Determination of sodium ion diffusion coefficients in sodium vanadium phosphate

Carbon-coated Na₃V₂(PO₄)₃ (NVP) was prepared by a standard sol–gel procedure. The apparent diffusion coefficients of sodium ions in the rhombohedral NVP have been determined by different techniques such as galvanostatic intermittent titration technique (GITT) and cyclic voltammetry (CV). It was found that the apparent diffusion coefficients range from 6?×?10^?13 cm² s^?1 to 2?×?10^?15 cm² s^-1. These sodium ion apparent diffusion coefficients follow a similar trend as observed for lithium ions in the closely related monoclinic modification of Li₃V₂(PO₄)₃, demonstrating a minimum at the potential where the ion extraction/insertion occurs.     

Electrocatalytic oxidation of methanol by ZSM-5 nanozeolite-modified carbon paste electrode in alkaline medium

Development of a novel modified electrode for electrocatalytic oxidation of methanol in order to decrease overvoltage is importance. In this paper, carbon paste electrode (CPE) was modified by ZSM-5 nanozeolite. The average diameter of used nanozeolite was 97 nm. Ni²⁺ ions were incorporated to the nanozeolite by immersion of the modified electrode in a 0.1 M nickel chloride solution. Then, electrochemical studies of this electrode were performed by using cyclic voltammetry(CV) in alkaline medium. This modified electrode was used as an anode for the electrocatalytic oxidation of methanol in 0.1 M of NaOH solution. The obtained data demonstrated that ZSM-5 nanozeolite at the surface of CPE improves catalytic efficiency of the dispersed nickel ions toward methanol oxidation. The values of electron transfer coefficient, charge-transfer rate constant, and the electrode surface coverage are obtained 0.61, 0.2342 s^?1, and 4.33 × 10^?8 mol cm^?2, respectively. Also, the mean value of catalytic rate constant between the methanol and redox sites of electrode and diffusion coefficient were found to be 2.54 × 10⁴ cm³ mol^?1 s^?1 and 1.85 × 10^?8 cm² s^?1, respectively. Obtained results from both CV and chronoamperometric techniques indicated that the electrode reaction is a diffusion-controlled process.     

Synergistic solvent extraction of copper, cobalt, rhodium and iridium into 1, 2-Dichloroethane at trace level by newly synthesized 25, 26, 27, 28-tetrahydroxy-5, 11, 17, 23-tetra-[4-(N-hydroxyl-3-phenylprop-2-enimidamido) phenylazo] calix[4]arene

A spectrophotometric method for determination of copper, cobalt, rhodium and iridium ions from nitric acid media after extraction of these ions by 25, 26, 27, 28-tetrahydroxy-5, 11, 17, 23-tetra-[4-(N-hydroxyl-3-phenylprop-2-enimidamido) phenylazo] calix [4] arene (THPAC) has been developed and possible synergistic effect has been investigated. The maximum enhancement was obtained in the presence of 30% 1, 2-dichloroethane in DMF and 3M nitric acid. The trace amounts of the metal were determined spectrophotometrically. Beer’s law was obeyed in concentration range 5.0–10.0 μg, 6.0–120.0 μg, 12.0–100.0 μg, and 10.0–130.0 μg/10 mL of the final solution of copper, cobalt, rhodium and iridium, respectively. The molar absorptivities (l mol^?1 cm^?1) and Sandell’s sensitivities (μg cm^?1) were calculated: Cu (II) = 0.96 × 10^4, 0.0066; Co (II) = 1.13 × 10⁴, 0.0052; Rh (III) = 0.98 × 10⁴, 0.012; and Ir (III) = 2.03 × 10⁴, 0.0095, respectively. Seven replicate analyses containing of 20.0 μg of Cu (II), 24.0 μg of Co (II), 36.0 μg of Rh (III) and 25.0 μg of Ir (III) gave mean absorbance 0.302, 0.462, 0.344, 0.264; and relative standard deviation 0.65, 0.85, 1.10, 1.08%, respectively. The interference of various ions was studied and optimum conditions were developed for determination of metals in certain alloys, environmental, pharmaceutical and synthetic samples.     

Ion-Molecule reactions in methylamine and dimethylamine and trimethylamine systems

Fourier transform ion cyclotron resonance mass spectrometry has been used to measure the reaction rates for ions derived from methylamine with dimethylamine or trimethylamine. The use of the selective ion ejection technique greatly simplifies the elucidation of the ion-molecule reaction channels. The rate constants for proton transfer from protonated metwlamine, CH₃NH ₃ ⁺ (m/z 32), to dimethylamine and trimethylamine are 16.1 ± 1.6 × 10^?10 and 9.3 ± 0.9 × 10^?10 cm³ molec^?1s^?1, respectively. The rate constants for charge transfer from methylamine molecular ion, CH₃NH ₂ ⁺ (m/z 31), to dimethylamine and trimethylamine are 9.3 ± 1.8 x 10^?10 and 15.0 ± 5 × 10^?10 cm³molec^?1s^?1, respectively.     

Equilibrium isotherms and isosteric heat for CO<Subscript>2</Subscript> adsorption on nanoporous carbons from polymers

Four nanoporous carbons obtained from different polymers: polypyrrole, polyvinylidene fluoride, sulfonated styrene–divinylbenzene resin, and phenol–formaldehyde resin, were investigated as potential adsorbents for carbon dioxide. CO₂ adsorption isotherms measured at eight temperatures between 0 and 60 °C were used to study adsorption properties of these polymer-derived carbons, especially CO₂ uptakes at ambient pressure and different temperatures, working capacity, and isosteric heat of adsorption. The specific surface areas and the volumes of micropores and ultramicropores estimated for these materials by using the density functional theory-based software for pore size analysis ranged from 840 to 1990 m² g^?1, from 0.22 to 1.47 cm³ g^?1, and from 0.18 to 0.64 cm³ g^?1, respectively. The observed differences in the nanoporosity of these carbons had a pronounced effect on the CO₂ adsorption properties. The highest CO₂ uptakes, 6.92 mmol g^?1 (0 °C, 1 atm) and 1.89 mmol g^?1 (60 °C, 1 atm), were obtained for the polypyrrole-derived activated carbon prepared through a single carbonization-KOH activation step. The working capacity for this adsorbent was estimated to be 3.70 mmol g^?1. Depending on the adsorbent, the CO₂ isosteric heats of adsorption varied from 32.9 to 16.3 kJ mol^?1 in 0–2.5 mmol g^?1 range. Overall, the carbons studied showed well-developed microporosity and exceptional CO₂ adsorption, which make them viable candidates for CO₂ capture, and for other adsorption and environmental-related applications.     

Synthesis and electrochemical properties of a novel calix[4]arene derivative for facilitated transfer of alkali metal ions across water/1,2-dichloroethane micro-interface

The alkali metal ion transfers facilitated by a novel calix[4]arene derivative (OPEC) across the water/1,2-dichloroethane (1,2-DCE) micro-interface supported at the tip of a micropipette were presented. The well-defined voltammetric behaviours except Cs⁺ was obtained by cyclic voltammetry and differential pulse voltammetry. The bulk concentration of metal ions was much higher than that of OPEC in the performed measurements. The diffusion coefficient of OPEC in the 1,2-DCE phase was calculated as 5.18 ± 0.70 × 10^? 6 cm² s^? 1. On the basis of the changes of the half-wave transfer potentials, the logarithms of the association constants having 1:1 ionophore–ion complex stoichiometry for Li⁺, Na⁺, K⁺ and Rb⁺ in 1,2-DCE were determined as 4.80, 4.62, 4.98 and 5.32, respectively. The facilitated ion transfers were also evaluated by the Randles equivalent circuit used for ac-impedance data analysis.     

Electroanalytical Characteristics of Lercanidipine and its Voltammetric Determination in Pharmaceuticals and Human Serum on Boron-Doped Diamond Electrode

The electrooxidative behavior and determination of lercanidipine (LRC) were investigated in aqueous acetonitrile medium at a boron-doped diamond electrode using voltammetric techniques. The LRC in selected supporting electrolyte presents a well-defined anodic response at 0.944 V, studied by the proposed method. The linear response was obtained in the ranges of 4 × 10^?6 to 2 × 10^?4 mmol L^?1 range in 0.5 mmol L^?1 sulfuric acid supporting electrolyte and 1 × 10^?5 to 8 × 10^?5 mmol L^?1 range in spiked serum sample for square wave voltammetric technique. No electroactive interferences from the excipients and endogenous substances were found in the pharmaceutical dosage form and in the biological sample, respectively.     

Self-assembling of Prussian blue nanocubic particles on nanoporous glassy carbon and its use in the electrocatalytic reduction of hydrogen peroxide

In this paper, self-assembled Prussian blue nanocubic particles on nanoporous glassy carbon was developed. The morphology of the PBNP-modified porous glassy carbon was characterized by scanning electron microscopy. The PBNP-GCE-red film-modified electrode was used for the sensitive detection of hydrogen peroxide. The electrochemical behavior of the resulting sensor was investigated using cyclic voltammetry and chronoamperometry. The value of α, k _cat, and D was calculated as 0.35, 1.7 × 10⁵ cm³ mol^?1 s^?1, and 2.6 × 10^?5 cm² s^?1, respectively. The calibration curve for hydrogen peroxide determination was linear over 0–600 μM with a detection limit (S/N = 3) of 0.51 μM.     

Adsorption of 103Ru from aqueous solutions by clinoptilolite

The aim of this research is adsorption of ruthenium by natural zeolite, clinoptilolite. The experimental conditions were optimized in order to obtain higher adsorption capacity and the study was done under optimum conditions. Maximal adsorption capacity was obtained using ¹⁰³Ru as a tracer at 25 °C, pH 2.0 and contact time of 10 h and found to be 0.074 meq g^?1. Ruthenium measurments were done using inductively coupled plasma-optical emission spectrometry (ICP-OES) and gamma spectrometer methods. Break points were calculated from breakthrough curve at the 1%, 5% and 50%. The obtained results are respectively 2.8, 4.5 and 19.5 mL, which are equal to 2.5 × 10^?3, 1.35 × 10^?2 and 5.85 × 10^?2 meq g^?1. Desorption behavior of column packed zeolite using some eluents was also investigated. The highest recovery of 97.4 ± 0.2% was obtained using 2 mol L^?1 HCl solution as an eluent. The results of this study can be used for separation and preconcentration of ruthenium.     

Synthesis of γ-LiV2O5 nanorods as a high-performance cathode for Li ion battery

One-dimension γ-LiV₂O₅ nanorods were synthesized using VO₂(B) nanorods as precursor in this study. The as-prepared material is characterized by X-ray diffraction, X-ray photoelectron spectrometry, Fourier-transform infrared, transmission electron microscopy (TEM), cyclic voltammetry, and charge–discharge cycling test. TEM results show that LiV₂O₅ nanorods are 90–250 nm in diameter. The nanorods deliver a maximum discharge capacity of 284.3 mAh g^?1 at 15 mA g^?1 and 270.2 mAh g^?1 is maintained at the 15th cycle. Good rate performance is also observed with the discharge capacity of 250.1 and 202.6 mAh g^?1 at 50 and 300 mA g^?1, respectively. The capacity retention at 300 mA g^?1 is 84.2% over 50 cycles. The Li⁺ diffusion coefficient of LiV₂O₅ is calculated to be 10^-10–10^?9 cm² s^?1. It is demonstrated that the nanorod morphology could greatly facilitate to shorten lithium ion diffusion pathways and increase the contact area between active material and electrolyte, resulting in high capacity and rate performance for LiV₂O₅.     

Construction of a new solid-state U(VI) ion-selective electrode based on polypyrrole conducting polymer

In this study, a potentiometric sensor based on a pencil graphite electrode (PGE) coated with polypyrrole doped with uranyl zinc acetate (termed PGE/PPy/U) have been prepared for potentiometric determination of uranyl in aqueous solutions. Electropolymerization reaction for preparing of U(VI) sensor electrode was carried via applying a constant current of 1.0 mA on PGA working electrode in a solution containing 8.0 mM pyrrole and 0.8 mM ZnUO₂(CH₃COO)₄ salt. The constructed electrode displayed a linear and near Nernstian response (22.60 ± 0.40 mV/decade) to U(VI) ions in the concentration range of 1.0 × 10^?6–1.0 × 10^?2 M. A detection limit of 6.30 × 10^?7 M and a fast response time (≤12 s) was observed during measurements. The working pH range of the electrode was 4.0–8.0 and lifetime of the sensor was at least 60 days. The electrode revealed good selectivity with respect to many cations including alkali, alkaline earth, transition and heavy metal ions. The introduced uranyl electrode was used for measurement of U(VI) ion in real samples without any serious inferences from other ions.     

Simple chemical route for nanorod-like cobalt oxide films for electrochemical energy storage applications

We used a simple chemical synthesis route to deposit nanorod-like cobalt oxide thin films on different substrates such as stainless steel (ss), indium tin oxide (ITO), and microscopic glass slides. The morphology of the films show that the films were uniformly spread having a nanorod-like structure with the length of the nanorods shortened on ss substrates. The electrochemical properties of the films deposited at different time intervals were studied using cyclic voltammetry (CV), galvanostatic charge–discharge (GCD), and electrochemical impedance spectroscopy (EIS). The film deposited after 20 cycles on ss gave the highest specific capacity of 67.6 mAh g^?1 and volumetric capacity of 123 mAh cm^?3 at a scan rate 5 mV s^?1 in comparison to 62.0 mAh g^?1 and 113 mAh cm^?3 obtained, respectively, for its counterpart on ITO. The film electrode deposited after 20 cycles on ITO gave the best rate capability and excellent cyclability with no depreciation after 2000 charge–discharge cycles.     

Polyvinyl alcohol fibers with functional phosphonic acid group: synthesis and adsorption of uranyl (VI) ions in aqueous solutions

PVA functionalized with vinylphosphonic acid was prepared as a new adsorbent for uranyl (VI) adsorption from aqueous solutions. The vinylphosphonic acid was cografted onto PVA fibers by preirradiation grafting technique. The adsorbent were characterized by Fourier transform infrared spectroscopy and scanning electron microscopy. The adsorbent was observed to possess a fibrous structure and was bonded with phosphonic acid groups successfully. The adsorbent was used for the adsorption of low levels uranyl (VI) ions from aqueous solutions. The influence of analytical parameters including pH, adsorption time, amount of adsorbent, metal ion concentration, and temperature were investigated on the recovery of uranyl (VI) ion in aqueous solution. The maximum adsorption capacity (32.1 mg g^?1) and fast equilibrium time (30 min) were achieved at pH of 4.5 at room temperature. Thermodynamic parameters (ΔH° = 2.695 kJ mol^?1; ΔS° = 31.15 J mol^?1 K^?1; ΔG° = ?6.748 kJ mol^?1) show the adsorption of an exothermic process and spontaneous nature, respectively. The possible coordination mechanism was illustrated. Adsorption and desorption coexist in aqueous solutions and then the system becomes equilibrium.     

Influence of sodium addition on taurine adduct formation generated in acetic acid/acetate salt buffer applied in LC–MS/MS analysis

To investigate the influence of sodium ion addition on analyte adduct formation generated in acetic acid/acetate salt buffer appropriate infusion experiments of a 1 and 10 μg/mL taurine solution prepared both in methanol with a 1 mmol L^?1/10 mmol L^?1 CH₃COONH₄/CH₃COOH buffer and with a 1 mmol L^?1/10 mmol L^?1 CH₃COONa/CH₃COOH buffer were performed. The results achieved revealed that sodium ion concentration has a relevant influence on taurine adduct formation in the negative electrospray ionisation mode since depending on conditions applied different analyte adducts are favored. Sodium ions which originate from the glassware/chemicals make an effective detection of taurine dimer adducts possible, but taurine adducts with sodium acetate are not formed effectively. On the other side sodium ion addition enables an effective taurine adduct formation with sodium acetate, but taurine dimer based adducts can be observed only at higher analyte concentrations.     

Electrochemical reduction of ytterbium in perchloric media

The electrochemical behavior of Yb³⁺ in perchloric media was studied by cyclic voltammetry and current reversal chronopotentiometry at several temperatures. The results show that the reversible electrochemical reduction of Yb³⁺ is followed by homogeneous reactions. The experimentally determined diffusion coefficients of ytterbic ion are 0.41×10^?5, 0.48×10^?5 and 0.53×10^?5 cm² s^?1 at 4.2, 9.2 and 14.7°C, respectively, in 0.5 M NaClO₄ solutions. From these data a value of 16 kJ mol^?1 (3830 cal mol^?1) was obtained for the activation energy for diffusion of ytterbic ion. From the activation energy the diffusion coefficient of ytterbic ion at 25.0°C was estimated. The value of 0.67×10^?5 cm² s^?1 was obtained. In all the experiments the initial pH was maintained at 4.1.     

Electrocatalysis of Horseradish Peroxidase Immobilized on Cobalt Nanoparticles Modified ITO Electrode

Abstract

It is the first time that Horseradish peroxidase (HRP) was successively immobilized on the magnetic cobalt nanoparticles modified ITO (indium tin oxide) electrode. Morphologies of electrode surface were featured by the field emission‐scanning electron microscope (FSEM). Cyclic voltammetry (CV) and electrochemical impedance spectroscopy (EIS) were used to characterize the modified process of electrode. Direct electrochemistry and electrocatalysis of HRP immobilized on nano‐Co/ITO were investigated. The biosensor exhibited high sensitivity, good stability, and excellent electrocatalytic activity to the reduction of H₂O₂. Under the optimized experimental conditions, a calibration curve over 2.0×10^?9～2.0×10^?8 mol l^?1 and 2.0×10^?7～2.0×10^?6 mol l^?1, with a limit of detection of 1.9×10^?9 mol l^?1 was obtained. The apparent Michaelis‐Menten constant (K _M ^app ) for HRP/nano‐Co/ITO electrode was calculated to be 0.79 mmol l^?1, indicating a higher affinity of HRP attached on the modified electrode.     

Dielectric and conductivity studies of 90 MeV O7+ ion irradiated poly(ethylene oxide)/montmorillonite based ion conductor

In the present work effect of 90 MeV O⁷⁺ ions with five different fluences on poly(ethylene oxide) (PEO)/Na⁺-montmorillonite (MMT) nanocomposites has been investigated. PEO/MMT nanocomposites were synthesized by solution intercalation technique. With the increase in irradiation fluence, gallery spacing of MMT increases in the composite and an exfoliated nanostructure is obtained at the fluence of 5?×?10¹² ions/cm² as revealed by X-ray diffraction results. Highest room temperature ionic conductivity of 4.2?×?10^?6?S?cm^?1 was found for the fluence 5?×?10¹² ions/cm², while the conductivity for unirradiated polymer electrolyte was found to be 7.5?×?10^-8?S?cm^?1. The increase in intercalation of PEO chains inside the galleries of MMT results in the increase in interaction between Na⁺ cation and oxygen heteroatom leading to the increase in ionic conductivity of the composites. Surface morphology and interactions among the various constituents in the nanocomposites at different fluence have been examined by scanning electron microscopy and Fourier transform infrared spectroscopy, respectively. The appearance of peak for each fluence in the loss tangent suggests the presence of relaxing dipoles in the polymer nanocomposite electrolyte films. With the increase in ion fluence the peak shifts towards higher frequency side, suggesting decrease in the relaxation time.     

Electrochemical Properties of Th(IV)‐Hexacyanoferrate Sol‐Gel Carbon Composite Electrode: Electrocatalytic Oxidation of Dopamine and Ascorbic Acid

A new sol‐gel carbon composite electrode using hexacyanoferrate (HCF)‐Th(IV) ion pair as a suitable modifier is fabricated in the present study. The Th(IV)‐HCF‐sol‐gel carbon composite electrode (THCF‐CCE) has been prepared by mixing methyl trimethoxysilan (MTMOS) sol‐gel precursor and carbon powder with ion pair and then to fix in a plastic tube. Cyclic voltammetry and chronoamperometry were employed to study the electrochemical and electrocatalytic properties of proposed electrode. The apparent charge transfer rate constant, k_s, and transfer coefficient, α, for electron transfer between ion‐pair and sol‐gel CPE were calculated as 3.10 ± 0.10 s^?1 and 0.52, respectively. The THCF‐CCE showed a significant electrocatalytic activity towards oxidation of ascorbic acid (AA) and dopamine (DA) in 0.1 M acidic phosphate buffer solutions (pH 3) containing KCl as a supporting electrolyte. The mean value of the diffusion coefficients for ascorbic acid and dopamine were found 4.12 × 10^?5 and 4.43 × 10^?5 (cm²s^?1), respectively. High stability, good reproducibility, rapid response, easy surface regeneration and fabrication are the important characteristics of the proposed sensor. The resulting peaks from the electrocatalytic oxidation of AA and DA were well resolved with good sensitivity. A linear response was observed for AA and DA in the concentration range of 1 × 10^?5 to 3 × 10^?3 M and 4 × 10^?6 to 2.2 × 10^?4 M, respectively.     

Study of 10Be in the sediments from the Krossfjorden and Kongsfjorden Fjord System,Svalbard

The distribution of ¹⁰Be, as well as the major elements concentrations and the grain size in surface and core sediment samples, collected from Krossfjorden and Kongsfjorden, Svalbard have been studied for understanding the origin of ¹⁰Be and an estimation of its accumulation rate. The ¹⁰Be concentration in sediments varies between 0.90 × 10⁸ and 2.53 × 10⁸ atoms g^?1. Our results show that atmospherically produced ¹⁰Be dominates over terrigenous (in situ) sources of ¹⁰Be in the studied samples. The calculated ¹⁰Be accumulation rate varies from 3.1 × 10⁶ atoms cm^?2 year^?1 to 8.6 × 10⁶ atoms cm^?2 year^?1 which is higher than the accumulation rate observed in the deep sea sediment cores of the Arctic Ocean and the Norwegian Sea. The higher accumulation rate of ¹⁰Be is attributed to the higher influx of glacier melt water into the fjord system.     

Spectrophotometric Determination of Cobalt,Nickel and Palladium after Extraction with Thioxanthate into Molten Naphthalene

Cobalt, nickel and palladium have been extracted with thioxanthate into molten naphthalene (85–90°C). Various parameters involved in the extraction have been studied and composition of the extracted complex established in each case. Cobalt. nickel and palladium thioxanthates are extracted in the pH range, Co: 5.0–9.5. Ni: 3.9–7.4 and Pd: 2.0–9.5 and can be determined spectrophotometrically at 390. 500 and 345 nm respectively. The molar absorptivities are calculated to be Co: 6.187×10³ ? mol^?1 cm^?1, Ni: 8.8×10³ ? mol^?1 cm^?1 and Pd: 1.16×10⁴ ? mol^?1 cm^?1 with sensitivities in terms of Sandell's defication are; 0.0095 μg Co/cm² at 390 nm, 0.0060 μg Ni/cm² at 500 nm and 0.0091 μg Pd/cm² at 345 nm respectively. These conditions have been utilized for the determination of these metals in alloys and also for the simultaneous determination of cobalt and nickel in an alloy.