Studies on ion-isotopic exchange reactions using nuclear grade ion exchange resins

The present paper deals with the study of iodide and bromide ion-isotopic exchange reactions by application of radioactive tracer technique. The specific reaction rate (per minute) of both the reactions decreases with rise in temperature and increases with concentration of ionic solution. It was observed that due to solvation effect, the iodide ion-isotopic exchange reaction take place at a faster rate than bromide ion-isotopic exchange reaction. Also for iodide ion-isotopic exchange reaction, the distribution coefficient (K _d ) values were higher than that for bromide ion-isotopic exchange reaction. The application of tracer technique was further extended for characterization of two widely used nuclear grade ion exchange resins Tulsion A-33 and Duolite ARA 9366. It was observed that the values of K _d, specific reaction rate (per minute), amount of ion exchanged (millimoles), and percentage of ions exchanged for Tulsion A-33 resins are higher than that for Duolite ARA 9366 resins under identical experimental conditions.     

Studies on kinetics and thermodynamics of ion adsorption reactions by applications of short-lived radioactive tracer isotopes

The short-lived radiotracer isotopes were applied to study the kinetics and thermodynamic feasibility of iodide as well as bromide ion adsorption reactions using industrial-grade resin materials. Free energy of activation (ΔG ^?) and energy of activation (E _a) were calculated by using Arrhenius equation, enthalpy of activation (ΔH ^?), and entropy of activation (ΔS ^?) calculated by using the Eyring-Polanyi equation. These parameters were used to predict the thermodynamic feasibility of the two ion adsorption reactions performed by using Dowex SBR LC and Indion-810 resins. It was observed that during iodide ion adsorption reactions, the values of energy of activation (?18.79 kJ mol^?1), enthalpy of activation (?21.37 kJ mol^?1), free energy of activation (58.13 kJ mol^?1), and entropy of activation (?0.26 kJ K^?1 mol^?1) calculated for Indion-810 resins were lower than the respective values of ?4.28 kJ mol^?1, ?6.87 kJ mol^?1, 64.97 kJ mol^?1, and ?0.23 kJ K^?1 mol^?1 calculated for Dowex SBR LC under similar experimental conditions. Identical trends were observed for the two resins during bromide ion adsorption reactions. The low values of different thermodynamic parameters obtained for Indion-810 resins during both the ion adsorption reactions indicate that the reactions are thermodynamically more feasible using Indion-810 resins as compared to Dowex SBR LC resins. It is expected here that the present nondestructive technique can be extended further for different ions in the solution in order to predict the thermodynamic feasibility of different ion adsorption reactions for the range of resins which are widely used for treatment of industrial waste water effluent.     

A Sensitive Chemiluminescence Flow Injection Procedure for Assay of Fluoride in Waters and Humane Urine by Use of Immobilized Reagents

A new simple, rapid, selective and sensitive analytical procedure based on chemiluminescence (CL) detection is described for the determination of free fluoride at sub‐nanogram levels by use of controlled‐reagent‐release technology in a flow injection system. The analytical reagents involved in the CL reaction, including luminol and periodate, were both immobilized on anion‐exchange resins in a flow injection system. Through water injection luminol and periodate were eluted from the anion exchange column to generate the chemiluminescence, which was enhanced in the presence of fluoride. The increased CL intensity was linear with fluoride concentration in the range from 0.1 to 10 ng·mL^? 1. The limit of detection was 20 pg·mL^? 1 (3σ) and the relative standard deviation (RSD) was 1.02% (n = 5) for a 1.0 ng·mL^? 1 fluoride. At a flow rate of 2.0 mL·min^? 1, including sampling and washing, a typical analytical procedure could be performed in 0.5 min with a RSD of less than 3.0%. The proposed method was successfully applied to determine the free fluoride in water and human urine, and the results were in good agreement with those obtained by ion chromatography.     

Novel cross-linked membrane for direct methanol fuel cell application: sulfonated poly(ether ether nitrile)s

In order to reduce water uptake, swelling ratio, and methanol permeability in sulfonated proton exchange membranes (PEM), novel-sulfonated aromatic poly(ether ether nitrile)s-bearing pendant propenyl groups had been synthesized by direct copolymerization method. All the results showed that the propenyl groups were suitable cross-linkable groups, and that this method was an effective way to overcome the drawbacks of sulfonated polymers at high ion exchange capacity (IEC) values. By cross-linking, the water uptake, swelling ratio, and methanol diffusion could be restricted owing to the formation of compact network structure. For example, CSPEN-60 membranes showed the proton conductivity of 0.072 S cm^?1 at 80 °C, while the swelling ratios and water uptake (17.9 and 60.7 %) were much lower than that of the SPEN-60 membrane (60.8 and 295.2 %). Meanwhile, a 1.1 × 10^?7 cm² s^?1 of methanol diffusion was obtained which was much lower than that of Nafion 117 (14.1 × 10^?7 cm² s^?1). Although the proton conductivity of the CSPEN-60 membranes is lower than that of the SPEN-60 membrane, the selectivity is much higher. The CSPEN-60 membrane exhibited the highest selectivity among the tested membranes, about 5.8 times higher compared with that of Nafion117.     

STUDIES ON COPPER-CONTAINING NAD GLYCOHYDROLASE FROM AGKISTRODON ACUTUS VENOM BY FLUORESCENCE AND CD SPECTROSCOPY

ABSTRACT

The properties of NAD Glycohydrolase (NADase), purified from Agkistrodon acutus venom, have been studied by fluorescence and CD spectroscopy. The fluorescence intensities of NADase decrease by about 1% or 3% when the concentrations of I^? ion are 0.1 mol/L or 0.2 mol/L in the NADase solutions, respectively. However, the fluorescence intensities of the NADase are quenched by about 25% and 48%, respectively, with further addition of 1 mmol/L EDTA into solutions. CD spectra also suggested that EDTA could remove Cu²⁺ ion from NADase molecule and the conformation of NADase changed much. So Cu²⁺ ion is very important to maintain the geometrical structure of NADase.     

Enhanced Upconversion Luminescence of Erbium–Nitrogen-Doped Zinc Oxide Nano-Wires by Implantation of Ytterbium Ions

Erbium–nitrogen codoped zinc oxide nanowires of ytterbium-doped are prepared by thermal evaporation and ion implantation methods. Ytterbium ions are doped into nanowires at a fluence of (0, 1, 3, 5, and 9) × 10¹⁵ cm^?2. Microstructural and optical properties of specimen are investigated by X-ray diffractometer, absorption spectra, Raman, and upconversion photoluminescence examinations. Upconversion photoluminescence emissions at 550 nm and 660 nm are obtained under 980-nm light excitation. Both intensities of green and red peaks are enhanced by the introduction of ytterbium ions. When ytterbium ion fluence is 5 × 10¹⁵ cm^?2, light emission intensity reaches maximum value. The energy transfer and cross-relaxation processes are responsible for the change of emission intensity.     

Study on factors governing the conductivity performance of acylated chitosan-NaI electrolyte system

Hexanoyl chitosan and lauroyl chitosan were prepared by acyl modification of chitosan. Films of hexanoyl chitosan- and lauroyl chitosan-based polymer electrolytes incorporated with different weight concentrations of sodium iodide (NaI) were prepared using the solution casting technique. FTIR and differential scanning calorimetry (DSC) results suggested that NaI interacted with both hexanoyl chitosan and lauroyl chitosan. Maximum conductivities of 1.3 × 10^?6 and 1.1 × 10^?8 S cm^?1 are achieved for hexanoyl chitosan and lauroyl chitosan, respectively. Higher conductivity in hexanoyl chitosan is attributed to higher ion mobility as supported by DSC results. The dielectric constants of neat hexanoyl chitosan and lauroyl chitosan are 2.7 and 1.9, respectively, estimated from impedance spectroscopy. Higher dielectric constant of hexanoyl chitosan resulted in greater NaI dissociation and hence higher conductivity. Deconvolution of O═C-NHR and OCOR bands of polymer has been carried out to estimate the amount of dissociated Na⁺ ions from NaI. The findings were in good agreement with conductivity results. In order to assess quantitatively, the conductivity, parameter number, n, and mobility, μ, of ions were calculated using impedance spectroscopy. XRD results showed the influence of NaI on the crystalline content of the electrolyte system. Sample with lower crystalline content exhibited higher conductivity.     

Induced absorption in yttrium aluminium perovskite crystals irradiated by 12C and 235U ions

The present work is devoted to investigation of optical absorption in pure and neodymium-doped YAlO₃ (YAP) single crystals in the spectral range 0.2–1.1 μm induced by the influence of ¹²C ions irradiation with energy 4.50 MeV/u (MeV per nucleon) and a fluence 2 × 10⁹ cm^?2 or of ²³⁵U ion irradiation with energy 9.35 MeV/u and a fluence 5 × 10¹¹ cm^?2. The induced absorption in the case of ¹²C ions irradiation is caused by recharging of point growth defects and impurities under the radiation influence. After irradiation by ²³⁵U ions with fluence 5 × 10¹¹ cm^?2 the strong absorption rise is probably caused by contribution of the lattice destruction as a result of heavy ion bombardment.     

Steady State Fluorescence Studies of Wild Type Recombinant Cinnamoyl CoA Reductase (Ll-CCRH1) and its Active Site Mutants

Fluorescence quenching and time resolved fluorescence studies of wild type recombinant cinnamoyl CoA reductase (Ll-CCRH1), a multitryptophan protein from Leucaena leucocephala and 10 different active site mutants were carried out to investigate tryptophan environment. The enzyme showed highest affinity for feruloyl CoA (K _a ?=?3.72?×?10⁵ M^?1) over other CoA esters and cinnamaldehydes, as determined by fluorescence spectroscopy. Quenching of the fluorescence by acrylamide for wild type and active site mutants was collisional with almost 100 % of the tryptophan fluorescence accessible under native condition and remained same after denaturation of protein with 6 M GdnHCl. In wild type Ll-CCRH1, the extent of quenching achieved with iodide (f _a?=?1.0) was significantly higher than cesium ions (f _a?=?0.33) suggesting more density of positive charge around surface of trp conformers under native conditions. Denaturation of wild type protein with 6 M GdnHCl led to significant increase in the quenching with cesium (f _a?=?0.54), whereas quenching with iodide ion was decreased (f _a?=?0.78), indicating reorientation of charge density around trp from positive to negative and heterogeneity in trp environment. The Stern-Volmer plots for wild type and mutants Ll-CCRH1 under native and denatured conditions, with cesium ion yielded biphasic quenching profiles. The extent of quenching for cesium and iodide ions under native and denatured conditions observed in active site mutants was significantly different from wild type Ll-CCRH1 under the same conditions. Thus, single substitution type mutations of active site residues showed heterogeneity in tryptophan microenvironment and differential degree of conformation of protein under native or denatured conditions.     

EPR, Optical Absorption and Superposition Model Study of Fe3+-Doped Ammonium Dihydrogen Phosphate Single Crystals

X-band electron paramagnetic resonance (EPR) studies are carried out on Fe³⁺ ions doped in ammonium dihydrogen phosphate (ADP) single crystals at room temperature. The crystal field and spin Hamiltonian parameters are evaluated from the resonance lines obtained at different angular rotations. The obtained values of spin Hamiltonian and zero-field parameters of the Fe³⁺ ion in ADP are: g = 1.994 ± 0.002, |D| = (220 ± 5) × 10^?4 cm^?1 and a = (640 ± 5) × 10^?4 cm^?1. On the basis of EPR data, the site symmetry of the Fe³⁺ ion in the crystal is discussed. The Fe³⁺ ion enters the lattice substitutionally replacing the NH₄ ⁺ sites. The optical absorption of the crystal is also studied at room temperature in the wavelength range of 195–925 nm. The energy values of different orbital levels are calculated. The observed bands are assigned as transitions from the ⁶ A _1g (S) ground state to various excited quartet levels of the Fe³⁺ ion in a cubic crystalline field. From the observed band positions, Racah interelectronic repulsion parameters (B and C), cubic crystal field splitting parameter (D _q ) and Trees correction are calculated. There values are: B = 970, C = 1,923, D _q  = 1,380 cm^?1 and α = 90 cm^?1, respectively. On the basis of EPR and optical data, the nature of bonding in the crystal is discussed. The zero-field splitting (ZFS) parameters are also determined theoretically using B _kq parameters estimated from the superposition model. The values of ZFS parameters thus obtained are |D| = (213 ± 5) × 10^?4 cm^?1 and |E| = (21 ± 5) × 10^?4 cm^?1.     

Electrical and complex dielectric behaviour of composite polymer electrolyte based on PEO,alumina and tetrapropylammonium iodide

In this study, the electrical, dielectric and morphological analysis of composite solid polymer electrolytes containing polyethylene oxide, alumina nano-fillers and tetrapropylammonium iodide are conducted. The temperature dependence of conductivity shows activation energy of 0.23, 0.20 and 0.29 eV for electrolytes containing 0, 5 and 15 wt.% alumina, respectively, when data fitted to the Arrhenius equation. These activation energy values are in good agreement with those determined from dielectric measurements. The result confirms the fact that conductivity is activated by both the mobility and the charge carrier density. The conductivity isotherms demonstrated the existence of two peaks, at 5 and 15 wt.% Al₂O₃ composition. The highest conductivity values of 2.4 × 10^?4, 3.3 × 10^?4 and 4.2 × 10^?4 S cm^?1 are obtained for the sample with 5 wt.% Al₂O₃ at 0, 12 and 24 °C, respectively, suggesting an enhancement of conductivity compared with that of alumina free samples.     

Effect of additional metal ions on the ratio between the rates of the transformation of the intermediate products of the hydrolysis of adenosine-5′-triphosphoric acid catalyzed the Cu2+ ion (Communication 2: Mathematical modeling of the kinetics of the hydrolysis in the presence of additional Mg2+ ions)

It was previously shown that the hydrolysis of the (CuATP^2? · OH₂)₂ dimeric complex to CuADP^? and an inorganic phosphate occurs in a sequence of two rapid and irreversible steps. Along with the hydrolysis through a common intermediate product, (CuATP^2?)₂OH^?-(DOH^?), the OH^? nucleophile at the Cu²⁺ ion is replaced by OH^? at the positively charged phosphorus atom to form an IntK pentacovalent intermediate (step 1). A mathematical modeling of the kinetics of the hydrolysis catalyzed by the Cu²⁺ base metal ion in the presence of additional Mg²⁺ ions at two pH values, 6.48 and 6.71 (at the ascending branch of the dependence of the initial rate of the hydrolysis on the pH value) is performed. Additional ions affect only the pathway of coupling of the conformational conversion of DOH^?. The rate constant for the forward reaction (IntK→ DOH^?), k ₁, increases from 2 · 10⁷ L mol^?1 min^?1 in the absence of Mg²⁺ to 2.9 · 10⁷ L mol^?1 min^?1 upon introduction of Mg²⁺ ions; rate constant of the reverse reaction IntK → DOH→, k ^?1, decreases from 1 · 10⁵ L mol^?1 min^?1 in the absence of Mg²⁺ to 3 · 10⁴ L mol^?1 min^?1 in the presence of Mg²⁺. The relative concentrations of the intermediate products are demonstrated to change during the irreversible hydrolysis. In the presence of Mg²⁺, IntK emerges at much earlier stages of the hydrolysis, the fraction of formed IntK in the balance of NuP₀ is substantially higher, and the growth of its relative concentration with time in the earlier stages of hydrolysis is much more dramatic.     

The centrifugally constructed and thermally activated three-dimensional graphene toward a binder-free highly performed anode of the lithium-ion battery

A binder-free three-dimensional porous interconnected graphene (a-3DrGO@NF) was centrifugally constructed and KOH-activated at 800 °C, leading a mechanically strong and pore-developed anode candidate for lithium ion batteries (LIBs). The unique approach of the integration of the mechanical construction and thermal activation demonstrated favorable frameworks to facilitate the stable and fast migrations of both ion and electron during the galvanostatic charge/discharge process, thus significantly improving its durability and electrochemical performance compared to those without the activated and thermal treatment. The a-3DrGO@NF LIBs showed a highly reversible capacity of 1250 mAh g^?1 at a current density of 0.1 A g^?1 after 50 cycles without degradation relative to the first cycle. More importantly, the a-3DrGO@NF LIBs exhibited excellent large current discharge property and cyclic stability of 965 mAh g^?1 in its first cycle and 545 mAh g^?1 after 150 cycles at a current density of 4 A g^?1. Furthermore, it can be quickly charged and discharged in a very short time of 92 s together with high-rate capability of 256 mAh g^?1 after 200 cycles at 10 A g^?1. At both lower and higher its current density as to 10 A g^?1, the coulombic efficiency was close to 100% and showed the reliability of a-3DrGO@NF LIBs.     

Preparation and properties of sulfonated polybenzimidazole-polyimide block copolymers as electrolyte membranes

Sulfonated polybenzimidazole-polyimide block copolymers are synthesized through condensation polymerization at high temperature. The length of the polyimide chain is varied to give a series of block copolymers with various block lengths. The as-synthesized block polymers are used to prepare the corresponding membranes through the solvent evaporation method. The structure of the block copolymers is characterized by Fourier transform infrared spectroscopy (FTIR) and nuclear magnetic resonance spectroscopy (NMR). Their mechanical strength, thermal behavior, water uptake, swelling ratio, and proton conductivity, as well as oxidative stability are also investigated. All the block copolymers exhibit good thermal stability, dimensional stability, mechanical strength, and proton conductivity. Compared to the random sulfonated polyimide-containing benzimidazole membranes with the same degree of sulfonation, the membranes prepared from the block copolymers show higher proton conductivities. The proton conductivities of the block copolymer membranes range from 6.2?×?10^?4 to 1.1?×?10^?2?S cm^?1 at 105 °C. The block copolymer membrane doped with phosphoric acid exhibits proton conductivity higher than 0.2 S cm^?1 at 160 °C, indicating its potential applications in proton exchange membrane fuel cells operated under high temperature and low humidity conditions.     

Investigation of gallium arsenide single crystals with various crystallographic orientations, after implantation of silicon ions and pulsed photon annealing

The results of experimental investigations of gallium arsenide single crystals with the orientations (100), (311)A, (211)A, (111)A, and (221)A are presented. The crystals were doped with silicon ions on the Iolla-3M setup (ion energy 75 keV, ion beam density 1 μA/cm², implantation dose 1.2×10³ cm⁻²) at room temperature and annealed on the Impul’s-5 setup at 950°C. Raman scattering and low-temperature photoluminescence methods established that the highest electrical activity of the implanted silicon under identical implantation and annealing conditions obtains for (100) and (311)A gallium arsenide. In the process n-type layers are produced. Zh. Tekh. Fiz. 69, 78–82 (May 1999) Deceased.     

Influence of fuel and media on membraneless sodium percarbonate fuel cell

This paper reports the media flexibility of membraneless sodium percarbonate fuel cell (MLSPCFC) using acid/alkaline bipolar electrolyte in which the anode is in acidic media while the cathode is in alkaline media, or vice versa. Investigation of the cell operation is conducted by using formic acid as a fuel and sodium percarbonate as an oxidant for the first time under ‘acid–alkaline media’ configurations. The MLSPCFC architecture enables interchangeable operation with different media combinations. The experimental results indicate that operating under acid–alkaline media conditions significantly improves the fuel cell performance compared with all-acidic and all-alkaline conditions. The effects of flow rates and the concentrations of various species at both the anode and cathode on the cell performance are also investigated. It has been demonstrated that the laminar flow-based microfluidic membraneless fuel cell can reach a maximum power density of 25.62 mW cm^?2 with a fuel mixture flow rate of 0.3 mL min^?1 at room temperature.     

Nitrogen-doped carbon nanofiber decorated LiFePO<Subscript>4</Subscript> composites with superior performance for lithium-ion batteries

Nitrogen-doped carbon nanofiber (NCNF) decorated LiFePO₄ (LFP) composites are synthesized via an in situ hydrothermal growth method. Electrochemical performance results show that the embedded NCNF can improve electron and ion transfer, thereby resulting in excellent cycling performance. The as-prepared LFP and NCNF composites exhibit excellent electrochemical properties with discharge capacities of 188.9 mAh g^?1 (at 0.2 C) maintained at 167.9 mAh g^?1 even after 200 charge/discharge cycles. The electrode also presents a good rate capability of 10 C and a reversible specific capacity as high as 95.7 mAh g^?1. LFP composites are a potential alternative high-performing anode material for lithium ion batteries.     

Determination of the Thermal Expansion Coefficient of Single-Wall Carbon Nanotubes by Raman Spectroscopy

We have examined the effect of high temperature on single-wall carbon nanotubes under air and nitrogen ambient by Raman spectroscopy. We observe the temperature dependence of the radial breathing mode and the G-band modes. The thermal expansion coefficient (β) of the bundled nanotubes is obtained experimentally using the estimated volume from Raman scattering. β behaves linearly with temperature from 0.33 × 10^?5 K^?1 to 0.28 × 10^?5 K^?1 in air and from 0.58 × 10^?5 K^?1 to 0.47 × 10^?5 K^?1 in nitrogen ambient, respectively. The temperature dependence of the radial breathing mode Raman frequencies is consistent with a pure temperature effect.     

Spectral and Computational Studies on Benzil Mono-(2-Pyridyl)Hydrazone

In the present study, structural properties of Mono-(2-Pyridyl) Hydrazone were studied extensively utilizing density functional theory (DFT) employing B3LYP exchange correlation. The Fourier transform infrared (solid phase) was recorded. The vibrational frequencies in the ground state were calculated by using density functional method (B3LYP) with 6-31G* and 6-311G** as basis sets. The spectral studies revealed that the title compound exists in Keto form. Spectral techniques that we employed include ¹H and ¹³C NMR, electronic, thermal techniques. Correlation between experimental chemical shifts and GIAO/B3LYP/6-311G**-calculated isotropic shielding constants, δ_exp = a + bσ_calc, are reported. Good linear regressions between experimental and theoretical results for ¹H and ¹³C were obtained.     

The conductivity and dielectric studies of solid polymer electrolytes based on poly (acrylamide-co-acrylic acid) doped with sodium iodide

Solid polymer electrolyte thin films based on polyacrylamide-co-acrylic acid (PAAC) doped with sodium iodide (NaI) with different ratios of polymer and salt added with fixed amount of additive of propylene carbonate (PC) were prepared by using solution casting method. The PC was added to the mixture of the solution to provide more flexibility to the polymer film by increasing the plasticity of the thin film membrane. The conductivity and dielectric studies were carried out on these thin films to understand the ion transport properties of the polymer electrolytes. The highest conductivity obtained was 1.88?×?10^?5 S cm^?1 for the 30% NaI salt-doped polymer electrolyte system at room temperature. The temperature-dependent conductivity agrees with Arrhenius relationship which shows that hopping mechanism of ions in the polymer matrix. The dielectric properties especially the loss tangent used to analyze the segmental relaxation of the polymer chain as more concentration of salt was incorporated. The electric modulus was studied to understand the electrical relaxation processes to overcome electrode polarization effect.