Interaction between co-deposited metals during stripping voltammetry at boron-doped diamond electrodes

Electrochemical processes, which underlie the use of conductive diamond electrodes for the simultaneous detection of two or more metal ions in solution by anodic stripping voltammetry (ASV), have been investigated. The model analyte system studied contains the two metal species, Ag+(aq) and Pb2+(aq), and the experimental techniques employed include cyclic and square wave voltammetries, along with X-ray photoelectron spectroscopy and secondary electron microscopy. Although the bulk metallic forms of Ag and Pb are immiscible, several interactions in the system between the two metal species present are observed, which significantly influence the electrodeposition and electrodissolution processes which underlie ASV. The subsequent nucleation and growth of a given metal on the electrode surface is enhanced by the presence of the second metal on the surface. The encapsulation of one metal by the other, within the metal particulates that form on the electrode surface, significantly reduces the stripping yield at the potentials characteristic of the individual metals. The stripping potentials are also influenced by bonding interactions between deposited Ag and Pb, which broaden the characteristic stripping peaks in cyclic voltammetry, as well as producing underpotential deposition and stripping. Given these interactions, the extent to which ASV at diamond electrodes can be used to determine the solution concentrations of Ag+(aq) and Pb2+(aq) is considered.     

A gas-phase electron-diffraction study of trvinylborane

Trivinylborane has been studied by standard electron-diffraction techniques. The best agreement with experiment is obtained with a planar dynamic model in which steric strain within the molecule is reduced by distortion of the vinyl groups, and shrinkages simulate considerable torsional motion about the B-C bonds. The following parameters (r_a basis) and e.s.d. were obtained: C-H = 1.092± 0.003 Å; C-C = 1.370 ± 0.006 Å; B-C = 1.558± 0.003 Å; ∠BCH = 116.5 ± 0.9 °; ∠BCC = 122.4 ± 0.9°; ∠CCH (trans to B) = 124.0 ± 1.6°; ∠CCH (cis to B) = 132.2 ± 2.3°. A static non-planar model has also been considered.The probable planarity of the molecule and the length of the C C bond are interpreted as evidence for π-electron delocalisation from carbon to boron.     

Derivations, isomorphisms, and second cohomology of generalized Witt algebras

Generalized Witt algebras, over a field of characteristic , were defined by Kawamoto about 12 years ago. Using different notations from Kawamoto's, we give an essentially equivalent definition of generalized Witt algebras over , where the ingredients are an abelian group , a vector space over , and a map which is linear in the first variable and additive in the second one. In this paper, the derivations of any generalized Witt algebra
, with the right kernel of being , are explicitly described; the isomorphisms between any two simple generalized Witt algebras are completely determined; and the second cohomology group for any simple generalized Witt algebra is computed. The derivations, the automorphisms and the second cohomology groups of some special generalized Witt algebras have been studied by several other authors as indicated in the references.

     

Fast electrochemical triple-interface processes at boron-doped diamond electrodes

Two important mechanisms for electron transfer processes at boron-doped diamond electrodes involving the oxidation of tetramethylphenylenediamine (TMPD) dissolved in aqueous solution and the oxidation of tetrahexylphenylenediamine (THPD) deposited in the form of microdroplets and immersed into aqueous eletrolyte solution are reported. For TMPD, the first oxidation step in aqueous solution follows the equation: Remarkably slow heterogeneous kinetics at a H-plasma-treated boron-doped diamond electrode are observed, consistent with a process following a pathway more complex than outer-sphere electron transfer. At the same boron-doped diamond electrode surface a deposit of THPD undergoes facile oxidation following the equation: This oxidation and re-reduction of the deposited liquid material occurs at the triple interface organic droplet|diamond|aqueous electrolyte and is therefore an example of a facile high-current-density process at boron-doped diamond electrodes due to good electrical contact between the deposit and the diamond surface. Received: 3 February 2000 / Accepted: 18 February 2000     

Electrochemistry of Methyl Viologen and Anthraquinonedisulfonate at Diamond and Diamond Powder Electrodes: The Influence of Surface Chemistry

The electrochemical behaviour of methyl viologen and anthraquinonedisulfonate was studied at electrodes produced from differing forms of diamond, including microcrystalline boron doped diamond, boron doped diamond powder and detonation nanodiamond powder. Two types of electrode pretreatment were employed to produce two dissimilar surface terminations: hydrophobic H‐terminated and hydrophilic O‐terminated. In the case of methyl viologen, it was found that the reduced neutral molecule adsorbed on all three electrodes if they were hydrogen terminated, but not if they were oxygen terminated. For anthraquinonedisulfonate, no adsorption was found on the solid diamond electrode, although again significant adsorption was noted on the powder electrodes, provided they were hydrogen terminated. The reasons underlying these observations are discussed in terms of hydrophobic and electrostatic interactions and the electrode morphology. The work provides information into the likely occurrence of adsorption and concomitant electrode fouling, which may be experienced in electroanalytical applications using solid and powdered forms of diamond.