On the Adsorption and Reduction of the Herbicide Picloram on Mercury and Carbon Electrodes

At concentrations higher than 2?10^?4 M , and below pH 3, the cyclic voltammograms of picloram (=4‐amino‐3,5,6‐trichloropyridine‐2‐carboxylic acid) on Hg electrodes show two prepeak systems (named I and II attending to the proximity to the main reductions peak), which can be attributed to the weak adsorption of reactant and the strong adsorption of the product at the electrode surface. The system II is due to the uncharged form of picloram, and system I to the picloram protonated at the pyridine N‐atom. Small amounts of the surfactant Triton X‐100 (=α‐[4‐(1,1,3,3‐tetramethylbutyl)phenyl]‐ω‐hydroxypoly(oxyethane‐1,2‐diyl)) cause the disappearance of system I, the shift of system II, and also affect the intensities and widths of anodic and cathodic peaks but not the charge passed in each peak. Thus, the adsorption process responsible for the appearance of system I is inhibited by the presence of Triton; by contrast, the process corresponding to system II is only modified by the surfactant, becoming an electrochemical process occurring at the potentials corresponding to system II, which is more reversible than that observed in the absence of Triton. The addition of Triton permitted the analysis of the main reduction process. Convolution voltammetry of the main reduction peak is consistent with the loss of a Cl‐atom in equilibrium which occurs after a reversible electron transfer and is followed by the reductions of both species present in the equilibrium (Scheme 2). This is also the reduction mechanism on a glassy carbon electrode but the electron transfer on the carbon electrode increases with respect to the mercury electrodes; in addition, the loss of the Cl‐atom does not take place on the electrode surface. From the recording of differential capacity–potential curves, it was concluded that picloram is adsorbed on the carbon electrode; but this adsorption is too weak to induce the appearance of prepeak systems.     

Electrochemical Reduction of Comenic and Meconic Acids on a Mercury Electrode

Russian Journal of Electrochemistry -     

Electrochemical Reduction Behavior and Polarographic Determination of Methoxy Triazine Herbicides in Environmental Samples

The electrochemical reduction behavior of 1,3,5-triazine herbicides, Atraton (AN), Prometon (PN), Secbumeton (SN), and Terbumeton (TN) at mercury electrodes was studied in aqueous Britton Robinson buffer (BR) solutions by using different voltammetric techniques. The nature of the electrode process was examined. Number of electrons involved in the reduction process of all the four compounds was evaluated and a reduction mechanism was proposed. The electrolysis products were separated and identified by IR spectra. For analytical purposes, BR buffer of pH 4.0 was chosen as working medium for all the four analytes. The detection limits were found to be 1.5 × 10^?8 mol l^?1, 2 × 10^?8 mol l^?1, 2.8 × 10^?8 mol l^?1, and 1 × 10^?8 mol l^?1 for AN, PN, SN, and TN, respectively. A differential pulse voltammetric method was developed for the determination of these compounds in agricultural formulations, water, and soil samples. The interference from the ions and other herbicides were also evaluated.     

酸性溶液中硝基苯在WC电极上的电化学还原

以聚四氟乙烯为粘接剂制成碳化钨(WC)电极.采用循环伏安法、线性扫描法和恒电位阶跃法研究了硝基苯在酸性溶液中WC电极上的电化学行为.实验表明:WC电极对硝基苯的还原具有较好的活性,电极过程受扩散和电化学步骤混合控制;表观活化能为23.7kJ·mol 1,其中,电化学步骤的活化能10.91kJ·mol 1.     

硝基苯在铜电极上的电还原特性研究

应用循环伏安法和线性扫描伏安法研究水溶液中硝基苯在铜电极上的电还原特性及其电还原为苯胺的中间步骤和反应机理.结果表明:铜电极上硝基苯的还原电位在-0.58V和-1.32V左右(vs.SCE),溶液的酸性和碱性均有益于该还原反应的发生;还原过程伴有反应物吸附现象,当硝基苯浓度较大时,还原过程受传质过程控制;随着厌氧程度的提高,还原速率加快.     

Cu/C-Nafion复合电极上硝基苯的电化学还原

制备性电解的结果表明，硝基苯在Cu／C－Nafion膜复合电极上的还原产物只有苯胺，可能与电极／Nafion界面的弱酸性环境和其还原中间产物本羟胺在界面的扩散较仅有关．生成苯胺的电流效率随电流密度的增大而减小，随反应液中硝基苯浓度的增大出现一个最大值．这可能是硝基苯的电化学还原过程受某种粒子的扩散控制、峰电流取决于硝基苯在Nafion膜中的溶解度所致．     

Electrochemical Reduction of Oxygen on Multi-walled Carbon Nanotubes Electrode in Alkaline Solution

The multi-walled carbon nanotubes (MWNTs) electrode was constructed using polytetrafluoroethylene as binder, and the electrochemical reductive behavior of oxygen in alkaline solution was first examined on this electrode. Compared with other carbon materials, MWNTs show higher electrocatalytic activity, and the reversibility of O2 reduction reaction is greatly improved. The experiments reveal that the electrochemical reduction of O2 to HO2 is controlled by adsorption. The preliminary results illustrate the potential application of MWNTs in fuel cells.     

贮氢合金电极在葡萄糖电化学还原中的应用

以贮氢合金电极作催化还原电极,恒电位电解葡萄糖,发现合金经表面处理及电极的活化后,即可提高电流效率,在最优条件下,电解葡萄糖制山梨醇电流效率高达90%,葡萄糖转化率达80%以上.测试了电极的使用寿命,同时对电极中毒及再生方法进行了探讨.     

Sn/Cu电极电化学还原CO2的研究

采用电沉积法制备Sn/Cu电极,由SEM观察并研究了电沉积电流密度对电极形貌的影响.在碱性三电极体系中考察了Sn/Cu电极对析氢、CO2还原的影响.发现10 mA.cm-2和15 mA.cm-2电沉积电流密度下制得的电极活性较高,尤以15 mA.cm-2时电极性能更佳,并指出了电还原CO2关键材料的结构特性.     

Electrochemical Redox Behavior of Omeprazole Using a Glassy Carbon Electrode

The electrochemical redox behavior of omeprazole (OMZ), a gastric acid pump inhibitor, was investigated at a glassy carbon electrode using cyclic, differential pulse and square‐wave voltammetry over a wide pH range. The pH‐dependent oxidation occurs in two irreversible consecutive charge transfer reactions. Adsorption of the nonelectroactive product was also observed. The first oxidation involves removal of one electron, followed by deprotonation and leads to the formation of a hydroxylated species. The second oxidation process is related to the hydroxyl and amino groups in the benzimidazole moiety. The reduction is irreversible, also pH‐dependent, and occurs in a single step at the sulfoxide group in a diffusion‐controlled mechanism. The diffusion coefficient of omeprazole was calculated to be D_OMZ=2.31×10^?6 cm² s^?1.     

Activationless Reduction of the Hexacyanoferrate Anion on a Mercury Electrode

Polarization curves for the electroreduction of [Fe(CN)₆]^3– on a mercury electrode in solutions containing different amounts of surface-inactive supporting cations are simulated on the basis of modern theory of charge transfer in polar media combined with quantum-chemical approaches. The conclusions about an activationless nature of the process in the overvoltage range 1.2 to 2.0 V accessible experimentally, which were drawn from the results of earlier calculations made within simpler models, are confirmed. The maximum contribution to the current is shown to be made by energy levels of metal that lie considerably (up to 1 eV) lower than the Fermi level. To establish the reasons for the anomalous behavior of the current in the activationless region at high overvoltages, the effect various factors sensitive to the electrode charge exert on the model curves at high negative charges of the electrode surface is analyzed. In connection with this, the stability of the results of a calculation of the electron overlap metal/reactant to a model of the interface is considered. The plausibility of the model proposed for the reaction layer and the approaches used for computing the activation energy and the preexponential factor is corroborated by good agreement between the temperature effect found for the region of a minimum current and its experimental value.     

Electrochemical Behavior of Thalidomide at a Glassy Carbon Electrode

Thalidomide is an oral drug marketed in the 1950s as a sedative and an anti‐emetic during pregnancy that was removed from the market when its teratogenic side effects appeared in new born children due to inadequate tests to assess the drug's safety. Recent studies evaluating the use of thalidomide in cancer and HIV diseases have sparked renewed interest. The electrochemical behavior of thalidomide on a glassy carbon electrode has been investigated using cyclic, differential and square‐wave voltammetry in aqueous media at different pHs. The oxidation mechanism of thalidomide is an irreversible, adsorption‐controlled process, pH dependent up to values close to the pK_a and occurs in two consecutive charge transfer reactions. A mechanism of oxidation of thalidomide involving one electron and one proton to produce a cation radical, which reacts with water and yields a final hydroxylated product is proposed. The reduction of thalidomide is also a pH dependent, irreversible process and occurs in a single step, with the same number of electrons and protons transferred. The reduction mechanism involves the protonation of the nitrogen that bridges the two cyclic groups, and the product of the protonation reaction causes irreversible dissociation. Both thalidomide and the non electroactive oxidation and reduction products are strongly adsorbed on the glassy carbon electrode surface.     

Study and Application of Electrochemical Behavior of Calcium-ARS on a Mercury Film Electrode

A sensitive complex absorptive wave of Ca-ARS was obtained by using differential pulse voltammetry when a mercury film glass carbon electrode was immersed in 0.1 mol L⁻¹ KOH and 4.5×10⁻⁴ mol L⁻¹ ARS solution. The peak potential obtained was −1.17 V (vs Ag-AgCl). The peak current was proportional to the concentration of calcium in the range of 5.0×10⁻⁸−4.2×10⁻⁵ mol L⁻¹. The detection limit was 2.0×10⁻⁸ mol L⁻¹. This method was applied successfully to determining traces of calcium in blood serum. The electrochemical behavior of the system was also studied by cyclic voltammetry, and the experiment results showed that the electrode process was an irreversible absorptive with two electrons participating. Translated from Journal of Beijing Normal University (Natural Science Edition), 2005, 41(2) (in Chinese)     

亚硫酰氯在铂电极上电化学还原的现场红外光谱研究

设计出适用于亚硫酰氯（ＳＯＣｌ２）电化学还原现场红外测试的电解池。采用具有时间分辨的电化学现场ＦＴ－ＩＲ差谱法研究ＳＯＣｌ２在铂电极上电化学还原过程，检测出ＳＯ２Ｃｌ２，ＳＯ．ＳＯＣｌ２，（ＳＯ２）ｘ，Ｃｌ３Ａｌ（←ＯＳＣｌ２）等中间物种。结果表明这些物种是不稳定的。ＳＯ２Ｃｌ２进一步电还原是全过程的速度控制步骤。根据实验结果讨论了可能的反应步骤。     

Molecular Description of the Persulfate Ion Reduction on a Mercury Electrode

The polarization curves for the S₂O₈ ^2- electroreduction on a mercury electrode at high overvoltages and various concentrations of a surface-inactive supporting electrolyte are modeled within modern theory of charge transfer in polar media and quantum-chemical approaches. Based on an analysis of the reactant adsorption in terms of a cluster model, the conclusion is drawn that the persulfate ion is localized in the diffuse part of EDL. When calculated the current, it was assumed that the transfer of the first electron, accompanied by the bond cleavage, is the limiting stage of the total two-electron process. The integration if performed over the entire electron spectrum of the metallic electrode and an attempt is made to account for electrostatic and solvation effects on a molecular level. It is shown that the experimentally-studied overvoltage interval corresponds to the occurrence of the process near the activationless region. The increase in the current at high negative charges of the surface is due to an increase in the reaction layer thickness. This effect arises from a change in the ratio between contributions made by the reactants at the distance of closest approach and the species farther away.     

Preparation and Electrochemical Properties of the Pd-modified Cu Electrode for Nitrate Reduction in Water

The reduction of nitrate has gained renewed attention due to environmental problems like overfertilization and the increasing costs of purification of drinking water. The usual techniques (e.g. ion-exchange and biofiltration) have some disadvantages1. So …     

基于电化学重氮还原的碳膜电极表面修饰及功函调控

基于高温裂解光刻胶制备的碳薄膜(PPF)是一种新型的性能优异的碳基电极. 为了拓展其在功能器件中的应用, 利用电化学重氮还原法在PPF电极表面生长了三氟甲基苯胺重氮盐(CF₃-PD)和对氨基苯甲醚重氮盐(OCH₃-PD)两种组分的混合膜. 通过调节两组分溶液在混合膜中的摩尔浓度比例, 实现了对PPF电极功函的可控调节. 紫外光电子能谱(UPS)和开尔文探针显微镜(KPFM)对修饰前后PPF电极功函(?)的表征表明, 随着混合溶液中CF₃-PD组分的摩尔分数从0增至100%, PPF电极的?(4.75 eV)从4.5 eV梯度增至5.14 eV. 研究结果实现了可在一定范围内“定制”PPF电极功函, 为碳膜电极在分子光电器件中的应用奠定了基础.     

Electrochemical Reduction and Voltammetric Determination of Metronidazole Benzoate at Modified Carbon Paste Electrode

Abstract

A metalloporphyrin incorporated carbon paste sensor has been developed for the determination of metronidazole benzoate (MTZB). Zn(II) complex of 5,10,15,20-tetrakis (3-methoxy-4-hydroxy phenyl) porphyrin (TMHPP) was used as the active material. The MTZB gave a well-defined reduction peak at?0.713 V in 0.1 mol l^?1 phosphate buffer solution of pH around 7. Compared with bare carbon paste electrode (CPE), the TMHPP Zn(II) modified electrode significantly enhanced the reduction peak current of MTZB as well as lowered its reduction potential. Under optimum conditions the reduction peak current was proportional to MTZB concentration over the range 1 × 10^?3 mol l^?1 to 1 × 10^?5 mol l^?1. The detection limit was found to be 4.36 × 10^?6 mol l^?1. This sensor has been successfully applied for the determination of MTZB in pharmaceutical formulations and urine samples.     

Electrochemical Reduction of Phosphor Thio- and Oxotrihalides on a Dropping Mercury Cathode

Russian Journal of Electrochemistry -     

Digital Harmonic Analysis of Cadmium Ion Reduction on a Dropping Mercury Electrode

The cadmium ions reduction on a mercury electrode is investigated. A sinusoidal voltage perturbation signal, superimposed on a linearly changing dc potential, is used. A total time–frequency analysis of the polarographic current of cadmium ions reduction on a dropping mercury electrode is performed. Classical Fourier transform leads to decomposition of the polarographic current into its harmonics. The current harmonics determined by Fourier transform are potential-independent. The STFT transform of the polarographic current also leads to its decomposition into harmonics. However, application of the STFT transform correctly reflects changes in the current harmonics as the function of potential.