V. E. Diyuk

Surface Response of Brominated Carbon Media on Laser and Thermal Excitation: Optical and Thermal Analysis Study

The present study is objected to develop an analytical remote optical diagnostics of the functionalized carbons surface. Carbon composites with up to 1 mmol g−1 of irreversibly adsorbed bromine were produced by the room temperature plasma treatment of an activated carbon fabric (ACF) derived from polyacrylonitrile textile. The brominated ACF (BrACF) was studied by elastic optical scattering indicatrix analysis at wavelength 532 nm. The obtained data were interpreted within results of the thermogravimetric analysis, X-ray photoelectron spectroscopy and temperature programmed desorption mass spectrometry. The bromination dramatically reduces the microporosity producing practically non-porous material, while the incorporated into the micropores bromine induces the dielectric and structural impact on surface polarizability and conductivity due to the charging effect. We have found that the elastic optical scattering in proper solid angles in the forward and the backward hemispheres is sensitive to the kind of the bromine bonding, e.g., physical adsorption or chemisorption, and the bromination level, respectively, that can be utilized for the express remote fabrication control of the nanoscale carbons with given interfaces.

Effect of the oxidation and thermal treatment on bromination of activated carbon

It has been shown that the same active surface sites of carbon matrix take part in the oxidation and bromination of activated carbon. The thermal treatment of oxidized samples of activated carbon has been defined to partially or completely restore the reactivity of the surface by removing oxygen-containing functional groups. It has been found that just the number and not the nature of the removed groups determines the increment of the surface reactivity of activated carbon. The thermal treatment of oxidized samples of activated carbons at 800°C virtually completely restores their reactivity to the addition of bromine.

Peculiarities of the reduction of NiO with carbon monoxide associated with a magnetic phase transition in nickel

The reduction of nickel oxide with carbon dioxide under non-isothermal conditions has been investigated. It has been shown that there is a relation of the change in mechanism of the reduction of nickel oxide by carbon monoxide to the temperature of a magnetic phase transition. The size of the active clusters of nickel, estimated by the Faraday method, is 10–15 Å.

Nonlinear optical analysis of bulk oxidized carbonaceous materials response

In this study the nonlinear optical response of porous μm sized carbonaceous particles (cp) was studied within the self-action of 42 ps laser pulses at 1064 nm. Photoinduced absorption efficiency (PAE) of air-thin layer of cp was examined versus the total surface area of cp. The porous thin layer shows predictably discrete response, depending on the level of the surface oxidation. Surprisingly, the ratio between PAE and the surface area show a constant trend within the experimental error range. This observation makes NLO response a promising regulator could be used in metrology of related bulk porous materials.

On multiwalled carbon nanotubes oxidation: Thermogravimetric, spectral and macrokinetic studies

ABSTRACT Multiwalled carbon nanotubes (MWCNTs) were purified and then characterized by nitrogen adsorption, scanning electron microscopy, and energy dispersion X-ray microanalysis. Infrared spectroscopy, Boehm titration, and thermal analysis in air and argon were used to estimate the effect of surface chemistry on the oxidation ability of MWCNTs. From macrokinetic experiments conducted at 450–503°C, the rate constants of MWCNTs oxidation and the parameters of the Arrhenius equation were determined. The oxidation intensity depends on the concentration and nature of the oxygen-containing surface groups. In fact, their thermal decomposition enhances the oxidation rate since frees the surface sites becoming additional active centers of the reaction.

Covalent bonding of sulfogroups to activated carbon fibers: The role of bromine plasma pretreatment

ABSTRACT Activated carbon fibers―nanographite systems, where graphene sheets of a size of a few nanometers are stacked into the porous structure, can serve as adsorbents and catalysts. For a successful catalytic application, graphene surface structures were intensively halogenated with bromine plasma and liquid bromine and then introduced sulfogroups at the brominated sites of the surface through a wet chemical route. The surface chemistry changes were controlled with thermal analysis methods. The catalytic SO3H groups, which covalent attachment was completed at the expense of the plasma-brominated sites, show the highest thermal stability and enhanced activity in catalytic dehydration. In particular, the propan-2-ol conversion to propene reaches 100% at 190–200 °C and the dehydration can be repeatedly conducted at a temperature below 250 °C.

Modification of the activated carbon surface by gaseous-phase chlorination with carbon tetrachloride

The modification of the surface of the SCN grade activated carbon by a gaseous-phase chlorination with a CCl4 vapor has been studied. The effect of the reaction temperature on the amount of the grafted chlorine in the temperature range from 200 to 500°C and the thermal stability of the joined chlorine have been examined. It has been shown that the chlorination by the CCl4 vapor in a gaseous phase results in grafting 19.5 wt % (5.5 mmol/g) chlorine to a carbon surface layer. It has been found that the amination of SCN chlorine-containing samples leads to the replacement of the surface halogen by nitrogen-containing groups in amounts to 1.14 mmol/g.