Vol 59, No 10 (2023)

Coatings based on cobalt-manganese spinel (Mn, Co)·(Mn, Co)2O4 were obtained on the surface of stainless steel by polarization with alternating asymmetric current. The study of the mechanical properties showed that the coatings are characterized by a sufficiently high adhesion to the substrate, their thickness is about 30 μm, and the microhardness value is 40 HV, which is comparable to similar oxide materials. The study of thermal stability in air shows their stability at temperatures up to 1000 °C, and the study of corrosion-protective properties - about the stability of the resulting coatings in a solution of 3.5% (wt.) NaCl.

Silver nanoparticles (Ag-NP) were obtained in MeCN/0.05 M Bu4NPF6 medium by сyclobis(paraquat-p-phenylene) (CBPQT4+) – mediated reduction of the silver ions generated by anodic oxidation of metallic silver during the electrolysis in an undivided cell. Due to multipoint donor-acceptor interaction CBPQT4+ binds the resulting electron-donor Ag-NP to each other, which leads to their enlargement, aggregation and adsorption. This property of the macrocycle allows to call it a “molecular glue” for NP-Ag. In the absence of stabilizers, aggregated polydisperse Ag-NP of indefinite shape are formed with sizes ranging from 20 to 500 nm. Electrosynthesis in the presence of a stabilizer, polyvinylpyrrolidone (PVP), also leads to the formation of aggregated smaller metal particles of 55 ± 26 nm, which have, in addition to the quasi-spherical shape, the shape of a flat triangle and hexagon. Ag-NP stabilized by PVP are partially bound on the surface of nanocellulose (NC). In the presence of NC, larger Ag-NP with an average size of 97 ± 29 nm are formed, the main shape of which is quasi-spherical; cubic, tetrahedral, and rod-shaped Ag-NP are also formed; the formation of Ag-NP with a flat structure is excluded. The catalytic activity of the obtained particles in the reduction of p-nitrophenol with sodium borohydride is extremely low due to the large size, aggregation, and coating of the NP-Ag surface with the stabilizer PVP and marcocycle. 

The electrotranspot and structural characteristics of the MK-40 and MF-4SK sulfocationic membranes modified with polyaniline in an electrodialysis apparatus were studied in solutions of nickel and chromium sulfates and sulfuric acid. The decrease in the conductivity of membranes and the increase in their diffusion permeability in solutions of all electrolytes after modification with polyaniline were estimated. The key effect of the charge of the counterion on the electrical conductivity of the initial and modified membranes was confirmed, and an unusual effect of reducing the electrical conductivity of the MF-4SK/PANI membrane with an increase in the concentration of a solution containing multi-charged counter-ion was found. The information on the effect of multi-charged ions on the structure of a homogeneous and heterogeneous membranes, obtained by the method of standard contact porometry, is supplemented by the estimation of transport and structural parameters of microheterogeneous model. Based on the analysis of the parameters of current-voltage curves in solutions of nickel and chromium sulfates and sulfuric acid, the prospects of using the polyaniline-modified membranes in the processes of electrodialysis treatment of acid solutions containing multi-charged ions are evaluated.

TiO2 films being a 1D nanotube structure were obtained by electrochemical anodic oxidation of titanium foil. Electrochemical reduction activation of electrodes based on TiO2 nanotubes was carried out using the method of cyclic voltammetry (CV). The activated electrodes showed significantly higher current density and quantum efficiency of the photoelectrochemical water splitting compared to native TiO2 nanotubes. Electrochemical treatment of electrodes by the CV method leads to an increase in the photocurrent density from 4 to 14 times, depending on both the wavelength used and the applied potential. The analysis of  electrochemical impedance spectra showed that the increase in the photoelectrochemical process performance is due to an increase in the charge transfer rate at the semiconductor/electrolyte interface, as well as improved electronic conductivity of the oxide layer, which contributes to better charge carrier separation and a decrease in their recombination rate. 

p-Aminophenol was prepared by electrocatalytic hydrogenation of p-nitrophenol using Ag + Fe + Fe3O4 (or Fe2O3) composites as catalysts formed during heat treatment and electrochemical reduction of silver ferrite, AgFeO2. AgFeO2 samples were synthesized by co-precipitation method without and in the presence of a polymer (polyvinyl alcohol, polyvinylpyrrolidone). The effect of the polymers on the phase constitutions of metal composites formed at the stage of synthesis, during the heat treatment and electrochemical reduction was established. The high electrocatalytic activity of prepared Fe-Ag-containing composites in electrohydrogenation of p-nitrophenol with an increase of hydrogenation rate by 2.2-2.7 times in comparison with its electrochemical reduction in similar conditions was shown.