碱性溶液中金电极上氧还原中间物研究

应用改进了的旋转全电极上的电势阶跃计时库仑法,分别测定了不同电极电势下氧还原过程中电极吸附中间物和溶解中间物氧化所需的电量,实验证明,在此过程中电极上确有吸附中间物存在,而且是电极电势的函数,但其分子属性尚需进一步鉴别。     

Role of dissolved oxygen reduction in improvement inhibition performance of ascorbic acid during copper corrosion in 0.50 mol/L sulphuric acid

<正>The kinetics of dissolved O_2 reduction and hydrogen evolution reactions on copper surface was studied in naturally aerated and air and O_2-saturated 0.50 mol/L H_2SO_4 solutions using polarization measurements combined with the rotating disc electrode (RDE).The Koutecky-Levich plot indicated that the dissolved O_2 reduction at the copper electrode was an apparent four-electron process.A correlation between the presence of dissolved O_2 and the formation of Cu_2O,confirmed from XRD,was discussed. Ascorbic acid(AA) was tested as a safe inhibitor for copper corrosion in H_2SO_4 solutions at 25℃.Measurements were carried out as a function of dissolved oxygen concentration using Tafel polarization measurements.The addition of AA slowed down the reduction reaction of dissolved O_2 more effectively than the anodic reaction.Dissolved O_2 was found to enhance the inhibition performance of AA.Adsorption via hydrogen bonding was considered.     

Metal-enhanced Singlet Oxygen Generation: A Consequence of Plasmon Enhanced Triplet Yields

In this Rapid Communication, we report the first observation of Metal-Enhanced singlet oxygen generation (ME¹O₂). Rose Bengal in close proximity to Silver Island Films (SiFs) can generate more singlet oxygen, a three-fold increase observed, as compared to an identical glass control sample but containing no silver. The enhanced absorption of the photo-sensitizer, due to coupling to silver surface plasmons, facilitates enhanced singlet oxygen generation. The singlet oxygen yield can potentially be adjusted by modifying the choice of MEF (Metal-Enhanced Fluorescence) & MEP (Metal Enhance Phosphorescence) parameters, such as distance dependence for plasmon coupling and wavelength emission of the coupling fluorophore. This is a most helpful observation in understanding the interactions between plasmons and lumophores, and this approach may well be of significance for singlet oxygen based clinical therapy.     

Study of the Complexation of Pb(II) with meso‐2,3‐ Dimercaptosuccinic Acid (DMSA) and 2,3‐Dimercapto‐1‐propanesulfonic acid (DMPS) Using a Bismuth‐Bulk Rotating Disk Electrode

For the first time, the suitability of bismuth bulk rotating disk electrode (BiB‐RDE) for the study of metal complexation has been tested. Cyclic (CV) and differential pulse (DPV) voltammetry have been used to study the complexation of Pb(II) with two of the most effective chelating agents for the treatment of Pb(II) poisoning (meso‐2,3‐dimercaptosuccinic acid, DMSA, and 2,3‐dimercapto‐1‐propanesulfonic acid, DMPS). Multivariate curve resolution has been applied to voltammetric data to obtain the stoichiometries and stability constants of the complexes formed. In both systems, the ML₂ complex was predominant, with log β₂ values of 10.13 and 8.80 for DMSA‐Pb(II) and DMPS‐Pb(II), respectively.     

高温处理对碳载吡啶钴催化氧还原性能的影响

利用碳黑(Vulcan XC-72R) 中加入硫酸钴和吡啶(Py)作为催化剂前躯体, 经溶剂分散热处理构建了一类新型的高效氧还原CoPy/C复合催化剂. 运用循环伏安法和旋转圆盘电极(RDE)技术研究了不同温度(600~900 ℃)处理CoPy/C催化剂在碱性介质中对氧还原的电催化性能. 结果表明, 热处理能显著提高CoPy/C的催化活性, 活性次序为800 ℃>900 ℃>600 ℃>未处理. 其中800 ℃处理的15%Co25%Py/C(质量分数)复合催化剂表现出最佳的氧还原催化性能, 以其制备的气体扩散电极在3.0 mol/L KOH 电解质溶液(O₂气氛)中的半波电位为-0.069 V(相对于标准可逆氢电极), 起峰电位为0.026 V, 同时表现出明显的极限扩散电流. 利用透射电镜、 能谱分析和X射线衍射技术对催化剂的微观形貌、 颗粒大小和活性位结构的研究结果表明, 所制备的碳黑负载吡啶钴催化剂(15%Co25%Py/C)平均粒径为17 nm, 经800 ℃处理后吡啶结构发生了坍塌, 形成了其它价态的钴氧化合物、 硫化物和单质钴, 并协同吡啶中的氮对氧起催化还原作用. RDE结果表明, O₂在CoPy/C催化剂上的反应动力学主要通过4e^-过程还原成H₂O.     

Fabrication of p-Si/β-FeSi2 balls/n-si structures by MBE and their electrical and optical properties

We report on the formation technique of single-crystalline β-FeSi₂ balls (<100 nm) embedded in a Si p–n junction region by Si molecular beam epitaxy (MBE). β-FeSi₂ films grown on Si (0 0 1) by reactive deposition epitaxy (RDE) aggregated into islands after annealing at 850°C in ultrahigh vacuum. The islands of β-FeSi₂ aggregated further into a ball shape by following the Si MBE overgrowth at 750°C. It was found from X-ray diffraction (XRD) patterns that the epitaxial relationship between the two materials, and single-crystalline nature were preserved even after the annealing and the Si overgrowth. Capacitance–voltage (C–V) characteristics and transmission electron microscope (TEM) images revealed that a lot of defects were introduced around the embedded β-FeSi₂ balls with an increase of embedded β-FeSi₂ quantity.     

Assessment of Lead and Cadmium in Canned Foods by Square-Wave Anodic Stripping Voltammetry

Abstract

This work reports the simultaneous determination of lead and cadmium in canned foods samples using square-wave anodic striping voltammetry (SWASV) on a bismuth film electrode (BiFE). The metal ions and bismuth were simultaneously deposited by reduction at ?1 V on a rotating carbon-paste disk electrode. Then, the preconcentrated metals were oxidized by scanning the potential of the electrode from ?1 to ?0.4 V using a square-wave waveform. The electrode displayed excellent linear behavior in the examined concentration range, from 5 to 150 µg/L of cadmium and lead (r² = 0.999 for both). Using the optimized conditions, the limits of detection were 0.27 µg/L for cadmium and 0.35 µg/L for lead. The reproducibility of the proposed sensor, evaluated in terms of relative standard deviation (RSD), were 5.8% and 3.7% of Cd and Pb, respectively for five measurements. Finally, the system based on BiFEs combined with rotating disk electrode was applied to determination of lead and cadmium in canned food samples. The results obtained were validated by inductively coupled plasma optical emission spectroscopy (ICP-OES).     

Determination of Cu in Tequila by Anodic Stripping Voltammetry

Abstract

Concentrations of metals such as copper in alcoholic beverages must be strictly regulated due to negative effects ranging from beverage spoilage and hazing, to sensorial and health consequences. In this paper, a voltammetric alternative is presented for the analysis of copper in tequila, a Mexican spirituous alcoholic beverage. Anodic Stripping Voltammetry is applied and the standard addition method is used to quantify copper in this beverage at concentrations commonly present in tequila (<10 ppm) without sample pretreatment. Copper can be reduced and then oxidized quantitatively and reproducibly. A comparison of Anodic Stripping Voltammetry with Atomic Absorption Spectrometry is presented.     

Modified Glassy Carbon Rotating Disk Electrode for Determination of Heterogeneous Reaction Rate Constant of H2O2 Decomposition

Modified glassy carbon RDE method is introduced in this work for the determination of heterogeneous reaction rate constant of H₂O₂ decomposition. This method is based on the analysis of RDE voltammograms of H₂O₂ reduction on a glassy carbon electrode covered with a catalyst layer. As a case study, the rate constant of H₂O₂ decomposition on nitrogen doped graphene is determined by using both glassy carbon and gold RDE methods. A good agreement is observed between the results of these two methods indicating the reliability of the glassy carbon method. Moreover, advantages and limitations of the glassy carbon method are discussed.     

Zinc Oxide/Zinc Hexacyanoferrate Hybrid Film‐Modified Electrodes for Guanine Detection

An electroactive polynuclear hybrid films of zinc oxide and zinc hexacyanoferrate (ZnO/ZnHCF) have been deposited on electrode surfaces from H₂SO₄ solution containing Zn(NO₃)₂ and K₃[Fe(CN)₆] by repetitive potential cycling method. Simultaneous cyclic voltammetry and electrochemical quartz crystal microbalance (EQCM) measurements demonstrate the steady growth of hybrid film. There are two redox couples present in the voltammograms of hybrid film and it is obvious in the case of pH 2. Surface morphology of hybrid film was investigated using scanning electron microscopy (SEM) and atomic force microscopy (AFM). Energy dispersive spectrometer (EDS) data confirm existence of zinc oxide in the hybrid film. The effect of type of monovalent cations on the redox behavior of resulting film was investigated. In pure supporting electrolyte, electrochemical responses of modified electrode resemble with that of a surface immobilized redox couple. The electrocatalytic activity of ZnO/ZnHCF hybrid film was investigated towards guanine using cyclic voltammetry and rotating disc electrode (RDE) techniques. Finally, feasibility of using ZnO/ZnHCF hybrid film‐coated electrodes for guanine estimation in flow injection analysis (FIA) was also investigated.