Ionic Liquid as an Alternative Greener Sensing Medium for the Chemical Warfare Agent

Greener electrochemical detection method developed for chemical warfare agent (CWA) nitrogen mustard‐2 (NM‐2) using room temperature ionic liquid (RTIL). The diffusion coefficient calculated for NM‐2 in acetonitrile and RTIL was 1.57×10^?4 cm²/s and 1.82×10^?10 cm²/s, respectively. NM‐2 addition to RTIL enhanced RTIL conductivity. Moreover, heterogeneous rate constant (0.192 s^?1), transfer coefficient (0.231) and the number of electron involved (1.0) were deduced for NM‐2 in RTIL. The calibration plot showed linearity between 2.94×10^?5 and 1.17×10^?3 M with detection limit 1.47 ×10^?5 M (S/N=3). The large number of available RTIL can be used for greener detection of toxic CWAs.     

Direct electrochemistry and electrochemical biosensing of glucose oxidase based on CdSe@CdS quantum dots and MWNT-modified electrode

The direct electron transfer of glucose oxidase (GOx) was achieved based on the immobilization of CdSe@CdS quantum dots on glassy carbon electrode by multi-wall carbon nanotubes (MWNTs)-chitosan (Chit) film. The immobilized GOx displayed a pair of well-defined and reversible redox peaks with a formal potential (E ^θ’) of ?0.459 V (versus Ag/AgCl) in 0.1 M pH 7.0 phosphate buffer solution. The apparent heterogeneous electron transfer rate constants (k _s) of GOx confined in MWNTs-Chit/CdSe@CdS membrane were evaluated as 1.56 s^?1 according to Laviron's equation. The surface concentration (Γ*) of the electroactive GOx in the MWNTs-Chit film was estimated to be (6.52?±?0.01)?×?10^?11?mol?cm^?2. Meanwhile, the catalytic ability of GOx toward the oxidation of glucose was studied. Its apparent Michaelis–Menten constant for glucose was 0.46?±?0.01 mM, showing a good affinity. The linear range for glucose determination was from 1.6?×?10^?4 to 5.6?×?10^?3?M with a relatively high sensitivity of 31.13?±?0.02 μA?mM^?1?cm^?2 and a detection limit of 2.5?×?10^?5?M (S/N=3).     

Nanostructured Cobalt(II) Tetracarboxyphthalocyanine Complex Supported Within the MWCNT Frameworks: Electron Transport and Charge Storage Capabilities

The electrochemical redox properties of a surface‐confined thin solid film of nanostructured cobalt(II) tetracarboxyphthalocyanine integrated with multiwalled carbon nanotube (nanoCoTCPc/MWCNT) have been investigated. This novel nanoCoTCPc/MWCNT material was characterized using SEM, TEM, zeta analysis and electrochemical methods. The nanoCoTCPc/MWCNT nanohybrid material exhibited an extra‐ordinarily high conductivity (15 mS cm^?1), which is more than an order of magnitude greater than that of the MWCNT‐SO₃H (527 µS cm^?1) and three orders of a magnitude greater than the nanoCoTCPc (4.33 µS cm^?1). The heterogeneous electron transfer rate constant decreases as follows: nanoCoTCPc/MWCNT (k_app≈19.73×10^?3 cm s^?1)>MWCNT‐SO₃H (k_app≈11.63×10^?3 cm s^?1)>nanoCoTCPc (k_app≈1.09×10^?3 cm s^?1). The energy‐storage capability was typical of pseudocapacitive behaviour; at a current density of 10 µA cm^?2, the pseudocapacitance decreases as nanoCoTCPc/MWCNT (3.71×10^?4 F cm^?2)>nanoCoTCPc (2.57×10^?4 F cm^?2)>MWCNT‐SO₃H (2.28×10^?4 F cm^?2). The new nanoCoTCPc/MWCNT nanohybrid material promises to serve as a potential material for the fabrication of thin film electrocatalysts or energy‐storage devices.     

Electrochemical Behaviors of Adenosine‐5′‐triphosphate on Molecular Wire Modified Carbon Paste Electrode and Its Sensitive Detection

A new electrochemical method was proposed for the determination of adenosine‐5′‐triphosphate (ATP) based on the electrooxidation at a molecular wire (MW) modified carbon paste electrode (CPE), which was fabricated with diphenylacetylene (DPA) as the binder. A single well‐defined irreversible oxidation peak of ATP appeared on MW‐CPE with adsorption‐controlled process and enhanced electrochemical response in a pH 3.0 Britton‐Robinson buffer solution, which was due to the presence of high conductive DPA in the electrode. The electrochemical parameters of ATP were calculated with the electron transfer coefficient (α) as 0.54, the electron transfer number (n) as 1.9, the apparent heterogeneous electron transfer rate constant (k_s) as 2.67 × 10^?5 s^?1 and the surface coverage (Γ_T) as 4.15 × 10^?10 mol cm^?2. Under the selected conditions the oxidation peak current was proportional to ATP concentration in the range from 1.0 × 10^?7 mol L^?1 to 2.0 × 10^?3 mol L^?1 with the detection limit as 1.28 × 10^?8 mol L^?1 (3σ) by sensitive differential pulse voltammetry. The proposed method showed good selectivity without the interferences of coexisting substances and was successful applied to the ATP injection samples detection.     

Space charge influenced photocurrent transients in fluid solution

The dependence of space charge influenced current transients on the spatial distribution of photogenerated carriers in the bulk of a conductivity cell was investigated with the aim of correlating the observed time evolution of the currents with carrier properties such as mobilities and recombination constant. Approximate analytical solutions for the limiting cases of sheet and full interelectrode illumination show how experimental transients result from the competition between the dynamically interdependent processes: interionic recombination, charge carrier migration and discharge at the electrodes, and space charge buil-up. The voltage dependence of the time at which the secondary photocurrent maxima are observed yield mobilities of 2.0 × 10^?4 and 2.8 × 10^?3 cm² V^?1 s^?1 respectively for the pyrene cation and the solvated electron in tetrahydrofuran at room temperature. A bimolecular recombination rate constant of 2.3 × 10^?9 cm³ s^?1 is shown to be consistent with the space charge densities present after total separation of the positive and negative carriers for various periods of charge carrier recombination.     

UV absorption spectrum of CF3CFClO2 and kinetics of the self reaction of CF3CFCl and CF3CFClO2 and the reactions of CF3CFClO2 with NO and NO2

The ultraviolet absorption spectrum of CF₃CFClO₂ and the kinetics of the self reactions of CF₃CFCl and CF₃CFClO₂ radicals and the reactions of CF₃CFClO₂ with NO and NO₂ have been studied in the gas phase at 295 K by pulse radiolysis/transient UV absorption spectroscopy. The UV absorption cross section of CF₃CFCl radicals was measured to be (1.78 ± 0.22) × 10^?18 cm² molecule^?1 at 220 nm. The UV spectrum of CF₃CFClO₂ radicals was quantified from 220 nm to 290 nm. The absorption cross section at 250 nm was determined to be (1.67 ± 0.21) × 10^?18 cm² molecule^?1. The rate constants for the self reactions of CF₃CFCl and CF₃CFClO₂ radicals were (2.6 ± 0.4) × 10^?12 cm³ molecule^?1 s^?1 and (2.6 ± 0.5) × 10^?12 cm³ molecule^?1 s^?1, respectively. The reactivity of CF₃CFClO₂ radicals towards NO and NO₂ was determined to (1.5 ± 0.6) × 10^?11 cm³ molecule^?1 s^?1 and (5.9 ± 0.5) × 10^?12 cm³ molecule^?1 s^?1, respectively. Finally, the rate constant for the reaction of F atoms with CF₃CFClH was determined to (8 ± 2) × 10^?13 cm³ molecule^?1 s^?1. Results are discussed in the context of the atmospheric chemistry of HCFC-124, CF₃CFClH. © 1994 John Wiley & Sons, Inc.     

Direct Voltammetry of Copper,Zinc‐Superoxide Dismutase Immobilized onto Electrodeposited Nickel Oxide Nanoparticles: Fabrication of Amperometric Superoxide Biosensor

Direct electron transfer of immobilized copper, zinc‐superoxide dismutase (SOD) onto electrodeposited nickel‐oxide (NiOx) nanoparticle modified glassy carbon (GC) electrode displays a well defined redox process with formal potential of ?0.03 V in pH 7.4. Cyclic voltammetry was used for deposition of (NiOx) nanoparticles and immobilization of SOD onto GC electrode. The surface coverage (Γ) and heterogeneous electron transfer rate constant (k_s) of immobilized SOD are 1.75×10^?11 mol cm^?2 and 7.5±0.5 s^?1, respectively. The biosensor shows a fast amperometric response (3 s) toward superoxide at a wide concentration range from 10 µM to 0.25 mM with sensitivity of 13.40 nA µM^?1 cm^?2 and 12.40 nA µM^?1 cm^?2, detection limit of 2.66 and 3.1 µM based on anodically and cathodically detection. This biosensor exhibits excellent stability, reproducibility and long life time.     

A Planarized Triphenylborane Mesogen: Discotic Liquid Crystals with Ambipolar Charge‐Carrier Transport Properties

A discotic liquid‐crystalline (LC) material, consisting of a planarized triphenylborane mesogen, was synthesized. X‐ray diffraction analysis confirmed that this compound forms a hexagonal columnar LC phase with an interfacial distance of 3.57 Å between the discs. At ambient temperature, this boron‐centered discotic liquid crystal exhibited ambipolar carrier transport properties with electron and hole mobility values of approximately 10^?3 and 3×10^?5 cm² V^?1 s^?1, respectively.     

Kinetics of the reactions of O3 and OH radicals with furan and thiophene at 298 ± 2 K

Rate constants for the reactions of O₃ and OH radicals with furan and thiophene have been determined at 298 ± 2 K. The rate constants obtained for the O₃ reactions were (2.42 ± 0.28) × 10^?18 cm³/molec·s for furan and <6 ×10^?20 cm³/molec·s for thiophene. The rate constants for the OH radical reactions, relative to a rate constant for the reaction of OH radicals with n-hexane of (5.70 ± 0.09) × 10^?12 cm³/molec·s, were determined to be (4.01 ± 0.30) × 10^?11 cm³/molec·s for furan and (9.58 ± 0.38) × 10^?12 cm³/molec·s for thiophene. There are to date no reported rate constant data for the reactions of OH radicals with furan and thiophene or for the reaction of O₃ with furan. The data are compared and discussed with respect to those for other alkenes, dialkenes, and heteroatom containing organics.     

Kinetics of the reactions of CH3 with O(3P) and O2 at 295 K

The reactions of CH₃ radicals with O(³P) and O₂ have been studied at 295 K in a gas flow reactor sampled by a mass spectrometer. For the reaction between CH₃ and O, conditions were such that [O] » [CH₃] and the methyl radicals decayed under pseudo-first-order conditions giving a rate coefficient of (1.14 ± 0.29) × 10^?10 cm³/s. The reaction between CH₃ and O₂ was studied in separate experiments in which CH₃ decayed under pseudo-first-order conditions. In this case, the rate coefficient obtained increased with increasing concentration of the helium carrier gas. This was varied over the range of 2.5–25 × 10¹⁶ cm^?3, resulting in values for the apparent two-body rate coefficient ranging from 1 × 10^?14 to 5.2 × 10^?14 cm³/s. No evidence was found for the production of HCHO by a direct two-body process involving CH₃ + O₂, and an upper limit of 3 × 10^?16 cm³/s was placed on the rate coefficient for this reaction. The experimental results for the apparent two-body rate coefficient exhibit the curvature one would expect for an association reaction in the fall-off region. Calculations used to extrapolate these measurements to the low-pressure limit yield a value for k₀ of (3.4 ± 1.1) × 10^?31 cm⁶/s, which is more than a factor of 2 higher than previous estimates.     

Rate constants for the reactions of O3 and OH radicals with a series of alkynes

Rate constants for the reactions of O₃ and OH radicals with acetylene, propyne, and 1-butyne have been determined at room temperature. The rate constants obtained at 294 ± 2 K for the reactions of O₃ with acetylene, propyne, and 1-butyne were (7.8 ± 1.2) × 10^?21 cm³/molecule · s, (1.43 ± 0.15) × 10^?20 cm³/molecule · s, and (1.97 ± 0.26) × 10^?20 cm³/molecule · s, respectively. The rate constants at 298 ± 2 K and atmospheric pressure for the reactions with the OH radical, relative to a rate constant for the reaction of OH radicals with cyclohexane of 7.57 × 10^?12 cm³/molecule · s, were determined to be (8.8 ± 1.4) × 10^?13 cm³/molecule · s, (6.21 ± 0.31) × 10^?12 cm³/molecule · s, and (8.25 ± 0.23) × 10^?12 cm³/molecule · s for acetylene, propyne, and 1-butyne, respectively. These data are discussed and compared with the available literature rate constants.     

Kinetic studies of the reaction of C2H5 with O2 at 295 K

The reaction between C₂H₅ and O₂ at 295 K has been studied with a flow reactor sampled by a mass spectrometer. With helium as the carrier gas the rate coefficient was found to increase from (1.2 ± 0.3) × 10^?12 to (3.6 ± 0.9) × 10^?12 cm³/s as [He] was increased from 2 × 10¹⁶ to 3.4 × 10¹⁷ cm^?3. The importance of has been determined from a knowledge of the initial C₂H₅ concentration together with a measurement of the C₂H₄ produced in reaction (5). F, the fraction of the C₂H₅ radicals removed by path (5), was found to decrease from 0.15 to 0.06 as [He] increased from 2 × 10¹⁶ to 3.4 × 10¹⁷ cm^?3. The rate coefficient for reaction (5) was found to be independent of [He] and to have a value of (2.1 ± 0.5) × 10^?13 cm³/s. The variation in F reflects the fact that k_1b increases as [He] increases. These observations are taken as evidence for a direct mechanism for C₂H₄ production and a collision-stabilized route for C₂H₅O₂ formation. Calculations indicate that the high-pressure limit for reaction (1b) is ～4.4 × 10^?12 cm³/s and that in the polluted troposphere the branching ratio for reactions (1b) and (5) will be ～l20.     

The ultraviolet absorption spectra of the acetyl radical and the kinetics of the CH3 + CO reaction at room temperature

A continuum-absorption spectrum between 200 and 240 nm is assigned to the acetyl radical. Kinetic measurements using molecular modulation spectroscopy show for the reaction CH₃ + CO (+M) → CH₃CO + M the rate constants are (1.8 ± 0.2) × 10^?18 cm³ molecule^?1 s^?1 at 100 Torr and (6 ± 1) × 10^?18 at 750 Torr. The rate constant for acetyl combination 2CH₃CO → (CH₃CO)₂ is (3.0 ± 10) × 10^?11 at 25°C.     

Pulsed photoconductivity and current oscillations in poly(vinyl chloride)

Transient photocurrents in poly(vinyl chloride) films are shown to be due to photo-injection of electrons from metallic cathodes. Most of the injected electrons are promptly trapped, but some drift across the sample to the anode under the influence of an external electric field. The mobility of these electrons, determined by transient photoconductivity techniques, is 4.7 ± 0.5 × 10^?4 cm²/V-sec at 27°C, and rises to 3.4 ± 0.5 × 10^?3 cm²/V-sec at 43°C, the measuring cell having been evacuated to a pressure of 10^?6 torr at both temperatures. Diffusion of helium into the samples appears to decrease the electron, mobility. It is suggested that electron transport is correctly described by using an energy-band model for intramolecular motion and an activated hopping model for intermolecular transfer. Oscillations observed in the transient photocurrents in the frequency range 10³–10⁵ Hz are attributed to electron avalanche formation at the anode, with photosuccessors.     

Nanostructured Alpha‐Nickel Hydroxide Electrodes for High Performance Hydrogen Peroxide Sensing

Nanostructured alpha‐nickel hydroxide (α‐Ni(OH)₂) immobilized on a Fluorine‐doped Tin Oxide (FTO) surface was explored for the construction of hydrogen peroxide amperometric Flow Injection Analysis (FIA) sensors. Their notable electrocatalytic activity and heterogeneous electron‐transfer rate were confirmed by the appearance of a broad and intense peak associated with the oxidation of hydrogen peroxide and the enhancement of sensibility in hydrodynamic conditions. The α‐Ni(OH)₂ electrodes exhibited a broad dynamic range (5×10^?6 to 1×10^?3 mol L^?1), low detection limit (2×10^?7 mol L^?1), good repeatability (RSD=1.29 % for 20 successive analyses), and a sensitivity greater than 500 µA mmol^?1 L^?1 cm^?2.     

Triiodide PVC Membrane Electrode Based on a Charge‐Transfer Complex of Iodine with Ditertbutyl‐Dicyclohexyl‐18‐Crown‐6

A new triiodide ion‐selective electrode based on a charge‐transfer complex of iodine with ditertbutyl‐dicyclohexyl‐18‐crown‐6 (t‐Bu)₂DC18C6 as membrane carrier was prepared. The electrode has a linear dynamic range from 6.3 × 10^?3‐5 × 10^?6 with a Nernstian response of 58.6 ± 1 mV decade^?1 and a detection limit of 1.3 × 10^?6 M. The response time of the sensor was 25 s. The membrane could be used for two months without any divergence in potentials. The electrode exhibits an anti‐Hofmeistetr selectivity sequence with a preference for triiodide at pH 2.0‐10.0. The response mechanism of the electrode was investigated by Uv‐Vis spectroscopic technique. The electrode can be used for the determination of ascorbic acid in orange juice.     

Kinetics of the reactions of CCl3 with O and O2 and of CCl3O2 with NO at 295 K

The reactions of CCl₃ with O(³P) and O₂ and those of CCl₃O₂ with NO have been studied at 295 K using discharge flow methods with helium as the bath gas. The rate coefficient for the reaction of CCl₃ with O was found to be (4.2 ± 0.6) × 10^?11 cm³/s and that for CCl₃O₂ with NO was (18.6 ± 2.8) × 10^?12 cm³/s with both coefficients independent of [He]. For reaction between CCl₃ and O₂ the rate coefficient was found to increase from 1.51 7times; 10^?14 cm³/s to 7.88 × 10^?14 cm³/s as the [He] increased from 3.5 × 10¹⁶ cm^?3 to 2.7 × 10¹⁷ cm^?3. There was no evidence for a direct two-body reaction, and it is concluded that the only product of this reaction is CCl₃O₂. Examination of these results for CCl₃ + O₂ in terms of current simplified falloff treatment suggests that the high-pressure limit for this reaction is ～ 2.5 × 10^?12 cm³/s, which may be compared with a direct measurement of the high-pressure limit of 5 × 10^?12 cm³/s. A value of (5.8 ± 0.6) × 10^?31 cm⁶/s has been obtained for k₀, the coefficient in the low-pressure region. This value is compared with corresponding values found earlier for the (CH₃, O₂) and (CF₃, O₂) systems and with estimates based on unimolecular rate theory.     

Acetylferrocene Modified Carbon Paste Electrode; A Sensor for Electrocatalytic Determination of Hydrazine

The electrocatalytic oxidation of hydrazine at a carbon paste electrode spiked with acetylferrocene as a mediator was studied by cyclic voltammetry, differential pulse voltammetry, and chronoamperometry. In contrast to other ferrocenic compounds, acetylferrocene exhibits a chemical irreversible behavior, but it can act as an effective mediator for electrocatalytic oxidation of hydrazine, too. The heterogeneous electron transfer rate constant between acetylferrocene and the electrode substrate (carbon paste) and the diffusion coefficient of spiked acetylferrocene in silicon oil were estimated to be about 3.45×10^?4 cm s^?1 and 4.45×10^?9 cm² s^?1, respectively. It has been found that under the optimum conditions (pH 7.5) the oxidation of hydrazine occurs at a potential of about 228 mV less positive than that of an unmodified carbon paste electrode. The catalytic oxidation peak current of hydrazine was linearly dependent on its concentration and the obtained linear range was 3.09×10^?5 M–1.03×10^?3 M. The detection limit (2σ) has been determined as 2.7×10^?5 M by cyclic voltammetry. Also, the peak current was increased linearly with the concentration of hydrazine in the range of 1×10^?5 M–1×10^?3 M by differential pulse voltammetry with a detection limit of 1×10^?5 M. This catalytic oxidation of hydrazine has been applied as a selective, simple, and precise new method for the determination of hydrazine in water samples.     

Electrocatalytic Determination of Ascorbic Acid at the Surface of 2,7‐Bis(ferrocenyl ethyl)fluoren‐9‐one Modified Carbon Paste Electrode

A chemically modified carbon paste electrode with 2,7‐bis(ferrocenyl ethyl)fluoren‐9‐one (2,7‐BFEFMCPE) was employed to study the electrocatalytic oxidation of ascorbic acid in aqueous solution using cyclic voltammetry, differential pulse voltammetry and chronoamperometry. The diffusion coefficient (D=1.89×10^?5 cm² s^?1), and the kinetic parameter such as the electron transfer coefficient, α (=0.42) of ascorbic acid oxidation at the surface of 2,7‐BFEFMCPE was determined using electrochemical approaches. It has been found that under an optimum condition (pH 7.00), the oxidation of ascorbic acid at the surface of such an electrode occurs at a potential about 300 mV less positive than that of an unmodified carbon paste electrode. The catalytic oxidation peak currents show a linear dependence on the ascorbic acid concentration and linear analytical curves were obtained in the ranges of 8.0×10^?5 M–2.0×10^?3 M and 3.1×10^?5 M–3.3×10^?3 M of ascorbic acid with correlation coefficients of 0.9980 and 0.9976 in cyclic voltammetry and differential pulse voltammetry, respectively. The detection limits (2δ) were determined to be 2.9×10^?5 M and 9.0×10^?6 M with cyclic voltammetry and differential pulse voltammetry, respectively. This method was also examined for determination of ascorbic acid in pharmaceutical preparations.     

Electro‐optical properties of electropolymerized poly(3‐hexylthiophene)/carbon nanotube composite thin films

3‐hexylthiophene was electropolymerized on a carbon nanotube (CNT)‐laden fluorine‐doped tin oxide substrate. Scanning electron microscopy and Raman spectroscopy revealed that the polymer was infused throughout the thickness of the 150‐nm thick CNT mat, resulting in a conducting composite film with a dense CNT network. The electropolymerized poly(3‐hexylthiophene) (e‐P3HT)/CNT composites exhibited photoluminescence intensity quenching by as much as 92% compared to the neat e‐P3HT, which provided evidence of charge transfer from the polymer phase to the CNT phase. Through‐film impedance and J‐V measurements of the composites gave a conductivity (σ) of 1.2 × 10^?10 S cm^?1 and zero‐field mobility (μ₀) of 8.5 × 10^?4 cm² V^?1 s^?1, both of which were higher than those of neat e‐P3HT films (σ = 9.9 × 10^?12 S cm^?1, μ₀ = 3 × 10^?5 cm² V^?1 s^?1). In electropolymerized samples, the thiophene rings were oriented in the (010) direction (thiophene rings parallel to substrate), which resulted in a broader optical absorbance than for spin coated samples, however, the lack of long‐range conjugation caused a blueshift in the absorbance maximum from 523 nm for unannealed regioregular P3HT (rr‐P3HT) to 470 nm for e‐P3HT. Raman spectroscopy revealed that π‐π stacking in e‐P3HT was comparable to that in rr‐P3HT and significantly higher than in regiorandom P3HT (ran‐P3HT) as shown by the principal Raman peak shift from 1444 to 1446 cm^?1 for e‐P3HT and rr‐P3HT to 1473 cm^?1 for ran‐P3HT. This work demonstrates that these polymer/CNT composites may have interesting properties for electro‐optical applications. © 2011 Wiley Periodicals, Inc. J Polym Sci Part B: Polym Phys 49: 1269–1275, 2011