Showing papers on "Supporting electrolyte published in 1998"

Electrochemical incineration of benzoquinone in aqueous media using a quaternary metal oxide electrode in the absence of a soluble supporting electrolyte

Abstract: Electrochemical incineration of p-benzoquinone was evaluated as a model for the mineralization of carbon in toxic aromatic compounds. A Ti or Pt anode was coated with a film of the oxides of Ti, Ru, Sn and Sb. This quaternary metal oxide film was stable; elemental analysis of the electrolysed solution indicated the concentration of these metal ions to be 3μg L−1 or less. The anode showed good reactivity for the electrochemical incineration of benzoquinone. The use of a dissolved salt matrix as the so-called ‘supporting electrolyte’ was eliminated in favor of a solid-state electrolyte sandwiched between the anode and cathode. This substitution permitted the electrolysis solution to be analysed by electrospray mass spectrometry (ESMS); however, as a consequence, electrolysis periods were excessively long. Total organic carbon (TOC) and chemical oxygen demand (COD) decreased to 1–2 mgL−1 after 64h of electrolysis. The solution pH changed from 5 to 4. Phenolic and carboxylic acid intermediate products such as hydroquinone, maleic acid, fumaric acid, succinic acid, malonic acid, acetic acid and formic acids were identified and quantified using solid phase microextraction with gas chromatography with mass spectrometric detection (GCMS) or liquid chromatography (LC) with conductivity detection, absorbance detection, or electrosprary mass spectrometry (ESMS). Less than 1% of the carbon in benzoquinone was converted to acetone and acetaldehyde.

Formation of Redox-Active, Two-Component Films by Electrochemical Reduction of C60 and Transition Metal Complexes

Abstract: Electrochemical reduction of C60 in 4:1 toluene/acetonitrile solution in the presence of (PhCN) 2- PdCl2, Ir(CO)2Cl(p-toluidine), or (CF3CO2)4Rh2 produces three different, redox-active, black films that coat the electrode. These films are insoluble in common organic solvents and adhere strongly to the electrode surface. Film formation has been monitored by multiscan cyclic voltammetry, which gives information about the requirements for film growth. The three different films (on the original electrodes) can be transferred to a solution of acetonitrile that contains only the supporting electrolyte, tetra( n-butyl)ammonium perchlorate, where the films retain their redox activity. Each film displays a significant decrease in resistivity ( i.e. a window of conductivity) in the potential region in which it is grown and in which it displays redox activity. The films have been examined by scanning electron microscopy, which shows variations in the nature of the three films' morphologies with the film formed from (PhCN)2PdCl2 displaying the greatest uniformity and smoothest surface. Analysis of the films by infrared spectroscopy and laser desorption mass spectrometry reveals that intact C 60 units are present within each film. Treatment of the palladium/C60 film with triphenylphosphine results in film dissolution and the formation of the previously characterized complex, ( 2 -C60)Pd(PPh3)2. The rhodium/ C60 film dissolves in pyridine and 19 F{ 1 H} NMR spectroscopy reveals that (CF3CO2)4Rh2 is extracted intact from the film. The structure of the films is discussed in terms of covalent bonding between the fullerenes and the metal atoms or complexes within the film.

Differential pulse voltammetric determination of nitrite with gold ultramicroelectrode

Abstract: The application of disk shaped gold ultramicroelectrode for nitrite determination with and without addition of supporting electrolyte was studied using the differential pulse voltammetric method The well-defined peak for nitrite oxidation near 08 V (vs Ag/AgCl reference electrode) was used to obtain analytical plots in the concentration range from 01 to 06 mmol L−1 and from 100 to 500 μmolL−1 The calculated detection limit was 065 μmolL−1 in purified water, in the absence of supporting electrolyte, with relative standard deviation of 136% (n = 6) for analyzing 100 μmol L−1 nitrite solutions, and accuracy of 1009 %, based on recovery studies The application of this analytical method to mineral and river water samples of natural pH also showed improved sensitivity when compared with the linear sweep voltammetric method previously reported

Anion Detection by Electro‐Insertion into N, N, N′, N′‐Tetrahexyl‐Phenylenediamine (THPD) Microdroplets Studied by Voltammetry, EQCM, and SEM Techniques

Abstract: The electrochemical oxidation and re-reduction of N′,N′,N,N-tetrahexylphenylene diamine (THPD) deposited in form of microdroplets on a basal plane pyrolytic graphite or gold electrode is shown to be a chemically reversible process in the presence of aqueous electrolyte media containing NO3−, SCN−, ClO4−, or PF6−. Sharp voltammetric responses with a mid point potential, Emid, characteristic of the type of anion and its concentration are observed. The oxidation product, an ionic liquid, undergoes rapid ion exchange when the anion of the aqueous electrolyte is exchanged with anions of lower Emid replacing anions of higher Emid. Although the effect of the supporting electrolyte cation in the case of the alkali metals K+, Na+, and Li+ is not significant, a considerable change in the voltammetric peak shape and Emid occurs in the presence of protons. This effect, attributed to the protonation of THPD, is also sensitive to the type of anion present with anions of lower Emid causing more facile protonation. After protonation of THPD, oxidation and re-reduction can be shown to be associated with H+ expulsion and uptake. Deposited onto the rough surface of a gold coated planoconvex quartz crystal oscillator the [THPD+ClO4−]oil deposit can be observed in form of micron-sized droplets in SEM images. A strong frequency response of the crystal oscillator in an electrochemical quartz crystal microbalance experiment associated with the oxidation and re-reduction of THPD can be detected but is not related to changes in mass. Rather, this frequency response may be attributed to changes in the viscosity and/or coverage of the oily deposit.

Dinuclear and Dendritic Polynuclear Ruthenium(II) and Osmium(II) Polypyridine Complexes: Electrochemistry at Very Positive Potentials in Liquid SO2

Abstract: The electrochemistry in liquid SO2 of RuII and OsII dendritic polynuclear complexes (two hexanuclear species, having as the core a bis-chelating ligand, and one decanuclear species, built around a metal core) has been performed together with that of several of their lower-nuclearity analogues (five dinuclear and one trinuclear species), which can be considered as components of the larger dendritic species. All of the compounds contain 2,3- or 2,5-bis(2-pyridyl)pyrazine (2,3- or 2,5-dpp) as bridging ligands and 2,2‘-bipyridine (bpy) as terminal ligands. The identification of the redox sites for the compounds with high nuclearity was made possible by a bottom-up approach based on an extensive comparison of their electrochemical behavior with that of the simpler species. Owing to the large anodic potential window of liquid SO2 (to ∼4.3 V vs SCE under our experimental conditions) in conjunction with tetrabutylammonium hexafluoroarsenate as supporting electrolyte, several metal- and ligand-centered oxidations ...

Electrochemical Behavior of Copper Porphyrin Synthesized into Zeolite Cavity: A Sensor for Hydrazine

Abstract: The copper tetraphenylporphyrin (CuTPP) was prepared within a NaY zeolite cavity to investigate the electrocatalytic behavior of CuTPP upon the oxidation of hydrazine and cysteine. The amount of 0.067 mmol g−1 of CuTPP was obtained in the zeolite cavities. Cyclic voltammetry showed only an anodic peak at 320 mV that was assigned to the oxidation of CuI to CuII. This peak was not affected by the supporting electrolyte nature or by solution pH. The electrode showed electrocatalytic activity to oxidize both cysteine and hydrazine, however for cysteine the activity was weak, possibly as a result of the adsorption of oxidation product (cystine). Although hydrazine oxidation was efficient, neither oxidation was diffusion controlled. A linear correlation between catalytic current and hydrazine concentration allows sensing of hydrazine in the 0.2 × 10−6 to 1.0 × 10−6 mol L−1 concentration range. The detection limit was 1.0 × 10−7 mol L−1, and the response time was 1.1 s. The sensor was stable for at least 6 months under continuous use.

Highly Ordered Poly(cyclopentabithiophenes) Functionalized with Crown-Ether Moieties for Lithium- and Sodium-Sensing Electrodes

Abstract: Functionalized cyclopentadithiophenes 2 and 3 were synthesized and polymerized by anodic coupling, in acetonitrile solution, in the presence of 0.1 M tetraethylammonium perchlorate as supporting electrolyte. The former carries a 16-crown-5-ether ring coplanar to the bithiophene moiety, while a perpendicular 15-crown-5-ether ring is present in the latter. The cyclic voltammogram of poly-2 shows two redox processes at E° = −0.3 and +0.3 V, whereas that of poly-3 consists of a single response at E° = 0.0 V. The difference in electrochemical behavior is attributed to the occurrence of strong polaron π-dimerization in poly-2. The redox potential (E°) of this polymer moves toward more positive values passing from lithium to sodium salts as supporting electrolytes in acetonitrile solution. The redox cycle of poly-3 is instead completely insensitive to the change of the cationic species in solution. EQCM analysis shows that (i) both neutral polymers incorporate one alkaline ion per crown ring, (ii) the p-doping p...

Electrolytic removal of lead using a flow-through cell with a reticulated vitreous carbon cathode

Abstract: The aim of this work was to establish an electrolytic method for the removal of lead from wastewater using a three-dimensional, reticulated vitreous carbon cathode. During the development of the experimental setup, particular attention was paid to the electrolyte flow rate and to the cathode porosity. The electrolytic cell employed potential values in such a way that the lead reduction reaction occurred under mass transport control. The potentials were determined by hydrodynamic voltammetry using a borate/nitrate solution as the supporting electrolyte on a viterous carbon rotating disc electrode. The cell proved to be efficient in removing lead and was able to reduce the levels of this metal to 0.1mgdm-3 in 20min of recirculation, using the ratio catholyte volume/cathode volume equal to 0.027. The best configuration for this removal was a cathode porosity of 80ppi and a solution flow rate of 240dm3h-1.

Stripping Voltammetric Determination of Iodide with Synergistic Accumulation at a Carbon Paste Electrode

Abstract: Carbon paste electrodes (CPEs) of various compositions were studied to elucidate the stripping voltammetric behavior of iodide. At an accumulation potential of +0.7 V (vs. Ag/AgCl), the CPE containing tricresyl phosphate as a pasting liquid was able to preconcetrate iodide effectively via ion-pairing reaction followed by oxidation to iodine and its extraction onto pasting liquid. In a supporting electrolyte containing 0.5 M NaCl and 0.1 M HCl, the reduction signal was proportional to iodide concentration from 5 × 10−6 to 5 × 10−7 mol/L with a detection limit of approximately 2.5 × 10−7 mol/L (accumulation for 5 min). Other halides and pseudohalides did not interfere with the determination, except for a high concentration excess of thiocyanate and bromide (100:1). The method was tested on model solutions and was applied to determine total iodine in samples of table salts and mineral water. The results were compared to those obtained by reference methods.

Perylene polyether hybrids: Highly soluble, luminescent, redox-active dyes

Abstract: A new class of hybrid redox polyether melts has been prepared by covalent attachment of short polyethylene oxide “tails” to perylene, resulting in highly viscous materials with improved solubility in common solvents ranging from alcohols to toluene Solid-state voltammetry of the neat, undiluted materials is made possible by dissolution of LiClO4 supporting electrolyte in them The perylene0/1- electron self-exchange rate constants (kEX) are large Temperature studies show that the energy barrier is also large but that the reactions are adiabatic The ionic conductivity of the melts was measured to assess the effects of electron migration The absorption and fluorescence properties of the perylene derivatives in dilute solution are independent of polyether tail length, while the fluorescence of thin undiluted films of the hybrids is red-shifted (relative to dilute solution) by ca 125 nm and is dominated by excimer emission

Electrochemical reduction of dichloromethane to higher hydrocarbons

Abstract: The electroreduction of CH2Cl2 at Ni, Cu, Pt and Ag electrodes in acetonitrile and (C4H9)4NI 0.1m as supporting electrolyte was studied. The half-wave potential was found to be in the range −2.2 to −2.5V vs SCE at room temperature. From the analysis of the gaseous products it was found that methane, ethylene, chloromethane, propene and butene isomers were the main products, while at silver and platinum cathodes methane was mainly produced. The effect of the potential on the current efficiency of the gaseous products was also studied. The current efficiency of the products increases at concentration levels of CH2Cl2 up to 0.2m, whereas at higher values its CE is not significantly influenced. The application of the Schultz–Flory distribution analysis to the experimental data showed that the hydrocarbons are mainly formed via polymerization of methylene radicals on the surface of Ni and Cu electrodes. At Ag and Pt electrodes the mechanism appears to be different.

Surface Raman spectroscopic investigation of pyridine adsorption at platinum electrodes—effects of potential and electrolyte

Abstract: Surface enhanced Raman spectra of pyridine (Py) at Pt electrodes have been investigated as a function of potential and supporting electrolyte. The results show a large difference from those reported for coinage metal electrodes of Ag, Au and Cu, emphasising the effective involvement of chemical enhancement on Pt surfaces. At very negative (or positive) potentials, Raman spectra show the competitive coadsorption of hydrogen (oroxygen-containing species) with Py, and in acidic solutions, PyH+ ions prefer to dissociate into Py adsorbed on Pt surfaces even in the presence of chloride ions. The differences in the surface bonding strength for Py on Pt and coinage metal electrodes are explained in terms of the different electronic configurations of the metals.

Analysis of simulated reversible cyclic voltammetric responses for a charged redox species in the absence of added electrolyte

Abstract: We present an analysis of simulated cyclic voltammetric responses of a dissolved redox salt with no added supporting electrolyte. The redox system of interest is a reversible one electron transfer: AzA + e = BzA-1. Only the charged, oxidized species AzA and counterion XzX are initially present in solution (analogous systems where the reduced species and counterion are initially present are not explicitly discussed); their relative concentrations are dictated by zA, zX, and the constraint of electroneutrality (systems where zA = 0 or 1 are not considered). Cyclic voltammetric responses are simulated assuming Nernst−Planck transport, and electroneutrality with perfect IR compensation (easily simulated but experimentally unattainable) and with partial IR compensation. Simulations assuming perfect compensation allow us to elucidate the change in the resistance, Rref, between the working and reference electrodes effected by changes in the depletion layer during the course of the cyclic voltammetric perturbati...

A Novel Gold Electroplating System: Gold(I)‐Iodide‐Thiosulfate

Abstract: The electrodeposition of gold from a new electroplating system for gold that contains iodide and thiosulfate has been studied using rotating disk voltammetry. The cathodic electron transfer is slow, with a transfer coefficient of α = 0.76 ± 0.02, and is coupled with a preceding chemical reaction, the formation of the complex ion Au(S 2 O 3 ) 2 3 . The magnitude of the current contribution from the chemical step can be made negligible by using high concentrations of thiosulfate and by the proper choice of supporting electrolyte. High quality gold deposits with a very high aspect ratio have been obtained through a photoresist mask from this plating bath under optimized conditions. The choice of univalent salt as supporting electrolyte affects markedly the electroreduction of Au(I).

Solvent friction mechanism of an elementary charge-transfer step and cation-regulated preequilibrium for a pt/fe(cn)64-/3- electrode process

Abstract: The apparent standard rate constant, k0, for a Pt/hexacyanoferrate(II/III) electrode process, known to be strongly dependent on the nature and the concentration of supporting electrolyte (viz., of ...

Differential Pulse Anodic Stripping Voltammetric Determination of Cobalt(II) with N‐p‐Chlorophenylcinnamohydroxamic Acid Modified Carbon Paste Electrode

Abstract: A new preconcentration and voltammetric method was developed for the determination of Co(II) with N-p-chlorophenylcinnamohydroxamic acid (CPCHA) modified carbon paste electrode The measurements were carried out using differential pulse anodic stripping voltammetry The effects of several experimental parameters such as modifier composition in the carbon paste electrode, pH and concentration of supporting electrolyte, deposition potential, deposition time, and other instrumental parameters were studied for analytical application A linear response was obtained in the concentration range 1 × 10−6– 4 × 10−5 M Co(II) with a detection limit of 33 × 10−7 M for a 5 min deposition time A relative standard deviation of 31 % was obtained for eight successive determinations of 1 × 10−5 M Co(II) Many coexisting metal ions had little or no effect on the determination of cobalt(II) The method was applied for the determination of cobalt in vitamin B12 The new electrode offered many attractive properties such as high stability, self cleaning ability, the use of nondearated solutions and can be used repeatedly without regeneration