The electrical properties of glasses composed of 8Na2O–(22 – x)B2O3–70SiO2–xCr2O3, where x varies from 0.3 to 6 mol

Porous glass (PG) obtained by leaching of sodium borosilicate glass (NBS) is actively used in sorption and separation technologies. Modifying the NBS system with additives can drastically affect the resulting PG. Here, we report on the effect that Cr2O3 had on the leaching behavior of phase-separated glasses in the Na2O-B2O3-SiO2-Cr2O3 system in 3 M HCl solution. The structure of these glasses was investigated by means of XRPD, EPR, and SEM. All chromium ions exist in the Cr3+ state and are octahedrally coordinated. Most Cr2O3 crystallized as eskolaite in the silica-rich phase. The leaching process is limited by the interdiffusion in the leached porous layer. Cr2O3 did not get extracted from the glass into a leaching solution. PGs containing a significant amount of eskolaite were obtained. The component extraction rate for Cr-doped glasses was higher than for Fe-containing glasses with similar compositions, which was explained by the difference in their structural roles.

Porous glasses (PGs) obtained from sodium borosilicate (NBS) phase-separated glasses via leaching are promising inorganic membranes. Introducing Fe2O3 into NBS glasses imparts ferrimagnetic properties due to magnetite crystallization. Leaching of such glasses leads to the formation of magnetic PGs with interesting electro-surface characteristics. This work aimed to investigate the process of obtaining magnetite-containing PGs from NBS glasses depending on silica content, using XRPD and Raman spectroscopy, studying the PG membranes’ structural characteristics and their sorption properties with respect to methylene blue (MB). Obtained PGs were characterized by a polymodal distribution of mesopores and a small number of micropores with specific surface area values of 32–135 m2/g and an average mesopore diameter of 5–41 nm. The kinetic data were analyzed using pseudo-first-order, pseudo-second-order, and intra-particle diffusion equations. The equilibrium isotherms were fitted with Langmuir, Freundlich, Temkin, and Dubinin-Radushkevich models. MB adsorption was found to be a complex process. The glass with the highest specific surface area demonstrated the maximum sorption capacity (10.5 mg/g). The pore size of PGs allowed them to be considered potential novel magnetic membranes for ultrafiltration.

We have studied glass formation and crystallization in the CdO–B2O3–SiO2 system. Glasses were prepared in the composition range from 21.12 to 87.00 mol

Glasses with compositions 6Na 2 O⋅ x B 2 O 3 ⋅(86 – x )SiO 2 ⋅8Fe 2 O 3 , where x varies from 16 to 21 mol %, are preliminarily heat treated at a temperature of 550°C for 8–144 h and studied by scanning electron microscopy and dilatometry. The density and Vickers microhardness are measured, and the molar volume is calculated. It is found that in the course of heat treatment, a phase-separated structure with interpenetrating phases is formed in all studied glasses. As the SiO 2 content increases the diameter of the liquation channels decreases. It is shown that after 8 h, the coexisting liquid glass phases reach their equilibrium compositions, as indicated by the invariability of the glass transition temperature with an increase in the duration of heat treatment. With the maximum duration of heat treatment of 144 h for all the studied glasses, there is a decrease in the glass transition temperature of the low-viscosity phase and an increase in the density of glasses; this is accompanied by crystallization of the tridymite and cristobalite silica phases. The microhardness of the studied glasses does not depend on the SiO 2 content, and is about 2.5 GPa.

Glasses with compositions 6Na2O⋅xB2O3⋅(86 – x)SiO2⋅8Fe2O3, where x varies from 16 to 21 mol %, are preliminarily heat treated at a temperature of 550°C for 8–144 h and studied by scanning electron microscopy and dilatometry. The density and Vickers microhardness are measured, and the molar volume is calculated. It is found that in the course of heat treatment, a phase-separated structure with interpenetrating phases is formed in all studied glasses. As the SiO2 content increases the diameter of the liquation channels decreases. It is shown that after 8 h, the coexisting liquid glass phases reach their equilibrium compositions, as indicated by the invariability of the glass transition temperature with an increase in the duration of heat treatment. With the maximum duration of heat treatment of 144 h for all the studied glasses, there is a decrease in the glass transition temperature of the low-viscosity phase and an increase in the density of glasses; this is accompanied by crystallization of the tridymite and cristobalite silica phases. The microhardness of the studied glasses does not depend on the SiO2 content, and is about 2.5 GPa.

In this work, a reversed-phase dispersive liquid-liquid microextraction procedure based on the decomposition of deep eutectic solvent was suggested for the first time. The procedure was utilized for fast and simple separation of lead and cadmium from vegetable oil samples. The procedure assumed mixing of oil sample and DES based on menthol, formic acid and water. Water as component of DES promoted its decomposition in sample matrix resulting menthol dissolution in the sample phase and dispersion of aqueous formic acid solution. In this procedure menthol acted as a dispersive solvent during DES decomposition for dispersion of aqueous formic acid solution. The metals were determined by the square-wave anodic stripping voltammetry. The limits of detection, were 0.01 mu g kg(-1) for lead and 0.006 mu g kg(-1) for cadmium. The RSD was less then 6% for both analytes. The enrichment factor was 36 and 39 for lead and cadmium, respectively.

Composite materials (CMs) were synthesized on the basis of nanoporous silicate glasses (PGs) with small additives of P 2 O 5 and fluoride ions doped by silver bromide in the presence or in the absence of cerium or erbium. The obtained CMs were characterized by a complex of methods (X-ray powder diffraction (XRD) technique, energy-dispersive X-ray spectroscopy, and UV-Vis-NIR spectroscopy). According to the XRD data, the CMs contain the cubic phases of AgBr (No. 01-071-3754) and KBr (No. 01-089-3620). It was foundby energy-dispersive X-ray spectroscopy that the concentrations of oxygen, silicon, potassium, and silver are uniformly distributed over the whole thickness of the samples. The optical properties of the CMs depending on their composition and heat treatment temperature (in the range from 120 to 870 °C) were compared. The absorption bands characteristic of molecular clusters and nanoparticles of silver, as well as cerium and erbium ions were revealed.

Electrochemical methods of analysis are usually characterized by high sensitivity, ease of automation, and a wide range of analytes and test samples. The development of electrochemical methods of analysis at the present stage is mostly determined by the creation of new nanostructured electrode materials with electrocatalytic properties. The use of such materials ensures an increase in the sensitivity and selectivity of the determination of a number of analytes. Another conventional way to decreasing the limit of detection for electrochemically active substances is the development of new measurement methods for improving the signal-to-noise ratio in nonequilibrium electrochemical methods of analysis. This article is devoted to the consideration of some new electrode materials and methods of electrochemical measurements.

Glasses in the Na2O-B2O3-SiO2-Fe2O3 system with a constant SiO2 content 70 mol% were synthesized using conventional melting in platinum crucibles in SiC-furnace in air. After synthesis and annealing, glasses were heat treated at 550 degrees C for 96-144 hrs to promote phase separation. A tentative region of phase separation for this temperature was outlined. X-ray powder diffractometry results showed three iron-containing phases (Fe3O4, FeSiO3 and beta-Fe2O3) forming in the investigated glasses with magnetite being the main phase as it is observed in most of the glasses. Chemical durability studies showed that compositions of phase-separated glasses suitable for synthesis of porous glasses, both iron-free and iron-containing lie in between 4 and 8 mol% of Na2O. Bulk samples of porous glasses were obtained within the chosen region having the following parameters: specific surface area 40-185 m(2)/g, porosity 30%-45%, pore diameter 3-14 nm. The parameters of porous structure of iron-containing porous glasses are of the same order of magnitude as the porous glass used for the multiferroic nanocomposite synthesis.

The new method, interrupted amperometry, is proposed to increase the sensitivity of amperometric measurements. Analytical possibilities of interrupted amperometry on solid electrodes are studied on an example of the determination of phenolic compounds in aqueous solutions.

Interrupted amperometry is a new highly sensitive method for diffusion current measuring. The main feature of the proposed technique is the use of capacitive current as the analytical signal together with the faradaic current. The conventional electrical circuit for amperometric measurements is complemented by a switcher that enables periodical interruption of the circuit. The technique was successfully applied for direct amperometric determination of lead, cadmium and iron ions, phenol and hydroquinone; for determination of dichromate ion via titration; for determination of dissolved oxygen in water by Clark-type sensor. In all the mentioned cases the achieved values of analytical characteristics are significantly better than for conventional amperometric methods. There are limitations and perspectives of the proposed technique considered.

Interaction of copper, lanthanum, thallium and mercury salts solutions with an inorganic ion exchanger “polysurmin” was investigated. It was shown that the ion exchanger adsorbs the ions of these metals and exhibits specific selectivity for Hg2+ ions demonstrating abnormally high capacity.