Determination of Silver Traces in Pure Metallic Copper and Zinc by a Catalytic Photometric Method

Determination of silver traces in the presence of copper, zinc and sulphate ions by a catalytic method was studied. The highly sensitive method of silver determination is based on the catalytic effect of silver ions on the oxidation of salicylic acid by persulphate in the presence of 2,2\u27-dipyridyl as an activator. The reaction was followed spectrophotometrically by measuring the rate of change in absorbance with time at 420 nm after 10 min of reagents mixing. The sensitivity, precision and accuracy of the determination of silver traces were investigated in solutions containing excesses of interfering ions. The studied range of interfering ions concentrations was 8 × 10–6 to 2.4 × 10–2 mol dm–3 and corresponds to an amount ratio of interfering to silver ions from 50 to 150 000. The performed analyses showed that the accuracy and precision of silver trace determination by the proposed method is high even in the presence of a huge amount excess of interfering ions. The method was used for quantitative determination of silver contents in a copper foil and in a zinc rod. The obtained results were compared with the analyses performed by FAAS

Formation of Nanoporous Tin Oxide Layers on Different Substrates during Anodic Oxidation in Oxalic Acid Electrolyte

Nanoporous tin oxide layers were obtained on various Sn substrates including high- and low-purity foils and wire by one-step anodic oxidation carried out in a 0.3 M oxalic acid electrolyte at various anodizing potentials. In general, amorphous oxide layers with the atomic ratio of Sn : O (1 : 1) were grown during anodization, and a typical structure of the as-obtained film consists of the “outer” layer with less regular, interconnetted pores and the “inner” layer with much more uniform and regular channels formed as a result of vigorous gas evolution. It was found that the use of electrochemical cell with the sample placed horizontally on the metallic support and stabilized by the Teflon cover, instead of the typical two-electrode system with vertically arranged electrodes, can affect the morphology of as-obtained layers and allows fabrication of nanoporous oxides even at anodizing potentials up to 11 V. An average pore diameter in the “outer” oxide layer increases with increasing anodizing potential, and no significant effect of substrate purity on the structure of anodic film was proved, except better uniformity of the oxides grown on high-purity Sn. A strong linear relationship between the average steady-state current density and anodizing potential was also observed

Polypyrrole–Silver Composite Nanowire Arrays by Cathodic Co-Deposition and Their Electrochemical Properties

A simple electrochemical one-step method of synthesis of polypyrrole–silver (PPy–Ag) nanowire arrays is presented. The method is based on simultaneous cathodic polymerization and silver electrodeposition in the nanopores of homemade porous anodic aluminum oxide (AAO) templates. The synthesized 80 nm in diameter PPy nanowires have embedded Ag nanoparticles. The nanowires are characterized by scanning electron microscopy, transmission electron microscopy, X-ray photoelectron spectroscopy, ultraviolet–visible–near-infrared absorption spectroscopy, and electrochemical techniques. The morphology, chemical structure, and optical, electrochemical, and catalytic properties of the synthesized PPy–Ag nanowires are examined and compared with those of PPy nanowires. The effect of annealing the PPy–Ag nanowires above the glass transition temperature of polypyrrole on properties of the nanowires is studied. A surface segregation/aggregation of silver nanoparticles and degradation of polymer chain integrity occur during annealing. The as-prepared PPy–Ag and annealed PPy–Ag nanowire arrays possess enhanced catalytic activity toward electroreduction of hydrogen peroxide and can be used as novel and inexpensive sensors for its determination. The highest sensing activity is exhibited by the freshly prepared and annealed PPy–Ag nanowire electrode because of accumulation of catalytic centers on the surface of the nanowires (segregation of silver). However, the sensitivity of amperometric determination of H₂O₂ for the annealed PPy–Ag nanowire array decreases dramatically after storage. On the other hand, the as-prepared PPy–Ag nanowire arrays provide a stable in time sensing activity toward reduction of hydrogen peroxide. This can be attributed to a distribution of active Ag nanoparticles deep within the polymer matrix

Polypyrrole–Nickel Hydroxide Hybrid Nanowires as Future Materials for Energy Storage

Hybrid materials play an essential role in the development of the energy storage technologies since a multi-constituent system merges the properties of the individual components. Apart from new features and enhanced performance, such an approach quite often allows the drawbacks of single components to be diminished or reduced entirely. The goal of this paper was to prepare and characterize polymer-metal hydroxide (polypyrrole-nickel hydroxide, PPy-Ni(OH)2) nanowire arrays demonstrating good electrochemical performance. Nanowires were fabricated by potential pulse electrodeposition of pyrrole and nickel hydroxide into nanoporous anodic alumina oxide (AAO) template. The structural features of as-obtained PPy-Ni(OH)2 hybrid nanowires were characterized using FE-SEM and TEM analysis. Their chemical composition was confirmed by energy-dispersive x-ray spectroscopy (EDS). The presence of nickel hydroxide in the synthesized PPy-Ni(OH)2 nanowire array was investigated by X-ray photoelectron spectroscopy (XPS). Both FE-SEM and TEM analyses confirmed that the obtained nanowires were composed of a polymer matrix with nanoparticles dispersed within. EDS and XPS techniques confirmed the presence of PPy-Ni(OH)2 in the nanowire array obtained. Optimal working potential range (i.e., available potential window), charge propagation, and cyclic stability of the electrodes were determined with cyclic voltammetry (CV) at various scan rates. Interestingly, the electrochemical stability window for the aqueous electrolyte at PPy-Ni(OH)2 nanowire array electrode was remarkably wider (ca. 2 times) in comparison with the non-modified PPy electrode. The capacitance values, calculated from cyclic voltammetry performed at 20 mV s−1, were 25 F cm−2 for PPy and 75 F cm−2 for PPy-Ni(OH)2 array electrodes. The cyclic stability of the PPy nanowire array electrode up to 100 cycles showed a capacitance fade of about 13%