The structure and chemical and acid-base state of the surface of solid solutions and binary components in the InSb-CdS system

The surface physicochemical properties, including microstructure, chemical composition, and acid-base surface properties, of solid solutions and binary components in the InSb-CdS system obtained for the first time were studied. Films of all the components had a polycrystalline structure with a nonuniform character of the distribution of crystallites, which associated into agglomerates. The chemistry of the surface was mainly determined by adsorbed H₂O and CO₂ molecules, OH⁻ groups, and, to a lesser extent, oxygen and hydrogen carbon compounds. The strength, concentration, and nature of acid centers were determined. Coordination-unsaturated In and Cd atoms, adsorbed water molecules, and OH-groups were responsible for acid-basic centers. Changes in the acid-base properties of the surface of InSb-CdS system components caused by composition variations were studied. They correlated with the “specific conductivity-composition” dependence, reflected the special features of donor-acceptor interactions in solid solutions, and could be used to predict adsorption-catalytic properties.     

Comparative acid-base properties of the surface of components of the CdTe-ZnS system in series of substitutional solid solutions and their analogs

The acid-base properties of the surface of solid solutions and binary components of the CdTe-ZnS system are studied by hydrolytic adsorption, nonaqueous conductometric titration, mechanochemistry, IR spectroscopy, and Raman scattering spectroscopy. The strength, nature, and concentration of acid centers on the original surface and that exposed to CO are determined. The changes in acid-base properties in dependence on the composition of the system under investigation in the series of CdB₆, ZnB₆ analogs are studied.     

New catalysts and adsorbents on the basis of the InSb-CdTe semiconducting system

The acid-base properties of solid solutions and binary components of the InSb-CdTe system were studied by IR spectroscopy, pH isoelectric point measurements, and conductometric titration; adsorption properties with respect to CO, O₂, NO₂, NH₃, CO + O₂, and NO₂ + NH₃, by piezoquartz microweighing; and catalytic properties in the oxidation of carbon(II) oxide and reduction of nitrogen(IV) oxide with ammonia, by the pulsed and circulation flow methods. The nature, strength, and concentration of acid centers were determined. Changes in the concentration of acid centers under the action of gases (NO₂ and NH₃), gamma irradiation, and composition variations were estimated. The experimental dependences, thermodynamic and kinetic adsorption characteristics, the electrophysical, acid-base, and other physicochemical characteristics of the adsorbents, and adsorption characteristic-composition phase diagrams were analyzed taking into account the electronic nature of adsorbate molecules to determine the mechanism and characteristics of adsorption processes depending on the conditions of adsorption and the composition of the system. The results of adsorption studies were used to preliminarily determine the temperature regions of the occurrence and the mechanism of the reactions studied. A shock mechanism was suggested. Separate components (predominantly, solid solutions) of the InSb-CdTe system showed high catalytic activity at comparatively low temperatures. Along with behavior common to the system and its binary compounds (InSb and CdTe), solid solutions exhibited features characteristic of multi-component systems. These were the presence of extrema in the pH_iso-composition, adsorption characteristic-composition, and catalytic activity-composition diagrams. The use of these diagrams allowed us to discover system components most active with respect to the gases and reactions studied and create high-sensitivity and selective sensors and high-activity and selective catalysts on the basis of these components.     

Electrochemical properties of 1-butyl-3-methylimidazolium bromide melt containing water impurities

The effect of a water impurity (1.8–10 wt %) on the conductivity of the ionic liquid-H₂O binary system was studied in a wide temperature range. It was shown that the interaction between components is characteristic of this system, and the molar ratio of components 1: 1 is boundary between the structures of solution and melt. The basic kinetic features of electrochemical reduction of water of the BMImBr-H₂O binary system were determined by voltammetry with linear potential sweep. The transfer coefficient for the cathodic process (α = 0.46) and H₂O molecule diffusivities were determined depending on the water content ( $ D_{H_2 O} The effect of a water impurity (1.8–10 wt %) on the conductivity of the ionic liquid-H₂O binary system was studied in a wide temperature range. It was shown that the interaction between components is characteristic of this system, and the molar ratio of components 1: 1 is boundary between the structures of solution and melt. The basic kinetic features of electrochemical reduction of water of the BMImBr-H₂O binary system were determined by voltammetry with linear potential sweep. The transfer coefficient for the cathodic process (α = 0.46) and H₂O molecule diffusivities were determined depending on the water content ( = (0.2–1.3) × 10⁻¹⁰ cm²s⁻¹). Original Russian Text ? E.P. Grishina, A.M. Pimenova, L.M. Ramenskaya, O.V. Kraeva, 2008, published in Elektrokhimiya, 2008, Vol. 44, No. 11, pp. 1352–1358.     

Acid-base properties of the surface of the α-Al2O3 suspension

The distribution of the acid-base centers on the surface of α-Al₂O₃ suspension particles was studied by potentiometric titration, and the corresponding pK spectra were constructed. It was inferred that the double electric layer created by the supporting electrolyte substantially affected the screening of the acid-base centers on the particle surface of the suspension.     

Changes in the State of Silver Sol Particles after Low-Temperature Treatments

The influence of the low-temperature treatment of Ag hydrosol on the properties of silver particles was studied by electron absorption spectroscopy over the temperature range 77–230 K. Low-temperature treatment caused the aggregation of particles because of an increase in the number of defects on the surface of Ag observed as an increase in the damping coefficient of electron plasma oscillations. These processes depended on the temperature and initial concentration of disperse silver. Defect formation is explained taking into account the tunnel mechanism of the interaction of low-atomic mobile H⁺(H₂O) _n and OH⁻(H₂O) _n clusters with the surface of silver particles at low temperatures. Original Russian Text ? E.A. Kononova, I.I. Mikhalenko, V.D. Yagodovskii, 2008, published in Zhurnal Fizicheskoi Khimii, 2008, Vol. 82, No. 4, pp. 774–779.     

Adsorption, electrophysical, and optical studies of the surface of solid solutions and the binary components of the InSb-ZnTe system

Piezoquartz microweighing, surface electroconductivity measurements, and IR and Raman spectroscopies were used to study the mechanism and regularities of the interaction of carbon monoxide, ammonia, and oxygen, gases of different electronic natures encountered in the environment and various technological processes, with the surface of solid solutions and the binary compounds of the InSb-ZnTe system. An analysis of the results with the use of the acid-base and other physicochemical characteristics of the adsorbents and of the electronic properties of the adsorbate molecules showed that the values of adsorption of the gases lie within α = 10⁻⁵−10⁻³ mol/m². It was demonstrated that, at temperatures above 293 K, the adsorption of CO and NH₃ occurs by the donor-acceptor mechanism, whereas oxygen is adsorbed through the ion-radical mechanism, with the predominant participation of coordinatively unsaturated metal atoms and vacancy defects, respectively. It was revealed that the acid-base, adsorption, electrophysical, and optical properties vary similarly with changing composition of the system, a behavior that suggests the same origin of adsorption sites and inherent surface states and makes it possible to predict the adsorption activity of a surface on the basis of its acid-base properties and the properties of the binary compounds and constituent elements. Similarities and distinctions in the behavior of (InSb) _x (ZnTe)_{1 − x} solid solutions and the binary compounds (InSb and ZnTe) were identified. Specific features of solid solutions, as multicomponent systems, are that adsorption on them is energetically more favorable, especially well pronounced in the acid-base characteristic-composition and adsorption characteristic-composition diagrams. Such diagrams made it possible to determine the solid solution most active with respect to ammonia, (InSb)_0.95(ZnTe)_0.05, which was used to make a selective high-sensitivity gas sensor.     

Adsorption of gases on binary and multicomponent semiconductors of the ZnSe-CdTe system

Adsorption of carbon monoxide(II) and oxygen on powders and nanofilms of solid solutions and binary compounds of the ZnSe-CdTe system was studied volumetrically, and by piezoquartz microweighing and IR spectroscopy of multiple disturbed complete internal reflections. The mechanisms and principles of adsorption were established in dependence on the conditions of the habitus of an experimental sample and the composition of the system’s semiconductors, based on an analysis of IR spectra; the thermodynamic and kinetic characteristics of adsorption; experimental dependences αp = f(T), αT = f(P), and αT = f(t); and the acid-base and other physicochemical characteristics of adsorbents and the electron nature of adsorbate molecules. Conclusions drawn earlier as to the retention of local active centers on the surface of a diamond-like semiconductor (which are responsible for adsorption and catalytic processes) upon a change in the habitus of a sample were confirmed. Certain features in the behavior of solid solutions (ZnSe) _x (CdTe)_{1 − x} were revealed alongside commonalities with binary compounds (ZnSe, CdTe), testifying to the presence of critical points on “adsorption characteristics-composition” diagrams. The most active adsorbents (with respect to CO and O₂) were discovered on the basis of these diagrams, which were used in creating highly sensitive and selective sensors.     

Polyurethane cationomers synthesised with 4,4′-methylenebis(phenyl isocyanate), polyoxyethylene glycol and <Emphasis Type="Italic">N</Emphasis>-methyl diethanolamine

Polyurethane cationomers with increased contents of ions were synthesised in the reaction of 4,4′-methylenebis(phenyl isocyanate) (MDI) with polyoxypropylene glycol (M = 450) and N-methyl diethanolamine (N-MDA). Amine segments were built-in to the urethane–isocyanate prepolymer in the reaction with formic acid and then they were converted to alkyl-ammonium cations. The obtained isocyanate prepolymers were then extended in the aqueous medium with the use of 1,6-hexamethylenediamine. That yielded stable aqueous dispersions, which were applied on the surfaces of test poly(tetrafluoroethylene) samples. After evaporation of water, the dispersions formed thin polymer coatings. ¹H and ¹³C NMR spectral methods were employed to confirm chemical structures of synthesised cationomers and to modify their quantitative composition in relation to that assumed on the basis of the stoichiometry of the reactions, which were conducted on successive stages of the polyaddition process. Furthermore, the GPC method was used to learn the sizes and distributions of mean molecular weights of those cationomers. Based on ¹H NMR spectra, the factor κ was calculated which represented the polarity level of the obtained cationomers. Good correlation was found between that factor and the free surface energy γ _S (increasing in the range 38–42 mJ/m²) as well as its polar and acid-base components, as determined from the van Oss–Good model on the basis of measured wetting angles between the coatings and model liquids with various polarities. The values of κ and γ _S parameters resulted principally from the increasing amounts of cations NH⁺, which were evaluated on the basis of the concentrations of tertiary nitrogen atoms increasing within 1.37–2.66 wt%. Those concentrations and amounts resulted, in turn, from the amounts of amine N-MDA which could be built into cationomers. The effects were discussed of chemical structures and polarity specifications of polyurethane cationomers on the viscosities of produced aqueous dispersions and on the sizes of their colloidal particles, on the values of free surface energy and on its polar and acid-base components, and on the glass transition temperatures T _g2 of the rigid segments as found by the differential scanning calorimetry (DSC) method.     

An installation for the preparation of foraminifera micro samples for the isotopic analysis of carbon and oxygen

A technical modification of the traditional method of decomposition of carbonates in phosphoric acid was proposed for the determination of δ¹³C and δ¹⁸O in organogenic carbonate samples weighing 10–30 μg with an accuracy of 0.05%. The extraction of CO₂ was carried out under a vacuum at 95°C in 105% phosphoric acid. The isotopic composition of CO₂ was measured by CG-IRMS. The used feed-motion of samples to the reactor provides a consecutive delivery of the samples from the sample holders to the acid. This sample feeding method prevents the contamination of the acid with impurities from the surface of the sample, obviates the necessity of removing the sample holders from the acid, and allows the use of the same acid for performing a very large numbers of analyses. The accuracy and reproducibility of the δ¹³C and δ¹⁸O values was estimated by measuring international standards and comparing with the δ¹³C and δ¹⁸O values for organogenic carbonate samples obtained by the proposed method of analysis at a microgram level and the traditional method at a milligram level. The proposed technology was successfully used to study the isotopic composition of oxygen and carbon in the plankton and benthos foraminifers in order to reconstruct the Okhotsk Sea palaeotemperatures.     

Effect of the method of production of TiO<Subscript>2</Subscript>/CdS nanohetero film structures on the effectiveness of photoinduced charge separation

The properties of TiO₂/CdS nanohetero structures produced by the chemical and photocatalytic deposition of CdS nanoparticles on the surface of nanocrystalline films of TiO₂ under the conditions of laser pulse photolysis were studied. It was shown that in the case of photocatalytically formed TiO₂/CdS nanocomposites the spatial separation of the photogenerated charges between the components of the hetero structure, leading to the formation of intermediates of the photochemical transformations (Ti^III centers in the TiO₂ nanoparticles and S^– radical-anions in the CdS nanoparticles), is an order of magnitude more effective.     

Evolution of wood surface free energy after heat treatment

Surface free energies of pine and beech wood were investigated before and after heat treatment using the Lifshitz-van der Waals/acid-base approach from contact angles measured by the Wilhelmy method. The results obtained showed that the decrease of the electron-donating component of the acid-base component was the major parameter affecting the wetting of the modified wood's surface. The Lifshitz-van der Waals component was slightly modified after heat treatment indicating that the atomic and molecular interactions due to permanent or induced dipoles between wood macromolecules were weakly modified. Modification of the surface chemical composition was studied by X-ray photoelectron spectroscopy (XPS) and titration of acidity. XPS indicated an important decrease of the O/C ratio after heat treatment explaining the decrease of the electron-donating component (γ⁻) of the surface free energy. The decarboxylation and degradation of glucuronic acids present in hemicelluloses, demonstrated by titration of carboxylic acid functions of wood, had only limited effect on the electron-accepting component (γ⁺).     

Increasing the sorption activity of carbon adsorbents by electron-beam processing and fullerene microadditives

The sorption capacity of activated carbon with respect to Cu²⁺ cations was found to be enhanced considerably upon its chemical modification with fullerenes and during its electron-beam processing. It was discovered that introducing fullerenes (20 μg/g) into activated carbon leads to a change in the chemical composition of its surface, due to changes in the system of conjugated bonds in activated carbon leading to an increase in the content of Br?nsted acid (pK _a 0–5) and weakly base (pK _a 8–11) sites capable of cation exchange on the material surface. We conclude that electron-beam processing (optimal dose, 25–50 kGy) facilitates the rearrangement of bonds on the surface of activated carbon, thereby increasing the number of Lewis base and Br?nsted acid sites capable of adsorbing metal ions in accordance with the donor-acceptor and cation-exchange mechanism, respectively.     

Hydrolytic precipitation of magnesium polyvanadates in vanadium (IV, V) solutions

The phase and chemical composition of precipitates formed in Mg(VO₃)₂-VOSO4-H₂O system at initial pH from 1 to 7 and temperature from 80 to 90°C was studied. Polyvanadates of variable composition Mg _x V _y ⁴⁺V_12-y ⁵⁺¹O_31–δ · nH₂O (0.7 ≤ x ≤ 1.3, 1.2 ≤ y ≤ 2.4, 0.7 ≤ δ = 1.4) were formed at pH from 1 to 4 and V⁴⁺/V⁵⁺ ratio from 0.43 to 9. Compounds with the general formula Mg _x V _y ⁴⁺V_6-y ⁵⁺O_16-δ · nH₂O (0.7 ≤ x ≤ 0.65, y = 1.0, 0.8 ≤ δ ≤ 0.85) were formed at pH from 6.0 to 7.0 and V⁴⁺/V⁵⁺ ratios from 0.11 to 0.25. The maximum V⁴⁺ concentration (y = 2.4) in the precipitates was achieved at the VV⁴⁺/V⁵⁺ solution ratio of 1.0 and pH = 3. The precipitates in solutions with pH 3 were formed only upon addition of VO²⁺ ions with the maximum rate at a V⁴⁺/V⁵⁺ ratio of 0.33. These processes were limited by second-order reactions on the surface of polyvanadates.     

Methane and nitrous oxide concentration and emission flux of Yangtze Delta plain river net

Methane (CH4) and nitrous oxide (N2O) saturation concentration and gas-water interface emission flux in surface water of the Yangtze Delta plain river net were investigated in summer at representative sites including the upper reaches of the Huangpu River and the rivers in the Chongming Island. The results show that the CH4 concentration in river water ranged from 0.30±0.03 to 6.66±0.14 μmol.L-1, and N2O concentration ranged from 13.8±2.33 to 435±116 nmol.L-1. River surface water had a very high satura- tio...     

Structure and Functional Composition of the Surface of Cambrian Clay as Influenced by Modification Conditions

The possibility of directed modification of the functional composition of the surface and sorption properties of a disperse Cambrian clay was examined. The concentration of donor-acceptor centers was determined and changes in the structure and composition of the adsorption centers in the course of the acid-base treatment were evaluated. The mineralogical composition of the Cambrian clay and of the products of its chemical modification was analyzed by the successive dissolution procedure.     

Metal-oxide based nanocomposites as materials for gas sensors

Correlations between the composition, structure, and sensor properties of SnO₂-M^IIO (M^IIO = Fe₂O₃, MoO₃, V₂O₅) nanocomposites prepared by wet chemistry synthesis were elucidated. The elemental and phase compositions of the materials, distribution of components between the bulk and surface, particle size, and specific surface area were examined. Surface modification of semiconductor oxides allows controlling the type and density of surface acid centers and redox properties of materials. The result is an increase in the sensor selectivity.     

Chemical composition and acid-base properties of the surface of GaAs-CdS solid solutions

Chemical composition and acid-base properties of the surfaces of GaAs-CdS solid solutions and the constituent binary compounds exposed to air, vacuum, CO, and NH₃ were analyzed using mass spectrometry, IR spectrometry, isoelectric-point pH (pH_iso) analysis, and mechanochemical methods. Powders and films were prepared from the solid solutions by isothermal diffusion and discrete vacuum evaporation, respectively. XRD and Raman analysis revealed that a solid solution has a sphalerite or wurtzite structure, depending on its composition. The initial surface of all the systems studied exhibited acidic properties: the pH value ranged from 4.9 to 6.45. The surfaces contained Lewis (electron accepting) and Brönsted (adsorbed H₂O and CO₂ molecules, OH^? groups) sites. The acidity of the surface increased upon treatment with CO and decreased upon treatment with NH₃. For all types of treatment, the concentration dependence of the acid-base properties of the surface exhibited an extremum. The strongest acidic sites were revealed on the surface of the (GaAs)_0.95 (CdS)_0.05 solid solution. The adsorption activity of this solution, a promising material for manufacturing gas sensors, was evaluated.     

Solvent extraction of chromium(VI) from base metal ions with diphenyl-2-pyridylmethane as a liquid anion exchanger

The extraction of chromium(VI) from aqueous hydrochloric, nitric and sulfuric acid solutions by diphenyl-2-pyridylmethane(DPPM) dissolved in chloroform has been studied. Chromium(VI) is quantitatively extracted from hydrochloric acid solutions in the range 0.1–1M. With increasing acid concentration, the extraction of chromium diminishes and in concentrated acid solutions practically all the chromium remains in the aqueous phase. The quantitative back-extraction of chromium from the organic phase is possible with HCl or HNO₃ at concentrations higher than 5M through the use of reducing agents. The composition of the extracted chromium(VI) species was studied in solution. The complexes (DPPMH)⁺HCrO ₄ ⁻ and (DPPMH)₂Cr₂O ₇ ⁻ are extracted for tracer and macro amounts of chromium(VI) respectively. The data have been utilized for the separation of chromium(VI) from base metal ions.