Vol 12, No 11-12 (2017)

In this paper we use a macrokinetics approach to propose and develop a mechanism for the ignition and passivation of a pyrophoric nanopowder layer. Assuming that the oxidizer diffusion is the rate-limiting step in the wave-propagation mechanism of passivation, we are able to determine the dependence of the maximum temperature of the nanopowder passivation on key parameters. As a result, two-stage passivation with an increasing oxidant concentration in the gas phase at the second step is proposed. We have shown that, at an allowable warm-up level, the two-stage process reduces the time required for the passivation of a nanopowder layer to be completed by several times. The minimum time of the transition to the second stage at a given rate of temperature growth has been analytically predicted. We have also made numerical simulatons that show a good agreement with the results of our approximate calculations, additionally supporting the conclusions based on the theoretical analysis used. The macrokinetic approach is successfully applied to adeqautely described the passivation of pyrophoric nanopowders when it is strictly limited due to small particle sizes by the diffusion transfer of the passivating gas into the backfill.

Catalytic properties of nondoped and copper-doped Mayenite have been studied. During ethanol conversion and ethanol steam reforming, the initial Mayenite and specimens containing 0.58 and 0.92 wt % of copper have been analyzed. All catalysts are active in both processes. The influence of the ethanol/water mole ratio on product distribution has been studied. In the course of experiments, the fact of reversible hydrogen sorption has been detected upon the thermal treatment of catalysts containing copper.

This study aims to find a way for the creation of polyethyleneimine-modified biofunctionalized zinc oxide (ZnO) nanoparticles, stable in phosphate buffered saline (PBS). Biofunctionalized ZnO nanoparticles are promising for bioanalitycal applications due to a combination of diverse physico-chemical ZnO properties and selectivity of biomolecules. ZnO nanoparticles were synthesized in diethylene glycol media at 150°C. Different strategies were utilized for ZnO nanoparticle modification in order to disclose the role of polyethylenimine (PEI) in stability of colloidal system. Synthesized and modified ZnO nanoparticles were characterized by X-ray diffraction (XRD), scanning electron microscopy (SEM) and infrared spectroscopy measurements, and stability of colloidal system was investigated using DLS data. Finally, ability of ZnO nanoparticles to attach proteins for potential analytical applications was proved using Bradford protein assay. Among different strategies of modification, ZnO nanoparticles modified by trisodium citrate, PEI and glutaraldehyde (GA) have showed the best stability in PBS while preserving low aggregation level and high positive surface charge.

The effect of filler concentration (C ≈ 0–100 vol %) and film thickness (d ≈ 0.02, 0.2, 0.5, and 1.0 μm) on the optical absorption spectra and surface morphology of thin nanocomposite films based on poly(p-xylylene) and cadmium sulphide (PPX–CdS) has been studied. The PPX–CdS films are prepared by low-temperature vapor deposition polimerization on quartz and silicon substrates. A nonmonotonic dependence of the absorption spectrum red shift on the filler concentration is revealed. The red shift of the spectrum reaches a maximum at some critical concentration of the filler C₀. It is observed that the value of the critical concentration C₀ increases with the film thickness and equals C₀ ≈ 11, 30, and 50 vol % for d ≈ 0.02, 0.5, and 1 μm, correspondingly. The average size of the nanoparticles is evaluated by an analysis of the absorption spectra (via estimating the exciton-peak wavelength). It is found that the shift in the absorption spectra is determined by a variation in the nanoparticle size. Atomic force microscopy reveals the effect of the filler content on the surface morphology of the polymer matrix in nanocomposite films and their surface roughness. The size distribution of the polymeric grains is evaluated. The most significant changes in the absorption spectra and surface morpology of the composites with a variation in the filler content are observed in the filler concentration range from 0 to C₀. The absorption spectra of the composites with the filler concentration above C₀ are similar, which can be attributed to the almost equal nanoparticle size in these nanocomposites. The correlation between changes in the matrix morphology and filler optical properties is established.

In this study the influence of nitrogen pressure in the reaction chamber on the parameters of the synthesized nanosized TiN using plasmodynamic direct synthesis method has been investigated. It is shown that the pressure factor is not important in the synthesis of a nanosized product.

The modification of an electrode produced by a matrix printing head with the use of glucose oxidase (GOD), single-walled carbon nanotubes (SWCNTs), and thermoexpanded graphite (TEG) has been studied. During glucose oxidation, modification by SWCNTs leads to the effect of direct electron transfer. Both nanomaterials increase the magnitude of the sensitivity coefficient (SC) from 0.11 to 0.24 mA M^–1 in the case of glucose oxidase–and ferrocene-based electrodes when modification is done with the addition of TEG and up to 0.62 mA M^–1 when modification is done with the addition of SWCNTs. A comparison of the characteristics of the biosensors with ferrocene and nanomaterials with those of the mediator-free biosensors based on SWCNTs and GOD shows that the biosensor provides higher sensitivity detection; the magnitude of sensitivity coefficient is 1.5 mA M^–1. The higher magnitude of the SC can be explained by the occurrence of more effective electron transfer from active centers of the enzyme to the electrode. Voltammetric measurements demonstrate that electron transfer in a mediator-free biosensor is not complicated by a chemical reaction and is carried out under the control of diffusion factors. After testing the mediator-free biosensor in practice, it is possible to talk about the applicability of such a biosensor in detecting glucose in different environments, including the fermentation industry.