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.     

Detonation nanodiamonds as catalysts of steam reforming of ethanol

Physicochemical properties and catalytic performance of detonation nanodiamonds were studied. Original samples of nanodiamonds and nanodiamonds modified by hydrogen, oxygen, and nitric acid with hydrogen peroxide and infrared-treated were investigated. The catalyst structure and morphology were examined by transmission electron microscopy and IR spectroscopy. All the investigated catalysts were active in the steam reforming of ethanol. The correlation of catalytic properties with composition and structure of the described systems is discussed. The specific surface area of nanodiamonds is changed insignificantly upon modification.     

Structural variation in palladium nanoparticles of the C-Pd system when dissolving hydrogen in them

The structure of nanocomposites of the C-Pd system has been studied by X-ray diffraction analysis and transmission electron microscopy. Variations in the lattice period of nanosized palladium, the average amount of hydrogen dissolved in it, and the size distribution of palladium nanoparticles have been analyzed as functions of the nanocomposite fabrication temperature. Based on the structural data, the solubility of hydrogen in nanosized palladium has been estimated.     

Synthesis and study of the photochromic behavior of 3-[6′-nitro-1,3,3-trimethylspiro(indolino-2,2′-[2H]-chromen-5-yl)]propenoic acid and its ethyl ester

A new photochromic probe containing a spacer with the reactive carboxyl terminal group at the C5 atom of the photochrome molecule was synthesized. The spectral and kinetic study of the behavior of the new photochromic probes in toluene and ethanol was performed.     

Phase formation in nanocomposites of the C-Pd-Fe system

Metal-carbon nanocomposites consisting of a carbon matrix with dispersed nanosize bimetallic Pd-Fe particles were obtained. It was established that at 500–700°C, the bimetallic particles form a solid solution of iron in palladium. It was concluded that raising the intensity of infrared pyrolysis to 800–1100°C leads to the formation of intermetallic compounds whose composition depends on the temperature of nano-composite fabrication.     

Reactions of fluorinated silanes with 2-nitrocinnamates

The interaction of 2-nitrocinnamates with silicon reagents Me₃SiR_f (R_f = CF₃, C₂F₅, and C₆F₅) promoted either by sodium acetate in DMF or by tetrabutylammonium acetate in dichloromethane has been described. The reactions proceed as conjugate addition of fluorinated carbanion at the CC bond and afford 3-aryl-2-nitrobutanoates bearing a fluorinated substituent in good yields as diastereomeric mixtures in ratio from 1:1 to 1.6:1.     

Resonance luminescence of a nonuniformly heated dense vapor

The thermal luminescence spectra of a dense, nonuniformly heated resonance medium (sodium vapor) are investigated experimentally under conditions when the resonance corrections to the relative permittivity are not small compared to unity and the photon mean free path is comparable to the wavelength of the radiation. The shape of the recorded spectra agrees well with a previously developed general theory of resonance radiation transfer which predicts a strong asymmetry of the spectra. The prospects for performing more-sensitive measurements in order to make a quantitative check of the theoretically predicted anomalous intensity (an order of magnitude higher than in the standard theory of resonance radiation transfer) of the radiation from a dense nonuniform medium are discussed. Pis’ma Zh. éksp. Teor. Fiz. 65, No. 1, 15–19 (10 January 1997)