Electrode In Aqueous Solution Research Articles

Offset-free bidirectional current source for impedance measurement

In order to minimize the influence of electrode polarization and noise in impedance measurements, especially in the low frequency region, current injection shows several advantages compared to voltage application. Although the existence of a great variety of current sources, they meet our requirements only partially. We developed a voltage controlled current source for active front ends for a wide range of impedances, from Ω up to TΩ. A broad bandwidth from dc to 100 MHz was ensured by minimizing the parasitic capacitances. The current source outputs a symmetric signal without dc-offset. This is accomplished by a differential driver where the non-inverting branch was used for creating a current conveyor while the inverting branch host the feedback for offset control. We focused especially on the stability of the current source for usage with small metal electrodes in aqueous solutions.

The Adsorption Configuration of Valine on Ge(100)

The Adsorption Configuration of Valine on Ge(100)

Visible Light Photoelectrocatalytic Properties of Novel Yttrium Treated Carbon Nanotube/Titania Composite Electrodes

‡Photoelectrocatalytic decolorization of methlene blue (MB) in the presence of two types of carbon nanotube/titania and yttrium-treated carbon nanotube/titania electrodes in aqueous solutions were studied under visible light. The prepared composite electrodes were characterized by X-ray diffraction, transmission and scanning electron microscopy, energy dispersive X-ray analysis, and photoelectrocatalytic activity. The photoelectrocatalytic performances of the supported catalysts were evaluated for the decolorization of MB solution under visible light irradiation. The results showed that yttrium incorporation enhanced the decolorization rate of MB. It was found that the photoelectrocatalytic degradation of a MB solution could be attributed to the combined effects caused by the photo-degradation of titania, the electron assistance of carbon nanotube network, the enhancement of yttrium and a function of the applied potential. The repeatability of photocatalytic activity was also tested. The presence of yttrium enhanced the hydrophillicity of yttrium-carbon nanotubes/titania electrode because more OH groups can be adsorbed on the surface.

ELECTROCHEMICAL STUDIES AND EXTRACTION OF CHEMICAL AND ELECTROCHEMICAL PARAMETERS OF ZN(II) ION AT MERCURY ELECTRODE VIA CONVOLUTIVE VOLTAMMETRY AND DIGITAL SIMULATION METHODS

aBstract The electrochemical behaviour of Zn(II) ion as example of C rev E irr system was studied at hanging mercury drop electrode in aqueous solution in the presence of 1M KCl using cyclic voltammetry and convolutive voltammetry methods. Digital simulation technique was used to test the chemical and electrochemical parameters of Zn(II) ion estimated experimentally as well as verifying the proposed electrode mechanism. Keywords: Electrochemical behaviour, C rev E irr system, cyclic voltammetry, convolutive Voltammetry, digital simulation. introduction The electroreduction of Zn(II) has been extensively studied in aqueous and non-aqueous solutions and found to be controlled by both diffusion and charge transfer. 1-6 At mercury electrode different mechanisms have been proposed for electrode reduction of metal cations, e.g., a simple electron transfer process 7,8 , stepwise electron transfer 9 , a CE or CEE mechanism. 10,11 Several literature reports a possible validity of a mechanism involving two one-electron transfer has been discussed.

Complexation Studies of N, N′-ethylenedi-L-cysteine with Some Metal Ions

As part of a search for environmentally friendly metal chelating ligands, the stability constants of N, N′-ethylenedi-L-cysteine (EC) complexes with Ca(II), Cu(II), Mg(II) and Mn(II) were determined by potentiometry with a glass electrode in aqueous solutions containing 0.1 mol⋅L−1 KCl at 25 °C. Final models are proposed. For the Ca(II)–EC system, the overall stability constants are log 10 β CaHL=14.53±0.03, log 10 β CaL=4.79±0.01 and log 10 β CaL2=8.38±0.04. For the M(II)–EC systems, where M=Cu(II) or Mg(II), the overall stability constants are log10 β CuHL=31.19±0.02 and log 10 β CuL=27.02±0.06 for Cu(II), and are log 10 β MgHL=14.84±0.02 and log 10 β MgL=6.164±0.008 for Mg(II). For the Mn(II)–EC system, the overall stability constant is log 10 β MnL=10.12±0.01. Metal–chelate speciations simulations showed that EC is an efficient chelating agent for Cd(II), Co(II), Cu(II), Ni(II), Pb(II) and Zn(II) for pH≥7.

Preparation of Polypyrrole/Nuclear Fast Red Films on Gold Electrode and Its Application on the Electrocatalytic Determination of Methyl‐dopa and Ascorbic Acid

AbstractA novel voltammetric method using the Ppyox/NFR/Au (poly pyrrole – nuclear fast red – gold) modified electrode was developed for simultaneous measurement of various combinations of ascorbic acid (AA) and methyldopa (MDA). Polypyrrole film was prepared by incorporation of nuclear fast red (NFR) as doping anion, during the electropolymerization of pyrrole onto a gold (Au) electrode in aqueous solution using cyclic voltammetric (CV) method, and then it was overoxidized at constant potential. Differential pulse voltammetry was utilized for the measurement of both analytes using modified electrode. Well‐separated voltammetric peaks were observed for ascorbic acid (AA) and methyldopa at the Ppyox/NFR/Au modified electrodes with peak separation of 0.210 V. It has been found that under optimum condition (pH 3.0), the oxidation of AA and MDA at the surface of the electrode occurs at a potential about 260 and 50 mV less positive than unmodified Au electrode respectively. The current catalytic oxidation peaks showed a linear dependent on the concentration of AA and MDA in the range of 9.0×10−6 to 1.0×10−3 and 1.0×10−7 to 2.0×10−5 mol L−1 respectively. The detection limit of 5.8×10−6 and 5.0×10−8 mol L−1 (S/N=3) were obtained for AA and MDA respectively. The modified electrode was used for determination of AA and MDA in some real samples such as human serum and tablet.

Electrochemical determination of nitrite at a bare glassy carbon electrode; why chemically modify electrodes?

The oxidation of nitrite was studied at a bare glassy carbon (GC) electrode in aqueous solution using cyclic voltammetry, square wave voltammetry and chronoamperometry. A mechanism for the electrode reaction is proposed. A limit of detection (LOD) of 4 × 1 0 − 7 M was obtained for amperometry and this is evaluated with reference to literature reports for NO 2 − detection; in particular, the possible merits of using chemically modified electrodes as compared to ‘bare’ unmodified electrodes are critically assessed.

Voltammetric studies on the potent carcinogen, 7,12-dimethylbenz[ a]anthracene: Adsorptive stripping voltammetric determination in bulk aqueous forms and human urine samples and detection of DNA interaction on pencil graphite electrode

7,12-Dimethylbenz[ a]anthracene (DMBA), is a widely studied polycyclic aromatic hydrocarbon that has long been recognized as a very potent carcinogen. Initially, the electrochemical oxidation of DMBA at the glassy carbon and pencil graphite electrodes in non-aqueous media (dimethylsulphoxide with lithium perchlorate) was studied by cyclic voltammetry. DMBA was irreversibly oxidized in two steps at high positive potentials, resulting in the ill-resolved formation of a couple with a reduction and re-oxidation wave at much lower potentials. Special attention was given to the use of adsorptive stripping voltammetry together with a medium exchange procedure on disposable pencil graphite electrode in aqueous solutions over the pH range of 3.0–9.0. The response was characterized with respect to pH of the supporting electrolyte, pre-concentration time and accumulation potential. Using square-wave stripping mode, the compound yielded a well-defined voltammetric response in acetate buffer, pH 4.8 at +1.15 V (vs. Ag/AgCl) (a pre-concentration step being carried out at a fixed potential of +0.60 V for 360 s). The process could be used to determine DMBA concentrations in the range 2–10 nM, with an extremely low detection limit of 0.194 nM (49.7 ng L −1). The applicability to assay of spiked human urine samples was also illustrated. Finally, the interaction of DMBA with fish sperm double-stranded DNA based on decreasing of the oxidation signal of adenine base was studied electrochemically by using differential pulse voltammetry with a pencil graphite electrode at the surface and also in solution. The favorable signal-to-noise characteristics of biosensor resulted in low detection limit ( ca. 46 nM) following a 300-s interaction. These results displayed that the electrochemical DNA-based biosensor could be used for the sensitive, rapid, simple and cost effective detection of DMBA–DNA interaction.

Quantitative Voltammetry in Weakly Supported Media. Two Electron Transfer, Chronoamperometry of Electrodeposition and Stripping for Cadmium at Microhemispherical Mercury Electrodes

Double potential step chronoamperometry for the two-electron transfer amalgam-forming deposition and stripping of cadmium at a hemispherical mercury electrode in aqueous solution containing different concentrations of supporting electrolyte is compared with simulated results using the Nernst-Planck-Poisson system of equations. The latter were generated using an approximation of zero electric field at the interface [J. Phys. Chem. C 2008, 112, 13716−13728]; the approximation gives a good agreement between theory and experiment, so validating its use for the description of macroelectrode and microelectrode (but not nanoelectrode) problems involving low or negligible levels of supporting electrolyte.

Surface-Enhanced Raman Scattering Studies on the Interaction of Phosphonate Derivatives of Imidazole, Thiazole, and Pyridine with a Silver Electrode in Aqueous Solution

Surface-enhanced Raman scattering (SERS) spectra from phosphonate derivatives of N-heterocyclic aromatic compounds immobilized on an electrochemically roughened silver electrode surface are reported and compared to Raman spectra of the corresponding solid species. The tested compounds contain imidazole [ImMeP ([hydroxy-(1H-imidazol-5-yl)-methyl]-phosphonic acid) and (ImMe)2P (bis[hydroxy-(1H-imidazol-4-yl)-methyl]-phosphinic acid)]; thiazole [BAThMeP ((butylamino-thiazol-2-yl-methyl)-phosphonic acid) and BzAThMeP ((benzylamino-thiazol-2-yl-methyl)-phosphonic acid)]; and pyridine ((PyMe)2P (bis[(hydroxy-pyridin-3-yl-methyl)]-phosphinic acid) aromatic rings. Changes in wavenumber, broadness, and the enhancement of N-heterocyclic aromatic ring bands upon adsorption are consistent with the adsorption primarily occurring through the N lone pair of electrons with the ring arranged in a largely edge-on manner for ImMeP and BzAThMeP or in a slightly inclined orientation to the silver electrode surface at an intermediate angle from the surface normal for (ImMe)2P, BAThMeP, and (PyMe)2P. A strong enhancement of a roughly 1500 cm(-1) SERS signal for ImMeP and (PyMe)2P is also observed. This phenomenon is attributed to the formation of a localized C=C bond, which is accompanied by a decrease in the ring-surface pi-electrons' overlap. In addition, more intense SERS bands due to the benzene ring in BzAThMeP are observed than those observed for the thiazole ring, which suggests a preferential adsorption of benzene. Some interaction of a phosphonate unit is also suggested but with moderate strength between biomolecules. The strength of the P=O coordination to the silver electrode is highest for ImMeP but lowest for BzAThMeP. For all studied biomolecules, the contribution of the structural components to their ability to interact with their receptors was correlated with the SERS patterns.

DC Aqueous Electrodeposition of Sm-Co Permanent Magnets

DC electrodeposition of permanent magnets has been studied using parallel electrodes in aqueous solutions of Sm, Co and glycine. It has been shown that reproducible metallic SmCo alloy electrodeposits of high Sm content sufficient to achieve the intermetallic compounds, SmCo5 and Sm2Co17, have been obtained. These alloys after appropriate heat treatment can provide inexpensive nano- and micron-size as well as electroform materials with high performance permanent magnetic properties. A temperature of 60oC is optimum for producing deposits of at least 32 at % Sm or higher. Some desirable properties can be obtained by the use of certain specific supporting electrolytes. Magnetic hysteresis loops of SmCo deposits at both 25 and 60oC show that as Sm content increases deposits are transformed from anisotropic to isotropic magnetics. Magnetic properties of electrodeposits are comparable to sputtered deposits before heat treatment.

Preconcentration of the lipid-lowering drug lovastatin at a hanging mercury drop electrode surface

Adsorption and reduction of lovastatin were investigated by cyclic and square-wave voltammetry on a hanging mercury drop electrode in aqueous solutions over a wide pH range (4–9). The electroreduction of lovastatin proceeds via a surface EC mechanism in the whole pH range investigated. Using adsorptive stripping voltammetry, the drug yielded a well-defined voltammetric response in Britton-Robinson buffer, pH 6 at −1.49 V which can be used to determine trace amount of lovastatin. The linear concentration range of application was 1.0 × 10−8–1.0 × 10−7 M by using an accumulation potential of −0.5 V and a 90 s pre-concentration time. The method has been successfully applied for the determination of lovastatin in a spiked human serum sample.

Electrochemical quartz crystal microbalance study on the two-electrode-system cyclic voltammetric behavior of Prussian blue films

A two-channel electrochemical quartz crystal microbalance (EQCM) was used to investigate the cyclic voltammetric behavior of two Prussian blue (PB) film-modified Au electrodes in a two-electrode configuration in aqueous solution. The redox peaks observed in the two-electrode cyclic voltammogram (CV) are assigned to the intrinsic redox transitions among the Everitt’s salt, PB, and Prussian yellow for the film itself, the redox process of the Au substrate and the redox process of small-quantity ferri-/ferrocyanide impurities entrapped in the PB film, as also supported by ultraviolet-visible (UV-Vis) spectroelectrochemical data. The profile of the two-electrode solid-state CV for the PB powder sandwiched between two gold-coated indium-tin oxide (ITO) electrodes is similar to that for two PB-modified Au electrodes in aqueous solution, implying similar origins for the corresponding redox peaks. The two-channel EQCM method is expected to become a highly effective technique for the studies of the two-electrode electrochemical behaviors of many other species/materials.

Photoanodic response of iron oxide electrode in aqueous solution and its application to Pb 2+ removal under visible light irradiation

The iron oxide electrode was prepared from thermal oxidation of iron at 600 °C for 3 h in air atmosphere. This electrode with the structure of Fe 3O 4 and α-Fe 2O 3 showed the response of photoanodic current to the light with wavelength shorter than 600 nm. The band gap energy of this electrode was 1.99 eV. The onset potential of distinct steady photocurrent and also the flatband potential were 0.80 and 0.09 V vs. Ag/AgCl, respectively, in 0.1 M HNO 3 aqueous solution. The cell consisting of the iron oxide photoanode in HNO 3–Pb(NO 3) 2 and the graphite cathode in H 2SO 4–Ce(SO 4) 2 caused the PbO 2 deposit on the surface of the former electrode due to visible light irradiation without application of voltage. By holding the potential of this electrode at more positive value than 0.90 V, the photoanodic removal rate of Pb 2+ in HNO 3–Pb(NO 3) 2 solution was higher than that observed when Ce 4+ was used as electron acceptor.

Electrochemical Determination of NDPhA via its Electrocatalysis at Porous Au Electrode in Room Temperature Ionic Liquid

AbstractN‐Nnitrosodiphenylamine (NDPhA) is a typical kind of nonvolatile nitrosamine. Its electrochemical oxidation occurs usually at relative positive potentials (>1.1 V) even at catalytic noble metal electrodes in aqueous solutions. The formation of oxide and evolution of oxygen at such high potentials makes the analysis of NDPhA on noble metal electrodes difficult. Accordingly, its electrochemical analysis is usually performed in anhydrous organic electrolytes. In this work, room temperature ionic liquid [BMIM+] [BF$\rm{ {_{4}^{-}}}$] acting as electrolyte was introduced in this electrochemical analysis systems. It acts as supporting electrolyte itself, has good solubility of organic compounds, and allows a wide performance potential window of noble electrode, and in turn, highly electrocatalytic noble electrode of platinum or gold can be used as working electrodes. After the investigation of the electrocatalytic behavior of NDPhA at a gold electrode in this room temperature ionic liquid electrolyte, high sensitive determination of NDPhA was designed. It is demonstrated that the electrochemical response of NDPhA is determined by a surface‐controlled process. Therefore, a sensor with high sensitivity was constructed by applying porous Au electrodes with highly electrocatalytic activity and large active surface area. The present approach on one hand broadens the application field of room temperature ionic liquids, and on the other hand provides a sensitive analytical method for environmental detection.

Electrochemistry of Sc3N@C78 embedded in didodecyldimethylammonium bromide films in aqueous solution

The electrochemical behavior of trimetallic nitride clusterfullerene (Sc3N@C78) embedded in films of the cationic surfactant didodecyldimethylammonium bromide (DDAB) on glassy carbon (GC) electrodes in aqueous solution was investigated. Four pairs of reversible redox peaks were observed in the potential range between +0.6 and −0.9 V vs. SCE. Different to the electrochemistry of pristine Sc3N@C78 in organic solution, the first reduction is a one-electron rather than simultaneous two-electron process because of the strong binding between DDA+ and the monoanion of Sc3N@C78. The generated radial monoanion, dianion and trianion of Sc3N@C78 are stable during continuous potential cycling, while some chemical reactions take place when the third anion is further reduced in the films. The cyclic voltammograms of Sc3N@C78/DDAB films checked at different temperatures pointed to strong temperature dependence. The electrochemical processes were also measured in different electrolytes, which showed pronounced anionic dependence and no cathodic dependence on either the cation or anions present. A possible electron-transfer mechanism of a Sc3N@C78/DDAB film was presented.

Adsorption phenomena on a mercury electrode in aqueous cryptand[2.2.2] solutions by the background of tetraalkylammonium salts

The electrochemical behavior of cryptand[2.2.2] (Cry) is studied on a mercury electrode in aqueous solutions of tetraalkylammonium tetrafluoroborates (Me4N+, Et4N+, and Bu4N+). Cryptand [2.2.2] is shown to exhibit high surface activity in Me4 NBF4 nd Et4NBF4 solutions. Based on the model of two parallel capacitors supplemented by the Frumkin adsorption isotherm, the adsorption parameters of Cry by the background of Me4BNF4 were calculated using the regression analysis methods. The calculated dependences of the differential capacitance on the potential adequately agree with experimental curves. The adsorption characteristics of Cry in the studied solutions are compared with those in MgSO4 solutions. By the background of Bu4NBF4, Cry molecules and Bu4N+ cations exhibit very close surface activity and form a mixed adsorption layer.

Electrocatalytic reduction of NAD+ at glassy carbon electrode modified with single-walled carbon nanotubes and Ru(III) complexes

A simple procedure was developed to prepare a glassy carbon electrode modified with carbon nanotubes and Ruthenium (III) complexes. First, 25 μl of dimethyl sulfoxide–carbon nanotubes solutions (0.4 mg/ml) was cast on the surface of the glassy carbon electrode and dried in air to form a carbon nanotube film at the electrode surface. Then, the glassy carbon/carbon nanotube-modified electrode was immersed into a Ruthenium (III) complex solution (direct deposition) for a short period of time (10–20 s for multiwalled carbon nanotubes and 20–40 s for single-walled carbon nanotubes). The cyclic voltammograms of the modified electrode in aqueous solution shows a pair of well-defined, stable, and nearly reversible redox couple, Ru(III)/Ru(II), with surface-confined characteristics. The attractive mechanical and electrical characteristics of carbon nanostructures and unique properties and reactivity of Ru complexes are combined. The transfer coefficient (α), heterogeneous electron transfer rate constants (ks), and surface concentrations (Γ) for the glassy carbon/single-walled carbon nanotubes/Ru(III) complex-, glassy carbon/multiwalled carbon nanotubes/Ru(III) complex-, and glassy carbon/Ru(III) complex-modified electrodes were calculated using the cyclic voltammetry technique. The modified electrodes showed excellent catalytic activity, fast response time, and high sensitivity toward the reduction of nicotinamide adenine dinucleotide in phosphate buffer solutions at a pH range of 4–8. The catalytic cathodic current depends on the nicotinamide adenine dinucleotide concentration. In the presence of alcohol dehydrogenase, the modified electrode exhibited a response to addition of acetaldehyde. Therefore, the main product of nicotinamide adenine dinucleotide electroreduction at the Ru(III) complex/carbon nanotube-modified electrode was the enzymatically active NADH. The purposed sensor can be used for acetaldehyde determination.

Study of the Underlying Electrochemistry of Polycrystalline Gold Electrodes in Aqueous Solution and Electrocatalysis by Large Amplitude Fourier Transformed Alternating Current Voltammetry

Polycrystalline gold electrodes of the kind that are routinely used in analysis and catalysis in aqueous media are often regarded as exhibiting relatively simple double-layer charging/discharging and monolayer oxide formation/removal in the positive potential region. Application of the large amplitude Fourier transformed alternating current (FT-ac) voltammetric technique that allows the faradaic current contribution of fast electron-transfer processes to be emphasized in the higher harmonic components has revealed the presence of well-defined faradaic (premonolayer oxidation) processes at positive potentials in the double-layer region in acidic and basic media which are enhanced by electrochemical activation. These underlying quasi-reversible interfacial electron-transfer processes may mediate the course of electrocatalytic oxidation reactions of hydrazine, ethylene glycol, and glucose on gold electrodes in aqueous media. The observed responses support key assumptions associated with the incipient hydrous oxide adatom mediator (IHOAM) model of electrocatalysis.

Amperometric and voltammetric detection of hydrazine using glassy carbon electrodes modified with carbon nanotubes and catechol derivatives

A simple procedure was developed to prepare a glassy carbon (GC) electrode modified with carbon nanotubes (CNTs) and catechol compounds. First, 25 μL of DMSO–CNTs solutions (0.4 mg/mL) was cast on the surface of GC electrode and dried in air to form a CNTs film. Then the GC/CNTs modified electrode immersed into a chlorogenic acid, catechine hydrate and caffeic acid solution (electroless deposition) for a short period of time (2–80 s). The cyclic voltammogram of the modified electrode in aqueous solution shows a pair of well-defined, stable and nearly reversible redox couple (quinone/hydroquinone) with surface confined characteristics. The combination of unique electronic and electrocatalytic properties of CNTs and catechol compounds results in a remarkable synergistic augmentation on the response. The electrochemical reversibility and stability of modified electrode prepared with incorporation of catechol compound into CNTs film was evaluated and compared with usual methods for attachment of catechols to electrode surfaces. The transfer coefficient ( α), heterogeneous electron transfer rate constants ( k s) and surface concentrations ( Γ) for GC/CNTs/catechol compound modified electrodes were calculated through the cyclic voltammetry technique. The modified electrodes showed excellent catalytic activity, fast response time and high sensitivity toward oxidation of hydrazine in phosphate buffer solutions at pH range 4–8. The modified electrode retains its initial response for at least 2 months if stored in dry ambient condition. The properties of modified electrodes as an amperometric sensor for micromolar or lower concentration detection of hydrazine have been characterized.