Nitrogen effects in multi-matrix calibrations by radiofrequency glow discharge – optical emission spectrometry

A study about the effect of nitrogen in the calibration curves of a series of analytical emission lines has been carried out in this work. Fifteen reference materials with different matrices (Fe, Al, Zn, Cu and Ni) were used (three of these reference materials contain nitrogen in their composition) and plots of intensity versus the product “sputtering rate times element concentration” were constructed for emission lines of the analytes considered in this work (Al, Fe, Cu, Cr, C, Mo, Zn, Si, Ti and Ni). Two different fits were performed in each plot, first considering only the points corresponding to samples without nitrogen in their composition and secondly including all the points. The results show almost negligible differences in the emission yields calculated. On the other hand, a mixture of Ar containing 0.5% N₂ was employed to check if the nitrogen effect was present at higher concentrations than those expected in analysis when samples with high nitrogen concentrations are used. Differences between the slopes of the calibration curves with the Ar/N₂ and pure Ar discharges were obtained (up to 30%). A study of the molecular bands recorded in the spectra when nitrogen is present in the discharge and determination of the resulting interferences on the analytes have been performed. Figure Glow discharge powered with radiofrequency energy     

Comparative material study and synthesis of 4-(4-nitrophenyl)oxazol-2-amine via sonochemical and thermal method

The present paper deals with the synthesis of aminooxazole derivatives via thermal and ultrasonic methods using deep eutectic solvent as medium. It was observed that ultrasound-assisted method gave 90% yield in just 8 min as against 3.5 h required to get 69% yield by thermal method. One of the compounds 4-(4-nitrophenyl)-1,3-oxazol-2-amine synthesized by both methods were subjected to material characterization study via XRD, TGA and SEM analysis. It was observed that use of ultrasound not only increased the rate of reaction but also improved the quality of product obtained. The crystallinity of the product from ultrasound method was 21.12% whereas thermal method fetched only 8.33% crystallinity thereby improving crystallinity by almost 60%. In addition, sonochemical synthesis also saved more than 70% energy as depicted by energy calculations.     

Effect of potassium chloride on diffusion of theophylline at T = 298.15 K

Ternary mutual diffusion coefficients measured by Taylor dispersion method (D₁₁, D₂₂, D₁₂, and D₂₁) are reported for aqueous solutions of KCl + theophylline (THP) at T = 298.15 K at carrier concentrations from (0.000 to 0.010) mol · dm^?3, for each solute. These diffusion coefficients have been measured having in mind a better understanding of the structure of these systems and the thermodynamic behavior of potassium chloride and theophylline in solution. For example, from these data it will be possible to make conclusions about the influence of this electrolyte in diffusion of THP and to estimate some parameters, such as the diffusion coefficient of the aggregate between KCl and THP.     

Influence of polar groups on the wetting properties of vertically aligned multiwalled carbon nanotube surfaces

In this work, we have studied superhydrophilic and superhydrophobic transitions on the vertically aligned multiwalled carbon nanotube (VACNT) surfaces. As-grown, the VACNT surfaces were superhydrophobic. Pure oxygen plasma etching modified the VACNT surfaces to generate superhydrophilic behavior. Irradiating the superhydrophilic VACNT surfaces with a CO₂ laser (up to 50?kW?cm^?2) restored the superhydrophobicity to a level that depended on the laser intensity. Contact angle and surface energy measurements by the sessile drop method were used to examine the VACNT surface wetting. X-ray photoelectron spectroscopy (XPS) showed heavy grafting of the oxygen groups onto the VACNT surfaces after oxygen plasma etching and their gradual removal, which also depended on the CO₂ laser intensity. These results show the great influence of polar groups on the wetting behavior, with a strong correlation between the polar part of the surface energy and the oxygen content on the VACNT surfaces. In addition, the CO₂ laser treatment created an interesting cage-like structure that may be responsible for the permanent superhydrophobic behavior observed on these samples.     

Structure analysis and photocatalytic properties of spinel zinc gallium oxonitrides

This report describes a detailed structural, electronic, and catalytic characterization of zinc gallium oxonitride photocatalysts with a spinel crystal structure. The bandgap decreases to less than 3 eV with increasing nitrogen content (<3 wt%) and these photocatalysts are active in visible light (λ>420 nm) for the degradation of cresol and rhodamine B. Density functional theory calculations show that this bandgap reduction is in part associated with hybridization between the dopant N 2p states and Zn 3d orbitals at the top of the valence band. X-ray photoelectron measurements indicate that nitrogen is indeed interacting with the oxide precursor through the formation of both nitride- and oxonitride-type species. The incorporation of nitrogen reduces the uniformity of the local structure of the spinel Zn-Ga-O-N (ZGON) species, as reflected in X-ray absorption spectra and Raman measurements relative to zinc gallate, which suggests the presence of defects. The oxonitrides exhibit faster photocatalytic rates of reaction than the oxide precursor. The degradation mechanisms were determined to be via the attack by hydroxyl radicals and holes for rhodamine B and cresol, respectively. Addition of Pt as a co-catalyst increased the rate of photodegradation, a result attributed to better charge separation.     

Biomineralization of superhydrophilic vertically aligned carbon nanotubes

Vertically aligned carbon nanotubes (VACNT) promise a great role for the study of tissue regeneration. In this paper, we introduce a new biomimetic mineralization routine employing superhydrophilic VACNT films as highly stable template materials. The biomineralization was obtained after VACNT soaking in simulated body fluid solution. Detailed structural analysis reveals that the polycrystalline biological apatites formed due to the -COOH terminations attached to VACNT tips after oxygen plasma etching. Our approach not only provides a novel route for nanostructured materials, but also suggests that COOH termination sites can play a significant role in biomimetic mineralization. These new nanocomposites are very promising as nanobiomaterials due to the excellent human osteoblast adhesion.     

Photoinduced effects in nematic liquid crystals

Temperature, concentration of the solvent and pressure are the parameters that are well known to bring about phase transitions in liquid-crystalline systems. In recent years a new parameter has been added to this list: light. The principle behind these photoinduced transitions is the light-driven shape transformation of certain photoactive materials like, e.g., azobenzene. In this article, we present results of various aspects of our recent investigations on such photoinduced transitions in the nematic phase and highlight the feature that light is a new tool to study phase transitions and the associated critical phenomena.