Adsorption of chlorobenzenes on ultrafine diamond modified with palladium and nickel nanoparticles

Dynamic sorption is used to study the adsorption properties of palladium and nickel nanoparticles immobilized on a surface of ultrafine diamond (UFD). The test adsorbates are n-alkanes (C₆-C₈), benzene, chloroform, diethyl ether, chlorobenzene, and o-dichlorobenzene. For each adsorbate, the adsorption isotherms are measured, the isosteric heats of adsorption and contributions to them from the energies of dispersion Q _disp and specific (donor-acceptor) Q _spec interactions are calculated, and the electron-donor and electron-acceptor characteristics of the surface of the original UFD and the UFDs with immobilized metal nanoparticles are estimated. It is shown that chlorobenzene is sorbed by the physical adsorption mechanisms on the original support and on a sample modified with nickel nanoparticles, and is chemisorbed on a support modified with palladium nanoparticles. The highest heats of chemisorption are obtained on UFD modified with Pd nanoclusters; a surface of UFD modified with Ni nanoclusters is less active with respect to these chlorobenzenes than a surface of unmodified UFD. Benzene, chloroform, and diethyl ether are sorbed on unmodified and modified UFDs by a physical adsorption mechanism; the highest and lowest values of Q _spec for these materials are obtained on UFDs modified with Pd and Ni nanoclusters, respectively.     

Stimulated Raman amplification and high-order Raman sideband generation in a polymer waveguide on a printed circuit

The ultrafast Raman response of C-H vibrations in polymer waveguides on a printed circuit is shown to enable a high-gain amplification and high-order stimulated Raman transformation of ultrashort laser pulses. The pump and Stokes fields coupled by the C-H vibration mode with a vibration cycle of 11 fs give rise to multiple Raman sidebands, suggesting the way toward ultrafast optical data processing and few-cycle optical waveform synthesis on a printed-circuit polymer waveguide platform.     

Photoinduced changes in UV absorption spectra of nitrogen-doped silica caused by exposure to ArF excimer laser

Absorption spectra of high-purity silica, in which 1.2% or 3.0% oxygen atoms are replaced by nitrogen, are measured in the spectral interval of 3.0–6.5 eV. Photoinduced changes of these spectra when exposed to 193 nm wavelength excimer laser radiation, pulse intensity being ～50 mJ/cm², are examined. Absorption spectra relaxation under subsequent annealing as well as changes brought about by saturation of glass with molecular hydrogen are studied. Parts of graded-index fiber ～1 mm in length and 200 μm thick transverse slices of a fiber preform served as samples. It is found that exposure of fiber samples to laser irradiation brings about a significant decrease of initially more intense absorption band of Si-ODC in the region of 5.0 eV and an increase of initially less intense band centered at 5.8 eV at a time. In bulk samples correlation of these bands is opposite, photoinduced changes are less expressed against structureless absorption tail increase in the spectral interval of 3.0–6.5 eV. It is shown that subsequent 20 min 700 °С annealing leads to the relaxation of photoinduced changes in absorption spectra in bulk and fiber samples. By placing irradiated samples into molecular hydrogen atmosphere at room temperature absorption bands are suppressed and transparency at shorter wavelengths of UV region is increased. Data obtained is discussed in the context of photosensitivity of nitrogen-doped silica-core fibers, which serve a technological platform for thermoresistant in-fiber Bragg gratings fabrication.     

Electron band structure detection by high-order optical harmonic generation in solids

As the threshold field strength for the breakdown in air significantly exceeds the maximum measured thundercloud strength 3 kV/cm/atm, the problem of lightning initiation remains unclear. According to the popular idea, lightning can be initiated from streamer discharges developed in the enhanced electric field in a vicinity of hydrometeors. To test the idea, we carry out numerical simulations of positive streamer development around charged water drops at air pressure typical at thundercloud altitudes and at different background fields, drop sizes and charges. With real drop sizes and charges, the electric field required for the streamer formation is stronger than the measured fields; therefore, second mechanism is required to amplify the local field.     

Octave phase matching for optical parametric amplification of single-cycle pulses in the mid-infrared range

Analysis of optical properties of mid-infrared-transparent nonlinear crystals reveals octave phase matching for a highly efficient optical parametric amplification of single-cycle electromagnetic field waveforms within the 3- to 12-μm wavelength range, recently demonstrated in experiments.     

Adsorption properties of aluminium oxide modified with palladium,gold, and cerium oxide nanoparticles

The adsorption properties of nanocomposites based on γ-Al₂O₃ modified with CeO_x, Au/CeO_x, and Pd/CeO_x nanoparticles with contents of deposited metals ranging from 0.07 to 1.71 wt % are investigated by means of dynamic sorption method. n-Alkanes (C₆–C₈), acetonitrile, diethyl ether, tetrahydrofuran, and dioxane are used as test adsorbates. Adsorption isotherms are measured, and the isosteric heats of adsorption of a number of test adsorbates are calculated. Electron-donor and electron-acceptor characteristics of the surfaces of γ-Al₂O₃-based nanocomposites are estimated. It is shown that Au(0.1%)/CeO_x(0.07%)/γ-Al₂O₃ nanocomposite, which has the lowest content of nanoparticles of the deposited metals, has the highest adsorption activity.     

Liquid chromatography of palladium and non-ferrous metal chelates with 1-(2-pyridylazo)-2-naphthol

1-(2-Pyridylazo)-2-naphthol has been used for extraction concentration of palladium, copper, cobalt and nickel from aqueous solutions and subsequent separation of the chelates obtained, by means of high-pressure liquid chromatography. A technique for determining microamounts of palladium in aqueous solutions in the presence of 100-fold ratio of copper and 80-fold ratio of cobalt has been developed.     

Measurement of the Time Structure of the Field and Carrier Phase of Single-Cycle Near- and Mid-Infrared Pulses

JETP Letters - A method of direct measurement of the light field has been implemented. It allows one to reveal features of the time structure of single-cycle pulses formed through soliton...     

Sorption of nitrogen-containing aromatic compounds on ultradispersed diamonds

Adsorption of a number of aniline and pyridine derivatives from water-acetonitrile solution on ultradispersed diamonds was investigated using dynamic sorption method. It was shown that the nature of functional substitutes and their position in molecules of nitrogen-containing compounds of pyridine and aniline have a pronounced effect on adsorption on the surface of ultradispersed diamonds. The dependence of chromatographic sorbate retention on the content of mobile phase could be described by a curve with a minimum. Such nonlinear relationship was explained by the change in the ratio of contribution of specific and non-specific interaction to the sorbate retention that was observed on varying the volume content of an organic component in mobile phase. The influence of temperature on sorption of pyridine and aniline derivatives on ultradisperesed diamonds was investigated. The changes in enthalpy and entropy factors of competitive sorption of sorbates were determined.