Reaction kinetics of hydrated electrons in a quaternary micro emulsion system: A pulse radiolysis study

The pulse-radiolysis technique has been employed to produce and study the kinetics of hydrated electrons (e_aq⁻) in a quaternary micro emulsion (Sodium Lauryl Sulfate (NaLS)/water/cyclohexane/1-pentanol) system. Two orders of magnitude higher life time (20 μs) of the e_aq⁻ has been obtained as compared to that in reverse micelles reported earlier. Several probes including a biomolecule have been used to determine the water pool concentrations and quenching constants (k_q). The observed yield and half life (t_1/2) of the hydrated electrons vary smoothly as the water droplet sizes are changed. The bimolecular rate constants for the reaction of e_aq⁻ with different solutes have been determined. It has been observed that the measured bimolecular rate constants for the reaction of hydrated electrons with different solutes are indicative of the solubilization sites, the water core sizes, and the surrounding environment. © 1998 John Wiley & Sons, Inc. Int J Chem Kinet: 30: 699–705, 1998     

Nanosecond kinetics of hydrated electrons upon water photolysis by high intensity femtosecond UV pulses

We report a nanosecond laser study of the transient absorption of hydrated electrons generated by multiphoton ionisation of liquid water upon excitation at 266 and 400 nm by femtosecond pulses with power densities higher than 1 TW/cm². For both wavelengths, as the pump power density increases, the signal amplitude increases and the decay becomes faster proving that more electrons are produced. However, we show that in the nanosecond time range, under pump power densities higher than 1 TW/cm², the distribution of the hydrated electrons is not uniform along the optical pathway of the pump beam in the water sample.     

Electrostatic charging and charge transport by hydrated amorphous silica under a high voltage direct current electrical field

This work was initially based on the casual observation of an electrostatic phenomenon, in which particles of amorphous silica were attracted by a dc electrical field. The first observations were recently shown in a communication in this journal. To explain the electrical charge transport process observed in this work, all forces acting on silica particles were estimated and the significant ones were used to formulate a model made up of three elementary steps. Analyzing the experimental observations using this model, it was possible to suggest that electrons can be introduced into and removed from electronic bands of water.     

Reactions of hydrated electrons with pyridinium salts in aqueous solutions

Rate coefficients for the reactions of the hydrated electron (e(aq)(-)) with pyridinium salts in aqueous solutions have been determined using pulse radiolysis techniques. The rate coefficients for pyridine, 1-hydropyridinium chloride, and 1-hydropyridinium nitrate were observed to be 1.4 x 10(10), 4.5 x 10(10), and 5.3 x 10(10) M(-1) s(-1), respectively. The e(aq)(-) was found to primarily attack the pyridine ring, the proton coordinated to the nitrogen atom, and the nitrate counterion, but not the chloride. Results for the corresponding dimer structures of 4,4'-dipyridyl, 1,1'-dihydro-4,4'-bipyridinium dichloride, and 1,1'-dihydro-4,4'-bipyridinium dinitrate had similar trends for e(aq)(-) attack sites. The rate coefficients for pyridinium salts were lower when the pyridinium nitrogen atom is coordinated to a methyl group rather than to a proton. This reduction is probably due to the increase in electron density of the pyridine ring due to the electron-donating methyl group. Pyridinium salts are not major contributors to the production of molecular hydrogen in the radiolysis of aqueous solutions and actually decrease molecular hydrogen yield due to scavenging reactions of the e(aq)(-). The yield of molecular hydrogen decreases from 0.45 to approximately 0.2 molecule/(100 eV) over the scavenging capacity range for the e(aq)(-) of 10(5)-10(9) s(-1). Absorption spectra of the transient species produced by the reactions of pyridinium salts with OH radical and H atom formed in water radiolysis were observed, and rate coefficients for these reactions were determined.     

High voltage supercapacitors using hydrated graphene film in a neutral aqueous electrolyte

The potential stability windows of chemical converted graphene in different aqueous electrolyte solutions were investigated for the first time. Based on this result, a supercapacitor with a high voltage and long cycle-life was prepared with the hydrated graphene films in the neutral aqueous solution at the maximum voltage of 1.6 and even 1.8 V. The electrochemical performance of the obtained sample was systematically investigated by cyclic voltammetry, galvanostatic charge/discharge and electrochemical impedance spectroscopy. According to the cyclic voltammetry, hydrated graphene film can still retain rectangular shape at the high scan rate of 0.5 V/s in the neutral aqueous electrolyte. At a galvanostatic charge/discharge rate of 1 or 200 A/g, the specific capacitance of 202.3 or 138.1 F/g was delivered, respectively. Furthermore, the EIS results also confirm its fast neutral ion diffusion and high operating frequency of 9.34 Hz.     

Solvation of excess electrons trapped in charge pockets on hydrated molecular surfaces

We have previously computed a set of hypothetical molecular surfaces, which formed charge pockets that were capable of excess electron entrapment. These charge pockets arose due to the fact that the molecular surfaces possessed an extended network of OH groups on one side of the surface and hydrogen atoms on the opposite side. The uneven distribution of the OH groups coupled to the partial positive charge of the hydrogen atoms caused electrons to be attracted to the surface. In the present investigation we will consider the ability of the hydrogen cyanide (HCN)‐water complex in stabilizing excess electrons on molecular surfaces. The computed vertical detachment energy (VDE) values are high, suggesting anion stability. © 2007 Wiley Periodicals, Inc. Int J Quantum Chem, 2008     

Particulates formed by a stabilized high voltage spark discharge

Light scattering was used to demonstrate the presence of small (?1 μm) particles in the immediate surroundings of a stable spark discharge. Several parameters, including electrode composition and surface condition, which are of importance in emission spectrochemical analysis, were found to be of importance in affecting the scattering signal. Electron micrographs of the heaviest particles revealed two distinct types of particles. Analytical implications are discussed.     

Sinusoidal voltage modulation of a copper rotating disk electrode

An experimental and theoretical study has been made of the sinusoidal potential modulation of a copper rotating disk electrode in acidic copper sulfate solution. The mathematical model takes into account the fluctuations of the surface concentration, the effect of the double capacitance, the surface overpotential, and the ohmic resistance in the electrolyte. Numerical computations were performed to show the effect of alternating voltage (av) on the shape of direct current polarization curves, the changes in the apparent rest potential, the apparent exchange current density and the apparent Tafel slopes. The agreement between the theory and the experiment was within ±15%. At sufficiently high av frequencies, the model can be further used to predict the av modulation of a rotating hemispherical electrode.     

Potentiometric detection in ion chromatography using a metallic copper indicator electrode

Summary A metallic copper electrode housed in a suitable flowcell is shown to be a sensitive and versatile potentiometric detector for ion chromatography. This electrode may be used for direct or indirect detection of many inorganic anions and cations and also for organic acids. In the direct detection mode, electrode response is based on either complexation of copper ions at the electrode surface by eluted species, or on oxidation and reduction reactions for eluted species which are strong oxidants or reductants. Direct detection is therefore applicable to such species as amino acids, organic acids, chloride, bromide, iodide, chlorate, bromate and iodate. Indirect detection is possible for anions which do not complex copper ions, provided a copper complexing ligand (such as phthalate) is used in the eluent; cations which complex this ligand are also detectable. Indirect detection may be used for species such as nitrite, nitrate, acetate, formate, succinate, benzoate, alkaline earth ions and transition metal ions. Electrode calibration relationships are discussed and sample separations are presented, together with some typical detection limits attainable in the direct and indirect detection modes.Presented in part at a National Symposium on Ion Chromatography, held at the University of New South Wales, Kensington, Australia, Nov. 21, 1984.     

Measurement of the room-temperature hall mobility of injected electrons in liquid tetramethylsilane

The electron Hall mobility in tetramethylsilane (TMS) has been measured at room temperature using the Redfield technique. The resulting mobility, 124 cm²/V s is 25% higher than the time-of-flight mobility. From their comparison we conclude that it is likely that the electron-scattering mechanism is due to acoustic phonons whose interaction with electrons can be described in the deformation potential approximation.     

Brownian dynamics simulations of the reactions of hydrated electrons with components of DNAs and a DNA double-helix

As a first step toward developing simulation models for studying the indirect mechanism of radiation damage to DNAs, we have carried out Brownian dynamics simulations to study the reactions of hydrated electrons with a 12-base-pair B-DNA, (dA)₁₂(dT)₁₂, and with bases, monodeoxynucleotides, and polydeoxynucleotides. We first studied in detail the sensitivity of diffusion reaction rate constants to different model and simulation parameters. Based on the sensitivity studies, a set of model and simulation parameters was obtained for the final production runs. The use of this set of parameters reduced the computational costs but delivered reasonably reliable results. The calculated reaction rate constants were in qualitative agreement with experiments. For the DNA double-helix, (dA)₁₂(dT)₁₂, the simulations demonstrated that hydrated electrons preferred to attack the two ends of the double-helix. Electrostatic interactions between the DNA and the hydrated electrons make the T strand more susceptible to attack than the A strand. The increased reactivity of the T strand due to electrostatic interactions results from the increased reactivity of the C6 sites of the thymine bases, at the expense of the reactivity of the C8 sites of the adenine bases. The reactivity of the relatively buried reactive sites of the adenine and thymine bases are less affected by electrostatic interactions. © 1997 by John Wiley & Sons, Inc. J Comput Chem 18: 888–901, 1997     

Preparation and characterization of graphite-coated metallic electrodes: the graphite-sprayed electrode

Graphite-coated metal electrodes were constructed and evaluated for use in voltammetry. Aluminium, copper and platinum electrodes were sprayed with a colloidal solution of graphite particles dispersed in methyl methacrylate polymer. The polishing step was omitted for anodic stripping voltammetry with a mercury film. The resistance is about 1 Ω. Electrode areas are readily reproduced by utilizing metal supports with equal areas. Background currents are very low and useful potential ranges are extended, with −1.3 to +1.7 V vs. SCE being possible, depending on the electrolyte. It is possible to achieve ±0.1% precision for the peak-currents in the electrochemical oxidation of ferrocyanide. For phenol, which is strongly adsorbed, a precision of 2.5% can be achieved by polishing the electrode before each determination.     

Investigation of the insertion of water in hydrated layers of silicate electrode glasses

The study distinctly shows that structural changes take place in the silicate framework during the swelling process of glasses in aqueous solutions. The presence of a modified Q³ group is evidence for the exchange of protons and sodium ions; condensation reactions also take place. Using various techniques (¹H NMR, infrared spectroscopy and thermal analysis) it has been demonstrated that water is present in the hydrated glass not only in the form of H₂O molecules and silanol groups, but also in different structures of these two species. A molar H₂O:SiOH ratio was found of approximately 1:1 (in agreement with the assumption that H₃O⁺ ions of the solution and sodium ions of the glass are exchanged and SiOH and H₂O are formed from the hydroxonium ions).