Development of the specific surface areas of natural coal in the course of thermolysis in the presence of potassium hydroxide

The development of the surface of natural coal from Donets field in the course of thermolysis with KOH was studied. The dependences of the specific surface area of coal containing 90% carbon on the activation time, temperature (400–800°C), and KOH/coal ratio (0.75–4.5 g g^–1) were determined. The effect exerted on the development of the porous coal structure by low-temperature (20±2°C) oxidative modification causing formation of oxygen functional groups and reorganization of the coal three-dimensional structure was studied.Translated from Zhurnal Prikladnoi Khimii, Vol. 77, No. 9, 2004, pp. 1452–1455.Original Russian Text Copyright © 2004 by Tamarkina, Kucherenko, Shendrik.     

The Treatment of Textile Materials in Air Plasma

The effect of treatment in an air glow-discharge plasma on a poly(ethylene terephthalate) film and fabric with different specific surface areas was examined. The rates of mass loss, oxygen uptake, and evolution of gaseous products (CO₂ , H₂O, H₂) were measured over the pressure range 50–200 Pa at a sample temperature of 357 K. It was found that textiles with different textures had different specific etching rates. Possible reasons for this phenomenon are discussed.     

Effect of Bismuth Additives on the Properties of Vanadium–Phosphorus Oxide Catalyst in the Partial Oxidation of n-Pentane

The selective oxidation of n-pentane on vanadium–phosphorus oxide (VPO) catalysts with bismuth additives (Bi/V = 0–0.30) is studied. The catalysts are characterized by XRD, XPS, and specific surface area measurements using nitrogen adsorption. Their acidic properties are studied (using ammonia TPD and the 2-methyl-3-butyn-2-ol reaction). It was found that the introduction of bismuth insignificantly affects the specific surface area but increases the surface concentration of phosphorus and changes the acidic properties of the catalysts. The specific catalytic activity of samples in n-pentane oxidation correlates with the effective charge of surface oxygen (E _b of O1s electrons). The selectivity to citraconic anhydride increases with an increase in the general surface acidity. The selectivity to maleic anhydride increases with an increase in the Brønsted acidity of the surface. The selectivity to phthalic anhydride increases with an increase in the Lewis acidity. The pathways of product formation in the partial oxidation of n-pentane are proposed.     

Isotopic Exchange and Oxygen Diffusion in the La0.88Sr0.12Ga0.82Mg0.18O3 – α–Molecular Oxygen System

The oxygen isotopic exchange kinetics in La_0.88Sr_0.12Ga_0.82Mg_0.18O_{3 –} and in the same electrolyte whose surface layer is enriched with cobalt ions is studied. Rates of different types of exchange and oxygen isotope diffusion coefficients in oxide are determined at 970–1200 K and oxygen pressures of 400–1200 Pa. The activation energy for the interphase oxygen exchange and the order of heteroexchange vs. oxygen pressure relationship are determined. The presence of cobalt ions in the near-surface layer alters the surface exchange parameters, such as the oxygen heteroexchange rate (which increases), order of the heteroexchange vs. oxygen pressure relationship, and the ratio between rates of different exchange types. The oxygen isotope diffusion coefficients coincide in both electrolytes but differ from those calculated from the electroconductivity data with the Nernst–Einstein equation.     

Kinetics of Gaseous Product Formation in the Surface Treatment of Polypropylene with Nitrogen–Oxygen Plasmas

The results of measurements on the composition and the formation rates of gaseous products in the surface treatment action of polypropylene with a low-temperature dc discharge plasma in a nitrogen–oxygen mixture are reported. The amount of oxygen in the mixture was varied within 0–100%. It was found that almost stoichiometric plasma-induced oxidative degradation occurred in an oxygen plasma, whereas the buildup of oxygen-containing functional groups on the surface took place in a mixed nitrogen–oxygen plasma at a nitrogen content of 10–60%.     

Reactivity of Copper Nanopowders in a Model Reaction of Isopropylbenzene Oxidation

The reactivity of copper nanopowders produced by an electric explosion of a conductor or mechanochemically was studied. Oxidation of isopropylbenzene was used as a model reaction. The dependence of the oxygen uptake rate on the specific surface area of a copper nanopowder and on the method used for its production is discussed. A possible mechanism of isopropylbenzene oxidation in the presence of copper nanopowders is suggested.__________Translated from Zhurnal Prikladnoi Khimii, Vol. 78, No. 5, 2005, pp. 767–771.Original Russian Text Copyright © 2005 by Skorokhodova, Kobotaeva, Sirotkina.     

The influence of calcination on the size of nanocrystals, porous structure and acid–base properties of mesoporous anatase used as catalytic support

Mesoporous anatase was prepared following sol–gel and using urea as template. The influence of calcination temperature on the phase stability, nanocrystal/aggregate size, pore size distribution and specific surface area as well as on the acid–base behavior in aqueous solutions was studied using X-ray diffraction, laser-Raman and diffuse reflectance spectroscopies, scanning electron microscopy and laser scattering as well as N₂ adsorption–desorption isotherms and potentiometric mass titrations.The crystal structure was kept constant upon calcination over the whole temperature range, 200–500 °C. In this range anatase is constituted from primary nanocrystals. These are assembled into larger, rather spherical, clusters of about 30–40 nm and then into aggregates of various sizes (0.2–0.3 μm and 2–100 μm) with a distribution centered at about 12 μm. Increase of the calcination temperature caused an increase in the size of the primary nanocrystals from 8.1 nm at 200 °C to 17.1 nm at 500 °C, whereas calcination does not influence the morphology at micro-scale. Moreover, increase of the calcination temperature from 200 °C to 500 °C brings about a shift in the mean pore diameter from 47 nm to 91 nm accompanied by a decrease in the specific surface area and pore volume. The above effects were related with the aforementioned increase in the size of the primary nanocrystals. The value of pzc and the values of surface charge determined at various pH do not practically depend on the calcination temperature. The absence of pore space confinement effects was explained in terms of the structure and size of the interface development between the anatase surface and the electrolytic solution.     

Dilatational properties and morphology of surface films spread from clinically used lung surfactants

The dilatational properties, structure, and morphology of the surface films spread at the air–water interface from complex lipid/protein systems were studied by measuring the surface pressure–area and surface potential–area isotherms, the surface rheological properties, and AFM images. The commercially available lung surfactants Alveofact, Curosurf, Survanta, and Exosurf were used as examples.The isotherms of the studied lung surfactant surface films are compared with model lipid and protein monolayers spread from bulk solutions. On the basis of a simple rheological model, the values for the elasticity and the specific time of relaxation related to the reorganization processes occurring in the monolayers were calculated. The spread films of natural surfactants Curosurf and Alveofact show a high effectiveness of spreading and respreading under the conditions of this study. These observations were confirmed by AFM imaging.     

Surface and Subsurface Oxygen on Platinum in a 0.5 M H2SO4 Solution

The oxidation of polycrystalline platinum in 0.5 M H₂SO₄ is studied by cyclic voltammetry at potential scan rates of 5–500 mV s^–1 while varying the potential cycling range. The scheme, which is proposed for explaining the observed acceleration and deceleration of oxygen sorption at 0.75–1.0 V, accounts for the presence of oxygen in the subsurface layers of platinum (O_ss) and the formation of a barrier layer comprising complexes O_ss–Pt _n –SO₄. Cycling platinum secures certain steady-state contents of O_ss at 0.01–1.35 V. In an anodic scan, O_ss accumulates at E > 0.85 V (slow post-electrochemical stage) due to exchange of platinum and oxygen atom sites. In a cathodic scan, the desorption of most oxygen gives way to the adsorption of anions, which prevent residual O_ss from appearing on the surface. The residual O_ss disappears at E < 0.1 V after a sufficiently complete desorption of anions and the destruction of stable complexes O_ss–Pt _n –SO₄. Varying the potential cyclic limit leads, after a delay, to other steady-state O_ss contents.     

Catalytic Oxidative Deformylation of Polyethylene Glycols with the Participation of Molecular Oxygen

The kinetics of oxidation of diethylene glycol, triethylene glycol, and polyethylene glycols (PEGs) with molecular weights ranging from 400 to 2000 in the presence of Cu(II) ions and bases was studied. It was found that ethylene glycols can be oxidized by molecular oxygen in anhydrous media in a temperature range of 30–60°C at anomalouosly high rates which are higher than the rates of chain-radical PEG autoxidation by several orders of magnitude. Only terminal hydroxyl groups were subjected to oxidation. The reaction occurs with the cleavage of a C–C bond and results in the formation of formic acid and a PEG with the number of –(CH₂CH₂O)– groups lower than that in the parent compound by unity. The rate and selectivity of PEG oxidation were found to strongly depend on the molecular weight of the polymer; from diethylene glycol to PEG 2000, the specific rate of oxidation increased by a factor of 60 in terms of terminal hydroxyl groups. An oxidation mechanism was suggested, which involves the formation of ternary complexes [Cu²⁺···A^–···O₂], which undergo further degradation by a many-electron concerted mechanism to form formic acid and, probably, an unstable hemiacetal {RO–CH₂OH}. The rapid oxidative degradation of the latter leads to the formation of PEG with a lower molecular weight.     

Physical Properties of Silica Aerogels Prepared with Polyethoxydisiloxanes

Silica aerogels were made by sol-gel techniques using industrial silicon derivatives (polyethoxydisiloxanes, E-40), followed by supercritical drying with ethanol. The morphology and microstructure of the silica aerogels were investigated by using specific surface area, S_BET, SEM, TEM and the pore size distribution techniques. The thermal conductivity was also measured as a function of air pressure. The results show that the diameter of the silica particles is about 13 nm and the pore size of the silica aerogels is 20–80 nm. The specific surface area of the silica aerogel is about 470 m²/g and the thermal conductivity of the silica aerogel prepared with E-40 is 0.014 w m^–1 K^–1 at room temperature and 1 atm.     

Synthesis of Ozone in a Surface Barrier Discharge with a Plasma Electrode

The synthesis of ozone from oxygen in a cylindrical ozonizer operating under surface discharge conditions with a plasma electrode was studied. The conditions of ozone synthesis were optimized. The dependence of ozone concentration and specific energy consumption on gas pressure in the plasma electrode and on distance between the coils of a corona electrode was determined. The results were compared with data obtained with the use of classical surface barrier discharge.__________Translated from Khimiya Vysokikh Energii, Vol. 39, No. 4, 2005, pp. 307–311.Original Russian Text Copyright © 2005 by Alemskaya, Lelevkin, Tokarev, Yudanov.     

Influence of the magnitude of the surface area of a catalyst on its specific activity in the heterogeneous-homogeneous reaction of oxidative coupling of methane

A mechanism for the heterogeneous-homogeneous reaction of oxidative coupling of methane on metal-like catalysts has been proposed to explain the dependence of the specific reaction rate on the magnitude of the total surface area of catalysts, including catalysts of the same chemical composition but different specific surface area.Translated from Teoreticheskaya i Éksperimental'naya Khimiya, Vol. 30, No. 3, pp. 158–162, May–June, 1994.The author is grateful to Yu. T. Pytnitskii for a very useful discussion of this work.     

Molecular simulation of oxygen on supported platinum clusters

Molecular dynamics simulations are performed to study oxygen adsorption on platinum clusters supported on a graphite surface. The Sutton–Chen many-body potential is used for the Pt–Pt interaction, whereas a Steele potential was used to represent the carbon surface. The oxygen–oxygen intramolecular force is modeled by a harmonic oscillator model and other interactions are described by the Lennard–Jones potential. The results indicate an optimum loading of platinum for maximum specific adsorption of oxygen. Adsorption isotherms are constructed and the energies and orientation of adsorbed oxygen are reported. The relevance of this study to electrode processes is discussed.     

Xerogels Modified with 4-(2-Pyridylazo)-Resorcinol and Cetylpyridinium Chloride: Determination of Zinc in Solutions by Solid-Phase Spectrophotometry

Silicon dioxide-based xerogels modified with 4-(2-pyridylazo)-resorcinol (PAR) and cetylpyridinium chloride (CP) were synthesized. The concentration of PAR and CP in the hydrolyzed mixture in the ranges (0.6–3.10) × 10^–3 and (5–12) × 10^–3 M, respectively, does not affect the rate of gel formation as well as the specific surface area and average pore diameter of xerogels obtained upon drying in a microwave oven with a power of 600 Wt. It was found that the retention of PAR can be significantly improved in the presence of CP. Reactions of zinc with modified xerogels were studied by solid-phase spectrophotometry at different concentrations of PAR and CP, pH of the solution, and equilibrium time. A procedure was developed for determining 0.1–4.5 mg/L zinc in solutions by solid-phase spectrophotometry. Results of determining zinc in acid soil extracts and milk ash are given.     

Development of an amperometric biosensor based on covalent immobilization of tyrosinase on a boron-doped diamond electrode

An amperometric enzyme electrode based on direct covalent immobilization of tyrosinase on a boron-doped diamond (BDD) electrode has been developed for the detection of phenolic compounds. Combined chemical and electrochemical modifications of the BDD film with 4-nitrobenzenediazonium tetrafluoroborate, an aminophenyl-modified BDD (AP–BDD) surface was produced, and then the tyrosinase was covalently immobilized on the BDD surface via carbodiimide coupling. The response dependences of the enzyme electrode (Tyr–AP–BDD electrode) on pH of solution, applied potential, oxygen level and phenolic compounds diffusion were studied. The Tyr–AP–BDD electrode shows a linear response range of 1–200, 1–200 and 1–250 μM and sensitivity of 232.5, 636.7 and 385.8 mA M⁻¹ cm⁻² for phenol, p-cresol and 4-chlorophenol, respectively. 90 percent of the enzyme activity of the Tyr–AP–BDD electrode is retained for 5 weeks storing in 0.1 M PBS (pH 6.5) at 4 °C.     

Oxygen States in Oxides with a Perovskite Structure and Their Catalytic Activity in Complete Oxidation Reactions: System La1 – x Ca x FeO3 – y (x = 0–1)

Oxygen states in the La_{1 – x} Ca _x FeO_{3 – y} perovskites prepared using different procedures are studied by temperature-programmed reduction (TPR). Results are compared to data on the catalytic activity in the oxidation of methane and carbon monoxide. The activity of the samples in the CO and CH₄ oxidation over a wide temperature range (200–600°C) is shown to correlate with the amount of reactive surface and subsurface oxygen removable during TPR below 420°C. These oxygen states in the samples of the La_{1 – x} Ca _x FeO_{3 – y} series can be associated with the domain or intergrain boundaries. No correlation is found between the amount of lattice oxygen removable during TPR and the activity of the La_{1 – x} Ca _x FeO_{3 – y} samples in the complete oxidation of methane at temperatures of 450–600°C. It is suggested that catalytic complete oxidation is determined by the most reactive surface and subsurface oxygen states located at the interphase boundaries, whereas the lattice oxygen does not participate in these reactions.     

Contribution of singlet oxygen to the accelerated decolorizing of dye mixtures

Binary mixtures of dispersed dyes, which during irradiation with polychromatic light give an effect of accelerated decolorization, were studied. Quantum yields of the formation of singlet oxygen by individual dyes were estimated during irradiation of solutions in ethyl acetate with light of 435 and 546 nm as well as quantum yields of the reaction of dyes with singlet oxygen. It was found that the contribution of the reaction of dyes with singlet oxygen to the effects of accelerated decolorization were vanishingly small. The quantum yield of the photodestruction of dyes in a mixture was 10^–3-10^–5 and the quantum yield of reaction with singlet oxygen was less than 10^–6. It was concluded that accelerated decolorization of the systems studied is not determined by reaction with singlet oxygen.Translated from Izvestiya Akademii Nauk SSSR, Seriya Khimicheskaya, No. 9, pp. 2014–2017, September, 1991.     

Surface and Subsurface Oxygen on Platinum in a 0.5 M H2SO4 + 0.01 M CuSO4 Solution

The formation of a copper adatom layer on polycrystalline platinum in a copper sulfate solution is studied by cyclic voltammetry in different cycling ranges at 0.1 V s^–1. The copper adatom deposition kinetics is controlled by the following factors. The substrate's top layer structure during the oxygen exit onto the surface may be unstable at anodic limits E _a = 0.90–1.35 V. The concentration of copper oxides (active centers) may be higher at E _a = 0.8–0.95 V. The balance between different adsorption sites differs in different cycling conditions. Of importance is the number of complexes O_ss–Pt _n –SO₄ and O_ss–Pt _n –O_c, where O_ss is subsurface oxygen and O_c is chemisorbed oxygen.     

Reaction of oxygen with adsorbed hydrogen species of a reduced Pt/TiO2 catalyst

Reaction of oxygen with the adsorbed hydrogen species of Pt/TiO₂ catalysts reduced in the temperature range of RT-773 K has been studied by temperature-programmed oxidation (TPO). It is obtained that the Pt-assisted reaction of oxygen with both the surface hydroxy groups and titanium hydride species occurs in the temperature range of 320–450 K; direct oxidation of the surface hydrogen species takes place on the surface of TiO₂ in the temperature range of 500–600 K; and oxygen reacts with the stored hydrogen species in the sublayer and bulk of the TiO₂ support when the temperature was increased to above 600 K.