New light-sensitive materials based on TiO2 and merocianin polymetine dye

The influence of the structure of a number of merocyanine dyes (D), which differ in the length of the polyethylene chain on one vinyl group, on their spectral, electrochemical and energy characteristics is established. Cyclic voltammetry determines their oxidation and reduction potentials. The values ​​of the HOMO and LUMO energy levels of the studied dyes from spectral and electrochemical data were calculated. It is shown that the obtained values ​​of the potentials of the energy levels of the dyes differ little (the energy difference ranges from 0,22–0,53 eV). The possibility of using merocyanins as sensitizers of titanium(IV) oxide and the creation of photosensitive heterostructures has been made. In order to investigate the possibility of using the merocyanin dyes under study as TiO2 sensitizers, the energy of the «semiconductor – dye – reagents» systems was considered. For this purpose, we compared the redox characteristics of merocyanine dyes with the electrophysical parameters of titanium(IV) oxide, as well as the redox characteristics of the reaction participants. It is established that in such systems the processes of photon transfer of the electron from the dye to the semiconductor are necessary for sensitization, and the regeneration of the original form of the sensitizers by the action of the reducing agent on the cation radicals formed is thermodynamically allowed. The conclusion about the possibility of using the studied merocyanines as effective sensitizers was confirmed by the results of the study of the photocatalytic activity of D/TiO2 heterostructures in the reaction of methylene blue formaldehyde recovery under different irradiation conditions and at different dye concentrations. The explanation for the found laws is offered. Scientific approaches to the production of new photosensitive systems with an expanded range of photosensitivity and a given level of photocatalytic activity have been developed.

Antioxidant properties of derivatives of 3,4-dihydropyrimidin-2-one with sterically hindered phenolic substituent in heterocycle

In the processes of free-radical oxidation of organic compounds, the inhibitory action of the inhibitor is mainly due to either the breakdown of the reaction chains on its molecules, or the slowdown of the decomposition of intermediate hydroperoxides, or both at the same time. We analysed the inhibitory properties of 4-[3,5-di(tert-butyl)-4-hydroxyphenyl]-5-ethoxycarbonyl-6-methyl-3,4-dihydropyrimidin-2-one (I) and 4-[4-methoxyphenyl]-5-ethoxycarbonyl-6-methyl-3,4-dihydropyrimidin-2-one (II) gasometry and hydroperoxide decomposition methods. These compounds were obtained by the three-component Biginelli reaction. The decomposition of cumene hydroperoxide in dimethylformamide under these conditions is described by a first-order kinetics equation. The first compound significantly inhibits the decomposition of hydroperoxide. The dependence of the effective rate constant of the decomposition of cumene hydroperoxide on the first concentration is described by the equation: . The second compound also slows the decomposition of hydroperoxide, but much less than the first compound. Therefore, both the phenolic moiety and the urea moiety of the dihydropyrimidinone cycle take part in slowing the cumene hydroperoxide decomposition. Initiated oxidation of cumene happened at 343 K with the presence of the initiator azodiisobutyronitrile. The concentration of the first compound varied from 1,5·10-4 to 2,5·10-3 mol/l. With a concentration of the first compound 1,25·10-3 and 2,5·10-3 mol/l, the duration of the induction period exceeds 80 min. In the concentration range (1,5÷6,3)·10-4 mol/l the linear change in the duration of the induction period is observed. 4-[3,5-Di(tert-butyl)-4-hydroxyphenyl]-5-aminocarbonyl-6-methyl-3,4-dihydropyrimidin-2-one is a more effective inhibitor than the ionol due to the urea moiety of the dihydropyrimidinone cycle. Confirmation is the notable antioxidant activity of the second compound. In conclusion, 4- [3,5-di (tert-butyl)-4-hydroxyphenyl]-5-ethoxycarbonyl-6-methyl-3,4-dihydropyrimidin-2-one is a bifunctional inhibitor.

Methods for extraction of mercury compounds from coal in Ukraine

The ways of prevention of environmental pollution by coal-containing mercury compounds are investigated in the paper. Coal mercury compounds are harmful and toxic impurities. In coal, the mercury is in the form of sulfides and mercury-containing organic compounds. Considerable amounts of native mercury and cinnabar are also recorded. The content of the mercury in terms of metal in the Donbass coal ranges from 0.01 to 1000 g / t. The highest concentrations of mercury compounds are due to hydrothermal and volcanic processes. In Donbass coal, the content of mercury compounds is on average 5 to 10 times greater than the background compared to other coal basins. The most common form of mercury compounds in coal are impurities in sulfide minerals. The content of mercury compounds in pyrite is two orders of magnitude higher than in the organic coal component. It is established that the bulk of the mercury compounds are contained in fine particles. The maximum content is fixed in a fraction of 0.1 - 15 microns. Thus, it can be assumed that the mercury compounds are predominantly contained in the mineral component of coal, which is more intensively ground. It is shown that washing with hot water and the complexing agent solution results in a decrease in the content of mercury compounds in the coal feedstock. The washing solutions become turbid, and this suggests that the mercury compounds are flushed out with fine particles. The increase in the degree of extraction of compounds of the mercury when applying the complexing solution is due to the ability of aurintricarboxylic acid to form complex compounds with the mercury ions. It can be assumed that in this case chemisorption occurs with the formation of complex compounds of the chelate structure on the surface of the particles, followed by dispersion of the particles of the dispersed phase. It was found that washing of the dispersed coal raw material is accompanied by weight loss. This indicates that the mercury compounds are leached from the coal in the form of dispersed particles. Waste sludge is to be disposed of with further disposal.

Application of knowledge test control in external independent evaluation format at chemistry

Pedagogical control is one of the components of the teacher's practical activity, which reveals the advantages and disadvantages of new teaching methods. It allows you to match the planned and achieved level of knowledge, to evaluate student achievement, to identify gaps in his knowledge and skills. The forms and methods of pedagogical control are quite diverse. Currently, testing is increasingly used in the practice of school assessment. Testing process has more advantages than classical methods of knowledge control because it is the most objective way of knowledge assessing. Objectivity of testing achieves by standardizing the process and by minimizing the subjective component of student knowledges assessment. The mentioned advantages of the testing control form became the basis for the test system of the External Independent Еvaluation while entering higher education institutions. It is advisable to introduce such a method of knowledge control as testing in the form of External Independent Еvaluation into the practice of school education for the gradual adaptation of the student to the form of testing that they will expect while entering the higher education institutions, as well as to reduce the negative psychological impact of the testing procedure on the student. To achieve this goal, eight sets of test assignments have been created on different topics of the program for 11th grade students who study chemistry at the profile level. The test tasks are designed in the format of External Independent Еvaluation. The methodological materials that have been created can be used for the current and final control of the knowledges in the practice of General Secondary Education, like any other instruments of student knowledges control. As a result of the pedagogical experiment, it was found that testing in the External Independent Evaluation format, was more successful and effective to students with higher levels of education, since the total percentage of good and excellent grades obtained by students at testing was higher than in writing classic control work. The main disadvantages and advantages of using the test system for monitoring the quality and success of knowledge acquisition by students of the institution of general secondary education are presented.

Study of melting and crystallization process of CsPbBr3 by differential thermal analysis

The crystalline CsPbBr3 was synthesized from CsBr (6N) and PbBr2 (5N) by the mechanochemical method with further fusion in quartz ampoule at 640-650 °С. After synthesis, the structure and chemical composition of the obtained material was confirmed by energy-dispersive X-ray spectroscopy (EDX) and X-ray diffraction analysis. The melting and crystallization of the obtained perovskite were investigated by the differential thermal analysis (DTA) with heating/cooling rates of 1, 5 and 10 °C/min. Measurements were carried on the self-constructed DTA-setup with S-type thermocouples in the range of 450-590 °C. Each cycle of heating/cooling was repeated three times to confirm the accuracy of the results obtained. A decrease in the melting point from ~ 568.1 °C to ~ 566.2 °C was demonstrated with an increase in the heating rate from 1 °C/min. up to 10 °C/min. respectively. Probably, it's due to the approach to equilibrium conditions of phase transformations at lower heating rates. We recorded an additional-endothermic effect during CsPbBr3 melting. This may indicate a complex process of melting the compound. The thesis of a two-stage melting mechanism of CsPbBr3 perovskite with an initial stage of fragmentation of the crystalline structure and subsequent dissolution of crystalline phase residues is proposed. It is reported that with increasing of the melt heating above a certain "critical" temperature (579-585 °C), its homogenization occurs, and the crystallization temperature is set at 540-550 °C for the heating/cooling rate of 1 ° C/min. and 538-543 °C for the rate of 5-10° C/min. All obtained data confirm the assumption of a two-step melting process of CsPbBr3 perovskite, and the relatively constant crystallization temperature after a critical point of overheating may also indicate a certain structure of the melt of the compound with short-range order in the arrangement of the structural units of the compound in the liquid phase.

High-temperature electrical properties of undoped Cd1-xMnxTe (x = 0.05-0.55) crystals under cadmium vapor pressure

For the first time, the results of a study of the high-temperature electrical characteristics of undoped Cd1-xMnxTe single crystals in a wide composition range x = 0.05-0.55 are described. For this purpose, a study of Hall effect was made at the temperatures of 723–1073 K and isothermal and temperature dependences of electrical parameters were constructed. At 300 K, all the samples studied had a p-type conductivity, and Cd1-xMnxTe crystals with x = 0.02 and 0.15 had a low resistivity (102-103 Ohm×cm) while with x = 0.3 and 0.55 they had a relatively high ρ~ 107 Ohm×cm, which is due to an increase in the band gap with an increase in the MnTe content. The sample with the lowest Mn content (x = 0.02) showed the instability of the impurity-defect system during the first heating-cooling cycles: the conductivity type changed from p- to n- above 750 K and the mobility gradually increased as a result of the introduction of Cd atoms from the gas phase to the interstitial positions of the lattice. In this sample, during the first heating, the influence of donor impurities is noticeable, since the experimental line lg[e-] is significantly (~ 1-1.4 orders of magnitude) higher than that for model (undoped) CdTe, probably due to the donor behavior of Mn atoms. The crystal with the highest MnTe content (Cd0.45Mn0.55Te) also demonstrated the instability of the impurity-defect system, which was reflected in the decrease in the electrical conductivity after heat treatment at 773-873 K by almost one order of magnitude, which can be explained by a superposition of the results of the interaction of donor Cd atoms introduced from the gas phase with its native acceptor point defects (compensation) and the interaction of impurities between the matrix and Te inclusions. It has been established that a peculiarity of Cd1-xMnxTe crystals with a high content MnTe (x = 0.15, 0.55, and partially 0.3) is the inverse dependence of the carrier concentration on the cadmium vapor pressure caused by the onset of mixed conductivity of these crystals at high temperatures (T> 873 K). Accordingly, for these crystals, the value 1/RH at the moment of the onset of mixed conductivity characterizes the conditional rather than real mobility of the charge carriers. On the pressure dependences of the charge carrier concentration, the corresponding dependences are lower than the undoped CdTe (especially at low temperatures) for samples with x≥0.15 indicating that the introduction of a significant amount of MnTe (x≥0.15) leads to a decrease in the charge carrier concentration by 0.5-0.8 orders of magnitude (at ~ 773 K). This is due to the influence of Mn atoms, which form a stronger bond with Te than Cd, and therefore the generation of electrons requires more energy than in pure CdTe.

Reduction of the Cd0.9Zn0.1Te surface conductivity by chemical treatment

The influence of Cd0.9Zn0.1Te crystals pretreatment on the effectiveness of the passivation was studied. The optimal conditions of passivation process are determined. Samples of Cd0.9Zn0.1Te were treated with Br2-DMF solution before the investigation. After treatment the surface of the sample was smooth without visible irregularities, which indicates the good polishing properties of this etching solution and the possibility of using the samples for further study. Passivation of samples surface was carried by the NH4F-H2O2 solution. The qualitative and quantitative composition of the Cd0.9Zn0.1Te sample surface was investigated by means of energy-dispersive X-ray spectroscopy (EDX). The formation of a uniform oxide surface layer was confirmed. The electrical characteristics of the passivated samples were investigated by measurent the current-voltage dependences. The expediency of applying of the Cd0.9Zn0.1Te sample treatment in 50% KOH solution after their chemical treatment in the NH4F-H2O2 solution was proved. It was shown that after etching, excess tellurium appears on the surface of the specimens and causes increasing surface conductivity. Measurement of current-voltage dependencies for pre-treated specimens with and without KOH solution showed that the application of this additional chemical treatment step leads to a significant increase in the surface resistance of the specimen. Visual changes in the surface are also observed. It was found that the optimal conditions for Cd0.9Zn0.1Te crystals surface passivation are chemical treatment with NH4F-H2O2 solution for 2 min at a temperature of 18 °C. The current-voltage characteristics of the sample Cd0.9Zn0.1Te were measured at different stages of surface treatment: after polishing, after etching and after passivation. It was done for compares the overall effect of the semiconductor's surface quality on their electrical properties.

Chemical-mechanical polishing of CdTe and based on its solid solutions single crystals using HNO3 + НІ + ethylene glycol iodine-emerging solutions

The interaction of the CdTe and Zn0.04Cd0.96Te, Cd0.2Hg0.8Te solid solutions single crystals with the iodine-emerging etchings based on aqueous solutions of HNO3 + НІ + ethylene glycol has been investigated and etching compositions have been developed and optimized, as well as methods of their chemical treatment for the formation of high-quality surface. The dissolution of these semiconductor materials in the aqueous solutions of the (HNO3+HI+EG)/EG have been investigated and dependences “etchant composition – etching rate” with determining the regions of polishing and unpolishing solutions have been constructed. It was found that the semiconductors etching rate (chemical-mechanical polishing) decreases from 73.2 to 0.5 μm/min and the polishing features of the HNO3+HI+EG etching composition improve when the EG content is increasing. The minimum value of the etching rates is achieved when the saturation of the organic component is maximum (95 vol. %). The dependences of the chemical-mechanical polishing rate on the dilution of the base polishing etchant with ethylene glycol and the surface condition after polishing have investigated using metallographic analysis and atomic force microscopy. It was established that chemical-mechanical polishing of the CdTe and Zn0.04Cd0.96Te, Cd0.2Hg0.8Te solid solutions single crystals by the (HNO3+HI+EG)/EG solutions promote decreasing of the structural damages of the substrate and obtaining the high-quality polishing surface. It has been shown that etchant compositions of HNO3+HI+ EG with EG as a solvent completely meet the requirements for CMP etchants. Treatment of the Cd0.2Hg0.8Te crystal surfaces with new etchant mixtures allows to obtain ultra-smooth surfaces Ra = 1.5 nm. The polishing etchant compositions (HNO3+HI+EG)/EG and technological procedures of the chemical mechanical polishing for the disturbed layer elimination, controlled thinning of the plates up to reference dimension, as well as the thin layers removing and CdTe single crystals and Zn0.04Cd0.96Te, Cd0.2Hg0.8Te solid solutions finishing polishing have been optimized.

Light-sensitive heterostructures based on TiO2 and squaraine dye-sensitizer

On the basis of nanodispersed titanium(IV) oxide and squaraine dye-sensitizer (D), new heterostructures (HS) have been created with a given level of photocatalytic activity and an expanded range of photosensitivity. On the basis of the analysis of the results of the measurement of spectral, electrochemical and energy characteristics, it is concluded that it is possible to use the tested squaraine as an effective TiO2 sensitizer. For the first time, using the method of cyclic voltammetry, the redox potentials of squaraine dye were determined and the redox processes were checked for reversibility. It is shown that the plot of the peak current versus the square root of the velocity sweep rate is described by a linear function. It has been found that the electrochemical processes are reversible and diffusion controlled. It is established that the values ​​of redox potentials can be used to calculate the values ​​of standard potentials and free energy. Based on the measured oxidation and reduction potentials of polymethine, the values ​​of the HOMO and LUMO energies were calculated and diagrams of the energy levels of squaraine relative to the electrophysical characteristics of titanium (IV) oxide were constructed. The peculiarities of the sensitizing ability of the studied squaraine dye were analyzed, the mechanism of photocatalytic action was proposed and its confirmation was obtained during the study of the methylene blue recovery reaction. The dependences of the photocatalytic activity of HS D/TiO2 on the dye concentration and irradiation conditions were revealed. It is shown that, when irradiated with heterostructures by light absorbed by the dye, at low concentrations of the latter (0.02÷0.2 mg/g), the photocatalytic activity increases, and at the content of the sensitizer 1.0÷2.0 mg/g, it decreases. When irradiated with HS by light absorbed by titanium(IV) oxide, photocatalytic activity decreases with increasing squaraine content.

Research of the mechanism of the impact of dispersion additives on the rheological properties of disperse systems based on wheat flour

In the paper the requirements to the physicochemical properties of the potential substitutes of the used food additives are considered. Cocoa is one of the products that is constantly looking for its potential substitutes. Studies have shown that when added to aquatic systems, cocoa is divided into two components: substances that pass into the volume of the system and are evenly distributed in it due to the passage of extraction processes, and resistant to the external influence of particles that swell and become nodes of the spatial structural network. Potential substitutes for cocoa in confectionery should not only preserve the relevant organoleptic properties of the final product, but also reproduce the behavior of cocoa in semi-finished products. We have shown that the separation of cocoa into soluble and insoluble component occurs in the ratio of 3: 1. The obtained results allow us to predict that in such systems the soluble component exerts a greater influence on their rheological characteristics. It has been found that the introduction of cocoa flour and its ingredients leads to a gradual increase in the viscosity of the dough. This is due to the processes of structure formation in the dispersed systems due to the leaching of substances from cocoa. It should be noted that cocoa powder works most effectively, the water-soluble component is less effective and finally the insoluble component has little effect on the viscosity of the dough samples. This indicates the decisive role of the intensity of interparticle interaction in the processes of structure formation in such systems. Substances that are contained in a water-soluble component capable of forming bridging bonds contribute to the formation of structure in the system. Purely mechanical impurities (insoluble component) have virtually no effect on the rheological characteristics of the system. It was found that the total effect of cocoa components on rheological characteristics is less than the effect of cocoa powder as a complex additive. This indicates that particles of the dispersed phase of a water-insoluble cocoa component are more likely to form a structural framework with molecules of a water-soluble component of cocoa. Therefore, the chemical affinity of soluble and insoluble components plays an important role in the structuring of dispersed systems based on wheat flour.