Underpotential Deposition Study and Determination of Bismuth on Gold Electrode by Using Voltammetry

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Ellipsometric study of anodic oxide films formed on niobium surfaces

Anodic oxide films formed potentiostatically on niobium surfaces, from open circuit potential (OCP) to 10 V, were studied by performing in situ and ex situ ellipsometric measurements. The kinetics of the film thickness growth in 1 M H₂SO₄ and complex indices of refraction of these films were determined. A strong influence of the surface preparation conditions on the complex refractive indices of the metal substrate and anodic oxide films was shown. By steady-state measurements at OCP, a small thickening of the natural air-formed oxide film with chemical composition Nb₂O₅ in 1 M H₂SO₄ solution was detected. With cathodic pre-treatment, only partial reduction and small thinning of the natural air-formed oxide film was possible. The thicknesses of the natural air-formed oxide films on fine mechanically polished and electropolished Nb surfaces were determined. The build up of the natural air-formed oxide film, at ex situ conditions, on the already formed anodic oxide films was confirmed. It was shown that electropolishing gives more similar optical surface properties to the bare metal than the fine mechanical polishing. Electronic Publication     

Peculiarities of Electrochemical Bismuth Film Formation in the Presence of Bromide and Heavy Metal Ions

Bi films were deposited on glassy carbon electrode from solutions with and without KBr. The morphology of both types of the films was characterized by scanning electron microscopy (SEM), and their electrochemical behavior was studied by square wave (SWV) and cyclic voltammetry (CV). Bi films were also co‐deposited with common analyte‐heavy‐metals in the presence of KBr and these films also were characterized by SEM, SWV and CV in order to understand the formation of the mixed metal films. All films studied had a different morphology. Bromide addition made the Bi films more compact and uniform, whereas Pb catalyzed Bi film deposition.     

Electrochemical Overoxidation of Polyindole and Its Cation‐Permselective Behavior

Polyindole films prepared by potentiostatic growth in dichloromethane solution were subjected to overoxidation studies in aqueous media. Overoxidation at potentials greater than 1.1 V (vs. SCE) in 0.1 M KNO₃ or 0.1 M H₂SO₄ was possible. Overoxidation in 0.1 M NaOH resulted in mechanically unstable films which were not adherent to the electrode surface. The overoxidation process in 0.1 M KNO₃ involved removal of one electron per four indole monomer moieties in the polymer film. Nucleophilic attack led to introduction of carboxylate functionality and to cation permselective behavior, as tested by cyclic voltammetry and hydrodynamic voltammetry of hexamminoruthenium(III) and hexacyanoferrate(III). Such films may be useful in various electrochemical sensor applications.     

Antimony Doped Tin Oxide Nanoparticles Deposited onto Nb−TiO2 Nanotubes for Electrochemical Degradation of Bio‐refractory Pollutions

To improve the service life of SnO₂?Sb electrodes in degradation of refractory wastewater, we report anodic information of tin oxide antimony on top of Nb?TiO₂ nanotubes (Nb?Ti/Nb?TiO₂?NTs/ATONPs) prepared through screen‐printing. It was found that the Nb?Ti/Nb?TiO₂?NTs/ATONPs anodes presented a significantly enhanced in electro‐catalytic oxidation performance (in Acid Red 73) compared to titanium‐based tin antimony electrodes (Ti/ATONPs). Additionally, the electrochemical properties and the stability were further studied by the electrochemical impedance spectroscopy (EIS), linear sweep voltammetry (LSV), cyclic voltammetry (CV), chronoamperometry (CA) measurements and accelerated life test, respectively. These results indicated that Nb?TiO₂?NTs/ATONPs anode possessed Nb?TiO₂ nanotubes which exhibited a higher oxygen evolution potential (2.24 V vs. Ag/AgCl), as well as a better wettability, a larger current at constant potential and 2.1 times longer lifetime than the conventional Ti/ATONPs anode.     

A Comparative Study of Functionalized High‐Purity Carbon Nanotubes towards the V(IV)/V(V) Redox Reaction Using Cyclic Voltammetry and Scanning Electrochemical Microscopy

Functionalized high purity carbon nanotubes (CNTs) with various amounts of oxygen containing surface groups were investigated towards the relevant redox reactions of the all‐vanadium redox flow battery. The quinone/hydroquinone redox peaks between 0.0 and 0.7 V vs. Ag|AgCl|KCl_sat. were used to quantifying the degree of functionalization and correlated to XPS results. Cyclic voltammetry in vanadyl sulfate‐containing 3 M H₂SO₄ as a common supporting electrolyte showed no influence of the amount of surface groups on the V(IV)/V(V) redox system. In contrast, the reactions occurring at the negative electrode (V(II)/V(III) and V(III)/V(IV)) are strongly affected by oxygen surface groups. However, under modified experimental conditions, SECM experiments detecting the consumption of VO²⁺ molecules by CNT thin films in pH=2 solution show improved onset potentials with increased surface oxygen content up to ∼ 3 at%. Further increase in surface oxygen up to 8 at% led to minor improvement. These dissimilar results under different experimental conditions are rationalized by suggesting that oxygen functional groups do not form the active site for the V(IV)/V(V) reaction but wetting of the catalyst layer is of high importance.     

Photoelectrochemical oxidation behavior of organic substances on TiO2 thin-film electrodes

The photoelectrocatalytic oxidation characteristics of salicylic acid, formic acid and methanol on anodized nanoporous titanium dioxide (TiO₂) thin-films were investigated by using electrochemical impedance spectroscopy (EIS) and potentiodynamic polarization techniques. From dark to ultraviolet illumination, the open circuit potential (OCP) and film resistance of TiO₂ films decreased markedly. A general equivalent circuit model was proposed for the photoelectrochemical system anodic TiO₂ thin-film electrode/test solution. The photoelectrochemical oxidation process of the organic compounds showed similar impedance features at OCP and was controlled by the charge transfer step. According to the polarization curves of the base solution and organic solutions, the kinetic rate curves for the photoelectrocatalytic oxidation of pure organic species were obtained as a function of the potential bias. One photooxidation peak was first observed at a bias potential of ca. 0.26 V for these species with low concentrations.     

Spectrophotometric determination of germanium with Catechol Violet and cetyltrimethylammonium bromide

A ternary complex between germanium, Catechol Violet (CV) and cetyltrimethylanunoniuni bromide is proposed for the determination of germanium. The stoichiometric ratio Ge:CV is 1:2. Beer's law is obeyed from 0.1 to 1.0 ppm of Ge. The method is highly selective. Interference from Sn(IV), Fe(III), Bi(III), Cr(VI), Mo(VI), V(V) and Sb(III) in mg amounts is eliminated by extracting the germanium into carbon tetrachloride from 9M HC1 and then stripping into water before the photometric determination.     

Electrochemical and spectroscopic behavior of iron(III) porphyrazines in Langmuir-Schafer films

Thin films of a newly synthesized iron(III) porphyrazine, LFeOESPz ( L = ClEtO, OESPz = ethylsulfanylporphyrazine), have been deposited by the Langmuir-Schafer (LS) technique (horizontal lifting) on ITO or gold substrates. Before deposition, the floating films have been investigated at the air-water interface by pressure/area per molecule (pi/ A) experiments, Brewster angle microscopy (BAM) and UV-vis reflection spectroscopy (RefSpec). The complex reacts with water subphase (pH 6.2) forming the mu-oxo dimer, which becomes the predominant component of the LS films ( LS-Fe) as indicated by optical, IR, XPS, and electrochemical data. LS-Fe multilayers exhibit, between open circuit potential (OCP) and +0.90 V (vs SCE), two independent peak pairs with formal potentials, E surf (I) and E surf(II) of +0.56 V and +0.78 V, respectively. According to dynamic voltammetric and coulometric experiments the peak pair at +0.56 V is attributed to one-electron process at the iron(III) centers on the monomer, while the peak pair at +0.78 V is associated to a four-electron process involving mu-oxo-dimer oligomers. LS-Fe films prove to be quite stable electrochemically between OCP and +0.90 V. The electrochemical stability decreases, however, when the potential range is extended both anodically and cathodically outside these limits, due to formation of new species. Upon incubation with TCA solutions, LS-Fe films show remarkable changes in the UV-vis spectra, which are consistent with a significant mu-oxo dimer --> monomer conversion. Addition of TCA to the electrochemical cell using a LS-Fe film as working electrode, results in a linear increase of a cathodic current peak near -0.40 V as the TCA concentration varies in the 0.1-2.0 mM range. This behavior is interpreted in terms of TCA inducing a progressive change in the composition of the LS-Fe films in favor of the monomeric iron(III) porphyrazine, which is responsible for the observed increase in the cathodic current near -0.40 V.     

Electrocatalysis and Amperometric Detection of the Reduced Form of Nicotinamide Adenine Dinucleotide at Toluidine Blue/Zinc Oxide Coated Electrodes

Thin toluidine blue (TBO) and zinc oxide (ZnO) hybrid films have been grown on glassy carbon electrode (GCE) and indium tin oxide coated (SnO₂) glass electrodes by using cyclic voltammetry (CV). Scanning electron microscopy (SEM) images revealed spherical and beads‐like shape of highly oriented TBO/ZnO hybrid films. Energy dispersive spectrometry (EDS) results declared that the films composed mainly of Zn and O. Moreover, TBO/ZnO hybrid films modified electrode is electrochemically active, dye molecules were not easily leached out from the ZnO matrix and the hybrid films can be considered for potential applications as sensor for amperometric determination of reduced nicotinamide adenine dinucleotide (NADH) at 0.0 V. A linear correlation between electrocatalytic current and NADH concentration was found to be in the range between 25 μM and 100 μM in phosphate buffer. In addition, we observed that dopamine, ascorbic acid and uric acid are not interference in amperometric detection of NADH in this proposed method. In addition, TBO/ZnO hybrid film modified electrode was highly stable and its response to the NADH also remained relentless.     

电化学还原预处理对BiVO_4薄膜电极光电化学氧化水性能的提高

在酸性水溶液中(pH=2.0),采用电化学还原(ER)方法对BiVO4薄膜电极进行预处理,并探讨了其对薄膜电极光电化学氧化水性能的影响.结果表明,这种预处理可显著提高电极的光电化学氧化水的性能,且具有良好的光电化学稳定性.利用扫描电子显微镜、X射线衍射、拉曼光谱、光电子能谱、紫外-可见漫反射光谱、荧光光谱、电化学阻抗谱及Mott-Schottky等方法对ER处理前后的电极进行了表征.结果表明,ER预处理使电极粗糙度增大,表面积增大约1.4倍;电极材料的晶型无明显变化,但V—O对称伸缩振动略有红移;表面Bi,V和O结合能变小,Bi3+部分被还原,Bi/V原子比增大;ER处理导致电极平带电位负移,光生载流子在薄膜电极/溶液界面转移速率加快,表面复合速率降低.这些变化和表面积增加是BiVO4电极光电化学性能提高的主要原因.     

层层静电自组装构筑壳聚糖/磷钨酸复合膜的研究

将正电荷的壳聚糖与负电荷的磷钨酸溶液通过静电作用交替沉积在基底上组装复合多层膜。使用紫外可见光谱(UV-Vis)、红外光谱(FTIR)、X-射线光电子能谱(XPS)、原子力显微镜(AFM)和循环伏安法(CV)等手段对复合膜进行了表征。UV-Vis结果显示多层膜在特征吸收峰处的吸光度数值随膜双层数增加逐渐增大，呈良好的线性关系，表明多层膜是均匀组装的；XPS和FTIR结果证实了壳聚糖和磷钨酸被组装到膜上，AFM图形显示膜表面有一定的粗糙度，CV结果说明多层膜保留了磷钨酸的电化学性质。     

Thin films of vanadium oxide grown on vanadium metal: oxidation conditions to produce V2O5 films for Li‐intercalation applications and characterisation by XPS,AFM, RBS/NRA

Thin films of vanadium oxide were grown on vanadium metal surfaces (i) in air at ambient conditions, (ii) in 5 mM H₂SO₄ (aq), pH 3, (iii) by thermal oxidation at low oxygen pressure (10^?5 mbar) at temperatures between 350 and 550 °C and (iv) at near‐atmospheric oxygen pressure (750 mbar) at 500 °C. The oxide films were investigated by atomic force microscopy (AFM), X‐ray photoelectron spectroscopy (XPS), X‐Ray diffraction (XRD) and Rutherford backscattering spectrometry (RBS) and nuclear reaction analysis (NRA). The lithium intercalation properties were studied by cyclic voltammetry (CV). The results show that the oxide films formed in air at room temperature (RT), in acidic aqueous solution, and at low oxygen pressure at elevated temperatures are composed of V₂O₃. In air and in aqueous solution at RT, the oxide films are ultra‐thin and hydroxylated. At 500 °C, nearly atmospheric oxygen pressure is required to form crystalline V₂O₅ films. The oxide films grown at pO₂ = 750 mbar for 5 min are about 260‐nm thick, and consist of a 115‐nm outer layer of crystalline V₂O₅. The inner oxide is mainly composed of VO₂. For all high temperature oxidations, the oxygen diffusion from the oxide film into the metal matrix was considerable. The oxygen saturation of the metal at 450 °C was found, by XPS, to be 27 at.% at the oxide/metal interface. The well‐crystallized V₂O₅ film, formed by oxidation for 5 min at 500 °C and 750 mbar O₂, was shown to have good lithium intercalation properties and is a promising candidate as electrode material in lithium batteries. Copyright © 2005 John Wiley & Sons, Ltd.     

不锈钢载波钝化膜的半导体性质

运用交流阻抗法和光电化学法研究了不锈钢载波钝化膜层的半导体性质。讨论了交流阻抗测试中扰动频率的变化对Mott-Schottky曲线的影响，讨论了不锈钢载波钝化膜的n/p型、杂质施主密度和平带电位等半导体性质，同时结合光电化学法对交流阻抗测试结果进行了验证分析，实验结果认为不锈钢载波钝化膜层具有与直流钝化膜层相似的半导体性质，并通过膜层的组成结构对其半导体性质作了分析。     

OH functionalized Multi-Walled Carbon Nanotube modified electrode as electrochemical sensor for the detection of Aceclofenac

ABSTRACT

The rapid electrochemical determination of Aceclofenac (ACF) has been employed by cyclic voltammetry (CV), differential pulse voltammetry (DPV) using developed OH-functionalised multiwalled carbon nanotube carbon paste electrode (OH-MWCNT/CPE). Modified electrode was characterised by scanning electron microscopy (SEM), energy dispersive X-ray spectroscopy (EDAX), X-ray diffraction spectroscopy (XRD), electrochemical impedance spectroscopy (EIS) and cyclic voltammetry (CV). The ACF exhibits two oxidation peaks at +0.4 V, +0.66 V and one reduction peak at +0.3 V. The active surface area of the bare carbon paste electrode (BCPE) and modified electrode have been characterised by using K₃[Fe(CN)₆] solution containing 0.1 M KCl. In DPV mode, variation of ACF gave the limit of detection (LOD = 3s/m) 0.246 μM over the concentration range 1.0 to 190.0 μM (R² = 0.9994). The developed electrode has good stability, reproducibility and could be successfully validated for the detection of ACF in pharmaceutical samples and biological fluids.     

A Role of the Plating Regime in the Deposition of Bismuth Films onto a Carbon Paste Electrode. Microscopic Study

A microscopic study is presented based on observations of bismuth films deposited from various plating solutions and under different experimental conditions onto the carbon paste surface. Electrolytic plating of bismuth films was performed either as simulation of preconcentration in‐situ from a 0.2 M acetate buffer containing 5×10^?5 M Bi³⁺ (pH 4.25), or as external deposition from various plating solutions: 0.1 M acetate buffer with 5×10^?4 M Bi³⁺ (pH 4.50), 0.5 M HCl with either 0.001 M BiCl₃ or 0.005 M BiCl₃ , 0.5 M HCl+0.5 M KBr+0.005 M BiCl₃ , and 0.5 M HCl+0.5 M KI+0.005 M BiCl₃ (all pH≈0.5). Scanning electron microscopic images of the bismuth films showed a considerable variability in structure and compactness of the deposited layer in dependence on experimental conditions chosen such as the concentration of Bi(III) species, the total acidity of plating media, the stability of complexes of Bi(III) with halogenide anions or the deposition potential applied.     

聚合物前驱体法制备立方相WO_3薄膜的光电化学性质

以(NH4)6W7O24·6H2O为钨源,聚乙二醇1000(PEG 1000)为配位聚合物,采用聚合物前驱体法制备了WO3薄膜,利用X射线衍射(XRD)、扫描电子显微镜(SEM)、紫外-可见(UV-Vis)吸收光谱等手段对其结构进行表征.采用循环伏安法、Mott-Schottky测试、瞬态光和稳态光电流谱等方法研究了WO3薄膜电极的光电化学性能.结果表明,制备的WO3薄膜为立方晶系,禁带宽度约为2.7eV.当热处理温度为450℃时,载流子浓度达到最大2.44×1022cm-3,平带电位为0.06V,在500W氙灯光源照射和1.2V偏压下,光电流密度为2.70mA·cm-2.进一步探讨了热处理温度对其光电性质的影响及其机理.     

Electrochemical and electrocatalytic properties of meso-triphenylcorrole and its complexes with Mn(III), Co(III), Cu(III), and Zn(II)

The method of cyclic voltammetry (CV) was used to compare electrochemical and electrocatalytic properties of meso-triphenylcorrole [H₃(ms-Ph)₃Cor] and also its complexes with Mn(III), Co(III), Cu(III), and Zn(II) in 0.1M KOH. Metal-localized redox transitions are detected in the complexes of Mn (III ?? IV) and (III ?? II), Co (III ?? II), Cu (III ?? II). It is shown that the manganese complex features most effective catalytic properties in the reaction of molecular oxygen electroreduction.     

Direct electrochemistry of hemoglobin in layer-by-layer films with poly(vinyl sulfonate) grown on pyrolytic graphite electrodes

Stable layer-by-layer electroactive films were grown on pyrolytic graphite (PG) electrodes by alternate adsorption of layers of polyanionic poly(vinyl sulfonate) (PVS) and positively charged hemoglobin (Hb) from their aqueous solutions. Cyclic voltammetry (CV) of [PVS/Hb]n films showed a pair of well-defined and nearly reversible peaks at about - 0.28 V vs. SCE at pH 5.5, characteristic of Hb heme Fe(III)/Fe(II) redox couple. The process of (PVS/Hb) bilayer growth was monitored and confirmed by CV, X-ray photoelectron spectroscopy (XPS) and UV-Vis spectroscopy. While the amount of Hb adsorbed in each bilayer was the same, the amount of electroactive Hb in each bilayer decreased dramatically with increase of the number of bilayer, and electroactivity was just extended to 8 [PVS/Hb] bilayers. CVs of [PVS/Hb]8 films maintained stable in buffers containing no Hb. Positions of Soret band of Hb in [PVS/Hb]n films grown on transparent glass slides suggest that Hb in the films keeps its secondary structure similar to its native state in a wide pH range. Trichloroacetic acid and nitrite were catalytically reduced by [PVS/Hb]8 films with significant lowering of the electrode potential required.     

Chromatography of inorganic ions on polyethyleneimine cellulose layer in hydrochloric acid — Ammonium thiocyanate media

Summary Thin-layer chromatographic behavior of 58 inorganic ions on polyethyleneimine (PEI) cellulose has been systematically surveyed in hydrochloric acid — ammonium thiocyanate media. In this media most of the ions distribute chromatographically on the layer. Ag(I), Hg(II), Pd(II), Au(III), Bi(III), Ru(III), Pt(IV), Nb(V), Ta(V), Mo(VI), and W(VI) are strongly retained, while alkali earths(II), Mg(II), As(III), Ti(IV), and Te(VI) are not absorbed to any great extent in this system. An interesting correlation was found between the R_f values on PEI-cellulose in the thiocyanate media and the paramagnetic moment of the rare earths(III). An oddeven fluctuation against the atomic number is also found for the heavy rare earths(III). Chromatographic separation of many inorganic ions of analytical interest is demonstrated in this system.