Adsorption of 1-heptanol on bismuth single-crystal plane electrodes

Cyclic voltammetry, impedance and chronocoulometry have been employed for the quantitative study of 1-heptanol (1-HepOH) adsorption on the bismuth single-crystal plane|aqueous Na₂SO₄ solution interface. The adsorption isotherms, Gibbs energies of adsorption, , the limiting surface excess, Γ_max, and other adsorption parameters have been determined. The adsorption of 1-HepOH on Bi single-crystal planes is mainly physical and is limited by the rate of diffusion of organic molecules to the electrode surface. Comparison of the adsorption data for 1-HepOH with other alcohols shows that the adsorption characteristics depend on the structure of the hydrocarbon chain. The adsorption activity of adsorbates at the bismuth|solution interface increases in the sequence 1-propanol<1-butanol<1-pentanol<1-hexanol<1-heptanol as the adsorption activity at the air|solution interface increases. For all the compounds studied, the adsorption activity increases in the sequence of planes as .     

Impedance analysis of the transport of counter ions at polypyrrole-Nafion composite electrodes

The ion transport accompanying the redox reactions of polypyrrole at a polypyrrole-Nafion composite electrode was investigated with systems containing specifically selected electrolytes. From the cyclic voltammetric and impedance data obtained, transport of cations was found to be responsible for the charge transfer process and parameters such as the charge transfer resistance, R_ct, the low frequency polymer resistance, R_e, the limiting capacitance, C_e and the diffusion coefficient, D_ct for the related cations were estimated. The electrochemical behaviour (i.e., electronic insulation and electronic conductance) of polypyrrole-Nafion composite electrodes was found to be the same as that of the polypyrrole electrodes, except that they appeared in regions of more negative potentials.     

CO2在铜电极上的电还原行为

对常温常压下的MeCN, DMF和DMSO等3种有机溶剂中的CO2的电还原反应行为进行了研究, 求得了传递系数和扩散系数, 并证明了在MeCN, DMF和DMSO中, CO2的还原反应是受扩散控制的不可逆过程.     

Isobaric vapour–liquid equilibria data for the binary system 1-propanol+1-pentanol and isobaric vapour–liquid–liquid equilibria data for the ternary system water+1-propanol+1-pentanol at 101.3 kPa

Consistent vapour–liquid equilibrium (VLE) data for the binary system 1-propanol+1-pentanol and for the ternary system water+1-propanol+1-pentanol are reported at 101.3 kPa. An instrument using ultrasound to promote the emulsification of the partly miscible liquid phases have been used in the determination of the vapour–liquid–liquid equilibrium (VLLE). The VLE and VLLE data were correlated using UNIQUAC.     

Adsorption of n-pentanol from KPF6 aqueous solution on the (100) and (110) faces of Ag single crystal electrodes

The potential dependence of the adsorption of n-pentanol (NP) on the (100) and (110) faces of Ag single crystal electrodes from aqueous KPF₆ solutions has been studied at 10 mV s⁻¹ potential scan rate by measuring the impedance both at constant frequency (f) and by sweeping f from 11 kHz to 0.1 Hz. The adsorption of NP has been found to be strongly dependent on crystal orientation. The results have been compared with those obtained on Ag(111) with the same kind of single crystal preparation, as well as with Ag(100) electrolytically grown in a Teflon capillary [A. Popov, O. Velev, T. Vitanov, J. Electroanal. Chem. 256 (1988) 405].     

离子液体中间硝基苯酚在玻碳电极上的电化学还原行为研究

在[EMIM]Br体系中,以玻碳为工作电极,铂丝为辅助电极,饱和甘汞电极为参比电极,研究了间硝基苯酚的电化学行为.采用循环伏安法和计时电量法,研究了扫描速度、温度和底物浓度等因素对其电化学行为的影响,求得扩散系数D为9.184×10^-7cm²/s,传递系数α为0.37,证明了在[EMIM]Br体系中,此反应是受扩散控制的不可逆反应.     

The electrochemistry of antibody-modified conducting polymer electrodes

The modification of conducting polymer electrodes with antibodies (i.e. proteins) by means of electrochemical polymerization is a simple step that can be used to develop an immunological sensor. However, the electrochemical processes involved leading to the generation of analytical signals by the sensor have not been fully investigated. In this work, we report on the characterization of the interaction between an antigen, human serum albumin (HSA) and an antibody-immobilized polypyrrole electrode (such as anti-HSA) using cyclic voltammetry (CV) and impedance spectroscopy. This interaction was monitored using electrochemical impedance spectroscopy at three different potentials. The potentials correspond to the three redox states of the electroconducting polymer (i.e. reduced, doped and overoxidized states). Evidence from the CV experiments confirmed that there was a shift in the potential, which was found to be proportional to the concentration. Both the CV and the impedance experiments indicated that this potential-dependent shift could be attributed to antibody–antigen (Ab–Ag) binding.     

Liquid density of 1-pentanol at pressures up to 140 MPa and from 293.15 to 403.15 K

This work reports new density data (180 points) of 1-pentanol at twelve temperatures between 293.15 and 403.15 K, and pressures up to 140 MPa (every 10 MPa). A new Anton Paar vibrating-tube densimeter, calibrated with an uncertainty of ±0.5 kg m⁻³ was used to perform these measurements. The experimental density data were fitted with the Tait-like equation with low standard deviations. In addition, the isobaric thermal expansivity and the isothermal compressibility have been derived from the Tait-like equation.     

Sodium dodecyl sulfate-modified carbon paste electrodes for selective determination of dopamine in the presence of ascorbic acid

A carbon paste electrode (CPE) modified by a monolayer film of sodium dodecyl sulfate (SDS) was used for detection of dopamine (DA). Cyclic voltammetry demonstrated improved response of the DA sensor. This suggests the effectivity of surface modification of CPE by SDS. Impedance spectroscopy was used for the characterization of CPE surface properties. The effect of SDS concentration on the electrode quality also reveals that SDS formed a monolayer on CPE surface with a high density of negative-charged end directed outside the electrode. As a result, the carbon paste electrode modified with SDS (SDS/CPE) exerted discrimination against ascorbic acid in physiological circumstance. Thus, it can selectively determine dopamine even in the presence of 220-fold AA combined with differential pulse stripping voltammetry. In pH 7.40 phosphate buffer solution, the oxidation peak current on differential pulse voltammograms increases linearly with the concentration of DA in the range of 5.0 x 10(-7) to 8.0 x 10(-4) mol . L(-1) with a detection limit of 5.0 x 10(-8) mol . L(-1). Satisfying results are achieved when detecting the DA in injection and simulated biology sample.     

Effects of pretreatments and modifiers on electrochemical properties of carbon paste electrodes

The electrochemical properties of carbon paste electrodes (CPEs), including unmodified and modified with protein and polycations, were investigated by impedance spectroscopy (IS) using ferricyanide and ferrocene monocarboxylic acid (FcMA) as redox probes. Various electrochemical pretreatments were applied to the unmodified CPE. The heterogeneous charge transfer rate constant of ferro/ferricyanide couple is enhanced by 2 to 10 times compared with that obtained at untreated electrodes. It was found that for ferricyanide the more suitable pretreatments are successive cyclic voltammetric scans, cathodization and a square wave-like stepping rather than high-potential anodization. However, the pretreatment only exhibits a slight effect on the kinetics of FcMA. At the CPEs containing modifier, the electron transfer rate of the redox couple depends more on the pH of electrolyte solution if ferro/ferricyanide is used. The results can be explained by the differently charged states of the CPEs that were caused by the protonation or deprotonation of the modifiers in various pH solutions and demonstrate the importance of the electrostatic interaction on the kinetics of the highly polar species such as ferricyanide. The different adsorptive behavior of ferricyanide and FcMA is also discussed.     

Reactive groups on polymer-covered electrodes

Polythiophene films containing ester groups on the surface of electrodes are interesting potential carrier materials for reagents. Methyl thiophene-3-acetate (3) can be copolymerized with 3-methylthiophene (1) and 3-butylthiophene (2) by means of cyclic voltammetry (CV) at potentials of 0–2.2 V. Higher potentials (0–2.4 V) lead to overoxidation of the copolymers. The ester groups were confirmed by FTIR spectra. Electrochemical investigations of 2,2′-bithiophene (6) and 3 at equimolar ratios showed no successful copolymerization at potentials of 0–1.3 V. If the copolymerization experiments of 6 with 1 or 3 were carried out at molar ratios of 1:50 at 1.3 V, 6 with its low oxidation potential was polymerized without copolymerization of the other monomers. However, if the oxidation potential was increased stepwise from 1.3 V, the oxidation of 1 or 3 occurred, forming copolymers containing both monomer components. HPLC investigations of solutions containing mixtures of 6 and 3 and also 6 and 1 in acetonitrile/TEABF₄ showed, after exhaustive oxidation at a potential of 1.3 V, the complete absence of 6; 1 and the ester 3 were not oxidized and copolymerized at these potentials. From the results of the copolymerization experiments, as well as the HPLC investigations, it can be concluded that the dominant mechanism of the electrochemical polymerization is radical cation dimerization. Received: 21 August 1998 / Accepted: 11 January 2000     

Determination of ultratrace lead with bismuth film electrodes based on magneto-voltammetry

A novel method for the determination of Pb²⁺ with bismuth film electrodes (BFEs) based on magneto-voltammetry was investigated. In the presence of a 0.6?T external magnetic field, square wave voltammetry of Pb²⁺ was performed with BFEs. A high concentration of Fe³⁺ was added to the analytes to generate a large cathodic current during the preconcentration step. A Lorentz force from the flux of net current through the magnetic field resulted in convection. Then, more Pb²⁺ deposited onto the electrode and larger stripping peak currents were observed. BFEs that were prepared by simultaneously depositing the bismuth and Pb²⁺ on an electrode offered a mercury-free environment for this determination. This method exhibits a high sensitivity of 4.61?µA?µM^?1 for Pb²⁺ over the 1?×?10^?8 to 1?×?10^?6?M range. A detection limit as low as 8.5?×?10^?10?M was obtained with only 1-min preconcentration. The method was successfully applied to determine Pb²⁺ in real water samples.     

Voltammetric behavior and determination of bismuth on sodium humate modified carbon paste electrode

The preconcentration and voltammetric behavior of Bi^III on a sodium humate modified carbon paste electrode was studied by means of cyclic voltammetry (CV) and differential pulse stripping voltammetry (DPSV). The proposed measurement involves an initial nonelectrolytic preconcentration step in which Bi^III is complexed by the surface modifier in a solution of 0.05 M KNO₃-0.0106 M HNO₃ (pH 2.0) and a subsequent electrochemical scan step in which the preconcentrated Bi^III was reduced and then oxidized promptly in supporting electrolyte of 0.5 M HNO₃. The resulting DPSV anodic current was proportional to the concentration of Bi^III ion over the range of 4.78 × 10⁻⁸–1.44 × 10⁻⁵ M. The detection limit was 4.78 × 10⁻⁸ M. The proposed method was used to determine bismuth in various samples. Various factors affecting the electrode behavior were also investigated at the same time.     

Adsorption of diethylether on single-crystal gold electrodes: Calculation of adsorption parameters

In this paper quantitative studies of the adsorption of diethylether on the three low-index faces (111), (100) and (110) of the gold electrode are presented. The equilibrium charge densities at the gold electrode were determined from combined chronocoulometric and admittance measurements. The adsorption parameters such as free energy of adsorption ΔG_A, limiting Gibbs excess Γ_max, lateral interaction constant a, etc. were calculated and compared with earlier results relative to the mercury electrode surface. These adsorption parameters were next discussed in terms of the properties characteristic for the nature (liquid, solid) and the structure (crystallographic orientation) of the surfaces investigated. Under the assumption that: (1) diethylether adsorption is a water-substitution process, and (2) the ether-metal interactions are weak and change slightly with the nature and the structure of the surface, the free energies of adsorption ΔG_A⁰ were used as a probe of the surface hydrophilicity. The following series of increasing hydrophilicity was proposed:Au(111)≦Hg≦Au(100)<Au(110) and the earlier literature estimations of gold hydrophilicity were critically discussed.     

Electrochemical methods for analysing and controlling charge transfer at the electrode–tissue interface

There have been rapid advances in the development of new materials for use in electrode–tissue interfacing. The development of conducting polymers, conducting hydrogels, carbon nanotubes, graphene and other conducting materials has provided a rich landscape for controlling charge transfer at the electrode–tissue interface and hence to monitor and manipulate cell behaviour. These materials have been used in tissue-engineered constructs to direct and control cell proliferation, growth and differentiation. However, their translation to clinical devices has been less successful. In this review, the use of electroanalytical techniques to develop an understanding of charge transfer at the electrode–tissue interface is discussed. In particular, the impact of solution and electrode conditions on charge injection capacity is demonstrated. The importance of standardised testing methods and the correlation of electrochemical and electrophysiological performance show the limitations of empirical studies and help define key electrode properties for clinical devices. The development of a sound theoretical basis for charge transfer at this increasingly important interface is being advocated to improve clinical outcomes and device lifetime and reduce power usage.     

Oxidation of 2-mercaptobenzoxazole in aqueous solution: solid phase formation at glassy carbon electrodes

The redox reactions of 2-mercaptobenzoxazole (MBO) have been investigated by cyclic voltammetry at glassy carbon electrodes in aqueous solution. Four anodic and three cathodic processes could be identified. A more detailed analysis of the oxidation processes up to a potential of +0.6 V (SCE) and the corresponding reduction signals showed that the oxidation leads to bis(benzoxazolyl) disulfide (BBOD). Owing to its low solubility, the oxidation product remains at the electrode surface. This product has been identified by ex situ FTIR and XPS analysis. During the reduction of BBOD, mainly MBO is formed. The remarkable lower solubility of BBOD in aqueous solutions compared to MBO allows preparation of layers of BBOD in situ and to control the amount of deposited BBOD via the MBO solution concentration and electrolysis time. The peak potential and peak shape of the reduction signals change remarkably as the amount of BBOD increases from submonolayer coverage to coverages that correspond to multilayers. The behavior can be explained by assuming an electrochemical conversion of BBOD microcrystals, which are deposited on the electrode surface, if the amount of BBOD formed during the MBO oxidation exceeds one monolayer. Received: 21 January 1999 / Accepted: 15 March 1999     

Detection of dopamine using self-assembled diazoresin/single-walled carbon nanotube modified electrodes

Ultrathin films of diazoresin(DR)/single-walled carbon nanotube(SWNT) were fabricated on thioglycollic acid(TGA) decorated gold(Au) electrodes by the self-assembly method combined with the photocrosslinlcing technique.The electrochemical behavior of dopamine(DA) at the DR/SWNT modified electrodes was studied using the cyclic voltammetry(CV) and differential pulse voltammetry(DPV) methods.Under the optimal conditions,a linear CV response to DA concentration from 1 μmol/L to 40 μmol/L was observed,and the detection limit of DA was 2.1 ×10~(-3) μmol/L via the DPV method in the presence of 10 μmol/L of uric acid(UA) or 2.5 × 10~(-3) μmol/L via the DPV method in the presence of10 μmol/L of ascorbic acid(AA).Moreover,the modified electrodes exhibited good reproducibility and sensitivity,demonstrating its feasibility for analytical purposes.     

Underpotential deposition of tin(II) on a gold disc electrode and determination of tin in a tin plate sample

This work describes a study of the underpotential deposition (UPD) of Sn²⁺ on a polycrystalline gold disc electrode using cyclic voltammetry (CV) and chronocoulometry (CC). Sn²⁺ ions showed well-defined peaks from UPD and UPD stripping (UPD-S) in 1 mol/L HCl solutions, while bulk deposition (BD) and BD stripping (BD-S) of the ions were also observed. The measured UPD shifts, E_UPD, between the UPD-S and the BD-S peaks were more than 200 mV. The UPD charge and the surface coverage of tin were measured by CC. A new method for determining Sn²⁺ was therefore developed, based on the excellent electrochemical properties of the Au/Sn UPD system. A plot of the UPD-DPASV (differential pulse anodic stripping voltammetry) signal versus the Sn(II) concentration was obtained for [Sn(II)] of 1.98×10^–7 to 3.64×10^–5 M. The method developed here has been applied to determine the tin in a tin plate sample.     

Differential pulse anodic stripping voltammetry detection of metallothionein at bismuth film electrodes

As a representation of metalloproteins, metallothionein (MT), which plays important biological and environmental roles such as in the metabolism and detoxification of some metals, was detected at bismuth film electrode (BiFE) by differential pulse anodic stripping voltammetry (DPASV). In pH 2–5.5, two well-defined anodic peaks were produced and attributed to the Zn²⁺ and Cd²⁺ inherent to MT. The calibration plot of DPASV peak currents for Cd²⁺ inherent to MT versus MT concentrations showed a good linearity with a detection limit of 3.86 × 10⁻⁸ mol/L for MT. As a non-toxic excellent electrode material, BiFE shows good performance for detecting MT, and is expected to find further applications in the studies of many other metalloproteins.     

Probing the electrochemical double layer of an ionic liquid using voltammetry and impedance spectroscopy: A comparative study of carbon nanotube and glassy carbon electrodes in [EMIM][EtSO4]

Cyclic voltammetry (CV) and electrochemical impedance spectroscopy (EIS) are compared as techniques for analyzing double layer capacitances of ionic liquids (ILs) at the surfaces of two carbon-based electrodes. These systems are relevant for energy storage supercapacitors and often are associated with unconventional electrochemical properties. Certain theoretical and experimental aspects of CV and EIS necessary for quantitative evaluation of the capacitance characteristics of such systems are explored. The experiments use 1-ethyl-3-methyl imidazolium ethylsulfate as a model IL electrolyte in combination with a porous electrode of carbon nanotubes (CNTs). The results are compared with those obtained with a nonporous glassy carbon (GC) electrode. The time is constant, and hence the power delivery characteristics of the experimental cell are affected by the electrolyte resistance and residual faradaic reactions of the IL, as well as by the spatially inhomogeneous electrode surfaces. It is shown that adequate characterization of these IL-electrode systems can be achieved by combining CV with EIS. A phenomenological framework for utilizing this combination is discussed.