Spectroscopic and scattering investigation of isopoly-molybdate and tungstate solutions

Detailed spectroscopic and scattering investigations of isopoly-molybdate and -tungstate solutions as a function of concentration and pH were made. From scattering results the apparent molecular weights were determined as a function of time and concentration. We find that the result agree with the aggregation scheme of simple → hepta → octa → [Mo₃₆O₁₁₂]^?8 → protonated polymeric species, for molybdate solutions. Tungstate solutions aggregate according to simple → Y-polytungstate → paratungstate-A → paratungstate-B → Ψ-metatungstate. The molybdate solutions exhibited very rapid equilibration, but the tungstate solutions required several days to reach equilibrium. From the discrete changes in the Raman spectra of both systems we find that the formation of isopoly anions is not a continuous process and that only certain species are present in solution. Our results do not rule out the formation of significant quantities of the octamolybdate anion as suggested by previous investigators.     

Characterization of PDPA-b-PDMA-b-PDPA triblock copolymer Langmuir-Blodgett films for organic vapor sensing application

This study reports the synthesis, characterization, and gas sensing applications of the PDPA-b-PDMA-b-PDPA triblock copolymer material using NMR, UV-visible spectroscopy, atomic force microscopy (AFM), quartz crystal microbalance (QCM), and Langmuir-Blodgett (LB) thin film deposition techniques. The thin film deposition conditions of the copolymer material, which are prepared by LB film technique, are characterized by UV-visible spectroscopy, AFM, and QCM system. In this study, the swelling behaviors of the PDPA-b-PDMA-b-PDPA triblock copolymer Langmuir-Blodgett (LB) films were investigated with respect to volatile organic compounds (VOCs) at room temperature. The sensing responses of the films against VOCs were measured by QCM method. The swelling processes could be investigated using the early-time Fick's law of diffusion.     

Sugar-poly(para-phenylene ethynylene) conjugates as sensory materials: efficient quenching by Hg2+ and Pb2+ ions

Three polar poly(para-phenylene ethynylene)s (PPE) were synthesized by utilizing the Heck-Sonogashira protocol. Two of the PPEs carry beta-glucopyranose substituents. Depending upon the linker used between the glycol units and the backbone, the fluorescence of these PPEs can be quenched by Hg2+ and Pb2+ to a varying degree. Monomeric model compounds that are substituted with only one glucose unit are not efficiently quenched. The presence of many glucose substituents in one PPE assembly led to a large increase in the binding constant to Hg2+ and quenching of the fluorescence was amplified.     

Model systems for flavoenzyme activity: site-isolated redox behavior in flavin-functionalized random polystyrene copolymers

[reaction: see text] A model system has been developed to study the redox behaviors of flavin derivatives appended onto random polystyrene copolymers through "click" chemistry strategies. The results demonstrate that flavin units attached onto polymers exhibit site-isolated redox behaviors, yielding new materials with electrochemically tunable associations (K(a)(ox) = 450 M(-)(1), K(a)(red) = 18,200 M(-)(1)) to complementary diamidopyridine (DAP) functionality.     

Recent progress in pillar[n]arene-based thin films on chemical sensor applications

Journal of Inclusion Phenomena and Macrocyclic Chemistry - Pillar[n]arene is one of the most favorited supramolecular materials that possess a special chiral structure. The major property of...     

A smart nonstandard finite difference scheme for second order nonlinear boundary value problems

A new kind of finite difference scheme is presented for special second order nonlinear two point boundary value problems. An artificial parameter is introduced in the scheme. Symbolic computation is proposed for the construction of the scheme. Local truncation error of the method is discussed. Numerical examples are illustrated. Numerical results show that the method is very effective.     

Improving the Performance of Heterogeneous Borane Cocatalysts by Pretreatment of the Silica Support with Alkylaluminum Compounds

The treatment of silica with alkylaluminum compounds, triisobutylaluminum (TIBA) and triethylaluminum (TEA), dramatically enhanced the cocatalytic performances of the [CPh₃]⁺[B(C₆F₅)₃—SiO₂]^–. We measured the productivity and ethylene‐consumption profiles for [CPh₃]⁺[B(C₆F₅)₃—SiO₂]^– cocatalysts and Cp₂ZrCl₂/TIBA. Both of the treated cocatalyst systems improved the average molecular weight of the product when compared with the untreated cocatalyst system. The TIBA‐treated cocatalyst provided a narrow molecular weight distribution while the TEA‐treated cocatalyst system gave a broad distribution.     

Biosorbent for tungsten species removal from water: effects of co-occurring inorganic species

The effect of co-occurring inorganic species on the removal of tungsten from water was investigated using biosorbent (i.e., chitosan coated montmorillonite clay). Simulated natural water and well water from Fallon, NV were used for this study. The concentrations of tungsten (21-541 mg/L) and inorganic species ([H(2)CO(3)]=0-4.2 mg/L, [H(4)SiO(4)]=0-90 mg/L, and [SO(2-)(4)]=0-400 mg/L) in simulated feed water were varied. The concentration of tungsten in the well water was 26 microg/L. The pH level of simulated feed water and well water was adjusted to 4 since this pH was found to be the most effective pH for the tungsten removal using chitosan coated clay. Tungsten removal without the existence of co-occurring inorganic species decreases from 99.8 to 87.1% with an increase in initial tungsten concentration from 21 to 541 mg/L. It reduces further as the co-occurring inorganic species concentration increases. The percentage of the tungsten removal ranges between 68.2-93.8%, 66.7-94.2%, and 53.6-93.7% for simulated natural water containing varied amount of H(2)CO(3), H(4)SiO(4), and SO(2-)(4), respectively. The adsorption kinetic data could be best described by the pseudo second order expression. The adsorption equilibrium data was modeled with the Langmuir, Temkin, and Freundlich equations and was found to be represented well by the Langmuir equation. The essential characteristics of the Langmuir isotherm indicate that the adsorption of tungsten on chitosan coated clay is favorable regardless of the presence of interfering species. Compared to natural clay, chitosan coated clay has about 116 times larger adsorption capacity per gram of chitosan, which makes it a superior adsorbent. However, the maximum tungsten adsorption capacity decreases in the presence of co-occurring species since the co-occurring species suppress the adsorption. For the well water treated with biosorbent, the tungsten concentration in the product water was found to be lower than the detection limit (1 microg/L) of the inductively coupled plasma mass spectrometer (ICP-MS). The repeatable results obtained from the treatment of both simulated and well water suggest that using chitosan coated clay can be an efficient adsorbent for tungsten removal from contaminated sites.     

Angular Dependence of L X-ray Relative Intensities of Uranium and Thorium at 59.5 keV

INTRODUCTION

The knowledge of relative intensities of K, L and higher shell X-rays is needed for the investigation of various phenomena in atomic physics. In earlier studies, L X-ray relative intensities and energies have been reported for many elements by several investigators [1–5], but the angular dependence of L X-ray relative intensity has not been reported. According to Flugge et a1 [6], if the angular momentum J=1/2 and J>1/2 of the originating shell, then the angular distribution of X-rays is isotropic and anisotropic, respectively. From this idea, L_α, L_l and some of L_β, intensities are dependent on changing the scattering angles. In this study, we have measured the angular dependence of L_α, La_l, L_α/L_β, and L_α/L_γ, intensity ratios of U and Th at different angles varying from 45° to 135°.     

The viscosity of a polar fluid with suspensions

Summary The apparent viscosity of a polar fluid with suspensions of rigid spherical particles undergoing a prescribed bulk motion is calculated. It is shown that the increased rate of dissipation in a polar fluid with suspensions is greater than that of a Newtonian fluid. It is found that the relationship between the viscosity and the concentration has a same form with that of a Newtonian fluid suspension of which ambient fluid has a shear viscosity multiplied by a factor which is greater than unity.

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Zusammenfassung Die scheinbare Viskosität einer polaren Flüssigkeit mit suspendierten steifen, kugelförmigen Teilchen, die eine vorgeschriebene Bewegung ausführen, wird berechnet. Es wird gezeigt, daß die anwachsende Dissipationsgeschwindigkeit in einer polaren Flüssigkeit mit suspendierten Teilchen größer ist als die einerNewtonschen Flüssigkeit. Es zeigt sich, daß die Beziehung zwischen der Viskosität und der Konzentration die gleiche Form hat wie die einerNewtonschen Flüssigkeitssuspension, bei der die umgebende Flüssigkeit eine Scherviskosität besitzt, multipliziert mit einem Faktor größer als 1.