Adsorption leads to a decrease in their frequencies and a marked increase in the intensities of the symmetric stretching band of methane. At the same time the intensities of the asymmetric stretching bands decrease. To characterize the strength of LAS, Fukui functions were computed. A good linear correlation between the intensity of methane vibrations and the LAS strengths (Fukui function f ⁺) was found.     

Organic–inorganic hybrid material as zwitterion: Synthesis and structure of terminal ammonium ions-containing organosilyl species supported on mono-lacunary Dawson polyoxometalate

The title compound 1 with a formula of (Bu₄N)₄[α₂-P₂W₁₇O₆₁{Me₃N⁺(CH₂)₃Si}₂O] · CH₃CN was obtained in 77.1% (4.21 g scale) yield by a 1:2 molar-ratio reaction of the mono-lacunary Dawson polyoxometalate (POM) [P₂W₁₇O₆₁]¹⁰⁻ with N-trimethoxysilylpropyl-N,N,N-trimethylammonium chloride ([Me₃N(CH₂)₃Si(OMe)₃]Cl) in mixed water/acetonitrile solution under acidic conditions and unequivocally characterized with complete elemental analysis, thermogravimetric and differential thermal analyses (TG/DTA), FTIR, solution (³¹P, ¹H, ¹³C and ²⁹Si) NMR and X-ray crystallography. Compound 1 contained two types of the ammonium cations, i.e., the counterions Bu₄N⁺ (free cations) and the terminal quaternary ammonium ions (bound cations) which are connected to the POM through the organosilyl groups.     

Adsorption of heavy metal cations from aqueous solutions by wool fibers

Adsorption of metal cations by kivircik wool from aqueous NiCl₂, CuCl₂, ZnCl₂, CdCl₂, HgCl₂ and Pb(NO₃)₂ solutions at 25°C and 50°C was investigated using atomic absorption spectroscopy. A fiber diffusion controlled adsorption rate model was used to predict the effective diffusion coefficients of metal ions in wool. It has been shown that wool is a potential adsorbent for removing toxic metal ions from contaminated water.     

Mineral Cations Affect Microstructure of Egg Yolk Granules

Granule dialysis caused partial release of calcium and breakage of the granular structure. In the presence of sodium chloride, sodium replaced calcium bound to the proteins and destabilized the structure of granules. By contrast, iron binding was not modified by the presence of sodium. EDTA bound all the cations, broke the phosphocalcic bridges and destabilized the structure. On the other hand, the addition of bivalent or trivalent cations at low concentration strengthened the structure which resisted changes in pH or ionic strength. All data showed the importance of ionic bridges (especially phosphocalcic bridges) in the association of LDL, lipovitellin and phosvitin in the form of spherical structures.     

Hard-to-Cook Defect in Cowpeas: Storage-Induced and Treatment-Induced Development

Cowpea seeds with a range of hard-to-cook (HTC) levels induced by storage at various temperatures/relative humidities/times were subjected to heat incubation in water and/or soaking in CaCl_2. For control seeds, the hardening effect of Ca soaking was greatly increased by incubation at 60-85°C before soaking, but not after. For aged seeds, Ca soaking alone evoked a great increase in hardness whereas incubation slightly enhanced hardening. Trivalent cations induced HTC less effectively than divalent cations; univalent ions suppressed HTC. EDTA soaking completely reversed while EGTA partially reversed HTC state of aged seeds. HTC state in cowpeas apparently develops via two stages: an increase in cation-uptake capacity within cotyledons induced by moderate heat or adverse storage, followed by divalent cation binding.     

Purification and characterization of highly active and stable polyphosphatase from Saccharomyces cerevisiae cell envelope

Saccharomyces cerevisiae cell envelope polyphosphatase was isolated in highly active and stable form by extraction from cells with zwittergent TM-314 followed by chromatography of the extract on phosphocellulose and QAE-Sephadex in the presence of 5 mM -MgCl₂, 0·5 mM -EDTA and 0·1% Triton X-100. The enzyme possessed a specific activity of 220 U/mg and after 30 days retained 87% of its activity at ?20°C. Polyphosphatase molecular mass was determined to be about 40 kDa by gel filtration and polyacrylamide gel electrophoresis in the presence of sodium dodecyl sulfate. The enzyme hydrolysed polyphosphates with various chain lengths (n = 3–208), had low activity for GTP and did not split pyrophosphate, ATP and p-nitrophenylphosphate. On polyphosphates with chain lengths n = 3, 9 and 208, K_m values were 1·7 × 10^?4, 1·5 × 10^?5 and 8·8 × 10^?7 M respectively. Polyphosphatase was most active and stable at pH 6·0–8·0. The enzyme showed maximal activity at 50°C. The time of half inactivation of polyphosphatase at 40, 45 and 50°C was 45, 10 and 3 min, respectively. In the absence of divalent cations and also with Ca²⁺ or Cu²⁺, the enzyme showed practically no activity. The ability of divalent cations to activate polyphosphatase was reduced in the following order: Co²⁺ > Mg²⁺ > Mn²⁺ > Fe²⁺ > Zn²⁺. Polyphosphatase was completely inhibited by 1 mM -ammonium molybdate and 50 μM -Zn²⁺ or Cu²⁺ (in the presence of Mg²⁺).