A. V. Egorov

Planar SERS nanostructures with stochastic silver ring morphology for biosensor chips

Surface-enhanced Raman spectroscopy (SERS) of living cells has rapidly become a powerful trend in biomedical diagnostics. It is a common belief that highly ordered, artificially engineered substrates are the best future decision in this field. This paper, however, describes an alternative successful solution, a new effortless chemical approach to the design of nanostructured silver and heterometallic continuous coatings with a stochastic “coffee ring” morphology. The coatings are formed from an ultrasonic mist of aqueous diamminesilver hydroxide, free of reducing agents and nonvolatile pollutants, under mild conditions, at about 200–270 °C in air. They consist of 30–100 micrometer wide and 100–400 nm high silver rings composed, in turn, of a porous silver matrix with 10–50 nm silver grains decorating the sponge. This hierarchic structure originates from ultrasonic droplet evaporation, contact-line motion, silver(I) oxide decomposition and evolution of a growing ensemble of silver rings. The fabricated substrates are a remarkable example of a new scalable and low cost material suitable for SERS analyses of living cells. They evoke no hemolysis and reduce erythrocyte lateral mobility due to suitable “coffee ring” sizes and a tight contact with the silver nanostructure. A high SERS enhancement, characteristic of pure silver rings, made it possible to record Raman scattering spectra from submembrane hemoglobin in its natural cellular environment inside single living erythrocytes, thus making the substrates promising for various biosensor chips.

Carbon nanowalls: the next step for physical manifestation of the black body coating

The optical properties of carbon nanowall (CNW) films in the visible range have been studied and reported for the first time. Depending on the film structure, ultra-low total reflectance up to 0.13% can be reached, which makes the CNW films a promising candidate for the black body-like coating, and thus for a wide range of applications as a light absorber. We have estimated important trends in the optical property variation from sample to sample, and identified the presence of edge states and domain boundaries in carbon nanowalls as well as the film mass density variation as the key factors. Also we demonstrated that at much lower film thickness and density than for a carbon nanotube forest the CNWs yield one order higher specific light absorption.

Carboxylated and decarboxylated nanotubes studied by X-ray photoelectron spectroscopy

Carbon nanotubes (CNTs) of the conic and cylindrical structure were studied by X-ray photoelectron spectroscopy in the initial state and after carboxylation and decarboxylation reactions. The O=C—O and C—O groups were revealed on the surface of the chemically modified samples. It was found that both the carboxylated and decarboxylated cylindrical CNTs contain a smaller amount of oxygen than the corresponding conic CNTs apparently due to differences in their structures.

CO2 hydrogenation over cobalt-containing catalysts

Carbon dioxide hydrogenation over catalysts consisting of 0.56–45 wt % cobalt supported on carbon nanotubes (CNTs), carbon nanofibers, few-layer graphite fragments, or CNTs–Al2O3 composites has been investigated. All of the Co/support catalytic systems have been characterized by temperature-programmed reduction, transmission electron microscopy, and scanning electron microscopy. Under the conditions of our catalytic experiment (1 atm, 180–500°C), the CO2 hydrogenation products are CH4 and/or CO and the activity of the catalysts depends on the size and phase state of the cobalt particles. The CNTs-supported materials containing less than 5 wt % Co are catalytically inactive because of the amorphism of the metal. They can be activated by cobalt crystallization by means of heat treatment. The size of the cobalt particles deposited on the carbon supports is about 4 nm. Methods of functionalizing the carbon nanomaterial surface for additional stabilization of metal nanoparticles are suggested.

Chlorobenzene hydrodechlorination catalyst prepared via the pyrolysis of sawdust impregnated with palladium nitrate

Abstract(7% Pd)/C catalysts have been prepared by the pyrolysis of untreated sawdust and sawdust washed with an acid to remove of Group I and II metal impurities, both impregnated with palladium nitrate. Studies by transmission electron microscopy, X-ray photoelectron spectroscopy, and temperature-programmed reduction have demonstrated that the dominant palladium species in the catalysts is 2–5 nm Pd0 particles, there is no PdO on the surface, and the catalyst bulk contains small amounts of larger (10–20 nm) PdO particles. The catalysts are active in chlorobenzene hydrodechlorination in a fixed-bed flow reactor and ensure 100% conversion of the substrate into benzene in the temperature range from 250 to 350°C. At lower temperatures (150–200°C), the catalyst containing calcium is the most active and the sample subjected to reduction after pyrolysis shows the lowest activity.

New method for catalyst preparation based on metal-organic framework MOF-5 for the partial hydrogenation of phenylacetylene

Small (less than 2 nm) Pd nanoparticles immobilized in the matrix of the microporous phenylenecarboxylate metal-organic framework MOF-5 were prepared for the first time by the fluid method. The catalytic properties of samples Pd@MOF-5 were studied in the selective hydrogenation of phenylacetylene to styrene (methanol, 20 °C, PH2 = 1 atm). The catalytic experimental data and results of physicochemical studies indicate that palladium nanoparticles are mostly localized in pores of the composite material 1%Pd@MOF-5 obtained by the fluid synthesis. The specific positions of active sites in the intracrystalline volume results in the suppression of the undesirable conversion of styrene to ethylbenzene.

Effect of cobalt weight content on the structure and catalytic properties of Co/CNT catalysts in the fischer–tropsch synthesis

Cobalt-based Fischer–Tropsch synthesis (FTS) catalysts containing 1 to 40 wt % cobalt supported on multi-walled carbon nanotubes (CNTs) have been investigated. The CNTs have been characterized by low-temperature nitrogen adsorption, scanning electron microscopy, and X-ray photoelectron spectroscopy. All catalysts have been prepared by impregnating, with an ethanolic solution of cobalt nitrate, the CNTs preoxidized with concentrated nitric acid and have been tested in the FTS at 220°C and atmospheric pressure. Correlations have been established between the cobalt weight content of the catalyst and the Co particle size determined by transmission electron microscopy and X-ray diffraction. The Co content and particle size have an effect on the activity and selectivity of the catalyst and on the target fraction (C5+) yield in the FTS. The highest CO conversion is observed for the catalyst containing 20 wt % Co; the highest selectivity and activity, for the catalyst containing 5 wt % Co; the highest C5+ yield, for the catalyst containing 10 wt % Co.

About transformation of the deep-water methane bubbles into hydrate powder and hydrate foam

During the Russian Academy of Sciences “MIRI na Baikale, 2008–2010” expedition, deep-water experiments with the bubbles of methane seeping from the bottom at depths 405, 860 and 1400 meters were carried out. These depths correspond to gas hydrate stability zone. Bubbles were caught by the trap which was looked like an inverted glass. It was found that the behavior of bubbles in a trap depends on the depth. At depth of 405 meters formation of hydrates was not observed. Having got to a trap at the depth of 860 meters, bubbles became covered by solid hydrate envelope, kept the initial form, and after a time period collapsed in a number of hydrate fragments which showed all properties of a granular matter. No visible changes in the hydrate granular matter were observed in the course of lifting it to a depth of 380 meters. Shallower, the decomposition of the hydrate granular matter into methane gas was observed. In the experiments at depth of 1400 meters the caught bubbles, becoming covered by hydrate envelope formed solid hydrate foam in the trap. At lifting this foam structure was deformed slightly but simultaneously a free gas left the foam and filled the trap. The volume of free gas in the trap at lifting varied according to the Boyle-Mariotte law.

Heat and mass transfer effects during displacement of deepwater methane hydrate to the surface of Lake Baikal

The present paper focuses on heat and mass exchange processes in methane hydrate fragments during in situ displacement from the gas hydrate stability zone (GHSZ) to the water surface of Lake Baikal. After being extracted from the methane hydrate deposit at the lakebed, hydrate fragments were placed into a container with transparent walls and a bottom grid. There were no changes in the hydrate fragments during ascent within the GHSZ. The water temperature in the container remained the same as that of the ambient water (~3.5 °С). However, as soon as the container crossed the upper border of the GHSZ, first signs of hydrate decomposition and transformation into free methane gas were observed. The gas filled the container and displaced water from it. At 300 m depth, the upper and lower thermometers in the container simultaneously recorded noticeable decreases of temperature. The temperature in the upper part of the container decreased to –0.25 °С at about 200 m depth, after which the temperature remained constant until the water surface was reached. The temperature at the bottom of the container reached –0.25 °С at about 100 m depth, after which it did not vary during further ascent. These observed effects could be explained by the formation of a gas phase in the container and an ice layer on the hydrate surface caused by heat consumption during hydrate decomposition (self-preservation effect). However, steady-state simulations suggest that the forming ice layer is too thin to sustain the hydrate internal pressure required to protect the hydrate from decomposition. Thus, the mechanism of self-preservation remains unclear.

Sulphur-free synthesis of helical carbon nanotubes

Unique three-dimensional structure of helical carbon nanotubes renders them important in polymer composites, electrode materials of electrochemical devices and microwave absorbers. The most thoroughly studied synthetic method involves hydrocarbon pyrolysis in the presence of sulphur-containing compounds which provide coiling effect. However, sulphur compounds are toxic and are usually undesirable in the coils obtained. The present work describes a novel method for the synthesis of coiled nanotubes by the aerosol pyrolysis of ferrocene solution in methanol, which is easily scalable for high-quantity production and uses no sulphur. The results of systematic investigation of the synthetic procedure with the use of other metal nanoparticle precursors and oxygen sources as well as oxygen role are discussed in details.