Alexey Pestryakov

Influence of modifying additives on electronic state of supported gold

Using the methods of IR spectroscopy of adsorbed CO, electron spectroscopy of diffuse reflectance, XRD, XPS, EXAFS and electron microscopy the influence of modifying additions of Ce, Zr, La and Cs oxides on the surface electronic states of supported gold have been studied. The additions of Ce and Zr oxides stabilize the ionic states of supported gold and increase the effective charge of the ions. In contrast, La and Cs oxides lower the effective charge of gold cation and favor their fast reduction.

FORMATION OF GOLD NANOPARTICLES IN ZEOLITES

The formation of gold nanoparticles in mordenites has been studied by the methods of FTIR spectroscopy of adsorbed CO and diffuse reflectance UV-visible spectroscopy. Different states of ionic and metallic gold were detected in the zeolite cavities and on the external surface of the zeolite – Au+ and Au3+ ions, charged clusters Aunδ+, and neutral nanoparticles Aum. The relative amount of these states depends on the method of sample preparation, type of redox treatment and the SiO2/Al2O3 molar ratio.

Gold nanoparticles supported on magnesium oxide for CO oxidation

Au was loaded (1 wt%) on a commercial MgO support by three different methods: double impregnation, liquid-phase reductive deposition and ultrasonication. Samples were characterised by adsorption of N2 at -96°C, temperature-programmed reduction, high-resolution transmission electron microscopy, energy-dispersive X-ray spectroscopy and X-ray diffraction. Upon loading with Au, MgO changed into Mg(OH)2 (the hydroxide was most likely formed by reaction with water, in which the gold precursor was dissolved). The size range for gold nanoparticles was 2-12 nm for the DIM method and 3-15 nm for LPRD and US. The average size of gold particles was 5.4 nm for DIM and larger than 6.5 for the other methods. CO oxidation was used as a test reaction to compare the catalytic activity. The best results were obtained with the DIM method, followed by LPRD and US. This can be explained in terms of the nanoparticle size, well known to determine the catalytic activity of gold catalysts.

Potential application of silver nanoparticles to control the infectivity of Rift Valley fever virus in vitro and in vivo.

In this work we have tested the potential antiviral activity of silver nanoparticles formulated as Argovit™ against Rift Valley fever virus (RVFV). The antiviral activity of Argovit was tested on Vero cell cultures and in type-I interferon receptor deficient mice (IFNAR (-/-) mice) by two different approaches: (i) different dilutions of Argovit were added to previously infected cells or administrated to animals infected with a lethal dose of virus; (ii) virus was pre-incubated with different dilutions of Argovit before inoculation in mice or cells. Though the ability of silver nanoparticles to control an ongoing RVFV infection in the conditions tested was limited, the incubation of virus with Argovit before the infection led to a reduction of the infectivity titers both in vitro and in vivo. These results reveal the potential application of silver nanoparticles to control the infectivity of RVFV, which is an important zoonotic pathogen.

Catalytic activity in the hydrocarbon conversion of systems containing platinum, nickel, iron, and zinc nanoparticles (communication 2)

The catalytic activity of metal-containing zeolites modified by nanosized Pt, Ni, Fe, and Zn powders was studied in the process of upgrading the petroleum straight-run gasoline fractions. It was found that the introduction of metal nanoparticles into the zeolite increases the catalyst activity and allows the desired product to be obtained at a lower processing temperature. An enhancement of the aromatization reactions of the hydrocarbon feedstock was revealed on the catalyst samples deactivated in the first reaction cycle and calcined in air.

Comparison of cytotoxicity and genotoxicity effects of silver nanoparticles on human cervix and breast cancer cell lines

The wide application of silver nanoparticles (AgNPs) has pointed out the need to evaluate their potential risk and toxic effects on human health. Herein, the cytotoxic effects of Argovit™ AgNPs were evaluated on eight cancer cell lines. Further cytotoxic studies were performed in gynecological cancer cell lines from cervical (HeLa) and breast (MDA-MB-231 and MCF7) cancer. In both cases, the half maximal inhibitory concentration (IC50) of AgNPs produced the formation of reactive oxygen species (ROS) after 24 h of incubation, but it was not statistically significant compared with untreated cells. However, HeLa, MDA-MB-231, and MCF7 cells treated with the maximal IC of AgNPs induced the formation of ROS either at 12 or 24 h of incubation. Genotoxicity achieved by comet assay in HeLa, MDA-MB-231, and MCF7 cells revealed that exposure to IC50 of AgNPs does not induced noticeable DNA damage in the cells. However, the IC of AgNPs provoked severe DNA damage after 12 and 24 h of exposure. We conclude that, Argovit (polyvinylpyrrolidone-coated AgNPs) induce a cytotoxic effect in a time and dose-dependent manner in all the eight cancer cell lines tested. Nevertheless, the genotoxic effect is mainly restricted by the concentration effect. The results contribute to explore new therapeutic applications of AgNPs for malignances in murine models and to study in deep the cytotoxic and genotoxic effects of AgNPs in healthy cells at the surrounding tissue of the neoplasia.

Identification of Subnanometric Ag Species, Their Interaction with Supports and Role in Catalytic CO Oxidation

The nature and size of the real active species of nanoparticulated metal supported catalysts is still an unresolved question. The technique of choice to measure particle sizes at the nanoscale, HRTEM, has a practical limit of 1 nm. This work is aimed to identify the catalytic role of subnanometer species and methods to detect and characterize them. In this frame, we investigated the sensitivity to redox pretreatments of Ag/Fe/TiO2, Ag/Mg/TiO2 and Ag/Ce/TiO2 catalysts in CO oxidation. The joint application of HRTEM, SR-XRD, DRS, XPS, EXAFS and XANES methods indicated that most of the silver in all samples is in the form of Ag species with size <1 nm. The differences in catalytic properties and sensitivity to pretreatments, observed for the studied Ag catalysts, could not be explained taking into account only the Ag particles whose size distribution is measured by HRTEM, but may be explained by the presence of the subnanometer Ag species, undetectable by HRTEM, and their interaction with supports. This result highlights their role as active species and the need to take them into account to understand integrally the catalysis by supported nanometals.

Causes of Activation and Deactivation of Modified Nanogold Catalysts during Prolonged Storage and Redox Treatments

The catalytic properties of modified Au/TiO2 catalysts for low-temperature CO oxidation are affected by deactivation and reactivation after long-term storage and by redox treatments. The effect of these phenomena on the catalysts was studied by HRTEM, BET, SEM, FTIR CO, XPS and H2 TPR methods. The main cause for the deactivation and reactivation of catalytic properties is the variation in the electronic state of the supported gold, mainly, the proportion of singly charged ions Au+. The most active samples are those with the highest proportion of singly charged gold ions, while catalysts with a high content of trivalent gold ions are inactive at low-temperatures. Active states of gold, resistant to changes caused by the reaction process and storage conditions, can be stabilized by modification of the titanium oxide support with transition metals oxides. The catalyst modified with lanthanum oxide shows the highest stability and activity.

Catalytic activity in hydrocarbon conversion of pentasil containing platinum, nickel, iron, or zinc nanoparticles

Catalyst samples containing nanosized Pt, Ni, Fe, or Zn powder were prepared on the basis of high-silica zeolite ZSM-5 by mechanical mixing. The structure and state of active centers of zeolite catalysts (freshly prepared or calcined after the reaction cycle of upgrading the petroleum straight-run gasoline fraction) were studied by means of the X-ray diffraction, UV spectroscopy, and X-ray photoelectron spectroscopy techniques. It was shown that the oxidized forms of the metals are practically absent from the freshly prepared zeolite samples. After the heat treatment of the catalysts in air, nanosized metal powders transform into oxides on the zeolite surface, with iron and nickel producing the greatest variety of oxidized forms.

Acceleration measurement improvement by application of novel frequency measurement technique for FDS based INS

Inertial navigation systems have as sensing elements gyroscopes and accelerometers. The accelerometers with a frequency output domain have some outstanding characteristics like output of quasi-digital signals, high sensitivity, high resolution, wide dynamic range, anti-interference capacity and good stability. This work explains how this sensor works inside an inertial navigation unit and how the measurement of acceleration can be improved through a novel frequency measurement principle. Also it is examined how in a common accelerometer the frequency measurement by principle of rational approximation can be easily implemented with low cost-affordable components. The error analysis in the measurement process is introduced.