Vol 54, No 1 (2018)

A simple and sensitive method was used to develop a novel sensor for determination of dacarbazine on the surface of multi-walled carbon nanotubes/CuFe₂O₄ nanoparticles modified carbon paste electrode (MWCNTs/CuFe₂O₄/CPE). Cyclic voltammetry, differential pulse voltammetry, chronoamperometry, and electrochemical impedance spectroscopy were used to investigate the electrochemical behavior of dacarbazine at the chemically modified electrode. According to the results, MWCNTs/CuFe₂O₄/CPE showed high electrocatalytic activity for dacarbazine oxidation, producing a sharp oxidation peak current at about +0.80 vs. Ag/AgCl reference electrode at pH 5.0. The peak current was linearly dependent on dacarbazine concentration over the range of 0.10–76.0 μmol L^–1 with the detection limit (3σ) of 0.08 μmol L⁻¹. In addition, chronoamperometry was also used to determine diffusion coefficient of dacarbazine at MWCNTs/CuFe₂O₄/CPE.

Bismuth tellurate nanospheres have been successfully synthesized by a facile hydrothermal route. X-ray diffraction (XRD) shows that the nanospheres are composed of orthorhombic Bi₂Te₂O₇ phase. Scanning electron microscopy (SEM) displays that the diameter of the nanospheres is 100–500 nm. The bismuth tellurate nanospheres (BTS) modified glassy carbon electrode (GCE) has been prepared for the electrochemical detection of L-cysteine (L-CySH). A pair of semi-reversible CV peaks at +0.14 V and–0.84 V, respectively are observed. The BTS modified GCE displays high electrocatalytic activity toward L-CySH and exhibits a linear relationship in the range of 0.0001–2 mM with a detection limit of 0.046 μM in KCl solution. The broad linear range, low detection limit, good reproducibility and stability make the BTS modified GCE valuable for the practical application.

Studies of the oxygen reaction, including the oxygen ionization and evolution processes occurring at typical electrode materials in aqueous and nonaqueous electrolytes, are analyzed. A connection between the problematics of the oxygen electrode reaction in nonaqueous media and the developing of novel batteries, in the first place, Li–O₂ batteries, is emphasized. Unlike aqueous solutions, the oxygen reduction in aprotic electrolytes was shown to occur without breaking of the O–O bond; it is accompanied by formation of poorly soluble product of two-electron reaction (Li₂O₂) in the pores of positive electrode. The effect of the solvent donor number and the anion composition on the oxygen reduction mechanism and the lithium peroxide deposit structure is described. A marked reduction of the Li₂O₂ oxidation overvoltage when passing from carbonaceous materials to platinum-containing catalysts in the positive electrode is elucidated; in the latter case, the effect of electrocatalyst type upon the Li₂O₂ formation reaction is somewhat reduced. The elucidation of the contribution of processes occurring at the free and lithium-peroxide-covered electrode surface during the oxygen reaction for wide variety of active materials is formulated as the main basic problem of the future research.

In this study, a grafted polymer (GP) with ZnO nanoparticles (GP/ZnO NPs) was attached on the surface of glassy carbon electrode (GCE), in order to produce a new modified electrode (GP/ZnO NPs-GCE). The gamma irradiation method was used to grafted polystyrene (polymer) with acrylonitrile (monomer), while slow evaporation process was used to prepare the new modified electrode. The cyclic voltammetry (CV) of K₄[Fe(CN)₆] was used to study the electrochemical properties GP/ZnO NPs-GCE. The peak separation (ΔE_pa-c) was 500 mV between the redox peaks of Fe(II)/Fe(III) in an aqueous solution of 1 M KCl and the current ratio of redox current peaks (I_pa/I_pc) was ≈ 1 for the modified electrode. This indicated that the modified electrode has s good reversibility and conductivity, wherefore; it was applied in the voltammetric filed. It was found that the modified electrode GP/ZnO NPs-GCE have a reasonable solubility and stability at various pH medium. Additionally, the sensitivity of the electrochemical analysis by cyclic voltammetric (CV) method is extensively subjected to the pH medium and the scan rate (SR). A couple of redox current peaks of K₄[Fe(CN)₆] in KCl solution was observed with a reversible process: Fe³⁺/Fe²⁺. Finally a good diffusion coefficient of electroactive species (D) for the new modified electrode was found in this study by chronoamperometry method using Cottrell equation.

Single-phase solid solutions based on proton-conducting oxide La_0.9Sr_0.1ScO_3–δ (LSS) and containing from 0 to 47 at % Fe in the scandium sublattice are synthesized by the method of combustion with ethylene glycol at 1400°C. Their electric conductivity, thermal expansion, and parameters of orthorhombic lattice are studied. Anomalies in the temperature dependences of conductivity and thermal expansion associated with dissolution of water vapor in the oxides are observed, as well as the breaks in concentration dependences of orthorhombic lattice parameters in the region of low iron contents. The introduction of even small amounts of iron oxide (up to 3 at % Fe) into LSS leads to disappearance of protonic conductivity. The factors responsible for the appearance of defective structure and its model explaining this phenomenon are discussed.

This paper is concerned with a study of the influence of synthesis temperature on the properties of TiO₂ films and the performance of dye-sensitized solar cell (DSSC). The TiO₂ film samples synthesized via liquid phase deposition for 5 h at various temperatures, namely, 40, 50, 60, 70 and 80°C. It was found that the morphological shape of the film changes with growth temperature. The optical absorption increases with growth temperature. However, the photoluminescence decreases with growth temperature. These TiO₂ samples were applied in a DSSC of ITO/TiO₂/electrolyte/platinum. The DSSC utilizing the sample grown at 40°C demonstrated the highest photovoltaic parameters with the J_sc, and η of 1.40 mA cm^–2 and 0.44% respectively. This is due to the smallest grain size of TiO₂ films and the smallest bulk resistance of the device.

The effect of (0.05 M) tetraalkylammonium salt additions in aqueous 0.5 M KOH on the rate of impregnation of carbon black electrodes with a polytetrafluoroethylene binder (5–20 wt % PTFE) at hydrogen evolution potentials was studied. It was shown that tetraalkylammonium salts facilitate the fast filling of electrodes with electrolyte, and their effect increases with the molecular mass of the cation. Tetramethylammonium bromide showed the weakest effect. In solutions with tetrabutylammonium bromide, the electrodes were completely flooded with 5 wt % PTFE within 15 min. Diethyldibenzylammonium bromide had a similar effect. The influence of the PTFE concentration in the electrodes on their capacity was studied. The specific capacity of acetylene black in acid and alkaline aqueous solutions was evaluated from the electrode surface area determined by low-temperature nitrogen adsorption (BET).

The work presents the results of studies of the 2PbTe–AgSbTe₂ system using the EMF technique with the Ag₄RbI₅ solid electrolyte in the temperature range of 300–430 K. Formation of a wide (0–80 mol % AgSbTe₂) region of PbTe-based solid solutions in the system is shown. Partial thermodynamic functions \(\left( {\overline {\Delta G} ,\overline {\Delta H} ,\overline {\Delta S} } \right)\) of alloyed silver are calculated on the basis of the equations of the temperature dependences of EMF. Potential-forming reactions are determined on the basis of the data on solid-phase equilibriums in the Ag₂Te–PbTe–Sb₂Te₃–Te system that are used to calculate standard thermodynamic functions of formation and standard entropies of (2PbTe)_x(AgSbTe₂)_1–x (x = 0.2; 0.4; 0.6; 08; 0.9) solid solutions.