Experimental investigation of sheet flexibility of layered double hydroxides: One-pot morphosynthesis of inorganic intercalates

The sheet flexibility of layered double hydroxides (LDHs) has been investigated experimentally using co-precipitation and urea hydrolysis methods in an aqueous solution of long-chain anion surfactant in this work. Using dodecylsulfate (DS) anion as morphology-controlling agent, layer-bended or contorted Mg/Al-LDH is obtained successfully. The morphology of bent layers is retained during either in situ decomposition of interlayer DS to SO₄²⁻ or ion exchange of interlayer DS by CO₃²⁻. The direct synthesis of the layer-distorted LDHs intercalated with small inorganic anions is quite difficult. It has been achieved using layer-bended LDHs pillared with bulky organic anions as precursors in this paper. The morphosynthesis is expanded to Co/Al and Ni/Al-LDHs, indicative of the general flexibility of this kind of anionic clays.     

A competing risks analysis of the duration of federal target funds rates

The behaviour of short term interest rates has been the focus of extensive studies in economics and finance. This paper analyses the duration between changes in the Intended Federal Funds Rate (IFFR) taking into account different factors and the possibility of two outcomes (rate increase and rate decrease). Due to the lack of independence between these outcomes, the use of traditional survival analysis was ruled out and a novel approach based on competing risks is used. The estimation results show the influence of the current interest rate level, US GDP growth rate, US inflation rate, inflation rate differential with Euro-zone and the sign of the previous interest rate change. Test results also confirm that the duration previous to small changes (of a quarter point) and to large changes (above a quarter point) are statistically different for both rate hikes and rate cuts. Accurate confidence intervals for the Cumulative Incidence Function (CIF) are provided even with small sample size under non-normality.     

Preparation and characterization of monovalent ion‐selective poly(vinyl chloride)‐blend‐poly(styrene‐co‐butadiene) heterogeneous anion‐exchange membranes

New types of composite anion‐exchange membranes were prepared by blending of suspension‐produced poly(vinyl chloride) (S‐PVC) and poly(styrene‐co‐butadiene), otherwise known as styrene–butadiene rubber (SBR), as binder, along with anion‐exchange resin powder to provide functional groups and activated carbon as inorganic filler additive. Also, an ultrasonic method was used to obtain better homogeneity. In solutions with mono‐ and divalent anions, the effect of activated carbon and sonication on the morphology, electrochemical properties and selectivity of these membranes was elucidated. For all solutions, ion‐exchange capacity, membrane potential, permselectivity, transport number, ionic permeability, flux and current efficiency of the prepared membranes initially increased on increasing the activated carbon concentration to 2 wt% in the casting solution and then began to decrease. Moreover, the electrical resistance and energy consumption of the membranes initially decreased on increasing the activated carbon loading to 2 wt% and then increased. S‐PVC‐blend‐SBR membranes with additive showed a decrease in water content and a slight decrease in oxidative stability. Also, these membranes showed good monovalent ion selectivity. Structural images of the prepared membranes obtained using scanning optical microscopy showed that sonication increased polymer‐particle interactions and promoted the compatibility of particles with binder. Copyright © 2010 Society of Chemical Industry     

Influence of Chloride,Nitrate, and Sulphate on the Removal of Fluoride Ions by Using Nanofiltration Membranes

Abstract

This study investigates the removal of fluoride from various solutions(NaF, NaCl, NaNO₃, and Na₂SO₄) by using three commercial nanofiltration membranes denoted NF70(Filmtec), DESAL5 DL(Osmonics), and MT08(PCI) under 8 bars, 293 K in batch recirculation mode. The membranes were tested for their rejection potential of fluorides in the presence of chlorides, nitrates and sulphates. To identify the mechanisms of selectivity, we successively analyzed the rejections in turn of different combinations of NaF, NaCl, NaNO₃, and Na₂SO₄ in order to simulate the behavior of a real brackish water from Senegal. Fluorides rejection efficiency ranges from 78% to 95%. The efficiency of nanofiltration membranes improved is closely linked to the nature of the solution. The high rejection level(above 98%) of the divalent sulphate ions(50 or 200 mg/L) induces a Donnan effect establishment. In brackish water conditions, for all the membranes, there was a noticeable influence of anion size and hydration energy on fluoride rejection.     

Iridium‐Complex‐Modified Upconversion Nanophosphors for Effective LRET Detection of Cyanide Anions in Pure Water

Because of the extreme toxicity of cyanide anions, a great deal of effort has been invested in developing probes that use colorimetric and fluorometric methods to detect them. To date, most of the current optical probes require the use of organic solvents or a mixture of organic solvents and water. Upconversion nanophosphors (UCNPs) can serve as excellent emitters as a result of their sharp emission peaks and simple control of the emission wavelength. Here, the fabrication of hybrid material composed of iridium complex and UCNPs to detect cyanide anions selectively in pure water is described. In addition to the colorimetric detection, the upconversion luminescence emission can serve as a detection signal based on an effective luminescent resonance energy transfer (LRET) process within the hybrid nanoparticles.     

Electrogenerated base-promoted synthesis of N-benzylic rhodanine and carbamodithioate derivatives

Electrogenerated magnesium-associated cyanomethyl anions/bases obtained from the electrochemical reduction of acetonitrile and the oxidation of a sacrificial magnesium rod were successfully used to promote the addition of carbon disulfide to primary benzylic amines. Alkylation with ethyl 3-bromopropionate acid ester or with ethyl 2-bromoacetate acid ester yields the corresponding ring-opened carbamodithioate compounds or cyclic rhodanine derivatives, respectively. The effect of the amount of electrogenerated base on the yield of reaction was also evaluated.     

Preparation,characterization, and utilization of cationized hemp as anion exchanger for removing permanganates and dichromate anions

Using a software experimental design strategy and through 25 experiments, steam exploded hemp bast fibers (HBF) as well as their shives were cationized by the exhaustion method using 3‐chloro‐2‐hydroxypropyl trimethyl ammonium chloride solution. The results obtained revealed that at pH 13, raising the temperature of a bath containing 100 g/L cationizing agent aqueous solution at liquor to substrate ratio 1/15 to 80°C for 90 min produces the cationized forms of HBFs as well as their shives with percent nitrogen content 0.2240 and 0.4893 respectively. The statistical analysis for the results indicated that the percent nitrogen content is significantly influenced by factors of time, pH, and primarily the cationizing agent concentration. The cationized forms of HBFs as well as their shives, having amino contents 76 and 104 mequiv/100 g respectively, were characterized by studying their potentiometric titration and were analyzed by thermogravimetric analysis. Both of these cationized substrates were utilized as anion exchangers for adsorption of permanganate and dichromate anions from their acidic aqueous solutions. Adsorption dynamics of the removal of such anions were first‐order reactions whereas the adsorption isotherms showed that the adsorption of those anions on all the aforementioned anion exchangers was favorable. © 2007 Wiley Periodicals, Inc. J Appl Polym Sci 2007     

不同抗衡阴离子自旋交叉分子的制备与表征

基于三氮唑（1,2,4-1H-triazole,Htrz）体系的Fe（II）的配合物是一类非常重要的在室温附近发生自旋转变的自旋交叉分子,具有潜在的应用。本文报道了2种基于三氮唑体系的Fe（II）的配合物的制备与表征,分别为［Fe（Htrz）₂（trz）］（CF₃SO₃）和［Fe（Htrz）₂（trz）］（BF₄）,并研究了抗衡阴离子对自旋转变行为的影响。自旋交叉分子的制备由2种前驱体简单混合反应而得,结构表征表明三氮唑参与反应,并且产物中的Fe元素基本为Fe（II）,磁性测试证实了这2种分子存在自旋转变特性,并且这种自旋转变具有温度磁滞效应。实验结果还表明抗衡阴离子对于自旋交叉分子的自旋转变行为有重要的影响。抗衡阴离子空间位阻越小、抗衡阴离子的电负性越强、结构越对称规整,则自旋转变温度越高。     

Removal of transition metal cations and their counteranions by crosslinked epoxy—polymer

Reaction of epichlorohydrin with ethylenediamine is very exothermic, and severe explosions occur, even when a few milliliters of the reagents are interacted without solvent. A controlled reaction has been achieved safely by suspension polycondensation of epichlorohydrin with ethylenediamine. 1,2-Diaminoethane units in the resulting crosslinked polymer provide high chelating ability for transition metal ions, such as Cu(II), Ni(II), Co(II), Cd(II), Fe(III), and Cr(III). Having all-amine ligating groups, the polymer represents unique properties and can sorb not only metal cations but also their counteranions, such as chloride, sulphate, nitrate, and acetate. The crosslinked polymer is stable hydrolytically and regenerable by acid without losing its activity. It can be recycled and offers a means of simultaneous removal of cations and anions from aqueous solutions. © 1998 John Wiley & Sons, Inc. J Appl Polym Sci 68: 103–109, 1998     

Influence of the dopant on the polypyrrole moisture content: Effects on conductivity and thermal stability

Having in mind to produce electrically conductive carbon–epoxy composite materials, we have filled an insulating epoxy resin with an electronic conducting polymer, polypyrrole (PPy). To select the PPy that best suits this process, various PPys were chemically synthesized. The syntheses were performed in water via a dispersion polymerization route using, initially, either FeCl₃ (PPy–Cl⁻) or (NH₄)₂S₂O₈ (PPy–HSO₄⁻) as oxidizing agents. Then, using (NH₄)₂S₂O₈ as the oxidant, two other PPy doped with aromatic species were obtained due to the dissolution of paratoluenesulfonic acid (PPy–TS⁻) or naphtalenesulfonic acid (PPy–NS⁻) in the reaction media. The characterization of the PPy samples by conductivity measurements, together with elemental and thermal analysis, showed that PPy–TS⁻ exhibits the highest conductivity and thermal stability, with the conductivity remaining steady over 14 days. In addition, a stabilizing effect of the aromatic anions was observed. The experiments have shown that moisture in the PPy cannot be entirely removed and that, with increasing moisture content, the conductivity also increases, indicating an ionic conductivity superimposed on the electronic conductivity usually observed in PPy. © 1998 John Wiley & Sons, Inc. J Appl Polym Sci 70: 1567–1577, 1998