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.     

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.     

Phase equilibria in binary subsystems of urea–biuret–water system

Joint results of the differential scanning calorimetry (DSC) and thermogravimetry (TG) experiments were the basis for the fusion enthalpy and temperature determination of the biuret (NH₂CO)₂NH (synthesis by-product of the urea fertilizer (NH₂)₂CO). Recommended values are Δ_m H = (26.1 ± 0.5) kJ mol⁻¹, T _m = (473.8 ± 0.4) K. The DSC method allowed for the phase diagrams of “water–biuret,” “water–urea,” “urea–biuret” binary systems to be studied; as a result, liquidus and solidus curves were precisely defined. Stoichiometry and decomposition temperature of the biuret hydrate identified, composition of the compound in “urea–biuret” system was suggested.     

Clathrate formation in the liquid phase of (C4H9)4NF−NH4F−H2O

At a certain concentration of NH₄F, the solid allocyric solutions of the (C₄H₉)₄NF−NH₄F−H₂O system stratify into two liquid phases in the process of melting. The mutual solubility of the liquids decreases at elevated temperatures. The boundary surface of the stratification region was determined The solubility isotherms (27 and 30°C) of the stratification region are investigated by the solubility method This relatively rare mutual sulubility of liquids (retrograde solubility) is associated with clathrate formation in the liquid phase. Near the melting points of the solid clathrate solutions, both in the liquid and solid phases the tetrabutylammonium cation evidently forms surrounding cavities bounded by water and ammonium fluoride molecules linked by hydrogen bonds. The clathrate-like components of the solution are structurally compatible with “water-like” and “organic” components, i.e., they are homogenizing components. At higher temperatures, the homogenizing clathrate-like structures break down, and the structurally incompatible solution components stratify into two phases. Institute of Inorganic Chemistry, Siberian Branch, Russian Academy of Sciences. Translated fromZhurnal Strukturnoi Khimii, Vol 35, No. 6, pp. 122–128, November–December, 1994. Translated by L. Smolina     

“Spontaneous” growth of fibrous products on the surface of silicic acid gels

We have observed occurrence of fibrous products on gel surface in four-component system of KK (silicic acid sol)–H₂O–HCl–NH₃, KK–H₂O–HCl–NaOH and KK–H₂O–HCl–TEA (triethanolamine). Bundles of fibres occur in the system with NH₃, sticks and needles in system with NaOH, and finally in the system with TEA we can mostly observe the occurrence of crystalline products. Dependency of product morphology on initial sol composition is occurring in observed systems. In the case of system with NH₃, mostly the length of nascent fibres is influenced by the composition, and in the systems with NaOH and TEA it is also final shape of nascent products. Morphology of nascent products in systems with NH₃ and NaOH is controlled by quantity of added HCl, but in the system with TEA it is quantity of added TEA. It is characteristic for all observed systems that “spontaneously” occurring products consist of crystalline phase, that is chloride of respective alkali, and amorphous phase, that is SiO₂. Beginning of respective chloride crystallization in observed systems probably initializes occurrence of products on gel surface. Further growth of crystals is influenced by present colloid of SiO₂ that interacts with surface of growing crystal leading to anisotropy of its growth and therefore to “spontaneous” occurrence of fibrous products.     

Effect of some ammonium salts on thermal decomposition of impregnated wood and properties of activated carbons

Methods of chemical, thermal, IR spectral, and X-ray phase analysis were used to study the effect of ammonium additives NH₄Cl + NH₄NO₃ introduced into a phosphorus-nitrogen formulation on the thermal decomposition of impregnated wood in the temperature range 20–700°C and on adsorption characteristics of the resulting activated carbon.     

Anisotropy of lattice distortion in [Co(NH3)5ONO]X2, X=Cl−, Br−, under hydrostatic pressure of up to 5.0 GPA

Variation of the unit cell parameters of [Co(NH₃)₅ONO]X₂ (X=Cl⁻, Br⁻) as a function of hydrostatic pressure is studied by powder X-ray diffractometry in cooled diamond anvils. Pressures of up to 5.0 GPa lead to anisotropic lattice distortion but not to phase transitions. The anisotropy of lattice compression of the nitrito isomers is qualitatively distinct from that of the related structures of the corresponding nitro isomers, which differ mainly in the structure of complex cations. The following specific interactions are responsible for the anisotropy of compression for both nitrito and nitro isomers: hydrogen bonds between the NO₂ and NH₃ ligands of the neighboring cations and between the NH₃ ligands and the halide anions; specific interactions of the NO₂ ligands of the neighboring cations with each other and of the NO₂ ligands with the halide anions. Institute of Solid State Chemistry, Siberian Branch, Russian Academy of Sciences. Novosibirsk State University. Institute of Mineralogy and Materials Science and Technology Center, Marburg University (Germany). Translated fromZhurnal Strukturnoi Khimii, Vol. 39, No. 3, pp. 424–432, May–June, 1998. This work was supported by the Humboldt Foundation (Germany) and the “Universities of Russia” Program (projects 3H-34-94, 3H-375-92).     

Cd(II) extraction in PEG-based two-phase aqueous systems in the presence of iodide ions. Analysis of PEG-rich solid phases

Cd(II) plus iodide species were extracted into PEG-rich phases in the aqueous PEG(1550)-(NH₄)₂SO₄ system at pH 2.05–7.12. IR spectra show that increasing (NH₄)₂SO₄ solution acidity does not protonate PEG ether oxygen atoms, but decreases water content in the PEG-rich phases. Metallic species’ extraction into the PEG predominantly alters how water molecules bind to polymer chains; the changes in their absorption bands depend on pH. Microscopy shows that “fixation” of the extracted metal in the PEG-rich phase occurs by specific interactions which depend on the species. These also determine changes in the polymer chains’ conformation.     

Adsorption and electrophysical studies of the sensitivity and selectivity of the surface of the InSb-CdTe system with respect to toxic gases

The piezoquartz microweighing and probe compensation methods were used to study the adsorption properties with respect to NO₂ and changes in the electrical conductivity of solid solutions and the binary components of the InSb-CdTe system under the influence of NO₂ and NO₂ + SO₂ and NO₂ + CO mixtures at various temperatures and relative gas contents. Solid solutions were prepared by isothermal diffusion and certified using the results of X-ray, thermographic, IR spectroscopic, and electrophysical measurements. The (InSb)_0.03(CdTe)_0.97 component of the system was found to possess high selective sensitivity (adsorption and electronic) already at room temperature. This component was recommended for creating a sensor for NO₂ microimpurities.     

Effects of exchangeable cations on the adsorption character of mordenite

Summary Adsorption isotherms of water, n-butane, i-butane, benzene and cumene on synthetic and natural mordenites were determined by the gravimetric method and the effect of exchangeable cations on the adsorption character of mordenite was discussed. In the case of synthetic “Large-Port Mordenite”, even its Na-form adsorbs benzene or cumene, whereas the natural mordenite is a “Small-Port Mordenite” and its Na-form adsorbs n-paraffin but it does not adsorb benzene. NH₄-form of the natural mordenite, whose NH₄-exehange ratio is sufficiently high, adsorbs cumene, but the amount of cumene adsorbed is smaller than that of the synthetic Na-form. This result indicates that the pore diameter of the natural NH₄-form is smaller than that of “Large-Port Mordenite”. It may be considered that two causes will disturb the adsorption of large molecules on “Small-Port Mordenite”; one is the reduction of main channel radius by exchanged cations and the other the existence of amorphous substance.

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Zusammenfassung Die Adsorptionsisothermen von Wasser, n-Butan, Isobutan, Benzol und Cumol an den Natur- und synthetischen Mordeniten wurden mit der gravimetrischen Methode gemessen. Die Beziehung der Menge der austauschbaren Kationen mit der Adsorptionsf?higkeit der Mordenite wird diskutiert. Beim synthetischen Mordenit ist die Na-Form schon f?hig, Benzol oder Cumol zu adsorbieren. Der Naturmordenit geh?rt dagegen dem „small-port“-Typ an. Die Na-Form vom Naturmordenit, sofern die Menge von ausgetauschtem NH₄ hinreichend gro? ist, adsorbiert Cumol. Aber die Menge des adsorbierten Cumols ist geringer als bei der synthetischen Na-Form. Diese Tatsache weist darauf hin, da? bei der NH₄-Form vom Naturmordenit der Durchmesser der Poren kleiner ist als bei dem „large-port“-Typ. Um zu erkl?ren, was die Adsorption von gro?en Molekülen hindert, werden zwei m?gliche Deutungen angegeben, n?mlich der von ausgetauschten Kationen verkleinerte Querschnitt von Kan?len und das Vorhandensein amorpher Substanzen.

     

Ionic mobility and structure of fluorozirconates Rb2? x (NH4) x ZrF6 ( x > 1.5) by NMR, x-ray structure analysis, and impedance spectroscopy

The ionic mobility in the temperature interval 180 to 480 K, structure, and electrophysical properties of rubidium-ammonium hexafluorozirconates Rb_2−x (NH₄) _x ZrF₆ (1.5 ≤ x ≤ 2.0) are studied by methods of the ¹⁹F, ¹H NMR spectroscopy, x-ray structure analysis, differential thermal analysis, and impedance spectroscopy. Correlations between the composition of the cationic sublattice, the character of ionic motions, and the phase transition temperature (of the type order-disorder) are established in these compounds. The salient feature of the high-temperature modifications of these fluorozirconates with x ≥ 1.5 is the translation diffusion of ions inside the fluoride and ammonium sublattices and the ¹⁹F NMR spectra are characterized by monoaxial anisotropy of the magnetic shielding tensor of the fluorine nuclei. Fluorozirconates with x > 1.5 are shown to belong with the structural type (NH₄)₂ZrF₆. The rubidium cations isomorphically replace the ammonium cations. The electrophysical characteristics of the compounds are examined in the temperature interval 300 to 480 K. It is established that the electroconductivity of these compounds increases with x. Original Russian Text ? V.Ya. Kavun, A.V. Gerasimenko, A.B. Slobodyuk, N.A. Didenko, N.F. Uvarov, V.I. Sergienko, 2007, published in Elektrokhimiya, 2007, Vol. 43, No. 5, pp. 563–570. Based on the paper delivered at the 8th Meeting “Fundamental Problems of Solid-State Ionics”, Chernogolovka (Russia), 2006.     

(NH4)2SiF6 evaporation in the presence of SiO2

The kinetics and mechanism of the solid-phase reaction between (NH₄)₂SiF₆ and silica at molar ratios of (0.5–5): 1 were studied. SiO₂ is bound with (NH₄)₂SiF₆ to form volatile NH₄SiOF₃, which abruptly enhances the ammonium hexafluorosilicate evaporation. The activation energy and rate constants of evaporation were calculated for an (NH₄)₂SiF₆ + SiO₂ (2: 1) mixture in the range 220–300°C. The reaction with crystalline SiO₂ has a higher yield than with an amorphous “white soot.” The role of the SiO₂ surface in the formation of the volatile products is discussed. The phase and chemical composition of the sublimates was studied.     

Influence of the specific adsorption of anions on the “double layer region” of the cyclic voltammetric curves obtained with platinized platinum electrodes

Cyclic voltammetric study of platinized electrodes restricted to the potential range corresponding to the “double-layer region” (350–700 mV on RHE scale) was carried out in acid medium in the presence of, HSO⁻ ₄, H₂PO⁻ ₄, Cl⁻ and ClO⁻ ₄ anions. It is shown that the shape of the voltammetric curves strongly depends on the nature of the anions present in the system. The phenomena observed are ascribed to the specific adsorption of anions. A correlation is found between the results of radiotracer adsorption studies (differential voltradiometric curves) and the voltammetric measurements. Received: 24 September 1997 / Accepted: 25 November 1997     

Island formation in chemisorption 2. Chemisorption kinetics

Influence of “direct” and “indirect” pathways of dissociative chemisorption on the form of kinetic dependences ϕ(MCS) and S(ϕ) was studied by the Monte Carlo method. Langmuir adsorption observed at S_indir/S_dir≤0.1 gradually changes to island-mediated adsorption with an increase of the “indirect” adsorption contribution at 0.1≤S_indir/S_dir≤1.0. At S_indir/S_dir≥1.0 the island-mediated adsorption dominates: large adsorption islands arise and gradually grow.     

The adsorption of gases on the surface of solid solutions and binary compounds of the GaSb-ZnTe system

The adsorption of ammonia, carbon monoxide, and oxygen on solid solution and binary compound films of the GaSb-ZnTe system was studied. The mechanism of adsorption and rules governing adsorption processes depending on adsorption conditions and system composition were determined by analyzing adsorption isobars, equilibrium and kinetic isotherms, the thermodynamic and kinetic characteristics of adsorption, and the electronic nature of adsorbate molecules. The behavior of (GaSb)_x(ZnTe)_1?x solid solutions was similar to that of binary compounds (GaSb and ZnTe) and had special features characteristic of multicomponent systems. The latter manifested themselves by the presence of extrema in adsorption characteristic-composition diagrams. The use of such diagrams allowed us to identify system components most active with respect to NH₃, CO, and O₂ and use them to create high-sensitivity and selectivity sensors.     

Theoretical design of blue emitting materials based on symmetric and asymmetric spirosilabifluorene derivatives

Equilibrium ground state geometry configurations and their relevant electronic properties of four experimentally reported asymmetric spirosilabifluorene derivatives are calculated by the HF(DFT)/6-31G(d) method. Their excited state geometries are investigated using the CIS/6-31G(d) method. The absorption and emission spectra are evaluated using the TD-B3LYP/6-31G(d) and TD-PBE0/6-31+G(d) levels both in gas phase and CHCl₃ solvent. Our results show an excellent agreement with the experimental data on their optical properties. To predict the substitution effect, the H/R (R = –NO₂, –CN, –NH₂ and –OCH₃) substituted symmetric and asymmetric spirosilabifluorene derivatives are also investigated, and the optical properties of H/R substituted derivatives are predicted in gas phase and CHCl₃ solvent. In comparison with the parent compound, significant red-shift is predicted for the emission spectra of the di-substituted symmetric derivatives with –NH₂ (96 nm), –OCH₃ (61 nm) and the push–pull (containing both –NH₂ and –NO₂) derivative (56 nm). It is found that the performance and the optical properties of these derivatives can be improved by adding push–pull substitutents. The largest change in the electronic and optical properties of this system can be obtained upon symmetric di-substitution among mono-, di-, tri- and tetra-substitutions. Electronic supplementary material The online version of this article (doi:) contains supplementary material, which is available to authorized users.     

The kinetics of ethanol adsorption from the aqueous phase onto zeolite NaZSM-5

The kinetics of the isothermal adsorption of ethanol from an aqueous solution onto a hydrophobic zeolite of the NaZSM-5 type in the temperature range 298–333 K was investigated. Specific shape parameters of the adsorption degree curves were determined. The changes in the specific shape parameters of the adsorption degree curves with temperature were determined. The kinetic parameters of ethanol adsorption (E_a,ln A) were determined by the initial rate, the saturation rate and the maximum rate methods as well as from the Johnson, Mehl and Avramy equation. The kinetic model of ethanol adsorption kt=[1−(1−α)^1/3] was determined by the “model fitting” method. Ethanol adsorption from aqueous solution onto NaZSM-5 is a kinetically controlled process limited by the rate of three-dimensional movement of the boundary layer of the adsorption phase. A model for the mechanism of ethanol adsorption onto NaZSM-5 is suggested on the basis of the kinetic model. Ethanol molecules in aqueous solution are associated in clusters. The activation energy of the adsorption process corresponds to the energy required for the detachment of an ethanol molecule from a cluster and its adsorption onto the zeolite.     

Nanosized centers for mercury(II) ions adsorption on a surface of modified silica

The present work investigates the adsorptive interactions of Hg(II) ions in aqueous medium with hydroxylated silica, aminopropylsilica and silica chemically modified by β-cyclodextrin. Batch adsorption studies were carried out with various agitation times and mercury(II) concentrations. The maximum adsorption was observed within 15–30 min of agitation. The kinetics of the interactions, tested with the model of Lagergren for pseudo-first and pseudo-second order equations, showed better agreement with first order kinetics (k₁ = 3.4 ± 0.2 to 5.9 ± 0.3 min⁻¹). The adsorption data gave good fits with Langmuir isotherms. The results have shown that β-cyclodextrin-containing adsorbent has the largest adsorption specificity to Hg(II): K _L = 4125 ± 205 mmol⁻¹. “β-cyclodextrin-NO3-” inclusion complexes with ratio 1: 1 and super molecules with composition C₄₂H₇₀O₃₅ ⊎ 3 Hg(NO₃)₂ are formed on the surface of β-cyclodextrin-containing silica.      

Standardization of pH measurements based on the ion interaction approach

The Pitzer method was used to calculate the pH values on the conventional and “true” scales for the TRIS—TRIS·HCl−NaCl−H₂O buffer system in the 0–40 °C temperature region and 0–4 NaCl molality interval. This buffer can be used as a standard for pH measurements in a wide range of ionic strengths. The conventional scale is used in cells without a salt bridge. The “true” scale is recommended for pH measurements using cells with a salt bridge. At the same concentrations of the buffer solution, the “true” scale is essentially transformed into the scale of the National Bureau of Standards (NBS) of the USA. Translated fromIzvestiya Akademii Nauk. Seriya Khimicheskaya, No. 4, pp. 676–680, April, 2000.     

Reactions of 1,1,3,3-tetramethyldisilazane with dicobalt octacarbonyl and iron pentacarbonyl. Thermal decomposition of the cobalt and iron carbonyl silazane complexes

The reaction of (HMe₂Si)₂NH with Co₂(CO)₈ gives the complex [Co₂(CO)₇(SiMe₂)₂NH₂]⁺[Co(CO)₄]⁻. Its thermal decomposition starts with dissociation into the “acid” HCo(CO)₄ and the “base” Co₂(CO)₇(SiMe₂)₂NH. After that, the base and the initial complex decompose further under the action of HCo(CO)₄. The final products of this reaction are CO, NH₃, Co, volatile dimethylcyclosilazane, and a solid residue consisting of cobalt particles encapsulated into a polymethylsiloxane matrix and possessing properties of mixed para- and ferromagnetics with an ultimate specific magnetization of 64–74 G g⁻¹. Tetramethyldisilazane reacts with iron pentacarbonyl under UV irradiation to give relatively stable 1,3-bis(tetracarbonylthydrideiron)-1,1,3,3-tetramethyldisilazane. This product contains Fe−H…N hydrogen bonds, which stabilize it against dehydrogenation and cyclization to diironcyclodisilazane. Thermal decomposition of this product was investigated. Translated fromIzvestiya Akademii Nauk. Seriya Khimicheskaya, No. 12, pp. 2537–2544, December, 1998.