Electrocatalytic hydrogenolysis of lignin model dimers at Raney nickel electrodes

The electrocatalytic hydrogenolysis (ECH) of lignin model compounds has been investigated under galvanostatic control at Raney nickel electrodes in aqueous ethanol. The influence of current density, concentration of substrate and temperature on the efficiency of the carbon–oxygen bond hydrogenolysis was studied with benzyl phenyl ether and the optimum conditions leading to its total conversion were found. The effect, on the current efficiency, of replacing the phenyl group by an alkyl group (e.g. benzyl methyl ether) and of substituting hydrogens on aromatic rings by methoxy groups was investigated using the optimum electrolysis conditions. The electrocatalytic hydrogenolysis of -phenoxyethylbenzene and -phenoxyacetophenone, representatives of two other kinds of carbon–oxygen linkage in lignin, was also carried out.     

The Role of Sulfur in the Synthesis of Novel Carbon Morphologies: From Covalent Y‐Junctions to Sea‐Urchin‐Like Structures

A detailed characterization, using high resolution electron microscopy/microanalysis (SEM, TEM, HRTEM, and EDX), reveals tubular carbon nanostructures exhibiting complex and fascinating morphologies. The materials were obtained by sulfur‐assisted chemical vapor deposition. It is demonstrated that S not only acts on the catalyst, but also can be detected in the carbon lattice of the nanostructures. The experimental data presented here confirms the critical role of S, which is responsible for inducing curvature and therefore influencing the final carbon nanostructure morphology. In particular, different types of covalent Y‐junctions of CNTs and even sea urchin‐like nanostructures were produced and their experimental conditions are listed and discussed.     

Hydrogen activation of spectroscopic graphite surface by argon plasma etching

Argon plasma bombardment was successfully used for the hydrogen activation of spectroscopic graphite electrodes. The hydrogen evolution reaction (HER) in 1m KOH was investigated using electrochemical techniques such as galvanostatic polarization and a.c. impedence spectroscopy; the electrode surface was characterized by SEM. It is shown that the rate of HER at a given hydrogen overpotential value increases exponentially with the etching time (ET), up to ETs of 30min, and slightly decreases from 30 to 60min. The double-layer capacity (Cdl) was established against the hydrogen overpotential for different ETs, with Cdl reaching its maximum for ETs of 30min. Moreover, it is shown that the etching process also leads to a significant increase in intrinsic activity toward HER.     

ω-THIOCAPROLACTAM AS AN EXTRACTING REAGENT FOR Hg(II) FROM CHLORIDE,NITRATE, AND PERCHLORATE MEDIA.

ABSTRACT

Solvent extraction of Hg(II) from chloride, nitrate, and perchlorate media using ω-thiocaprolactam (R) dissolved in chloroform was studied. In all media the extraction equilibria are reached very fast, less than a 5 minute period of shaking time is needed. At high metal: extractant ratio (1:10) the percent of extraction of Hg(II) decreases in the order chloride > nitrate = perchlorate and in the pH range studied ( 0-3 ) is independent of this variable. At low metahextractant ratios (1:50, 1:100) the percent of extraction does not depend on the media used. In the latter case a dependence with the acidity in the chloride media is observed. The dimerization constant of the extractant in CHCI₃ was determined to be 109±15 by UV measurements. Graphical and numerical analysis of the data with the LETAGROP-DISTR program allowed to propose the extraction reactions involved and evaluate their equilibrium constants. Organic phase species of the type HgX₂R and HgX₂R₂ ( where X = CI, NO₃, or CIO₄) were found to explain better the experimental results obtained. However, in concentrated HCI the extraction of Hg(II) is explained by the formation of HgCI₃RH and HgCI₄(RH)₂ species.     

Characterization and stability of doped SnO2 anodes

Doped tin dioxide electrodes have been prepared by a standard spray pyrolysis technique. The electrochemical behaviour of these electrodes has been investigated by cyclic voltammetry in sulphuric acid using the Fe2+/Fe3+ redox couple system as test reaction. Oxygen evolution has been used to study the stability of doped SnO2 electrodes. The SnO2 electrodes doped with antimony and platinum exhibit the highest stability. XPS analysis shows that the oxidation state of Sn, Sb and Pt are +4, +3 and +2, respectively, the probable species being SnO2, Sb2O3 and PtO.     

Electrodeposition of Co–Ni alloys

Cobalt–nickel alloys were electrodeposited in an acid bath containing various ratios of metallic cations. The effect of the plating variables on the composition and morphology of the deposits obtained on vitreous carbon electrodes was investigated. Different proportions of the two metals can be obtained by using different deposition parameters, but at all Co(ii)/Ni(ii) ratios studied, preferential deposition of cobalt occurs and anomalous codeposition takes place. For a fixed solution composition, the nickel content in the deposit is enhanced by increasing the deposition potential. More homogeneous and fine-grained deposits can be obtained by increasing the cobalt(ii)/nickel(ii) ratio in solution and by ensuring that deposition takes place slowly. Deposits of constant composition throughout the depth of the deposit can be obtained only by stirring the solution during the deposition. In addition, the solution must be stirred in order to minimize the increase in local pH and to prevent hydroxide precipitation. An attempt was made to explain the anomalous codeposition. The results suggest the following sequence of events: first, nickel is deposited; then, cobalt(ii) adsorbs onto the freshly deposited nickel and begins to be deposited. The cobalt(ii) adsorption inhibits subsequent deposition of nickel, although it does not block it completely.     

A new five-parameter MOS transistor mismatch model

A new five-parameter MOS transistor mismatch model is introduced capable of predicting transistor mismatch with very high accuracy for ohmic and saturation regions, including short-channel transistors. The new model is based on splitting the contribution of the mobility degradation parameter mismatch Δ&thetas; into two components, and modulating them as the transistor transitions from ohmic to saturation regions. The model is tested for a wide range of transistor sizes (30), and shows excellent precision, never reported before for such a wide range of transistor sizes, including short-channel transistors     

A weak-to-strong inversion mismatch model for analog circuit design

This paper reports on a new CMOS transistor mismatch model that is continuous from weak to strong inversion. The model is completely described by analytical equations which are based on either the ACM or EKV transistor models. Large signal ACM and EKV transistor equations including the relevant parameters for mismatch are used for fitting the measured data. Five parameters are found to be relevant for predicting mismatch from weak to strong inversion: specific current I _s , threshold voltage V _T0, gamma γ, θ _o (dependent on mobility degradation and source-drain series resistances), and θ _e (dependent on velocity saturation and drain series resistance). Arrays of NMOS and PMOS transistors of 30 different sizes were fabricated in a 0.35 μm CMOS process. For each transistor size 12 different curves were measured. Different mismatch parameter extraction methods were used and compared. Average current mismatch prediction error was found to be in the range between 4 and 10% in the whole bias range from weak to strong inversion. Worst case mismatch prediction errors were in the range 23–61%. Since mismatch was predicted for a large number of sizes, the model could be implemented in a conventional circuit simulator to predict transistor mismatch not only as a function of transistor area but as function of transistor width and length independently. It was found that minimum mismatch is not always achieved by square transistors, and that mismatch is less sensitive to reducing width than to reducing length.     

Polymers and copolymers of pyrrole and thiophene as electrodes in lithium cells

The performance of pyrrole and thiophene polymer electrodes in lithium cells has been examined in the lithium perchlorate–propylene carbonate electrolyte by cyclic voltammetry. Polypyrrole films were synthesized in 'wet' and 'dry' conditions; pyrrole and thiophene copolymers were prepared at different potentials and bilayers were prepared by sequential deposition of polythiophene (PTh) and polypyrrole (PPy) films. The polymers were cycled between 2.0V and 4.0V in the lithium cells. The effects of disconnecting the electrodes from the cell on the behaviour of the polymers regarding doping and coulombic efficiency were also studied. The cycling performance of the 'wet' PPy is better than 'dry' PPy, bilayer PTh/PPy and copolymers. No mixed behaviour was observed for a bilayer where the inner layer was polythiophene and the outer layer was polypyrrol with a thickness PPy/Pth ratio equal to ten. The copolymer prepared at 3.9V vs Li/Li+ showed the higher energy capacity in Whkg–1 calculated from the anodic charge.     

Sodium hydroxide and hydrochloric acid generation from sodium chloride and rock salt by electro-electrodialysis

An electro-electrodialysis process (EED) is used to generate HCl and NaOH from trade NaCl. The key phenomenon limiting the current efficiency of this process is proton leakage through the anion selective membrane. Two new low proton leakage membranes: the ARA and ACM were used. NaOH and HCl solutions with purity higher than 99.9% are obtained. The experimental values of the fluxes for HCl and NaOH are compared with values calculated from integration of the Nernst–Planck electrodiffusion equations. This calculation requires several experimentally determined parameters: ionic diffusion coefficients, membrane conductance and amount of sorbed electrolyte. Algerian rock salt from El Outaya is used to compare electro-electrodialysis and electrodialysis using bipolar membranes.