Vol 55, No 3 (2019)

Molecular mechanisms of the electric polarization of supercooled water at its interface with the basal face of β-AgI crystal are studied by computer simulation. By the background of thermal fluctuations at 260 K, the gradual growth of the molecular film from vapor is reproduced from the submonomolecular stage to the bulk liquid and the mechanism of electric double layer formation is analyzed in detail. Polarization of the contact layer of water is caused by the local fields at its interface with the crystal surface. The potential difference in the electric double layer emerging on the basal face of the single crystal reaches 0.88 V but is different on different faces as regards both its magnitude and sign. The asymmetry in the spatial charge distribution in the H₂O molecule is responsible for the different strength of water adhesion to the surface of crystal faces containing either positive or negative ions in their crystallographic surface layer. In an aqueous electrolyte containing ionic impurities, the electric double layer field induces compensating motion of mobile charge carriers to the crystal surface and their adsorption. As a result of contact-layer polarization, a micro-crystal immersed into an electrolyte droplet exerts the distilling effect on the latter, and the adsorption of mobile ions on the surface of a solid-crystalline particle can affect its activity as the center of heterogeneous nucleation of atmospheric moisture.

Me₆-dibenzotetraaza[14] annulene type macrocyclic complexes of Ni(II) and Cu(II) have been synthesized by template method and characterized by employing various techniques like molar conductance measurement, elemental (C, H, N) analysis, IR, UV-Vis, mass spectra and cyclic voltammetry. On the basis of electronic studies saddle shape distorted octahedral structure have been assigned to these macrocyclic complexes. The redox behavior of Ni(II) and Cu(II) macrocyclic complexes showed reversible and quasiirreversible redox process that supported by the i_pc/i_pa ratio which is in good agreement with Randles-Sevcik equation. These macrocyclic complexes were also studied for the antimicrobial activity against E. coli, P. aeruginosa, B. subtilis, S. aureus and C. albicans compared with Gentamycinas standard drug.

The redox transformations in a conducting polymer film on a platinum electrode were studied by Raman spectroelectrochemistry at fixed potentials depending on the incidence angle of the laser beam. Raman scattering was excited with a laser at a wavelength of 532 nm. Polyaniline (PANI) and its complex with poly-2-acrylamido-2-methyl-1-propanesulfonic acid (PAMPSA) were used as a conducting polymer. The polymer films were deposited by potentiostatic electropolymerization. By varying the incidence angle of the beam it is possible to obtain a Raman spectrum without the bands of the substrate overlapping with the characteristic bands of the polymer to minimize the substrate effect on the interpretation of the results. A comparative study of the electrochemical oxidation/reduction of the PANI films taking into account the detected angular dependence showed that, unlike the PANI films obtained in the presence of hydrochloric acid, the films of the PANI-PAMPSA complex retained the radical cation state of PANI in the range of the cathodic potentials. The reason for this is the presence of a nonconductive polymer acid phase in the PANI-PAMPSA film, as a result of which the percolation threshold of the conducting domains of PANI appears at less cathodic potentials, hindering further extraction of the positive charge during the film reduction. In addition, the use of this approach can significantly improve the accuracy of determination of the threshold potential of the leucoemeraldine-emeraldine transition.

The systematic study of the effect of temperature (in the range from −45 to +60°C) on the process of lithium extraction from LiFePO₄ and its insertion into FePO₄ is carried out. At a current of about C/1.5, with decreasing temperature, the capacity decreases, the polarization increases, the range of compositions corresponding to nonequilibrium solid solutions widens, and the slope of the linear section of the galvanostatic curves corresponding to the two-phase system increases. The decrease in the capacity with decreasing temperature is not described by the simple Arrhenius equation. It is assumed that the process on the lithium iron phosphate electrodes has a mixed diffusion-activation nature. The polarization of the anodic and cathodic processes increases with decreasing temperature in a complicated way, and the polarization of the anodic process exceeds that of the cathodic process appreciably.

Synthesis of monodispersed NiFe₂O₄ nanospheres by a simple method was reported. Structure, morphology and characterization of the nanospheres were performed using field emission scanning electron microscopy, X-ray diffraction and FTIR spectroscopy. Electrochemical properties of the prepared nano-spheres were studied in order to realize their suitability and susceptibility as an electrode material for supercapacitor applications. NiFe₂O₄ nanospheres showed a high specific capacitance of 122 F g⁻¹ and a great specific energy of 16.9 Wh kg⁻¹ at a high current density of 8.0 A g⁻¹. The maximum specific capacity of the nanospheres was even more, which can reach 137.2 F g⁻¹ at 4 A g⁻¹ of current density. The results showed an excellent long-term cycling stability for the NiFe₂O₄ nanospheres-based electrodes. The capacitance did not decrease, compared to the initial value during 100 galvanostatic charge-discharge cycles.

Fast-scan anodic stripping voltammetry (FSASV) was applied to sensitively detect Pb²⁺ on a mercury film electrode (MFE). The method was involved with a controlled preconcentration by accumulation of Pb²⁺ on the MFE followed by FSASV measurement. At the scan rate of 500 V/s, a linear relationship between the anodic stripping peak current and the logarithm of Pb²⁺ concentration in the solution was observed in the range from 0.1 µmol/L to 0.1 pmol/L with a detection limit of 0.1 pmol/L. The proposed method was successfully applied for the determination of Pb²⁺ in spiked water samples with satisfying recoveries in the range of 98.6 to 104.3%, and the corresponding relative standard deviation ranged from 3.7 to 5.5%. Therefore, FSASV is a sensitive, fast, cost-effective and simple method for the detection of Pb²⁺ at picomolar level and would be very promising in heavy metal determination.

The detection of water-in-oil (w/o) droplet formation within an interfacial region formed by an interface between an aqueous phase and 1,2-DCE using transient impedance measurements in an unconventional electrochemical cell is herein reported. Droplet formation causes a large peak-like increase in transient real cell impedance. Peaks are likely caused by significant decrease in ion concentration within the interfacial region by formation of w/o droplets containing electrolyte. Droplet formation and an accompanying interfacial stability was observed when antagonistic salts (consisting of a hydrophobic ion of \({\rm{\Delta }}G_{{\rm{tr}}}^{^ \circ ,{\rm{water}} \to 1,2 - {\rm{DCE}}} \le \) TBA⁺) were mixed with conventional aqueous electrolytes in the aqueous phase. The instability manifests as Marangoni convection, causing rapid mass transport in the adjacent fluid on both sides of the liquid/liquid interface.