Performance improvement in chemical oxygen demand determination using carbon fiber felt/CeO<Subscript>2</Subscript>-β-PbO<Subscript>2</Subscript> electrode deposited by cyclic voltammetry method

A three-dimensional (3D) structured electrode in which a compact CeO₂-β-PbO₂ particle layer on each carbon fiber in the felt (denoted as CF/CeO₂-β-PbO₂) was fabricated using cyclic voltammetry (CV) method in the presence of CeO₂ nanoparticles in the electrolyte and supposed to be used as a sensor for in situ chemical oxygen demand (COD) detection. It was found that CeO₂ was codeposited with PbO₂ onto the anode, and the deposited crystals were tiny and compacted with each other. The electrochemical behaviors demonstrate that the fabricated CF/CeO₂-β-PbO₂ electrode possesses larger effective surface area, higher electrochemically catalytic activity, and better mechanical stability as compared with the anode without CeO₂ deposited by CV method or constant potential (CP) method. The results of COD determination by the fabricated CF/CeO₂-β-PbO₂ electrode show a sensitivity of (3.0 ± 0.02) × 10^?3 mA cm^?2/mg L^?1, a detection limit of 3.6 mg L^?1 (S/N = 3) and a linear range of 30–8500 mg L^?1 with correlation coefficient (R) of 0.9985 and RSD within 5 %.

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Graphical abstract A 3D CF/CeO₂-β-PbO₂ electrode with CeO₂-β-PbO₂ particle layer on each carbon fiber in the felt was supposed to be used as a sensor for in situ chemical oxygen demand (COD) detection. It was fabricated by cyclic voltammetry (CV) method in the presence of CeO₂ nanoparticles in the electrolyte containing Pb²⁺. It was found that CeO₂ was codeposited with PbO₂ onto the anode and the deposited particles became tinier and more compact. The addition of CeO₂ enhances the electrochemical catalytic activity. Tinier and more compact crystals enlarge the effective electrode area and improve the mechanical strength, which makes the CF/CeO₂-β-PbO₂ electrode possess higher detection sensitivity, wider linearity range, and longer service life in COD detection as compared with the anodes without CeO₂ fabricated by CV method or constant potential (CP) method.

     

Ro-vibrating energy states of a diatomic molecule in an empirical potential

An approximate analytical solution of the Schrödinger equation is obtained to represent the rotational–vibrational (ro-vibrating) motion of a diatomic molecule. The ro-vibrating energy states arise from a systematical solution of the Schrödinger equation for an empirical potential (EP) V _±(r) = D _e {1 ? (?/δ)[coth (ηr)]^±1/1 ? (?/δ)}² are determined by means of a mathematical method so-called the Nikiforov–Uvarov (NU). The effect of the potential parameters on the ro-vibrating energy states is discussed in several values of the vibrational and rotational quantum numbers. Moreover, the validity of the method is tested with previous models called the semiclassical (SC) procedure and the quantum mechanical (QM) method. The obtained results are applied to the molecules H₂ and Ar₂.     

Simultaneous Determination of Paracetamol and Caffeine in Human Plasma by LC–ESI–MS

A rapid, selective and convenient liquid chromatography–mass spectrometric method for the simultaneous determination of paracetamol and caffeine in human plasma was developed and validated. Analytes and theophylline [internal standard (I.S.)] were extracted from plasma samples with diethyl ether-dichloromethane (3:2, v/v) and separated on a C₁₈ column (150 × 4.6 mm ID, 5 μm particle size, 100 Å pore size). The mobile phase consisted of 0.2% formic acid–methanol (60:40, v/v). The assay was linear in the concentration range between 0.05 and 25 μg mL^?1 for paracetamol and 10–5,000 ng mL^?1 for caffeine, with the lower limit of quantification of 0.05 μg mL^?1 and 10 ng mL^?1, respectively. The intra- and inter-day precision for both drugs was less than 8.1%, and the accuracy was within ±6.5%. The single chromatographic analysis of plasma samples was achieved within 4.5 min. This validated method was successfully applied to study the pharmacokinetics of paracetamol and caffeine in human plasma.     

Enzymatic Hydrolysis of Black Liquor Xylan by a Novel Xylose-Tolerant,Thermostable β-Xylosidase from a Tropical Strain of <Emphasis Type="Italic">Aureobasidium pullulans</Emphasis> CBS 135684

From three cell-associated β-xylosidases produced by Aureobasidium pullulans CBS 135684, the principal enzyme was enriched to apparent homogeneity and found to be active at high temperatures (60–70 °C) over a pH range of 5–9 with a specific activity of 163.3 units (U) mg^?1. The enzyme was thermostable, retaining over 80% of its initial activity after a 12-h incubation at 60 °C, with half-lives of 38, 22, and 10 h at 60, 65, and 70 °C, respectively. Moreover, it was tolerant to xylose inhibition with a K _i value of 18 mM. The K _m and V _max values against p-nitrophenyl-β-d-xylopyranoside were 5.57 ± 0.27 mM and 137.0 ± 4.8 μmol min^?1 mg^?1 protein, respectively. When combining this β-xylosidase with xylanase from the same A. pullulans strain, the rate of black liquor xylan hydrolysis was significantly improved by up to 1.6-fold. The maximum xylose yield (0.812 ± 0.015 g g^?1 dry weight) was obtained from a reaction mixture containing 10% (w/v) black liquor xylan, 6 U g^?1 β-xylosidase and 16 U g^?1 xylanase after incubation for 4 h at 70 °C and pH 6.0.     

Synthesis,crystal structure,and thermodynamics of a high-nitrogen copper complex with <Emphasis Type="Italic">N</Emphasis>, <Emphasis Type="Italic">N</Emphasis>-bis-(1(2)H-tetrazol-5-yl) amine

A new high-nitrogen complex [Cu(Hbta)₂]·4H₂O (H₂bta = N,N-bis-(1(2)H-tetrazol-5-yl) amine) was synthesized and characterized by elemental analysis, single crystal X-ray diffraction and thermogravimetric analyses. X-ray structural analyses revealed that the crystal was monoclinic, space group P2(1)/c with lattice parameters a = 14.695(3) Å, b = 6.975(2) Å, c = 18.807(3) Å, β = 126.603(1)°, Z = 4, D _c = 1.888 g cm^?3, and F(000) = 892. The complex exhibits a 3D supermolecular structure which is built up from 1D zigzag chains. The enthalpy change of the reaction of formation for the complex was determined by an RD496–III microcalorimeter at 25 °C with the value of ?47.905 ± 0.021 kJ mol^?1. In addition, the thermodynamics of the reaction of formation of the complex was investigated and the fundamental parameters k, E, n, \( \Updelta S_{ \ne }^{{{\uptheta}}} \), \( \Updelta H_{ \ne }^{{{\uptheta}}} \), and \( \Updelta G_{ \ne }^{{{\uptheta}}} \) were obtained. The effects of the complex on the thermal decomposition behaviors of the main component of solid propellant (HMX and RDX) indicated that the complex possessed good performance for HMX and RDX.     

Fabrication and characterisation of a mixed oxide-covered mesh electrode composed of NiCo<Subscript>2</Subscript>O<Subscript>4</Subscript> and its capability of generating hydroxyl radicals during the oxygen evolution reaction in electrolyte-free water

A mixed oxide-covered mesh electrode composed of NiCo₂O₄ (MOME-NiCo₂O₄) was prepared on a stainless-steel substrate using thermal decomposition (slow-cooling rate method). Surface, bulk and electrochemical properties of MOME were studied using different techniques, namely scanning electron microscopy (SEM), X-ray diffraction (XRD), cyclic voltammetry (CV) with determination of the electrochemical porosity (?) and morphology factor (φ) parameters, quasi-stationary polarisation curves (PC) and electrochemical impedance spectroscopy (EIS). SEM images revealed a good coverage of the metallic wires by a compact oxide layer (absence of cracks). XRD analysis confirmed the formation of the spinel NiCo₂O₄ with the presence of NiO. The ‘in situ’ surface parameters denoted as ? and φ exhibited values of 0.39 and 0.33, respectively, revealing that the electrochemically active surface area is mainly confined to the ‘outer/external’ surface regions of the oxide layer. The PC was characterised by two Tafel slopes distributed in the low (b ₁ = 46 mV dec^?1) and high (b ₂ = 59 mV dec^?1) overpotential domains. The corresponding apparent exchange current densities were j ₀₍₁₎ = (3.43 ± 0.11) × 10^?6 A cm^?2 and j ₀₍₂₎ = (6.70 ± 0.08) × 10^?6 A cm^?2, respectively. The EIS study accomplished in the low-overpotential domain revealed a Tafel slope (b ₁) of 51 mV dec^?1. According to the spin-trapping reaction using N,N-dimethyl-p-nitrosoaniline (RNO), the MOME-NiCo₂O₄ electrode exhibited good performance for the generation of weakly adsorbed hydroxyl radicals (HO^?) during the OER in electrolyte-free water.     

Blue Photoluminescent Dimeric Cu(I) Dithiophosphates Bridged by a Flexible Ligand 1,2-Bis(4-Pyridyl)Ethane

The title compound {Cu[S₂P(OC₂H₅)₂](bpe)} _n (1) is constructed from flexible ligand bpe (bpe = 1,2-bis(4-pyridyl)ethane) and the Cu[S₂P(OC₂H₅)₂], which was characterized by single crystal structure determination, elemental analysis, XRD, and IR spectra. X-ray diffraction studies revealed that polymeric compound 1 consists of dinuclear module to form 1-D chains with the intramolecular Cu···Cu interactions (ca. 2.63 Å). This interaction may show a profound influence on the observed blue luminescence emission spectrum for 1. Crystal data for 1 at 293(2) K: Space group P ? 1, a = 9.277(3), b = 10.504 (4), c = 31.801(1) Å, α = 92.849(3), β = 90.401(2), γ = 114.547(7)°, V = 2813.9(2) ų, Z = 2, R ₁ = 0.041.     

Effect of Ag addition on crystallization kinetics and thermal stability of As–Se chalcogenide glasses

Chalcogenide glasses of (As₅₀Se₅₀)_100?xAg_x (0 ≤ x ≤ 25) were prepared using the melt quenching technique under non-isothermal conditions. Differential scanning calorimetry curves measured at different heating rates (5 ≤ β ≤ 40 K min^?1) are used to characterize the as-quenched samples. The thermal stability was monitored through the calculation of the temperature difference T _c ? T _g, stability parameter S and crystallization rate factor K _p. The glass-forming ability (GFA) was investigated on the basis of Hurby parameter H _r which is a strong indicator of GFA. In addition, the activation energy of glass transition E _t, activation energy of crystallization E _c and Avrami exponent n of the studied compositions were determined. The mechanism of crystallization was found to be a combination of two- and three-dimensional crystal growth.     

Synchrotron X-ray structures of cellulose I<Subscript>β</Subscript> and regenerated cellulose II at ambient temperature and 100 K

Synchrotron X-ray data have been collected to 1.4 Å resolution at the NE-CAT beam-line at the Advanced Photon Source from fibers of cellulose I_β and regenerated cellulose II (Fortisan) at ambient temperature and at 100 K in order to understand the effects of low temperature on cellulose more thoroughly. Crystal structures have been determined at each temperature. The unit cell of regenerated cellulose II contracted, with decreasing temperature, by 0.25%, 0.22% and 0.1% along the a, b, and c axes, respectively, whereas that of cellulose I_β contracted only in the direction of the a axis, by 0.9%. The value of 4.6×10^?5 K^?1 for the thermal expansion coefficient of cellulose I_β in the a axis direction can be explained by simple harmonic molecular oscillations and the lack of hydrogen-bonding in this direction. The molecular conformations of each allomorph are essential unchanged by cooling to 100 K. The room temperature crystal structure of regenerated cellulose II is essentially identical to the crystal structure of mercerized cellulose II.     

Yields of Hydrogen and Hydrogen Peroxide from Argon–Water Vapor in Dielectric Barrier Discharge

Controlled chemical transformation of water vapor in dielectric barrier discharge (DBD) of argon into hydrogen and hydrogen peroxide for its usability as in situ or ex situ H₂ and H₂O₂ source are reported. Online analysis of the product gas mixture by conventional wet-chemical colorimetric method using buffered KI absorber solution revealed typical H₂O₂ G-value = 6.4 × 10^?3 µmol J^?1 (G-value defines as the number of molecules produced/consumed per 100 eV of energy; in SI unit G-value is expressed in µmol J^?1) in the absence of ozone. On the other hand, H₂ in product mixture analyzed in gas chromatograph-thermal conductivity detector (GC-TCD) with argon carrier revealed its G-value = 0.134 µmol J^?1. Enhancements in products’ yields were explored by varying gas residence time inside the plasma zone, and applied voltage and frequency on the dielectric surfaces. Employing a double-DBD reactor, at applied high voltage ~2.5 kV mm^?1 @50 Hz and gas residence time ~20 s resulted in the highest yields of H₂O₂. However, the H₂ yield increased continuously with increase in gas residence time. On the other hand, the single-dielectric barrier surface reactors were more efficient for high and exclusive generation of ex situ H₂ (e.g. maximum 1260 ppm; G-value typically 0.498 µmol J^?1).     

The sol–gel chromium-modified V<Subscript>6</Subscript>O<Subscript>13</Subscript> as a cathodic material for lithium batteries

A new V₆O₁₃-based material has been synthesized via the sol–gel route. This sol–gel mixed oxide has been obtained from an appropriate heat treatment of the chromium-exchanged V₂O₅ xerogel performed under reducing atmosphere. This new compound, with the chemical formula Cr_0.36V₆O_13.50, exhibits a monoclinic structure (C2/m) with the following unit cell parameters, a=11.89 Å, b=3.68 Å, c=10.14 Å, β=101.18°. The electrochemical characterization of this compound has been performed using galvanostatic discharge–charge experiments in the potential range 4–1.5 V and completed by ac impedance spectroscopy measurements. It exhibits a specific capacity of about 370 mAh g^?1, which makes the compound Cr_0.36V₆O_13.50 the best one in the V₆O₁₃-based system: 85% of the initial capacity (315 mAh g^?1) after the 35th cycle is still available at C/25 without any polarization. From impedance spectroscopy, a high kinetics of Li transport (D _Li=1.8×10^?9 cm² s^?1) is found at mid-discharge.     

Structure,bioactivity and theoretical study of 1-cyano-<Emphasis Type="Italic">N</Emphasis>-p-tolylcyclo-propanecarboxamide

A novel cyclopropane derivative, 1-cyano-N-p-tolylcyclopropanecarboxamide (C₁₂H₁₂N₂O, Mr = 200.24) was synthesized and its structure was studied by X-ray diffraction, FTIR, ¹H and ¹³C NMR spectrum and MS. The crystals are monoclinic, space group P2_1/c with a = 7.109 (4), b = 13.758 (7), c = 11.505 (6) Å, α = 90.00, β = 102.731 (8), γ = 90.00 °, V = 1097.6 (9) ų, Z = 4, F(000) = 312, D _c  = 1.212 g/cm³, μ = 0.0800 mm^?1, the final R = 0.0490 and wR = 0.1480 for 1,375 observed reflections with I > 2σ(I). A total of 6,109 reflections were collected, of which 2,290 were independent (R _int = 0.0290). Theoretical calculation of the title compound was carried out with HF/6-31G (d,p), B3LYP/6-31G (d,p), MP2/6-31G (d,p). The full geometry optimization was carried out using 6-31G(d,p) basis set, and the frontier orbital energy. Atomic net charges were discussed, and the structure-activity relationship was also studied. The preliminary biological test showed that the synthesized compound is bioactive against the KARI of Escherichia coli.     

Stability of gold(I) glycinate complexes in aqueous solution

The stepwise substitution equilibrium AuCl ₂ ^? +iX^?=AuCl_2?i X _i ^? +iCl^?, β_i, where X^? is the glycinate ion (H₂N-CH₂-COO^?), i = 1 or 2, at 25°C in an aqueous solution with I = 1.0 mol/L (NaCl) has been studied pH-metrically. The corresponding constants are logβ₁ = 3.60 ± 0.10, and logβ₂ = 6.2 ± 0.2.     

Thermodynamic Study on the Protonation and Na<Superscript>+</Superscript>, Ca<Superscript>2+</Superscript>, Mg<Superscript>2+</Superscript>-Complexation of a Biodegradable Chelant (HEIDA) at Different Ionic Strengths and Temperatures

A potentiometric method has been used for the determination of the protonation constants of N-(2-hydroxyethyl)iminodiacetic acid (HEIDA or L) at various temperatures 283.15?≤?T/K?≤?383.15 and different ionic strengths of NaCl_(aq), 0.12?≤?I/mol·kg^?1?≤?4.84. Ionic strength dependence parameters were calculated using a Debye–Hückel type equation, Specific Ion Interaction Theory and Pitzer equations. Protonation constants at infinite dilution calculated by the SIT model are \( \log_{10} \left( {{}^{T}K_{1}^{\text{H}} } \right) = 8.998 \pm 0.008 \) (amino group), \( \log_{10} \left( {{}^{T}K_{2}^{\text{H}} } \right) = 2.515 \pm 0.009 \) and \( \log_{10} \left( {{}^{T}K_{3}^{\text{H}} } \right) = 1.06 \pm 0.002 \) (carboxylic groups). The formation constants of HEIDA complexes with sodium, calcium and magnesium were determined. In the first case, the formation of a weak complex species, NaL, was found and the stability constant value at infinite dilution is log₁₀K_NaL?=?0.78?±?0.23. For Ca²⁺ and Mg²⁺, the CaL, CaHL, CaL₂ and MgL species were found, respectively. The calculated stability constants for the calcium complexes at T?=?298.15 K and I?=?0.150 mol·dm^?3 are: log₁₀β_CaL?=?4.92?±?0.01, log₁₀β_CaHL?=?11.11?±?0.02 and \( \log_{10} \beta_{\text{Ca{L}}_{2}} \)?=?7.84?±?0.03, while for the magnesium complex (at I?=?0.176 mol·dm^?3): log₁₀β_MgL?=?2.928?±?0.006. Protonation thermodynamic functions have also been calculated and interpreted.     

Apparent Molar Volumes of Aqueous Solutions of Magnesium Tetraborate from 283.15 to 363.15 K and 0.1 MPa

Densities for aqueous solutions of magnesium tetraborate MgB₄O₇(aq) at the molalities of (0.00556–0.03341) mol·kg^?1 were measured with an Anton Paar Digital vibrating-tube densimeter at temperature intervals of 5 K from 283.15 to 363.15 K and 0.1 MPa. Apparent molar volumes were obtained based on the experimental density data, and the 3D diagrams of the apparent molar volume (V _? ) of MgB₄O₇(aq) against temperature (T) and molality (m) were plotted. On the basis of the Vogel–Tamman–Fulcher equation, the coefficients of the correlation equation for densities of MgB₄O₇(aq) against temperature and molality were parameterized. According to the Pitzer ion-interaction model of the apparent molar volume, the temperature correlation equations of Pitzer single-salt parameters F(i,p,T)?=?a₀?+?a₁?×?T?+?a₂?×?T ²?+?a₃/T?+?a₄?×?ln(T)?+?a₅?×?T ³ (where T is temperature in Kelvin, a _i are model parameters) for MgB₄O₇ were obtained for the first time.     

Enhanced lithium-ion intercalation and conduction of transparent tantalum oxide films by lithium addition with an atmospheric pressure plasma jet

An investigation is conducted on enhancing lithium-ion intercalation and conduction performance of transparent organo tantalum oxide (TaO _y C _z ) films, by addition of lithium via a fast co-synthesis onto 40 Ω/□ flexible polyethylene terephthalate/indium tin oxide substrates at the short exposed durations of 33–34 s, using an atmospheric pressure plasma jet (APPJ) at various mixed concentrations of tantalum ethoxide [Ta(OC₂H₅)₅] and lithium tert-butoxide [(CH₃)₃COLi] precursors. Transparent organo-lithiated tantalum oxide (Li _x TaO _y C _z ) films expose noteworthy Li⁺ ion intercalation and conduction performance for 200 cycles of reversible Li⁺ ion intercalation and deintercalation in a 1 M LiClO₄-propylene carbonate electrolyte, by switching measurements with a potential sweep from ?1.25 to 1.25 V at a scan rate of 50 mV/s and a potential step at ?1.25 and 1.25 V, even after being bent 360° around a 2.5-cm diameter rod for 1000 cycles. The Li⁺ ionic diffusion coefficient and conductivity of 6.2?×?10^?10 cm²/s and 6.0?×?10^?11 S/cm for TaO _y C _z films are greatly progressed of up to 9.6?×?10^?10 cm²/s and 7.8?×?10^?9 S/cm for Li _x TaO _y C _z films by co-synthesis with an APPJ.     

The solubility and kinetics of decomposition of ozone in aqueous solutions of nitrates

The influence of the concentration of NaNO₃ on the solubility of ozone in water was studied at 20, 30, and 40°C. The solubility coefficients of ozone were calculated, and the Henry constants and Sechenov coefficients determined. The Sechenov coefficients (K _c ) were found to decrease insignificantly as the temperature increased. The kinetics of dissolved O₃ transformations was analyzed. The decomposition of ozone was described by a pseudofirst-order equation with respect to salt concentration. The rate constant (k _c ) for the decomposition of ozone in the presence of NaNO₃ was found to be 3.5 × 10^?4 l mol^?1 s^?1.     

Simultaneous Spectrophotometric Determination of Paracetamol and <Emphasis Type="Italic">p</Emphasis>-Aminophenol in Pharmaceutical Products with Tiron Using Dissolved Oxygen as Oxidant

A simple, rapid, and specific method was developed for the determination of paracetamol and p-aminophenol. The method is based on the hydrolysis of paracetamol to p-aminophenol, which, using dissolved oxygen as an oxidant in the alkaline region, was further transformed into benzoquinoneimine, capable of reacting with tiron to produce a green indophenol dye. The stabilization of indophenol dye was achieved by the addition of copper(II) solution. The absorbance was measured at 601 nm in alkaline medium, and the molar absorptivity was found to be 1.1 × 10⁴ L/(mol cm). Paracetamol (PCT) and p-aminophenol (PAP) were determined in pharmaceutical products in the 1.5–15 mg/L PAP concentration range with a detection limit of 1.2 × 10⁻⁶ M or 0.13 μg/mL PAP. The developed method can be applied to the determination of p-aminophenol in the presence of paracetamol without prior separation. The proposed method is successfully employed for determination of paracetamol and p-aminophenol in various synthetic mixtures and pharmaceutical preparations. The obtained results were statistically compared with those given by the official method and the procedures evaluated as regards to both figures of merit and ease of applicability. __________ From Zhurnal Analiticheskoi Khimii, Vol. 60, No. 11, 2005, pp. 1147–1151. Original English Text Copyright ? 2005 by Cekic, Filik, Apak. This article was submitted by the authors in English.     

Experimental investigation of radiocesium sorption on ceramic clay using a batch method

In this study, radiocesium sorption on ceramic clay was investigated as a function of particle size and initial ¹³⁷Cs concentration using a batch method. Ceramic clay samples taken from the Sö?üt(?nisar) clay deposit were composed of kaolinite, dickite and quartz. The equilibrium time and the liquid–solid ratio were determined as 60 min and 250 mL g^?1, respectively. The distribution coefficients (K _d) for variable liquid–solid ratio and the percentage adsorption (P _Ad) were calculated. The values of K _d and P _Ad ranged from 483 to 3165 mL g^?1 and 34–93%, respectively. The K _d and P _Ad values increased with increasing particle size, but decreased with increasing initial concentration. The sorption data were interpreted in terms of a Langmuir isotherm. The results indicated that the Sö?üt(?nhisar) ceramic clay has good sorption capacity for cesium.     

Synthesis,crystal structure,and hydrogen-bonded displacive-type structural phase transition of guanidine dichloroacetate

Guanidine dichloroacetate was synthesized and separated as crystals. Differential scanning calorimetry (DSC) measurement shows that this compound undergoes a reversible phase transition at about 275 K with a heat hysteresis of 28 K. Step-like dielectric anomaly observed at 274 K further confirms the phase transition. The single-crystal X-ray diffraction data suggested that these was a transition from a room-temperature phase with the space group of P2₁/n (a = 8.030(5), b = 12.014(9), c = 8.124(6) Å, β = 96.089(1)°, V = 779.3(1) Å³, and Z = 4) to a low-temperature one with the space group of P2₁/c (a = 7.941(2), b = 11.828(3), c = 10.614(2) Å, β = 130.985(1)°, V = 752.6(3) Å³, and Z = 4). The displacements of hydrogen bonds induce the structure phase transition.